You use the quadratic formula all the time, but where did it come from?

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  • เผยแพร่เมื่อ 25 ม.ค. 2024
  • When we solve quadratic equations we often use the quadratic formula, but have you thought about where it came from? Let's learn how to prove the quadratic formula by using the completing the square method. Subscribe to @bprpmathbasics for more algebra tutorials.
    Check out two step-by-step examples of using the quadratic formula! 👉 • How to solve quadratic...
    A faster way to prove the quadratic formula: 👉 • quadratic formula (the...
    Solving the quadratic equation 2x^2-3x-9=0 by factoring and the quadratic formula: 👉 • Quadratic formula: by ...
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    #math #algebra #mathbasics

ความคิดเห็น • 195

  • @TaimTeravel
    @TaimTeravel 3 หลายเดือนก่อน +73

    Now prove the cubic formula 😂

    • @bprpmathbasics
      @bprpmathbasics  3 หลายเดือนก่อน +23

      You got it! th-cam.com/video/ULsPhWmqhyc/w-d-xo.htmlsi=v-8aw9bjPSCqA2Fc

    • @TaimTeravel
      @TaimTeravel 3 หลายเดือนก่อน +18

      @@bprpmathbasicsYou don't know how much this is helping me. Thank you so much 💟 😭

    • @nssinger4276
      @nssinger4276 3 หลายเดือนก่อน +4

      This is class 10 maths​@@TaimTeravel

    • @RikiFaridoke
      @RikiFaridoke 9 วันที่ผ่านมา

      To proof root of cubic formula is so easy guys.

  • @ronaldjensen2948
    @ronaldjensen2948 4 หลายเดือนก่อน +114

    0:12 Better to say "a cannot be zero because if it is, you don't have a quadratic equation, you have a line"

    • @anglaismoyen
      @anglaismoyen 4 หลายเดือนก่อน +13

      Even better: a line is just a degenerate quadratic:D

    • @Anik_Sine
      @Anik_Sine 4 หลายเดือนก่อน +9

      Taking the limit of the quadratic formula as a approaches 0 gives x = -c/b or -infinity, one of which is indeed the solution for bx +c = 0.

    • @microscopicallysmall
      @microscopicallysmall 2 หลายเดือนก่อน +2

      @@anglaismoyen does that mean a quadratic is a degenerate cubic

    • @anglaismoyen
      @anglaismoyen 2 หลายเดือนก่อน

      @@microscopicallysmall Why not?

    • @Wutheheooooo
      @Wutheheooooo 2 หลายเดือนก่อน

      @@microscopicallysmall a cube in 2 dimension is a square

  • @Adenfall
    @Adenfall 4 หลายเดือนก่อน +163

    This guy makes learning math easy and fun. Why can't all teachers be like him

    • @ErikOosterwal
      @ErikOosterwal 4 หลายเดือนก่อน +18

      Other teachers can't be like him because they don't have black and red markers. 🤣

    • @hookahsupplier.5155
      @hookahsupplier.5155 4 หลายเดือนก่อน +5

      Not all teachers have the merit to teach math, not only does it stipulate a formidable prowess, but also a level of self-composure and today we have a dearth of that type of teachers. Should only be thankful to have such people.

    • @kavinesh_the_legend
      @kavinesh_the_legend 4 หลายเดือนก่อน +3

      Those students are lucky

    • @MikehMike01
      @MikehMike01 4 หลายเดือนก่อน

      Most teachers are incompetent and overpaid (unions)

    • @blockyboxhead
      @blockyboxhead 4 หลายเดือนก่อน +2

      cuz hes him

  • @stephenhill4492
    @stephenhill4492 3 หลายเดือนก่อน +30

    I was aware of where the formula came from, but it’s great to see it explained in such an effective way.

    • @ruspg3d701
      @ruspg3d701 3 หลายเดือนก่อน

      same haha

    • @limwanjin361
      @limwanjin361 3 หลายเดือนก่อน

      Same

    • @Limited_Light
      @Limited_Light 3 หลายเดือนก่อน

      th-cam.com/video/mVI4HSwZTeQ/w-d-xo.html

  • @PatClevenger0709
    @PatClevenger0709 2 หลายเดือนก่อน +3

    49 years old, and i always accepted the quadratic equation without question. Thank you for showing the proof.

  • @illadiel6049
    @illadiel6049 4 หลายเดือนก่อน +48

    A short video explaining the logic behind the magic number would be handy

    • @AusterEngineer
      @AusterEngineer 4 หลายเดือนก่อน +9

      Idk if you already saw it but he did a video on that recently
      Edit: it was called solving an unfactorable quadratic equation from 7 days ago

    • @silver6054
      @silver6054 4 หลายเดือนก่อน +1

      I agree. The idea is to derive the formula and for those that care, showing the detail would be good. And it's all pretty trivial. You have x^2 + (b/a)x and you want to make that look like (x+K)^2 = x^2 + 2Kx +K^2. So matching the x term you must have 2K = (b/a) which quickly yields the magic thing that needs to be aded

  • @matteovillella1482
    @matteovillella1482 3 หลายเดือนก่อน +5

    It made me so happy as the familiar numbers started becoming apparent. As my math teacher would say: it gave me a “warm fuzzy feeling”

  • @Qermaq
    @Qermaq 3 หลายเดือนก่อน +5

    This is the best DIY channel. Learned to make my own quadratic equation on TH-cam today ;)

  • @Nikioko
    @Nikioko 4 หลายเดือนก่อน +10

    You can also use the pq formula: x₁,₂ = −p/2 ± √[(p/2)² − q]
    Advantage: Way easier to memorize.
    Disadvantage: You might have to divide the whole equation by a factor to get x² + px + q = 0.

  • @M1551NGN0
    @M1551NGN0 4 หลายเดือนก่อน +13

    Fun fact: it's also known as the Sridharacharya formula. Sridharacharya Formula is a mathematical formula that is used to solve quadratic equations. The Sridharacharya formula is commonly also known as the quadratic formula. Sridharacharya gave a method to solve the quadratic equations and hence it is named after the great mathematician and is called the Sridharacharya Formula. Source: cuemath

    • @drashokkumar9209
      @drashokkumar9209 4 หลายเดือนก่อน +2

      Shridharacharya multiplied the LHS by 4 . We get square of 2x . Completion of square looks easier then .

    • @M1551NGN0
      @M1551NGN0 4 หลายเดือนก่อน +2

      @@drashokkumar9209 yeah that's true though

    • @HAKUNAMATATA-wi3wi
      @HAKUNAMATATA-wi3wi 3 หลายเดือนก่อน

      Certainly this formula was the creation of SREEDHAR ACHARYA

  • @hyanparaiso7986
    @hyanparaiso7986 3 หลายเดือนก่อน

    This is by far the most amazing video explaining the quadratic formula that i have ever seen, thank you for making math a fun subject!!

  • @BulletWulf
    @BulletWulf 4 หลายเดือนก่อน +21

    Very Under-rated channel. Keep up the good work! I always wondered why the quadratic equation is true and never considered deriving it from the coefficients. Half way through I was wondering why the magic number was that value and you explained that too. Thanks for the cool lesson!

    • @bprpmathbasics
      @bprpmathbasics  4 หลายเดือนก่อน +2

      Thank you!

    • @highfall8145
      @highfall8145 4 หลายเดือนก่อน

      @@bprpmathbasics how did you upload the video and then theres comments over 4 months olkd

    • @amr0733
      @amr0733 4 หลายเดือนก่อน

      ​@@highfall8145it used to be unlisted

  • @TheTallRaver
    @TheTallRaver 4 หลายเดือนก่อน +4

    Fantastic explanation! I was just wandering about that this week and could not find a good video on TH-cam that would describe how this equation came about.
    Thank you and keep up the good work!👍👍

  • @maxhagenauer24
    @maxhagenauer24 4 หลายเดือนก่อน +14

    I always remembered it a different way that is faster.
    ax^2 + bx + c = 0
    ax^2 + bx = -c
    4a^2x^2 +4abx = -4ac
    4a^2x^2 + 4abx + b^2 = -4ac + b^2
    (2ax + b)^2 = b^2 - 4ac
    2ax + b = +- sqrt(b^2 - 4ac)
    2ax = -b +- sqrt(b^2 - 4ac)
    x = [-b +- sqrt(b^2 - 4ac)] / (2a)

    • @modemramachandraiah8038
      @modemramachandraiah8038 3 หลายเดือนก่อน +1

      Very good

    • @MathPhysicsEngineering
      @MathPhysicsEngineering 3 หลายเดือนก่อน +1

      On my chanel you can find a playlist with the derivation of formulas for all polynomial equations from order 2 up to order 4.
      I don't derive the full formula for the 4th-order equation, but show how can it be derived in principle. Anyone who watches my video for the 4-th order equation will be able to derive the formula by himslef given that he will be willing to put in the required patience and effort. I show 2 methods for the 4-th order equation.

    • @brandonsteele2826
      @brandonsteele2826 3 หลายเดือนก่อน

      Ok, but why would you start off by multiplying everything by 4a and then adding b²?

    • @maxhagenauer24
      @maxhagenauer24 3 หลายเดือนก่อน

      @@brandonsteele2826 So I could factor the left side.

    • @brandonsteele2826
      @brandonsteele2826 3 หลายเดือนก่อน

      @@maxhagenauer24 ok that makes sense

  • @russelllomando8460
    @russelllomando8460 4 หลายเดือนก่อน +5

    astounding - thanks 72 & keep learning

  • @user-zq6io5cs7f
    @user-zq6io5cs7f 4 หลายเดือนก่อน +3

    I was using it for many years but I didn't know why is it true
    I thought that it comes from square root completing but I wasn't sure
    Thanks for your work
    Your Chunnel is my favourite channel ( or channels ) in the math

  • @ROCKY-pu1zt
    @ROCKY-pu1zt 3 หลายเดือนก่อน +1

    Sir, Thank you. I will need to go over a few times, but thank you!

  • @andreonofre2625
    @andreonofre2625 3 หลายเดือนก่อน

    Very nice! I used the formula so many times but never had seen how to derive it.

  • @gleysonsantos3960
    @gleysonsantos3960 4 หลายเดือนก่อน

    You are amazing, thanks for making math enjoyable for us.

  • @someonespadre
    @someonespadre หลายเดือนก่อน +1

    I’m just a Grandpa making a hobby of relearning basic algebra, it’s fascinating.

    • @bprpmathbasics
      @bprpmathbasics  หลายเดือนก่อน

      That’s wonderful! Cheers!

  • @roger7341
    @roger7341 3 หลายเดือนก่อน +2

    I had been using "the quadratic formula" for decades without ever thinking about how it came into existence. So a while back I set out to derive it from an entirely different perspective. Assume that r and s are the two roots of ax^2+bx+c=0 or x^2+(b/a)x+(c/a)=0=(x-r)(x-s)=x^2-(r+s)x+rs. Thus, (r+s)=-(b/a) and rs=(c/a). How can we solve these two equations for r and s in terms of a, b, and c? Let u=(r+s)/2 and v=(r-s)/2. Then r=u+v and s=u-v. What does that get us? (r+s)=2u=-(b/a) so u=-b/(2a). rs=(u+v)(u-v)=u^2-v^2=c/a, which can be solved for v^2=u^2-c/a=[-b/(2a)]^2-c/a=(b^2-4ac)/(4a^2). From this equation we have v=√(b^2-4ac)/(2a). Finally, we have r=(u+v)=-b/(2a)+√(b^2-4ac)/(2a)=[-b+√(b^2-4ac)]/(2a) and s=(u-v)=-b/(2a)-√(b^2-4ac)/(2a)=[-b-√(b^2-4ac)]/(2a).

  • @prywatne4733
    @prywatne4733 3 หลายเดือนก่อน +2

    Here in Poland we are taught the quadratic formula a bit differently and I think it makes it easier for students to remember.
    so for ax² + bx + c = 0,
    we calculate the "Δ",
    Δ = b² - 4ac,
    if Δ > 0 then calculate the square root of this Δ, and then put it in
    x₁ = (-b-√Δ)/2a
    x₂ = (-b+√Δ)/2a
    if Δ = 0, just calculate x = -b/2a
    and if Δ < 0 then there is no answer

    • @Wutheheooooo
      @Wutheheooooo 2 หลายเดือนก่อน

      every equation have the same number of solution as their degree. I would rather say they have "no real solution" as there won't be confusion when we go further.

  • @muffinandme1
    @muffinandme1 2 หลายเดือนก่อน +1

    I went to high school from 1973 to 78, and excelled in maths. Recently I tried reviewing hs maths with the aid of my son's old text books and was going well until I hit logarithms ans trig. You see we learned both of these using log tables. Scientific calculators were not allowed to be used until the final part of 6th Form (or Year 12 as it had changed to). I found I had absolutely no clue how to proceed using a scientific calculator, and the text books unhelpfully assumed you already had that knowledge. I would give alot to have my old textbooks back from then, and a set of log tables of course!

  • @hbplayz4428
    @hbplayz4428 หลายเดือนก่อน

    when i started this chapter i viewed its derivation first, it makes a lot more sense after watching its derivation!

  • @ninjacodertech
    @ninjacodertech 3 หลายเดือนก่อน +1

    i literally thought about this yesterday!

  • @giantswingallday7001
    @giantswingallday7001 3 หลายเดือนก่อน

    Never have I appreciated the tic-tac-toe method in high school algebra, neither with the completing the square because it was so hard. That’s why I preferred the quadratic formula when it comes to solving these equations. Thanks so much sir!

  • @hv1785
    @hv1785 3 หลายเดือนก่อน +1

    Graduate degree in engineering… but never knew the derivation of this. Then again, I think most of us engineers are happy just knowing something works. But it’s really cool after all these years to find out where it comes from. Thanks!

  • @funprog
    @funprog หลายเดือนก่อน +1

    There is no magic number 2(b/2a)x is clearer to explain, it is the the product 2ab of the (a+b)^2 so for the b=b/2a => (x+ b/2a)^2. From that it is easy to note which term to add to complete the square i.e (b/2a)^2
    The formula is derived easily and it should be practised more to derive it.
    Saying magic numbers etc help you to forget it after a while if you dont know why you are doing something.
    1. Divide by a
    2. Make 2ab => 2/2 (b/a)
    3. Make clear the b factor 2x(b/2a)
    4. Add (b/2a)^2 to both sides
    5. Move the constant factors to the right side
    6. On the left you have a perfect square
    7. X^2+ (b/2a)^2 + 2x(b/2a) = -c/a + (b/2a)^2=>
    8. (X + b/2a)^2 = (b^2)4a^2 - ca
    9. Take the root etc...

  • @Solotris
    @Solotris 3 หลายเดือนก่อน

    This channel deserves billions of subscribers and views. 💜

  • @the.wealthversity
    @the.wealthversity 3 หลายเดือนก่อน

    One of the best math teachers!

  • @navi2710
    @navi2710 2 หลายเดือนก่อน

    If every student had you as a math teacher humanity would be experiencing a golden age.

  • @BuleriaChk
    @BuleriaChk 3 หลายเดือนก่อน +1

    There is no solutoin for x=0 because the three terms are affine vectors (thr polynimials of different orders span a vector space with real positive coefficients. Also, there are no negative numbers -c = a-b, b>a iff b-c=a, a-a =0, a=a If there are no negative numbers, there are no square roots of negative numbers.

  • @Yadavharsh.
    @Yadavharsh. 3 หลายเดือนก่อน +1

    It was given by Indian mathematician named shridhar acharya we learned it in India in class 7 as quadratic formula or so called shridhar acharya rule !!

  • @Yu1_H4X_
    @Yu1_H4X_ 4 หลายเดือนก่อน

    Thanks bro ❤

  • @mateuszpaczynski6195
    @mateuszpaczynski6195 3 หลายเดือนก่อน

    thank you so much :)

  • @mahmoudsaleh1292
    @mahmoudsaleh1292 4 หลายเดือนก่อน

    Excellent bro 💪👏👏👏

  • @amoghsod2212
    @amoghsod2212 3 หลายเดือนก่อน +1

    Well I proved the quadratic equation when it was taught to us a little differently,
    we have ax²+ bx +c = 0
    Firstly I would assume a ,b ,c are all real numbers
    So then we can tranform the equation by splitting the middle term , where let p + q = b , so ax² + px + qx + c = 0 , so if we assume that by splitting the middle term we can get all the answer of the quadratic (it will get in handy later) , we would get ax(x +p/a)+q(x+c/q) = 0 , which would get us (ax+q)(x+p/a) = 0 or( ax + q)(x + c/q) since we can split the terms to find the solutions the expression x+p/a and x+c/q must be equal , thus pq = ac , this would explain why when finding terms that would split we expect the coefficients of the split terms to = ac , but it is beneficial to us to use the former form , so we convert the form into (x+p/a)(x+q/a) so x = -p/a,-q/a
    But we know that p + q = b
    So by squaring, p²+q² + 2pq = b² , now lets subtract 4pq from both sides to get p² + q² -2pq = b² - 4pq , by applying some algebraic identities, (p-q)² = b² -4ac , since pq = ac
    So p - q = +or-√(b²-4ac)
    This is how we find if an equation has a real solution or not , since p + q = b a real number we also require p-q to be a real number since during addition the imaginary part of p and q may get cancelled so for the answers to be real p-q must be real and thus , +or-√(b²-4ac) must be a real number so b²-4ac>= 0 , for all real solutions .
    Now p + q = b
    p-q = I am not going to write it again
    so p = b +or- √(b² -4ac)
    So q would be identical as +or- decides which is p and which is q
    but we require x to be -p/a and -q/a
    So we do that and get
    x = {-b +or-√(b²-4ac)}/2a
    You can try and do that with equations of cubic and quartic it is going to get exponentially difficult or tetrationaly difficult, and if you are brave you may try for quintic , but you will not get it since galois theory , remember our assumption that we assume we can get all solutions by splitting the middle term , you would find if you want a complete solution I mean every solution, you won't get by basic arithmetic operations , since all the solutions of quintic equation aren't in the radical extension if the field of rationals 😀
    Edit :-
    Here you go for better reference
    th-cam.com/video/zCU9tZ2VkWc/w-d-xo.htmlsi=It38BrUP6lEqrg_y

  • @Aussiesnrg
    @Aussiesnrg 4 หลายเดือนก่อน +7

    I wish someone explained it that well when I was in high school

  • @edwardp7725
    @edwardp7725 3 หลายเดือนก่อน +1

    20 years later and I still remember this formula. The real question is why did I learn this formula in school? I have not once used this in real life to solve anything. Imagine if school taught me how to do my taxes, or make a resume, or invest and save money.

  • @Iomhar
    @Iomhar 4 หลายเดือนก่อน +4

    How about inserting this value of x into the original formula to see if it works?

    • @bprpmathbasics
      @bprpmathbasics  4 หลายเดือนก่อน

      Here’s an example th-cam.com/video/jCIfoKaHBX4/w-d-xo.htmlsi=SBBLgabSe0J8znHM

  • @juancarlossanchezveana1812
    @juancarlossanchezveana1812 3 หลายเดือนก่อน

    Excellent

  • @noo6423
    @noo6423 3 หลายเดือนก่อน

    i thought it was a bit more complicated than just moving everything around to make it x=, thank you for showing me i was wondering how about a week ago, thank you for showing me!

  • @samrudhb7855
    @samrudhb7855 3 หลายเดือนก่อน

    Awesome 👌

  • @darthrevan8376
    @darthrevan8376 3 หลายเดือนก่อน

    When I was in 8th grade I worked ahead in the math book because I was bored and came across a question which would require the quadratic formula. Since I did not know that it existed I ended up creating pretty much the formula but did not reach the last step of dividing both both under the 2a.

  • @StephenMarkTurner
    @StephenMarkTurner 3 หลายเดือนก่อน

    I do this derivation every year or to, just to keep it fresh. I think I first learned it in 1968 as a 12 year old.

  • @michaeledwards2251
    @michaeledwards2251 3 หลายเดือนก่อน

    An alternative method would be
    1. Assume the roots are equal, giving B/2A.
    2. Investigate the case of different roots, B/2A +/- delta
    3. Determine delta.
    I use this method, as it can be done by KISS, Keep It Simple.
    There are certainly many other methods : completing the square is only one example.

  • @drashokkumar9209
    @drashokkumar9209 4 หลายเดือนก่อน +6

    Another , and probably better , approach was suggested by Shridhara Acharya ( 8th century , India ) .
    Multiply the LHS by 4 . Then divide by a . You get square of 2x . Then, complete the square .

    • @jigglyCroissant
      @jigglyCroissant 3 หลายเดือนก่อน

      Literally the same thing . And an even better approach is to multiply both sides by 4a . Not boasting , just sayin'

    • @STEMHub18
      @STEMHub18 3 หลายเดือนก่อน

      Tell me you don't know anything about maths without telling me you don't know anything about maths. It is litreally the same. What he did and what you said is the same both are completing the squares...

  • @adriminecraft7000
    @adriminecraft7000 2 หลายเดือนก่อน +1

    "How exciting"

  • @khalidelgazzar
    @khalidelgazzar 3 หลายเดือนก่อน

    Awesome 😎👍

  • @88kgs
    @88kgs 4 หลายเดือนก่อน +1

    This is Shri DharaCharya formula, from Vedic maths

  • @TheJaguar1983
    @TheJaguar1983 3 หลายเดือนก่อน

    I remember this from Year 11 Maths Methods. I basically forgot the derivation of the formula and just used it.

  • @LearnerSupriya07
    @LearnerSupriya07 2 หลายเดือนก่อน

    This formula was given by Indian Mathematician name "Shridharacharya" Proud to be Indian.❤

  • @m.h.6470
    @m.h.6470 4 หลายเดือนก่อน +2

    I always dislike it, when people say that in √x² the √ and ² cancel each other. This is incorrect and leads to the common mistake, that people believe, that √ leads to ±, which it doesn't!
    The reality is, that √x² = |x|
    So if you have something like:
    x² = 25
    and you do √ on both sides, you don't end up with:
    x = ±5
    you actually end up with:
    |x| = 5
    This equation explains far better, what is going on and it has the same two solutions (x = 5 and x = -5), but it doesn't confuse anyone, that √25 = ±5, which simply isn't true!

    • @ZacharyBlue
      @ZacharyBlue 4 หลายเดือนก่อน

      I think you meant to write 5 instead of 25 in some of the lines

    • @m.h.6470
      @m.h.6470 4 หลายเดือนก่อน +1

      @@ZacharyBlue yes, you are correct, I fixed it.

  • @deanambrose1889
    @deanambrose1889 3 หลายเดือนก่อน +1

    श्री धराचार्य सूत्र 🇮🇳

  • @mimzim7141
    @mimzim7141 3 หลายเดือนก่อน

    A good exercise in also to plug back the solution for x in the quadratic and check that you do get zero.

  • @rcarioca
    @rcarioca 3 หลายเดือนก่อน

    How did they figure out to add (1/2 B) squared to both sides ?

    • @habl844
      @habl844 3 หลายเดือนก่อน

      See the Wikipedia page for "Completing the square", there's a nice geometric version as well. Back in the day it was much more common to write math with geometry.

  • @user-uq5qs5uh9k
    @user-uq5qs5uh9k 2 หลายเดือนก่อน

    Nostalgic ❤

  • @rykehuss3435
    @rykehuss3435 4 หลายเดือนก่อน

    When will you do something difficult like complex analysis or algebraic geometry?

  • @asheraley779
    @asheraley779 3 หลายเดือนก่อน

    8 minute video and it seems simple now that I'm learning series in calculus, but why wasn't I taught this?

  • @Ultranger
    @Ultranger 4 หลายเดือนก่อน +2

    I’ve been trying to find a similar formula but for cubic functions which is hard

    • @remus_lupin
      @remus_lupin 4 หลายเดือนก่อน

      Check Mathologer. It's a very complex equation, which he specializes in, often with visuals. Might need to scroll for a while, so do a search, instead.

    • @carultch
      @carultch 4 หลายเดือนก่อน

      Mathologer does an excellent job showing where the cubic formula comes from, and how to use it:
      th-cam.com/video/N-KXStupwsc/w-d-xo.html

  • @RikiFaridoke
    @RikiFaridoke 9 วันที่ผ่านมา

    Please, proof it by complex analysis method, can you do it sir?

  • @katathoombz
    @katathoombz 2 หลายเดือนก่อน

    I _might_ have taken my chances in the national abiturient test on maths during my upper secondary schooling, if we had had maths-tubers like this back then...

  • @AFSMG
    @AFSMG 3 หลายเดือนก่อน

    Brillante

  • @Rao_Sahab.700
    @Rao_Sahab.700 3 หลายเดือนก่อน +2

    It is shridharacharya formula

  • @user-uv9rn6ty9r
    @user-uv9rn6ty9r 3 หลายเดือนก่อน +1

    In Korea,15 years old students can prove that problem! That is very easy problem in Korea.

    • @papaysum183
      @papaysum183 3 หลายเดือนก่อน

      In INDIA 13 years old class 8th students can prove it. Because this is our school's syllabus .

    • @munindraboro228
      @munindraboro228 3 หลายเดือนก่อน

      ​​@@papaysum183no they don't💀,quadratic equation comes itself in 10th class where 15 or 16 years study

  • @sparshsharma5270
    @sparshsharma5270 4 หลายเดือนก่อน

    I remember learning Completing the Square method 6 years back in 9th grade.

    • @JayTemple
      @JayTemple 4 หลายเดือนก่อน

      I was self-taught, and I memorized the formula before I could complete the square!

  • @bprpmathbasics
    @bprpmathbasics  5 หลายเดือนก่อน +27

    A faster way to prove the quadratic formula: 👉 th-cam.com/video/3DSNBmK7W84/w-d-xo.html

    • @glorymanheretosleep
      @glorymanheretosleep 4 หลายเดือนก่อน +4

      We all know where it came from. It came from YOU bprpmathbasics!

    • @leonardobarrera2816
      @leonardobarrera2816 4 หลายเดือนก่อน +4

      Did you remember the partial derrivative for the quadratic formula on blackpenredpen’s channel!!!
      That was awesome

    • @bprpmathbasics
      @bprpmathbasics  4 หลายเดือนก่อน +3

      @@leonardobarrera2816 thanks!

    • @reminderIknows
      @reminderIknows 4 หลายเดือนก่อน +4

      how was this comment 1 month ago??
      was it unlisted?

    • @leonardobarrera2816
      @leonardobarrera2816 4 หลายเดือนก่อน

      @@bprpmathbasics you are well come

  • @fulltimeslackerii8229
    @fulltimeslackerii8229 4 หลายเดือนก่อน

    Basically, you get the solution by completing the square on the generic formula. It’s so cool.

  • @david_porthouse
    @david_porthouse 3 หลายเดือนก่อน

    The other version of the formula is x = 2c / (-b +- sqrt(b*b - 4ac)). Use whatever version avoids an arithmetic subtraction and does not lead to nonsense as a -> 0. In the real world, quadratic equations are often only slightly quadratic and we ought to know about this other version.

  • @Kyeetumus
    @Kyeetumus 4 หลายเดือนก่อน +2

    Cool

  • @champu823
    @champu823 4 หลายเดือนก่อน

    Its the perfect square method !!!!

  • @bellykumar1984
    @bellykumar1984 2 หลายเดือนก่อน

    sqrt (2x+3)=x^2-6, how to solve it

  • @imnotonmars
    @imnotonmars 3 หลายเดือนก่อน

    This man is a genius wtf

  • @Wandering_Horse
    @Wandering_Horse 4 หลายเดือนก่อน

    Bravo! I am going to go through that on my white board until it's burned into memory!

  • @RikiFaridoke
    @RikiFaridoke 3 หลายเดือนก่อน

    Hi guys, please try quarternion method to proof it, can you do it guys?

  • @youssefchihab1613
    @youssefchihab1613 4 หลายเดือนก่อน

    Shouldn't it be an equivalence instead of an implication ?

  • @stevenranck5478
    @stevenranck5478 3 หลายเดือนก่อน

    There’s a better form of the quadratic formula that does allow ‘a’ to be 0, and it should be taught in schools instead:
    X = -2c / (b + - sqrt( b^2 - 4ac ))

  • @morselclash6414
    @morselclash6414 3 หลายเดือนก่อน

    What's crazy is that I just proved the quadratic formula (to waste time), then I open youtube and see this. Stalkers, perhaps?

  • @rohitvsk93
    @rohitvsk93 2 หลายเดือนก่อน

    This is also known as Shreedharacharya rule/ Completing the square
    I'm a 10th grader

  • @Beyondskylimits32
    @Beyondskylimits32 4 หลายเดือนก่อน

    I came for here for my math test tomorrow 😂

  • @brucegreer7201
    @brucegreer7201 3 หลายเดือนก่อน

    In my view, completing the square is an easier method to use to solve quadratic equations. Everything falls out so easily and it's pretty easy to teach.

  • @notar2123
    @notar2123 4 หลายเดือนก่อน

    There is a much longer, but far more intuitive approach to prove the quadratic formula. In fact, you prove something more general that the quadratic formula, namely the fact that any polynomial of the form ax²+bx+c can be written as a(x-x₁)(x-x₂).
    Just put in the quadratic formula for x₁ and x₂, using the negative value of √(b² -4ac) for x₁ and the positive value for x₂. Now expand everything, and after a lot of calculation and cancelation, you will end up with ax²+bx+c, which is exactly what we wanted to prove. Thus, once you set ax²+bx+c = 0, you can rewrite the equation as a(x-x₁)(x-x₂) = 0, which is trivial and the only solutions are x=x₁ and x=x₂.
    Would I recommend this approach? Of course not, but it is interesting none the less.

    • @NadiehFan
      @NadiehFan 4 หลายเดือนก่อน

      There is a logical flaw in your reasoning, because if you start from the expressions for x₁ and x₂ in terms of a, b, c and show that a(x − x₁)(x − x₂) = 0 implies ax² + bx + c = 0 this does not imply that the converse is true, unless you also show that all steps are reversible (which they are). But this still would be insatisfactory, because then you only have demonstrated that the formula is true, not how it can be found if you don't already know it.
      But the idea to derive the quadratic formula from (properties of) the roots x₁ and x₂ is perfectly feasible and instructive. According to the factor theorem a polynomial P(x) has a factor (x − x₁), that is, P(x) = (x − x₁)Q(x) for some polynomial Q(x), _if and only if_ x = x₁ is a root of P(x), that is, P(x₁) = 0.
      With a repeated application of this theorem we can show that if a quadratic equation ax² + bx + c = 0 (a, b, c real, a ≠ 0) has the roots x₁ and x₂, then we must have
      ax² + bx + c = a(x − x₁)(x − x₂)
      Expanding the right hand side of this identity we have
      ax² + bx + c = ax² − a(x₁ + x₂)x + ax₁x₂
      Two polynomials are identical if and only if their corresponding coefficients are identical (this is also a theorem) so we have b = − a(x₁ + x₂) and c = ax₁x₂ and since a ≠ 0 this implies
      x₁ + x₂ = −b/a
      x₁x₂ = c/a
      These are of course Vieta's formulas for the roots of the quadratic equation ax² + bx + c = 0. Now, the question is if we can derive expressions for x₁ and x₂ in terms of a, b, c from these two relations between the roots and the coefficients of the quadratic equation, and the answer is yes.
      The idea is to first find an expression for the _difference_ x₁ − x₂ in terms of a, b, c, because if we have expressions for both x₁ + x₂ and x₁ − x₂ then x₁ and x₂ will be easy to find by adding and subtracting, because we have (x₁ + x₂) + (x₁ − x₂) = 2x₁ and (x₁ + x₂) − (x₁ − x₂) = 2x₂ so one root will be half the sum of x₁ + x₂ and x₁ − x₂ and the other root will be half the difference between x₁ + x₂ and x₁ − x₂.
      To get an expression for x₁ − x₂ in terms of a, b, c we can use the _identity_ (p − q)² = (p + q)² − 4pq with p = x₁ and q = x₂ to find
      (x₁ − x₂)² = (x₁ + x₂)² − 4x₁x₂ = (−b/a)² − 4c/a = b²/a² − 4ac/a² = (b² − 4ac)/a²
      This is interesting, because a² is positive since a ≠ 0 and if x₁ and x₂ and therefore also x₁ − x₂ must be real, then its square (x₁ − x₂)² cannot be negative so b² − 4ac cannot be negative if the equation ax² + bx + c = 0 (a, b, c real, a ≠ 0) is to have real roots. So we have already found what is known as the _discriminant_ b² − 4ac of the quadratic before we have even found a formula for its roots.
      Now, supposing that b² − 4ac is nonnegative, it follows that we can either have
      x₁ − x₂ = √(b² − 4ac)/a
      or
      x₁ − x₂ = −√(b² − 4ac)/a
      But we only need a single value for x₁ − x₂, because inverting the sign of x₁ − x₂ simply amounts to swapping the values of x₁ and x₂. So, let's take the first expression for x₁ − x₂, then we have
      2x₁ = (x₁ + x₂) + (x₁ − x₂) = −b/a + √(b² − 4ac)/a = (−b + √(b² − 4ac))/a
      2x₂ = (x₁ + x₂) − (x₁ − x₂) = −b/a + √(b² − 4ac)/a = (−b − √(b² − 4ac))/a
      and so we find that
      x₁ = (−b + √(b² − 4ac))/2a
      x₂ = (−b − √(b² − 4ac))/2a
      and we have derived the quadratic formula for the solutions of ax² + bx + c = 0 from the known sum and product of its roots.

    • @notar2123
      @notar2123 4 หลายเดือนก่อน

      @@NadiehFan Yes I am aware of what you wrote and that math teachers don't like it when a students use a regressive proof. In such a case, however, I find it pointless to insist on that, since all a student would have to do is rewrite the same steps in the reverse order and bam - the assertion follows from the presumption (I apologize if I don't use the correct terms, I did not study math in the English language).
      Also, your approach requires the use of the factor theorem, so either one would have to prove it, or its use would have to be explicitly allowed. The point of my original comment was, that is the easiest way an actual student could prove the formula - 0 brainpower needed, 0 creativity needed, it is a very naive approach that requires only the knowledge of the actual quadratic formula beforehand (you could call it a proof for dummies). Easy in terms of actual thinking, ridiculously hard in terms of calculations. That's also why I said I would never recommend someone to use it, I just found it to be interesting in a way. I am no mathematician, however.

    • @NadiehFan
      @NadiehFan 4 หลายเดือนก่อน

      @@notar2123 Of course proving Vieta's formulas without using the quadratic formula requires the use of the factor theorem, but there are elementary proofs for that which are accessible to high school students. In fact in my country this was taught in high school in my time, but that was a long time ago. I wouldn't recommend any high school math teacher to prove or derive the quadratic formula by starting from Vieta's formulas, but in my opinion that would still be preferable to working back from the quadratic formula to a quadratic polynomial.
      But all this is really a moot issue, because there is a far easier method to derive the quadratic formula which is known as Sridhara's method and which is perfectly suitable for high school usage:
      ax² + bx + c = 0
      ax² + bx = −c
      4a²x² + 4abx = −4ac
      4a²x² + 4abx + b² = b² − 4ac
      (2ax + b)² = b² − 4ac
      2ax + b = √(b² − 4ac) ⋁ 2ax + b = −√(b² − 4ac)
      2ax = −b + √(b² − 4ac) ⋁ 2ax = −b − √(b² − 4ac)
      x = (−b + √(b² − 4ac))/2a ⋁ x = (−b − √(b² − 4ac))/2a
      This is accesible to high school students who have had some exposure to solving quadratics by completing the square (which is also used for finding the coordinates of the vertex of a parabola which is the graph of a quadratic function) and indeed all steps are reversible. The advantage of Sridhara's approach over the conventional derivation which starts by converting the quadratic into a monic quadratic equation (by dividing both sides by a) is that this derivation avoids the use of fractions until the very last step by first multiplying both sides by 4a.

  • @ludoviclemaignen9432
    @ludoviclemaignen9432 3 หลายเดือนก่อน

    It is a long time since I left school, so I don't remember how to derive it, but I do remember that my math teacher showed us how to derive it. I am surprised that you feel the need to do a video about it. Does that mean that modern teachers just drop it on students without explaining it?

  • @dennissvensson7933
    @dennissvensson7933 3 หลายเดือนก่อน

    ax² + bx + c = 0
    ax² + bx = -c
    4a²x² + 4abx = -4ac
    (2ax)² + 4abx + b² = b² + 4ac
    (2ax + b)² = b² + 4ac
    Is a more Nice way

  • @JubeiKibagamiFez
    @JubeiKibagamiFez 3 หลายเดือนก่อน

    I can't believe I didn't leave a comment when I watched this.

  • @rgsboys3423
    @rgsboys3423 2 หลายเดือนก่อน

    It was given by mathematician named Shridharacharya in 8th century

  • @jbreezy101
    @jbreezy101 3 หลายเดือนก่อน

    0:12-0:17 then it would be linear, and you wouldn’t have to use the quadratic formula. You could just solve for x in terms of b & c.

  • @mimzim7141
    @mimzim7141 3 หลายเดือนก่อน

    You solved in 8 minutes what took ancient people centuries to find out.

  • @nigamroy
    @nigamroy 3 หลายเดือนก่อน +1

    This is called " Sridhar Acharya formula"

  • @nithinsirimanne2924
    @nithinsirimanne2924 2 หลายเดือนก่อน

    Simply the target is to find x

  • @divyam.1098
    @divyam.1098 3 หลายเดือนก่อน

    It was discovered by an Indian mathematician Shreedharancharya

  • @katathoombz
    @katathoombz 2 หลายเดือนก่อน

    Okay, so that's where it comes from. But...why do we want to to complete the square?
    • Why do we always want X²+BX on one side O__o
    why do we do that? Who came up with the need? How?
    The proof was shown even way back when in school, but I had, and have, no idea of the _why_ we want it.
    Tbh I don't even have any idea of how or why we come across with any quadratic functions. And I'm not even talking of the "real life use" sense, but the "how'd we end up pondering this from addition and multiplication" :D

  • @stevenlitvintchouk3131
    @stevenlitvintchouk3131 15 วันที่ผ่านมา +1

    The method of solving quadratics by completing the square was first discovered by an Islamic mathematician, Al-Khwarizmi, in the 9th century A.D. Completing the square is still taught to schoolchildren today.

  • @JulesMoyaert_photo
    @JulesMoyaert_photo 3 หลายเดือนก่อน

    👍

  • @motomadman573
    @motomadman573 2 หลายเดือนก่อน

    thats a lot of whiteboard pens

  • @comdo777
    @comdo777 4 หลายเดือนก่อน

    asnwer=1+2/5

  • @harrymatabal8448
    @harrymatabal8448 3 หลายเดือนก่อน

    That the problem with great people. Where did it come from. Take sir Isaac Newton. After lunch he was resting under an apple tree. An apple fell on his head. Instead of eating it and resting, he wants to know why the apple fall down and not shoot up😂😂😂

  • @poornimaappu3235
    @poornimaappu3235 4 หลายเดือนก่อน

    Why all teacher in college give pressure to score in exam rather than to understand the concept 😢

  • @joelchristophr3741
    @joelchristophr3741 3 หลายเดือนก่อน

    Master I have an integration challenge for you...
    Int 0 to 1 [ (e^x)/(x+1) ] dx
    no one still answered.. let me see if you can

  • @OrenLikes
    @OrenLikes 3 หลายเดือนก่อน

    Well, if a=0, then x=-c/b...