A Nice Exponential Equation | Math Olympiads

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  • เผยแพร่เมื่อ 18 พ.ย. 2024

ความคิดเห็น • 54

  • @stevenlitvintchouk3131
    @stevenlitvintchouk3131 ปีที่แล้ว +3

    Bunch of cases to consider. Case I: Exponent = 0. Case II: 2x+6 = 1 and exponent = 1. Case III: 2x+6 = -1 and the exponent is an even natural number.

    • @ferdinandtrefle912
      @ferdinandtrefle912 ปีที่แล้ว

      This EQUATION is as X^p=1
      So X^p=1 in R
      • base X=1 and exponent p in R,
      • or X=-1 and p even integer ,
      • or p=0 and X0:
      See origine here:
      th-cam.com/video/aGBe9ObqlwA/w-d-xo.html

    • @MyOneFiftiethOfADollar
      @MyOneFiftiethOfADollar ปีที่แล้ว

      "Bunch" must mean something different to you.

  • @axelkeithgranath
    @axelkeithgranath ปีที่แล้ว +6

    Easy mode:
    log both side ---> (x²-9)ln(2x+6) = 0 (any log of 1 = 0)
    expend ---> (x+3)(x-3)ln(2x+6) = 0
    check for the zero solutions :
    ---> ln(2x+6) = 0 so 2x+6 = 1 ---> x = -5/2
    ---> (x-3) = 0 ---> x = 3
    ---> (x+3) = 0 ---> plug it; gives 0⁰ ---> not a solution
    Done!

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว +2

      With log some solutions are lost as in:
      (2x-18)^(x^2-9)=1 ===>
      (x^2-9)ln(2x-18)=0 ===>for x=-3 and x=3, ln(2x-18) is not defined bcse 2x-18

    • @MyOneFiftiethOfADollar
      @MyOneFiftiethOfADollar ปีที่แล้ว

      logarithms completely unnecessary. Just check the cases B^0 = 1 and 1^n = 1. (Easier mode)

  • @kobalt4083
    @kobalt4083 ปีที่แล้ว +2

    How to Solve: When we have an exponent equal to 1, for example a^b=1, then there are only two possibilities: the base is 1 or the power is 0, so when a^b=1, a=1 or b=0! We also need to plug in our possible values of x, in case there are any extraneous solutions. Using this knowledge, the problem is quite straightforward!
    Our possibilities are 2x+6=1 and x^2-9=0. Solve both equations for x:
    2x+6=1 -> 2x=-5 -> x=-5/2=-2.5=-2 1/2.
    x^2-9=0 -> x^2=9 -> x=+/-3
    So our possiblities are x=-5/2 and x=+/-3. All are valid except x=-3, which, when substituted in, produces 0^0, an indeterminate expression.
    Therefore, the correct solutions for the value of x is x=3 and x=-5/2.

    • @mdyankee55
      @mdyankee55 ปีที่แล้ว

      One other possibility that needs to be checked is for the base to be equal to -1 and the exponent is also an even integer. For the base to be -1, x would have to be -7/2. But if x = -7/2, the exponent would not be an even integer. So there is no additional solution from this path, but it's an option that needed to be checked.

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว

      This EQUATION is as X^p=1 where X=2x+6 and p=x^2-9
      So X^p=1 in R
      • base X=1 and exponent p in R:
      2x+6=1 and x^2-9 in R ===>x=-5/2 is solution
      • or X=-1 and p even integer:
      2x+6=-1 and x^2-9 even: no solution
      • or p=0 and X0:
      x^2-9=0 and 2x+60 ==> x=3 solution but x=-3 is not solution bcse 2x+6=0.
      See origine here:
      th-cam.com/video/aGBe9ObqlwA/w-d-xo.html

    • @kobalt4083
      @kobalt4083 ปีที่แล้ว

      @@mdyankee55 Smart. Thanks for reminding me that.

  • @abhi38358
    @abhi38358 ปีที่แล้ว +3

    ×=3, x =-5/2.

  • @ManjulaMathew-wb3zn
    @ManjulaMathew-wb3zn 7 หลายเดือนก่อน

    If the base was 3x-12 then it will be -1 when x=11/3. The exponent will be 40/3
    So (-1)^(40/3) = ((-1)^1/3)^40
    =(1-)^40 =1. Even if you take 40th power first and then cubic root the same result.
    Basically when the base equals to -1 the exponent has to be a rational number with even numerator which include even integers.

  • @ilyashick3178
    @ilyashick3178 ปีที่แล้ว

    take both sides as log_10 and (x^2 - 9 ) log_10 (2x+6)=log_10 ( 1 ) =>> (x^2-9)log_10 (2x+6) =0. notice should 2x+6 > 0 or x > -3. next first step x^2-9 =0 === > x=3 or x+-3 so x=-3 nor sulution. second step log_10 (2x+6) = 0 means 10^0=2x+6 ====> 2x=-5 and x = - 2.5 which in domain of x>-3 resukt is x=3 or x=-2.5

  • @XJWill1
    @XJWill1 ปีที่แล้ว +1

    Have you ever tried to solve this equation? It is a tricky one...
    x^((x-1)^2) = 2*x + 1

  • @BorisRaifler
    @BorisRaifler ปีที่แล้ว

    For 3-rd case (b=-1) a is also can be rational non-integer, if a nominator is even and a denominator is odd. But as I know, the negative base for non-integer exponent is'n recommended...

    • @ManjulaMathew-wb3zn
      @ManjulaMathew-wb3zn 7 หลายเดือนก่อน

      I think you are correct. If the base was 3x-12 then it will be -1 when x=11/3. The exponent will be 40/3
      So (-1)^(40/3) = ((-1)^1/3)^40
      =(1-)^40 =1. Even if you take 40th power first and then cubic root the same result.
      Basically when the base equals to -1 the exponent has to be a rational number with even numerator.

  • @GreenMeansGOF
    @GreenMeansGOF ปีที่แล้ว

    If you’re using an iPad, that extra line at the end is a glitch that happens if you are charging the iPad so you may want to keep that in mind.

  • @fabriziosantin6063
    @fabriziosantin6063 ปีที่แล้ว +3

    For the 3rd case, what about rational numbers with even numerator and odd denominator for the exponent?

    • @mr.d8747
      @mr.d8747 ปีที่แล้ว

      *Yeah, but 49 is clearly odd and 4 is clearly even.*

  • @alextang4688
    @alextang4688 ปีที่แล้ว

    For 2x+6>=0, take log and find some answer.
    For 2x+6

  • @mcwulf25
    @mcwulf25 ปีที่แล้ว

    By inspection, either the exponent is 0 or the base is 1, or -1 if the exponent is even. So +/-3 or -5/2 but not -7/2. In fact not -3 either because the base will be zero. Haven't looked at complex solutions.

  • @broytingaravsol
    @broytingaravsol ปีที่แล้ว +1

    ​x=3, -5/2

  • @Wangkheimayum421
    @Wangkheimayum421 ปีที่แล้ว

    X²-9 =0
    X= 3 or x=-3

  • @cigancu4143
    @cigancu4143 ปีที่แล้ว

    or you can just multiply both sides with 0 and always get the correct answer😊

  • @Bertin-q3y
    @Bertin-q3y 8 หลายเดือนก่อน

    X=3

  • @franckplanks
    @franckplanks ปีที่แล้ว

    Solved by inspection. X= 3,-3,-2.5

    • @renfreak
      @renfreak ปีที่แล้ว +1

      -3 results in 0^0

    • @franckplanks
      @franckplanks ปีที่แล้ว

      @@renfreak Didn't see that initially. Thanks

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว

      Why are some comments are hidden ?

  • @rakenzarnsworld2
    @rakenzarnsworld2 ปีที่แล้ว

    x = *3* or -3 or *-5/2*

  • @kianmath71
    @kianmath71 ปีที่แล้ว

    X= -2.5, 3

  • @dinoslama8243
    @dinoslama8243 ปีที่แล้ว

    x=3

  • @MathOrient
    @MathOrient ปีที่แล้ว

    well done :)

  • @Roq-stone
    @Roq-stone ปีที่แล้ว

    What do you use to do your presentation (what software)?

  • @mbmillermo
    @mbmillermo ปีที่แล้ว

    What is the limit as x approaches -3? Does it matter if it approaches from the negative or positive side?

    • @Sugarman96
      @Sugarman96 ปีที่แล้ว +1

      From the positive side it's pretty straightforward, because then the base of the exponent is positive and you just use L'Hôpital's rule.
      The negative side is trickier, because then you're dealing with complex numbers. You can still use L'Hôpital's rule, but you gotta be careful with the branch of the power function you're taking.

    • @Roq-stone
      @Roq-stone ปีที่แล้ว +1

      Think of tangent 90 degrees. y= tan x as a function, you will notice that an asymptote occurs at 90 degrees and as x approaches the asymptote the values for y are totally different for each side. Well, a similar situation exists in this case. The graph plot shown in the end here demonstrates that.

  • @levskomorovsky1762
    @levskomorovsky1762 ปีที่แล้ว

    Why is the answer x = -3 not acceptable? After all, 0 ^0 = 1.

    • @rickdesper
      @rickdesper ปีที่แล้ว

      0^0 is undefined. There is no continuous extension of x^y as x, y both go to zero. If x=0 and y varies, the function is 0. If y=0 and x varies, the function is 1.

    • @levskomorovsky1762
      @levskomorovsky1762 ปีที่แล้ว

      @@rickdesper Thank you!
      But what about the well-known expressions: (0^O)^0 = 1^0 = 1, and: 0^(0^0) = 0^1 = 0?

    • @oenrn
      @oenrn 9 หลายเดือนก่อน

      ​@levskomorovsky1762 they're wrong

  • @dinoslama8243
    @dinoslama8243 ปีที่แล้ว

    x=plus ou moins 3

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว +3

      Pourquoi il masque certains commentares ?
      Sûrement pour masquer son copiage!
      Comme ici:
      X^p=1 in R
      • base X=1 and exponent p in R,
      • or X=-1 and p even integer,
      • or p=0 and X0,
      See origine here:
      th-cam.com/video/aGBe9ObqlwA/w-d-xo.html

  • @maryamsiapouri9203
    @maryamsiapouri9203 ปีที่แล้ว

    میتونین هم از همون اول کاراز دو طرف لگاریتم بگیرید تا جواب ها بدست بیاد

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว

      Why are some comments hidden ?

    • @Frank-kx4hc
      @Frank-kx4hc ปีที่แล้ว

      X^p=1 in R
      • base X=1 and exponent p in R,
      • or X=-1 and p even integer,
      • or p=0 and X0,
      See origine here:
      th-cam.com/video/aGBe9ObqlwA/w-d-xo.html

    • @maryamsiapouri9203
      @maryamsiapouri9203 ปีที่แล้ว

      @@Frank-kx4hcim from iran

    • @maryamsiapouri9203
      @maryamsiapouri9203 ปีที่แล้ว

      @@Frank-kx4hc
      If you take the logarithm of both sides of the equation, the answer will be much easier

    • @maryamsiapouri9203
      @maryamsiapouri9203 ปีที่แล้ว

      log 1 =log(2x+6)^x^2-9

  • @shariecebrewster5962
    @shariecebrewster5962 ปีที่แล้ว

    I am there's

  • @MyOneFiftiethOfADollar
    @MyOneFiftiethOfADollar ปีที่แล้ว

    You get plenty of page views without falsely representing this problem as Olympiad level in difficulty. B^0 = 1 and 1^n = 1 is all that is required.
    Still don't get how you get so much attention by working the same type of of small "nice" constant type problems. You literally have 7-8 problem types that you rework ad infinitum. I guess no need to expand your math knowledge.
    It must be your smooth psychiatrist couch voice.