Can you find the area of the Green Square? | Circle | (Step-by-step explanation) |

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  • @bigm383
    @bigm383 10 หลายเดือนก่อน +4

    Thanks Professor, great solution!❤

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Glad to hear that!
      You are very welcome!
      Thanks ❤️

  • @jimlocke9320
    @jimlocke9320 10 หลายเดือนก่อน +8

    Let the side of the square have length s. At 3:00, construct AO. Since the area of the circle is π, its radius is 1, as found in the video. So, OA = OB = OE = OF = 1. OP = PE - OE. PE is equal to the side of the square, or s, and OE = 1, so OP = s - 1. AP is half the length of the side of the square, or s/2. Apply the Pythagorean theorem to ΔAPO: 1² = (s - 1)² + (s/2)², 1 = s² -2s + 1 + s²/4, 0 = 5s²/4 - 2s, which has two roots, s = 0 and 5s/4 = 2, or s = 8/5. We discard s = 0, so s = 8/5. The area of the square is s² = (8/5)² = 64/25 = 2.56 sq. units, as PreMath also found.

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️

    • @jimlocke9320
      @jimlocke9320 10 หลายเดือนก่อน

      @@PreMath , thanks for the compliment and thank you for posting these challenging geometry problems, along with your solutions! You are enhancing our interest in geometry two ways. First, you stimulate us to try to solve the problem on our own before watching your solution, and, when we find that our methods are alternatives to yours, post our solutions. Secondly, when we watch your solution, we may see alternative ways to solve the problem. Take pride that we are carefully following and studying your solution. Sometimes, we will see a way to simplify your solution and you should not feel embarrassed that you overlooked the simplification! Other times, we are just finding different methods to reach the same end result. Keep up the good work!

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      @@jimlocke9320
      Thanks dear ❤

  • @ybodoN
    @ybodoN 10 หลายเดือนก่อน +3

    APE and BPE are 1:2:√5 right triangles, so ∠AEP and ∠BEP are tan⁻¹ 1/2 ⇒ ∠AEB is tan⁻¹ 4/3 (by trig. identities).
    Therefore, the chord AB is the major cathetus of a 3:4:5 right triangle whose hypotenuse is a diameter of the circle.
    Since the area of the circle is π, its diameter is 2 so AB is 2·4/5 = 8/5 and the area of the square is 64/25 = 2.56 u².

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️

  • @luigipirandello5919
    @luigipirandello5919 10 หลายเดือนก่อน

    Very nice solution. Easy to understand. Thank you.

  • @marcelowanderleycorreia8876
    @marcelowanderleycorreia8876 10 หลายเดือนก่อน +1

    Very good!! Thank you Sir!

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      You are very welcome!
      Thanks ❤️

  • @thomast.2060
    @thomast.2060 10 หลายเดือนก่อน +3

    thank you for this video
    I used the triangle OPA :
    OA = r = 1 , OP = x , AP = 1/2 AB = ( 1 + x )/2
    Pythagoras => x² + (( 1 + x )/2 )² = 1² x² + 1/4 ( 1 + 2x + x² ) = 1 5/4 x² + 1/2 x - 3/4 = 0
    x² + 2/5 x - 3/5 = 0 => x1,2 = - 1/5 +/- sqrt( 1/25 + 15/25 )
    with x = 3/5 we get AB = 8/5 and the Area of the square is : A = ( 8/5 )² = 64/25

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      You are very welcome!
      Thanks ❤️

    • @thomast.2060
      @thomast.2060 10 หลายเดือนก่อน

      thank you@@PreMath

    • @MrPaulc222
      @MrPaulc222 10 หลายเดือนก่อน +1

      Pretty close to how I did it (I invented F rather than P though).
      Using your labelling rather than mine, it gave me a right triangle of sides (1/2)x, (x-1), and 1, from which x can be calculated by Pythagoras.

  • @contillojakexander2003
    @contillojakexander2003 5 หลายเดือนก่อน

    Thank you so much

  • @AmirgabYT2185
    @AmirgabYT2185 9 หลายเดือนก่อน +1

    S=2,56

  • @Ramkabharosa
    @Ramkabharosa 9 หลายเดือนก่อน +1

    Let AD meet the circle at G & draw a perpendicular from G to meet EF at H.
    Since AD is parallel to EF, ∠GOE=∠ AOF. So we get |DG| = |EH| = |PF| = 1. By the
    tangent-secant theorem from the point D, we get |DE|²=|DG|.|DA|. ∴ [(2-x)/2]²=x(2-x).
    Since 2-x≠0, (2-x)/4=x. ∴ 5x-2=0. So x=2/5. ∴ area(ABCD)= (2 -2/5)²=(8/5)² = 64/25.

  • @raya.pawley3563
    @raya.pawley3563 10 หลายเดือนก่อน

    Thank you

  • @wackojacko3962
    @wackojacko3962 10 หลายเดือนก่อน +1

    Basic Concept Reviews are very nice! And like labeling everything, before proceeding too solve I include writing out Basic Concepts that I feel may help in solving any given problem by inspection. 🙂

    • @PreMath
      @PreMath  10 หลายเดือนก่อน +1

      Glad to hear that!
      Thanks ❤️

  • @wes9627
    @wes9627 10 หลายเดือนก่อน

    Use intersecting chord theorem. Radius of circle is 1 and diameter is 2. Let AB represent the side length of the square.
    Extend a horizontal line from E through O to F on the opposite side of the circle. Mark G where this line intersects AB.
    Then AG*BG=EG*FG yields (AB/2)^2=AB(2-AB) or 5AB^2-8AB=0; AB=8/5 units. Green area=AB^2=64/25 square units.

  • @jamestalbott4499
    @jamestalbott4499 10 หลายเดือนก่อน +1

    Thank you!

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      You are very welcome!
      Thanks ❤️

  • @phungpham1725
    @phungpham1725 10 หลายเดือนก่อน +1

    1/ Let a be the side of the square and F the intersecting point of DA and the circle.
    We have r=1 and BF is the diameter
    So OP= EP-EO=a-1 -->FA=2OP= 2a-2--> DF=DA-FA=2-a
    By using tangent theorem
    Sq ED=DF x DA--> sqa/4=a.(2-a)--> 5sqa-8a=0
    a=8/5
    Area=64/25=2.56 sq units

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️

  • @mathbynisharsir5586
    @mathbynisharsir5586 10 หลายเดือนก่อน +1

    Fantastic video sir ❤❤❤❤❤❤

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      So nice of you dear.
      Thanks ❤️

  • @weird8599
    @weird8599 10 หลายเดือนก่อน +1

    I have solved it in my own way . btw great solution premath sir :)

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Great job!
      Glad to hear that! 😀

  • @murdock5537
    @murdock5537 10 หลายเดือนก่อน +1

    ∎ABCD → AB = BC = CD = AD = 2a; r = 1 → OP = 2a - r = 2a - 1 →
    ∆ AOP → (2a - 1)^2 + a^2 = 1 → a = 4/5 → (2a)^2 = 64/25; sin⁡(ϑ) = AP/AE = √5/5
    or: r = 1; sin⁡(ϑ) = √5/5 → cos⁡(ϑ) = 2√5/5 → sin⁡(2ϑ) = 2sin⁡(ϑ)cos⁡(ϑ) = 4/5 = AP/AO = a/r → a = 4/5 →
    (2a)^2 = 64/25

    • @PreMath
      @PreMath  10 หลายเดือนก่อน +1

      Excellent!
      Thanks ❤️

  • @marcgriselhubert3915
    @marcgriselhubert3915 10 หลายเดือนก่อน

    Let's use an adapted orthonormal: E(0;0) A(k;k/2) B(k, -k/2) where k is the length of the square.
    The equation of the circle is x^2 + y^2 + ax + by +c = 0 where a, b and c are unknown.
    A is on the circle so c = 0; B is on the circle so k^2 + (k^2)/4 + ak + (bk)/2 = 0; B is on the circle so k^2 + (k^2)/4 +ak - (bk)/2 = 0.
    Its easy to obtain that c =0; a = -(5/4).k; b =0. So the equation of the circle is x^2 + y^2 -(5/4).k = 0, or (x - (5/8).k)^2 + y^2 = ((5/8).k)^2
    So we have O((5/8).k; 0) and the radius R of the circle is (5/8).k
    Now we know that R = 1 (as the area of the circle is Pi), so (5/8).k = 1 and then k = 8/5 is the length of the square.
    Finally the area of the square is (8/5)^2 = 64/25.

  • @MarieAnne.
    @MarieAnne. 9 หลายเดือนก่อน

    Let s = side length of square. Then in △AOP, we get:
    ∠APO = 90° (diameter EF perpendicular to tangent DC and AB parallel to DC, so EF perpendicular to AB)
    AP = AB/2 = s/2 (diameter that is perpendicular to chord bisects the chord)
    OP = EP − OE = s−r = s−1
    OA = r = 1
    Using Pythagorean theorem, we get
    (s/2)² + (s−1)² = 1²
    s²/4 + s² − 2s + 1 = 1
    5s²/4 − 2s = 0
    s/4 (5s − 8) = 0
    s = 0 or 8/5
    Since s is sidelength of square and is > r, then
    s = 8/5 = 1.6
    Area of square = s² = 64/25 = 2.56

  • @MrPaulc222
    @MrPaulc222 10 หลายเดือนก่อน

    This could be trickier than it looks at first.
    r=1.
    Call the square's sides s.
    Make a midpoint on AB and call it F.
    AOF is a right triangle with sides (1/2)s, s-1, and 1.
    ((1/2)s)^2 + (s-1)^2 = 1^2
    (1/4)s^2 + (s-1)^2 = 1^2
    (1/4)s^2 + s^2 - 2s + 1 = 1
    (5/4)s^2 - 2s = 0
    5s^2 - 8s = 0
    s = (8/5) so square is (64/25) sq units.
    2.56 sq units.
    I did assimilate additional information which I later discarded and deleted from this answer.
    EDIT: No intersecting chords needed - just straightforward Pythagoras for this one.
    Now to watch how you did it :)
    I see you used another method and, unusually, mine appears simpler :)
    Thank you once again.

  • @adept7474
    @adept7474 10 หลายเดือนก่อน +1

    ▲АВЕ -Inscribed. AB = x, AE = BE = (x√5)/2.
    S(ABE) = (AB × AE × BE)/4R = 5x³/16 = EP × BP = x²/2. 5x/8 = 1. x = 8/5, S(square) = 64/25.

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️

  • @AdemolaAderibigbe-j8s
    @AdemolaAderibigbe-j8s 10 หลายเดือนก่อน

    Let's label the length of the side of the square ABCD as"Y". (Y must be positive to be a viable solution)
    Set up the product of the component lengths of the intersecting chords APB and the diameter EOF for the circle of radius 1 (the two chords intersect at point "P" ):
    (AP)(PB) = (EP)(PF) or (Y/2)(Y/2)= Y(2-Y). Hence Y = 8/5 and area of square ABCD = Y^2 = 64/25

  • @christopherlinder7618
    @christopherlinder7618 10 หลายเดือนก่อน

    I didn't know the chord multiplication theorem. I immediately drew in sin M and cos M (angle at midpoint M, I don't write O as it looks like zero) and came up with 2 sin M as the vertical side and 1 + cos M as the horizontal side, and since it's a square you get the equation 2x = 1 + sqrt(1 - x^2) if you sub x = sin M and figure cos from the trig Pythagoras. This gives you (2x-1)^2 = 1 - x^2 or finally x(5x - 4) = 0. Since x is obviously not 0 from the sketch, it must be 4/5 = 0.8 , making the cos M = 0.6 and yielding the famous 3, 4, 5 shape. But since 0.8 was sin M and 2sinM is 1.6 was the side of the square, you get 2.56 for the area. I like the chord theorem solution, though, as it avoids trigonometry.

  • @tombufford136
    @tombufford136 9 หลายเดือนก่อน

    At a quick glance: The chord theorem, proposition 35 in Euclid's geometry is useful. The products of the two segments of two intersecting chords of a circle are equal.

  • @papilgee4evaeva
    @papilgee4evaeva 10 หลายเดือนก่อน +1

    When we got to the step where 4x(2 - x) = (2 - x)(2 - x), I divided both sides by (2 - x). The resulting work led me to the acceptable value of x.
    Not sure if that works every time, but it worked here. 🙂

    • @PreMath
      @PreMath  10 หลายเดือนก่อน +1

      It'd work as long as x is less than 2.
      Thanks ❤️

  • @misterenter-iz7rz
    @misterenter-iz7rz 10 หลายเดือนก่อน +1

    Let 2s×2s be the square, 2s=1+sqrt(1-s^2), (2s-1)^2=1-s^2, 5s^2-4s=0, s=4/5, as s >< 0, then the answer is (8/5)^2=64/25=2.56.😊

    • @PreMath
      @PreMath  10 หลายเดือนก่อน +1

      Excellent!
      Thanks ❤️

  • @santiagoarosam430
    @santiagoarosam430 10 หลายเดือนก่อน +1

    Area del círculo =π → Radio del círculo =r =1
    Los lados DA y CB del cuadrado definen las cuerdas FA y GB; ambas tienen una flecha de longitud "f" → La cuerda AB tiene una flecha de longitud 2f=DF → Potencia del punto D respecto a la circunferencia: DE²=DF*DA → (r-f)²=(2f)(2r-2f)→ 5f²-6f+1=0→ f=1/5→ AB=2r-2f =2-(2/5) =8/5 → Área ABCD =64/25 =2.56
    Interesante problema. Gracias y un saludo cordial.

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      You are very welcome!
      Thanks ❤️

  • @soli9mana-soli4953
    @soli9mana-soli4953 10 หลายเดือนก่อน

    In this problem applying the intersecting chords theorem on AB and diameter passing on EO, or applying Euclid’s theorem on right triangle whose hypotenuse is the diameter and its height AH, or applying the tangent secant theorem on points C,E,B we get always the same result:
    S^2 = 2S*(2 - 2S). Being 2S the side of the square 😊

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Thanks ❤️

  • @prossvay8744
    @prossvay8744 10 หลายเดือนก่อน +1

    Green square area= (1.6)^2=2.56 suqare units. ❤❤❤ Thanks

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      You are very welcome!
      Thanks ❤️

  • @الثورة-ص7ق
    @الثورة-ص7ق 10 หลายเดือนก่อน +1

    Let x^2 be the green square area.lets take triangle rectangle PAE at P, cos(alpha/2)=2x/x_/5 =2/_/5 》cos(alpha)=3/5.now lets take triangle rectangle PAO, cos(alpha)=×-1, now we get x-1=3/5》x=8/5 then x^2=2,56 square units

    • @PreMath
      @PreMath  10 หลายเดือนก่อน +1

      Thanks ❤️

  • @GaryBricaultLive
    @GaryBricaultLive 10 หลายเดือนก่อน

    A much simpler way of resolving the ab=cd and only leaves one solution instead of two.
    The steps are as follows;
    4x(2-x) = (2-x)(2-x) starting following the first simplification step
    4x = 2-x divide both sides by (2-x)
    4x + x = 2 add 'x' to both sides
    5x = 2 combine 'x' terms
    x = 2/5 divide both sides by x

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Thanks

  • @LuisdeBritoCamacho
    @LuisdeBritoCamacho 10 หลายเดือนก่อน

    Being the Area of the Circle Pi square units, the only solution is the solution below.
    The Area of the Square is equal to 1,6^2 square units = 2,56 square units.
    I solved this Problem by Geometrical Optimization.

  • @jan-willemreens9010
    @jan-willemreens9010 10 หลายเดือนก่อน +2

    ... Good day, Radius circle is R = 1 ... assume side length green square X ... I DA I = I EO I + I OP I ... X = 1 + I OP I ... we can find I OP I with Pythagoras in for instance right triangle (AOP) ... I OA I = R = 1 , I AP I = X/2 , so I AP I^2 + I OP I^2 = I OA I^2 ... so after doing the algebraic steps we obtain I OP I = SQRT(4 - X^2)/2 ... recalling X = 1 + I OP I ... X - 1 = SQRT(4 - X^2)/2 ... after a few algebraic steps solving for X we obtain ... 5X^2 - 8X = 0 ... X(5X - 8) = 0 ... X = 0 (rejected) v X = 8/5 .... finally Area green square = X^2 = ( 8/5 )^2 = 64/25 u^2 .... thank you for your clear alternative strategy ... best regards, Jan-W

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      You are very welcome!
      Thanks ❤️

  • @giuseppemalaguti435
    @giuseppemalaguti435 10 หลายเดือนก่อน

    r=1...l=r+√(r^2-(l/2)^2)=1+√(1-l^2/4)...(l-1)^2=1-l^2/4...5l^2/4-2l=0...5l/4=2...l=8/5

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Thanks ❤️

  • @jarikosonen4079
    @jarikosonen4079 10 หลายเดือนก่อน

    When x=2, the 'square' is just a dot at the point E.

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      True!
      Thanks ❤️

  • @sirchedr
    @sirchedr 10 หลายเดือนก่อน

    Scanavi - Сканави

  • @JSSTyger
    @JSSTyger 10 หลายเดือนก่อน +1

    A = 2.56

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️

  • @xianartman
    @xianartman 10 หลายเดือนก่อน

    Maybe I jumped to conclusions, but if:
    4x(2-x)=(2-x)(2-x)
    Then can you not divide by (2-x)?
    Thus
    4x=(2-x)
    4x+x=2
    5x=2
    Therefore:
    X=2/5

  • @hermannschachner977
    @hermannschachner977 10 หลายเดือนก่อน

    1+cos = 2 sin; 1,6 = 2 x 0,8 . . . . 1.6^2 = 2,56

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Thanks ❤️

  • @unknownidentity2846
    @unknownidentity2846 10 หลายเดือนก่อน +1

    Let's find the size of the green area:
    .
    ..
    ...
    ....
    .....
    May s be the side length of the square and may r be the radius of the circle. From the given area of the circle we can conclude:
    A(circle) = πr² = π ⇒ r = 1
    The line through the points E and O may intersect AB in point F. Then we get two congruent right triangles OFA and OFB, so we can apply the Pythagorean theorem:
    OA² = FA² + OF²
    r² = (s/2)² + (s − r)²
    r² = s²/4 + s² − 2sr + r²
    0 = 5s²/4 − 2sr
    0 = 5s²/8 − sr
    0 = s*(5s/8 − r)
    Since s≠0, we can follow:
    5s/8 = r
    ⇒ s = (8/5)r = 8/5
    ⇒ A(square) = s² = 64/25 = 2.56
    Best regards from Germany

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Great!
      Thanks ❤️

  • @weird8599
    @weird8599 10 หลายเดือนก่อน +1

    i did it by pythagoras

    • @weird8599
      @weird8599 10 หลายเดือนก่อน +1

      I became your new subscriber

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Welcome aboard🌹
      Thanks ❤️

  • @sergioaiex3966
    @sergioaiex3966 10 หลายเดือนก่อน +1

    Solution:
    A = π r²
    π = π r²
    r² = 1
    *r = 1*
    *Square Side = 2x*
    Let's assume a point F, that lies on the square side, in a streight line, such a way, OF = 2x - r
    *OF = 2x - 1*
    Applying The Pythagorean Theorem, we gonna have:
    OA² = OF² + FA²
    1² = (2x - 1)² + x²
    1 = 4x² - 4x + 1 + x²
    5x² - 4x = 0
    x (5x - 4) = 0
    x = 0 Rejected
    *x = 4/5* Accepted
    L = 2x
    L = 2 . 4/5
    *L = 8/5*
    A = L² = (8/5)²
    *A = 64/25 Square Units*
    *A = 2,56 Square Units*

    • @PreMath
      @PreMath  10 หลายเดือนก่อน

      Excellent!
      Thanks ❤️