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Area Under the Curves question

2024 · 5 Apr · Shift 1 · Q51
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  5. /2024 · 5 Apr · Shift 1 · Q51

Area Under the Curves question

2024 · 5 Apr · Shift 1 · Q51

JEE MainMathematicsArea Under the CurvesNumerical+4 / −1
The area of the region enclosed by the parabolas y=x2−5xy=x^2-5 xy=x2−5x and y=7x−x2y=7 x-x^2y=7x−x2 is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 72

  1. Write the two curves

    The parabolas are: y1=x2−5xy_1=x^2-5xy1​=x2−5x y2=7x−x2y_2=7x-x^2y2​=7x−x2

  2. Find the points of intersection

    For intersection: x2−5x=7x−x2x^2-5x=7x-x^2x2−5x=7x−x2

    Bring all terms to one side: 2x2−12x=02x^2-12x=02x2−12x=0 2x(x−6)=02x(x-6)=02x(x−6)=0

    Hence, x=0orx=6x=0 \quad \text{or} \quad x=6x=0orx=6

  3. Determine which curve is above the other

    Take a point between 000 and 666, say x=3x=3x=3.

    y1(3)=32−5(3)=9−15=−6y_1(3)=3^2-5(3)=9-15=-6y1​(3)=32−5(3)=9−15=−6 y2(3)=7(3)−32=21−9=12y_2(3)=7(3)-3^2=21-9=12y2​(3)=7(3)−32=21−9=12

    So on [0,6][0,6][0,6], the upper curve is: y=7x−x2y=7x-x^2y=7x−x2 and the lower curve is: y=x2−5xy=x^2-5xy=x2−5x

  4. Set up the area integral

    Area enclosed is: A=∫06[(7x−x2)−(x2−5x)]dxA=\int_0^6 \Big[(7x-x^2)-(x^2-5x)\Big]dxA=∫06​[(7x−x2)−(x2−5x)]dx

    Simplify the integrand: A=∫06(12x−2x2) dxA=\int_0^6 (12x-2x^2)\,dxA=∫06​(12x−2x2)dx

  5. Evaluate the integral

    A=[6x2−2x33]06A=\left[6x^2-\frac{2x^3}{3}\right]_0^6A=[6x2−32x3​]06​

    At x=6x=6x=6: 6(62)−2(63)3=6(36)−2(216)3=216−144=726(6^2)-\frac{2(6^3)}{3}=6(36)-\frac{2(216)}{3}=216-144=726(62)−32(63)​=6(36)−32(216)​=216−144=72

    At x=0x=0x=0: 000

    Therefore, A=72A=72A=72

  6. Compare with stored answer

    My derived answer is 727272, but the stored correct answer is 198198198.

    Hence, the stored answer does not match the correct computation.

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