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Area Under the Curves question

2024 · 30 Jan · Shift 1 · Q50
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Area Under the Curves question

2024 · 30 Jan · Shift 1 · Q50

JEE MainMathematicsArea Under the CurvesMCQ+4 / −1
The area (in square units) of the region bounded by the parabola y2=4(x−2)y^2=4(x-2)y2=4(x−2) and the line y=2x−8y=2 x-8y=2x−8, is :
  1. A
    7
  2. B
    8
  3. C
    9
  4. D
    6
View written solutionFree

Correct answer: C

  1. Write both curves in convenient form

    The parabola is y2=4(x−2)y^2=4(x-2)y2=4(x−2) so x=2+y24.x=2+\frac{y^2}{4}.x=2+4y2​.

    The line is y=2x−8y=2x-8y=2x−8 so x=y+82=4+y2.x=\frac{y+8}{2}=4+\frac y2.x=2y+8​=4+2y​.

  2. Find the points of intersection

    Substitute the line expression for xxx into the parabola equation: y2=4(y+82−2).y^2=4\left(\frac{y+8}{2}-2\right).y2=4(2y+8​−2).

    Simplify: y2=4(y+42)=2y+8.y^2=4\left(\frac{y+4}{2}\right)=2y+8.y2=4(2y+4​)=2y+8.

    Hence, y2−2y−8=0y^2-2y-8=0y2−2y−8=0 (y−4)(y+2)=0. (y-4)(y+2)=0.(y−4)(y+2)=0.

    So the intersection values are y=4andy=−2.y=4 \quad \text{and} \quad y=-2.y=4andy=−2.

    Corresponding xxx-coordinates:

    • For y=4y=4y=4: x=4+42=6x=4+\frac{4}{2}=6x=4+24​=6
    • For y=−2y=-2y=−2: x=4−1=3x=4-1=3x=4−1=3

    Thus intersection points are (6,4)and(3,−2). (6,4) \quad \text{and} \quad (3,-2).(6,4)and(3,−2).

  3. Determine which curve lies to the right

    For a fixed yyy between −2-2−2 and 444:

    • Line: x=4+y2x=4+\frac y2x=4+2y​
    • Parabola: x=2+y24x=2+\frac{y^2}{4}x=2+4y2​

    Check at y=0y=0y=0: xline=4,xparabola=2.x_{\text{line}}=4, \qquad x_{\text{parabola}}=2.xline​=4,xparabola​=2.

    So the line is to the right and the parabola is to the left.

  4. Set up the area integral

    Area bounded by the curves is A=∫−24[(4+y2)−(2+y24)]dy.A=\int_{-2}^{4}\left[\left(4+\frac y2\right)-\left(2+\frac{y^2}{4}\right)\right]dy.A=∫−24​[(4+2y​)−(2+4y2​)]dy.

    Simplify the integrand: A=∫−24(2+y2−y24)dy.A=\int_{-2}^{4}\left(2+\frac y2-\frac{y^2}{4}\right)dy.A=∫−24​(2+2y​−4y2​)dy.

  5. Evaluate the integral

    A=[2y+y24−y312]−24.A=\left[2y+\frac{y^2}{4}-\frac{y^3}{12}\right]_{-2}^{4}.A=[2y+4y2​−12y3​]−24​.

    At y=4y=4y=4: 2(4)+164−6412=8+4−163=12−163=203.2(4)+\frac{16}{4}-\frac{64}{12}=8+4-\frac{16}{3}=12-\frac{16}{3}=\frac{20}{3}.2(4)+416​−1264​=8+4−316​=12−316​=320​.

    At y=−2y=-2y=−2: 2(−2)+44−−812=−4+1+23=−3+23=−73.2(-2)+\frac{4}{4}-\frac{-8}{12}=-4+1+\frac{2}{3}=-3+\frac{2}{3}=-\frac{7}{3}.2(−2)+44​−12−8​=−4+1+32​=−3+32​=−37​.

    Therefore, A=203−(−73)=273=9.A=\frac{20}{3}-\left(-\frac{7}{3}\right)=\frac{27}{3}=9.A=320​−(−37​)=327​=9.

  6. Match with the options

    9\boxed{9}9​

    So the correct option is C.

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