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Area Under the Curves question

2023 · 12 Apr · Shift 1 · Q33
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  5. /2023 · 12 Apr · Shift 1 · Q33

Area Under the Curves question

2023 · 12 Apr · Shift 1 · Q33

JEE MainMathematicsArea Under the CurvesMCQ+4 / −1
The area of the region enclosed by the curve y=x3y=x^{3}y=x3 and its tangent at the point (−1,−1)(-1,-1)(−1,−1) is :
  1. A
    234\frac{23}{4}423​
  2. B
    194\frac{19}{4}419​
  3. C
    274\frac{27}{4}427​
  4. D
    314\frac{31}{4}431​
View written solutionFree

Correct answer: C

  1. Find the tangent to y=x3y=x^3y=x3 at (−1,−1)(-1,-1)(−1,−1).

    For the curve y=x3,y=x^3,y=x3, its derivative is dydx=3x2.\frac{dy}{dx}=3x^2.dxdy​=3x2.

    At x=−1x=-1x=−1, the slope is m=3(−1)2=3.m=3(-1)^2=3.m=3(−1)2=3.

    Using point-slope form at (−1,−1)(-1,-1)(−1,−1): y+1=3(x+1).y+1=3(x+1).y+1=3(x+1). So the tangent is y=3x+2.y=3x+2.y=3x+2.

  2. Find the points of intersection of the curve and the tangent.

    Solve x3=3x+2.x^3=3x+2.x3=3x+2. That is, x3−3x−2=0.x^3-3x-2=0.x3−3x−2=0.

    Factorizing: x3−3x−2=(x+1)2(x−2).x^3-3x-2=(x+1)^2(x-2).x3−3x−2=(x+1)2(x−2).

    Hence the intersection points are at x=−1andx=2.x=-1 \quad \text{and} \quad x=2.x=−1andx=2.

    So the enclosed region lies between x=−1x=-1x=−1 and x=2x=2x=2.

  3. Determine which graph is above the other in [−1,2][-1,2][−1,2].

    Consider x3−(3x+2)=x3−3x−2=(x+1)2(x−2).x^3-(3x+2)=x^3-3x-2=(x+1)^2(x-2).x3−(3x+2)=x3−3x−2=(x+1)2(x−2).

    On the interval [−1,2][-1,2][−1,2], we have (x+1)2≥0(x+1)^2\ge 0(x+1)2≥0 and (x−2)≤0(x-2)\le 0(x−2)≤0. Therefore, x3−(3x+2)≤0.x^3-(3x+2)\le 0.x3−(3x+2)≤0.

    So the line y=3x+2y=3x+2y=3x+2 lies above the curve y=x3y=x^3y=x3 on this interval.

  4. Set up the area integral.

    Area enclosed is A=∫−12[(3x+2)−x3]dx.A=\int_{-1}^{2}\big[(3x+2)-x^3\big]dx.A=∫−12​[(3x+2)−x3]dx.

  5. Evaluate the integral.

    A=∫−12(3x+2−x3)dxA=\int_{-1}^{2}(3x+2-x^3)dxA=∫−12​(3x+2−x3)dx =[3x22+2x−x44]−12.=\left[\frac{3x^2}{2}+2x-\frac{x^4}{4}\right]_{-1}^{2}.=[23x2​+2x−4x4​]−12​.

    At x=2x=2x=2: 3(2)22+2(2)−(2)44=122+4−164=6+4−4=6.\frac{3(2)^2}{2}+2(2)-\frac{(2)^4}{4}=\frac{12}{2}+4-\frac{16}{4}=6+4-4=6.23(2)2​+2(2)−4(2)4​=212​+4−416​=6+4−4=6.

    At x=−1x=-1x=−1: 3(−1)22+2(−1)−(−1)44=32−2−14\frac{3(-1)^2}{2}+2(-1)-\frac{(-1)^4}{4}=\frac{3}{2}-2-\frac{1}{4}23(−1)2​+2(−1)−4(−1)4​=23​−2−41​ =6−8−14=−34.=\frac{6-8-1}{4}=-\frac{3}{4}.=46−8−1​=−43​.

    Therefore, A=6−(−34)=244+34=274.A=6-\left(-\frac{3}{4}\right)=\frac{24}{4}+\frac{3}{4}=\frac{27}{4}.A=6−(−43​)=424​+43​=427​.

  6. Match with the options.

    274\frac{27}{4}427​ corresponds to Option C.

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