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Area Bounded by Parabolic Curves

The area of the region bounded by the curves x+3y2=0x + 3y^2 = 0 and x+4y2=1x + 4y^2 = 1 is equal to:

Options

A

13\frac{1}{3}

B

23\frac{2}{3}

C

43\frac{4}{3}

Correct
D

53\frac{5}{3}

Step-by-Step Solution

To find the area of the region bounded by the curves, we first rewrite the equations of the given curves in terms of yy:

  1. First curve: x=3y2x = -3y^2

  2. Second curve: x=14y2x = 1 - 4y^2

To determine the points of intersection of these two parabolas, we set the two expressions for xx equal to each other: 3y2=14y2-3y^2 = 1 - 4y^2

Rearranging the terms: 4y23y2=14y^2 - 3y^2 = 1 y2=1    y=±1y^2 = 1 \implies y = \pm 1

Thus, the curves intersect at y=1y = -1 and y=1y = 1.

For any yy in the interval [1,1][-1, 1], notice that 14y23y21 - 4y^2 \ge -3y^2 because: (14y2)(3y2)=1y20(1 - 4y^2) - (-3y^2) = 1 - y^2 \ge 0

Therefore, the curve x=14y2x = 1 - 4y^2 lies to the right of x=3y2x = -3y^2.

The area AA bounded by the two curves can be found by integrating with respect to yy: A=11[(14y2)(3y2)]dyA = \int_{-1}^{1} \left[ (1 - 4y^2) - (-3y^2) \right] dy A=11(1y2)dyA = \int_{-1}^{1} (1 - y^2) \, dy

Since f(y)=1y2f(y) = 1 - y^2 is an even function, we can simplify the integral as: A=201(1y2)dyA = 2 \int_{0}^{1} (1 - y^2) \, dy

Evaluating the integral: A=2[yy33]01A = 2 \left[ y - \frac{y^3}{3} \right]_{0}^{1} A=2(113)=2(23)=43A = 2 \left( 1 - \frac{1}{3} \right) = 2 \left( \frac{2}{3} \right) = \frac{4}{3}

Thus, the correct option is C.

Area Bounded by Parabolic Curves | Mathematics PYQ Solution - JEE Challenger