The Easiest IIT JEE Problem - 2

Calculus Level 3

What is the area bounded by the curves:

{ x 2 = y x 2 = y y 2 = 4 x 3 \large \begin{cases} x^2 = y \\ x^2 = - y \\ y^2 = 4x-3 \end{cases}

7 20 \frac{7}{20} 2 7 \frac{2}{7} 17 50 \frac{17}{50} 1 3 \frac{1}{3}

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1 solution

Tom Engelsman
Aug 25, 2018

Let us first find the points of intersection between these three parabolic curves. Substitution of either of the first two into the third yields:

( x 2 ) 2 = 4 x 3 x 4 4 x + 3 = 0 ( x 1 ) 2 ( x 2 + 2 x + 3 ) = 0 x = 1 , 1 ± 2 i . (x^2)^2 = 4x - 3 \Rightarrow x^4 - 4x + 3 = 0 \Rightarrow (x-1)^2 (x^2 + 2x + 3) = 0 \Rightarrow x = 1, -1 \pm \sqrt{2}i.

With x = 1 x = 1 being the only real root we now have y = ± 1 y = \pm 1 . To find the bounded area, I will integrate with respect to y as this area is symmetric with respect to the x-axis:

A = 2 0 1 y 2 + 3 4 y d y 2 [ y 3 12 + 3 y 4 2 3 y 3 2 ] 0 1 1 3 . A = 2 \int_{0}^{1} \frac{y^2 + 3}{4} - \sqrt{y} dy \Rightarrow 2[\frac{y^3}{12} + \frac{3y}{4} - \frac{2}{3}y^{\frac{3}{2}}]|_{0}^{1} \Rightarrow \boxed{\frac{1}{3}}.

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