Question #218806

Find the area of the curve y2 (2a – x) = x3
between the area and its asymptotes.

Expert's answer

The asymptote(s) of the curve parallel to yy -axis is given by 2a−x=0.2a-x=0.

Then the vertical asymptote is x=2a.x=2a.


y=x32a−xy=\sqrt{\dfrac{x^3}{2a-x}}

Let x=2asin⁡2θ.x=2a\sin^2\theta.



dx=4asin⁡θcos⁡θdθdx=4a\sin \theta \cos \theta d\theta

Area=A=∫02ax32a−xdxArea=A=\displaystyle\int_{0}^{2a}\sqrt{\dfrac{x^3}{2a-x}}dx

=∫0π/28a3sin⁡6θ2a−2asin⁡2θ4asin⁡θcos⁡θdθ=\displaystyle\int_{0}^{\pi/2}\sqrt{\dfrac{8a^3\sin^6\theta}{2a-2a\sin^2\theta}}4a\sin \theta \cos \theta d\theta

=8a2∫0π/2sin⁡3θsin⁡θcos⁡θcos⁡θdθ=8a^2\displaystyle\int_{0}^{\pi/2}\dfrac{\sin^3\theta\sin \theta \cos \theta}{\cos \theta}d\theta

=8a2∫0π/2sin⁡4θdθ=2a2∫0π/2(1−cos⁡(2θ))2dθ=8a^2\displaystyle\int_{0}^{\pi/2}\sin^4\theta d\theta=2a^2\displaystyle\int_{0}^{\pi/2}(1-\cos(2\theta))^2 d\theta

=2a2∫0π/2(1−2cos⁡(2θ)+cos⁡2(2θ))dθ=2a^2\displaystyle\int_{0}^{\pi/2}(1-2\cos(2\theta)+\cos^2(2\theta)) d\theta

=a2∫0π/2(2−4cos⁡(2θ)+1+cos⁡(4θ))dθ=a^2\displaystyle\int_{0}^{\pi/2}(2-4\cos(2\theta)+1+\cos(4\theta)) d\theta

=a2[3θ−2sin⁡(2θ)+14sin⁡4θ()]π/20=a^2\bigg[3\theta-2\sin(2\theta)+\dfrac{1}{4}\sin4\theta()\bigg]\begin{matrix} \pi/2 \\ 0 \end{matrix}

=3πa22(units2)=\dfrac{3\pi a^2}{2} (units^2)

Area=3π22Area=\dfrac{3\pi ^2}{2} square units.



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