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Q.Evaluate : ∫x2tan⁡−1x dx\displaystyle\int x^2 \tan^{-1} x \,dx.

Odisha ChseOdisha CHSE +2 Science Board Exam 2023Subjective· 4mImportance★★★★★
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Integration by parts with u=tan⁡−1xu=\tan^{-1}x, dv=x2dxdv=x^2dx, followed by polynomial division of x3/(1+x2)x^3/(1+x^2), gives the result.

Let u=tan⁡−1xu=\tan^{-1}x, dv=x2dxdv=x^2dx. Then du=dx1+x2du=\dfrac{dx}{1+x^2}, v=x33v=\dfrac{x^3}{3}.

By parts:

∫x2tan⁡−1x dx=x33tan⁡−1x−13∫x31+x2dx\int x^2\tan^{-1}x\,dx = \dfrac{x^3}{3}\tan^{-1}x - \dfrac13\int\dfrac{x^3}{1+x^2}dx

Divide: x31+x2=x−x1+x2\dfrac{x^3}{1+x^2} = x - \dfrac{x}{1+x^2} (since x3=x(1+x2)−xx^3=x(1+x^2)-x).

∫x31+x2dx=∫x dx−∫x1+x2dx=x22−12ln⁡(1+x2)\int\dfrac{x^3}{1+x^2}dx = \int x\,dx - \int\dfrac{x}{1+x^2}dx = \dfrac{x^2}2 - \dfrac12\ln(1+x^2)

So: …

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