Question
Integrate the function: $\frac{{{x^3}\sin \left( {{{\tan }^{ - 1}}{x^4}} \right)}}{{1 + {x^8}}}$

Answer

Let $I = \int {\frac{{{x^3}\sin \left( {{{\tan }^{ - 1}}{x^4}} \right)}}{{1 + {x^8}}}dx} $
$ = \frac{1}{4}\int {\sin \left( {{{\tan }^{ - 1}}{x^4}} \right).\frac{{4{x^3}}}{{1 + {x^8}}}dx} …(i)$
Putting $\tan^{-1}x^4 = t$
$\Rightarrow \frac{1}{{1 + {{\left( {{x^4}} \right)}^2}}}\frac{d}{{dx}}{x^4} = \frac{{dt}}{{dx}}$
$\Rightarrow \frac{{4{x^3}}}{{1 + {x^8}}}dx = dt$
$\therefore$ From eq. $(i), I = \frac{1}{4}\int {\sin tdt} $
$= \frac{{ - 1}}{4}\cos t + c$
$ = \frac{{ - 1}}{4}\cos \left( {{{\tan }^{ - 1}}{x^4}} \right) + c$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free