The integral $\int \frac{3 x^{13}+2 x^{11}}{\left(2 x^4+3 x^2+1\right)^4} d x$ is equal to (where $C$ is a…

The integral $\int \frac{3 x^{13}+2 x^{11}}{\left(2 x^4+3 x^2+1\right)^4} d x$ is equal to (where $C$ is a constant of integration.)
  1. $\frac{x^{12}}{\left(2 x^4+3 x^2+1\right)^3}+C$
  2. $\frac{x^4}{\left(2 x^4+3 x^2+1\right)^3}+C$
  3. $\frac{x^4}{6\left(2 x^4+3 x^2+1\right)^3}+C$
  4. $\frac{x^{12}}{6\left(2 x^4+3 x^2+1\right)^3}+C$

Solution

$\begin{aligned} & \int \frac{3 x^{13}+2 x^{11}}{\left(2 x^4+3 x^2+1\right)^4} d x=\int \frac{3 x^{13}+2 x^{11}}{x^{16}\left(2+\frac{3}{x^2}+\frac{1}{x^4}\right)^4} d x \\ & =-\frac{1}{2} \int \frac{-6 x^{-3}-4 x^{-5}}{\left(2+\frac{3}{x^2}+\frac{1}{x^4}\right)^4} d x=\frac{-1}{2} \times \frac{-1}{3}\left(2+\frac{3}{x^2}+\frac{1}{x^4}\right)^{-3}+C \\ & =\frac{1}{6}\left(\frac{2 x^4+3 x^2+1}{x^4}\right)^{-3}+C=\frac{x^{12}}{6\left(2 x^4+3 x^2+1\right)^3}+C\end{aligned}$

Asked in: MHT CET 2022 (06 Aug Shift 1)

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