$\int \sec ^4 x \cdot \tan ^4 x d x=\frac{\tan ^m x}{m}+\frac{\tan ^n x}{n}+c$ (where $c$ is constant of…

$\int \sec ^4 x \cdot \tan ^4 x d x=\frac{\tan ^m x}{m}+\frac{\tan ^n x}{n}+c$ (where $c$ is constant of integration), then $\mathrm{m}+\mathrm{n}=$
  1. 8
  2. 12
  3. 10
  4. 16

Solution

Let $I=\int \sec ^4 \tan ^4 x d x$ Put $\tan \mathrm{x}=\mathrm{t} \Rightarrow \sec ^2 \mathrm{x} d \mathrm{x}=\mathrm{dt}$ $\begin{aligned} & \therefore \mathrm{I}=\int \sec ^2 \mathrm{x}\left(\sec ^2 \mathrm{x}\right)\left(\tan ^4 \mathrm{x}\right) \mathrm{dx} \\ & =\int\left(1+\mathrm{t}^2\right)(\mathrm{t})^4 \mathrm{dt}=\int\left(\mathrm{t}^4+\mathrm{t}^6\right) \mathrm{dt}=\frac{\mathrm{t}^5}{5}+\frac{\mathrm{t}^7}{7}+\mathrm{c}=\frac{\tan ^5 \mathrm{x}}{5}+\frac{\tan ^7 \mathrm{x}}{7}+\mathrm{c} \end{aligned}$

Asked in: MHT CET 2021 (20 Sep Shift 2)

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