Question:
Evaluate $\int \operatorname{cosec}^{4} 2 x d x$
Solution:
$I=\int \operatorname{cosec}^{4} 2 x d x$
$=\int \operatorname{cosec}^{2} 2 x\left(1+\cot ^{2} 2 x\right) d x$
$=\int \operatorname{cosec}^{2} 2 x d x+\int \operatorname{cosec}^{2} 2 x \cot ^{2} 2 x d x$
Let us consider that $\cot 2 x=t$ then $-2 \cdot \operatorname{cosec}^{2} 2 x d x=d t$
$I=-\frac{\cot (2 x)}{2}-\frac{1}{2} \cdot\left(t^{2} d t\right)$
$I=-\frac{\cot (2 x)}{2}-\frac{1}{6} \cdot(\cot 2 x)^{3}$
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