Primitive of Power of Cotangent of a x by Square of Cosecant of a x

Theorem

$\ds \int \cot^n a x \csc^2 a x \rd x = \frac {-\cot^{n + 1} a x} {\paren {n + 1} a} + C$

$\ds z$

$=$

$\ds \cot a x$

$\ds \leadsto \ \ $

$\ds \frac {\d z} {\d x}$

$=$

$\ds -a \csc^2 a x$

$\ds \leadsto \ \ $

$\ds \int \cot^n a x \csc^2 a x \rd x$

$=$

$\ds \int \frac {-1} a z^n \rd z$

$\ds $

$=$

$\ds \frac {-1} a \frac {z^{n + 1} } {n + 1}$

$\ds $

$=$

$\ds \frac {-\cot^{n + 1} a x} {\paren {n + 1} a} + C$

substituting for $z$ and simplifying

$\blacksquare$