[tex]\displaystyle \int csc^2(9x) dx \\\\=\dfrac 19\displaystyle \int \csc^2 u ~du~~~~~~~;\left[\text{Let}~u= 9x \implies dx = \dfrac{du}9\right]\\\\=-\dfrac 19 \cot u + C\\\\=-\dfrac 19 \cot(9x)+C[/tex]
