$\frac{-12xy^2}{9x^2y^2}$

$\frac{-\cot\left(a\right)-\tan\left(a\right)}{\cot\left(a\right)}=-\sec^2\left(a\right)$

$2x+1>9$

$\frac{x^{-12}}{\frac{1}{4}y^{-6}}$

$\frac{x^3+2x^2-3x+4}{x^2+5x+6}$

$\left(3a^2+5\right)\left(3a^2-5\right)$

$\frac{x}{\sqrt{\left(x-3\right)^2-9}}$