$\left(x^{-2}x^4\right)^{-3}$

$\frac{x^2}{4}+\frac{9}{16}$

$\cot\left(x\right)-\cot^2\left(x\right)-1$

$\left(\frac{6}{x^2-9x+20}\right).\frac{5x-25}{15}$

$-5\left(\left(-8\right)\right)$

$\:\sec\theta\:-\:\sec\theta\sin^2\theta$

$cos^3t\left(cost-2\right)=cos^4t-2cos^3t$