$z^2-8z$

$\frac{9\cdot9^{-1}}{9}$

$19-6\left(-v-2\right)$

$xy'-5y=0$

$-2\right)\left(4-2x+3y\right)+5\left(8x-7y+12\right)$

$50\cos\left(2x\right)+50\cos\left(x\right)$

$\ln\left(\cot\left(u\right)\right)=\ln\left(\cos\left(u\right)\right)-\ln\left(\sin\left(u\right)\right)$