$x^2-1=99$

$\left(2\right)\frac{2}{3}mn$

$\lim_{x\to\frac{\pi}{2}}\left(\frac{8-\tan\left(x\right)}{\sin\left(x\right)+10}\right)$

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

$\frac{-9+3}{\sqrt{x}-3}$

$x\left(\frac{dy}{dx}\right)-15y^2=0$

$\frac{dy}{dx}=11e^{\left(x-y\right)}$