$\frac{d}{dx}\left(3\cdot x\cdot y-x\cdot y^3=3\cdot y\right)$

$\left(x+5\right)^2\left(x+2\right)^2$

$\frac{1}{ab}+\frac{b^2-a^2}{ab^3}+\frac{ab+b^2}{a^2b^2}$

$21-2x>0$

$-3\left(4k\:-\:8\right)$

$\sec^2\left(30\right)\cdot\cos\left(30\right)$