$18cos^2\left(x\right)-9cos\left(x\right)$

$\frac{x}{x+4}+\frac{4}{x+4}+2$

$\left(2n+5\right)^3$

$\frac{d^3}{dx^3}\left(x\left(2x+1\right)^3\right)$

$19-2\left(4.5-11\right)$

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

$4+\left(6+11\right)\cdot3$