$x^2+21x+90$

$2a^4-16xa^2b^2+1b^5$

$\left(3-x\right)+2x-4$

$\left(5-4v\right)^2$

$\lim_{x\to\infty}\left(\frac{-3x^2+7}{x}\right)$

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

$\frac{\cos\left(x\right)^2-\cos\left(x\right)}{\sin\left(x\right)-\sin\left(x\right)^3}=0$