$\lim_{x\to\pi}\left(\frac{1+\cos\left(x\right)}{\sin\left(x\right)}\right)$

$4\left(y^2-4y\right)+\left(z^2-4z\right)=\left(x+20\right)$

$12x^2y-20x^3y+4xy$

$y^3\sqrt{y^2}+4$

$y-e^x=-e$

$\int\frac{6}{\left(t+11\right)^9}dx$

$\lim_{x\to0}\left(\frac{\sqrt{x}}{x^2+1}\right)$