$\frac{tanxcosx}{sex}$

$\lim_{x\to4}\frac{x^2+x-20}{x^2-17x+52}$

$19x\left(x-1\right)-18x\left(x-2\right)=12\left(2x-1\right)$

$\lim_{x\to-2}\left(\frac{4-x^2}{3-\sqrt{x^2-4}}\right)$

$\int\frac{x^4+x^2-x-2}{x^3-1}dx$

$\lim\:_{x\to-\infty\:}\left(2e^{4x}\right)$