$\lim_{x\to0}\frac{e\left(x\right)-\left(\left(x+1\right)\cos\:\:\left(kx\right)\right)}{\left(x\right)\sin\:\left(kx\right)}$

$36x^2-25y^2$

$-28ab^2c^3+ab^2c^3$

$\sqrt[3]{abc}$

$4m-2n-6m+5n-m+n-2m-n$

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

$\lim_{u\to0}\left(\frac{u\tan\left(u\right)}{1-\cos\left(u\right)}\right)$