$\frac{1+\cos^2\left(3a\right)}{\sin^2\left(3a\right)}$

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

$\int\left(6x+19\right)^6dx$

$\frac{dy}{\:dx}+2xy=-xy^4$

$\lim_{x\to0}\left(\cos\left(x\right)+\sin\left(x\right)\right)^{\frac{1}{x}}$

$\frac{d^3}{dx^3}\left(sen\left(x^3\right)\right)$

$10^2+8-6^2$