$-4cosx=\frac{senx}{cosx}$

$2\ln\left(x\right)-\ln\left(9\right)=\ln\left(1\right)$

$\frac{cota}{csca-1}=\frac{csca+1}{cota}$

$\lim_{x\to6}\left(\frac{x\left(\sqrt{x+3}-3\right)}{x-6}\right)$

$x-\sqrt{x^2-8}=4$

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

$sec^2\left(x\right)-\sin^2\left(x\right)\sec^2\left(x\right)$