$\left(\frac{1}{e^{-y}+1}\right)dy=\left(\frac{senx}{1+cosx}\right)dx$

$7x^2-3xy-2y^2\:-9x^2+2xy+4y^2$

$\cos\left(u\right)+\tan\left(u\right)\sin\left(u\right)=\sec\left(u\right)$

$\frac{4\cot^2\left(x\right)+4}{\sin\left(x\right)\sec^2\left(x\right)-\sin\left(x\right)}$

$\int sin\left(x\right)\cdot sin\left(x\pi n\right)dx$

$x^2\frac{dy}{dx}+xy=e^x$