$\frac{d}{dx}\left(\cos\left(\frac{x}{y}\right)=\ln\left(x-y\right)\right)$

$2+\cos^2\left(z\right)$

$9x+9=900$

$\int\frac{2x+7}{\left(\left(x+1\right)\left(x+3\right)\right)}dx$

$x^2+7x+2x$

$\frac { \int d x } { x }$

$cos\left(a\right)+2tan\left(a\right)-\frac{1}{cos\left(a\right)}=\frac{-sen^2\left(a\right)+2sen\left(a\right)}{cos\left(a\right)}$