$\:3\left(x+3\right)\:and\:3x+6\:$

$4sen^2\theta\:\:+2cos^2\theta\:\:=\:4-2cos^2\theta\:$

$\ln\left(3x+7\right)-\ln\left(7x-2\right)=\ln\left(2\right)-\ln\left(6\right)$

$\frac{dy}{dx}=\left(x-1\right)y$

$\int\left(\frac{14x+8}{7x^2+8x+7}\right)dx$

$\frac{d}{dx}\frac{d}{dx}\left(-xe^{-x}+e^{-x}\right)$

$\lim_{x\to0}\left(\frac{1+10x-e^{-7x}}{x}\right)$