$\frac{9^2}{4}+ab+b^2$

$\frac{dy}{dx}\left(4x^2+9y^2\right)$

$\frac{dy}{dx}=\frac{x^3-4}{7y^2}$

$\frac{d}{dx}\frac{e^x}{x+y}=y^2+1$

$\cos\left(a\right)=\sec\left(a\right)-\tan\left(a\right)\cdot\sin\left(a\right)$

$\frac{dy}{dx}-y=4e^{9x}$

$1+tan\left(x\right)=\frac{sec^2\left(x\right)+2tan\left(x\right)}{1+tan\left(x\right)}$