$\frac{\left(2x\right)}{\left(x+9\right)}-4$

$\frac{\left(-2\right)^2-\left(3\right)^2}{\frac{1}{4}}$

$4x^2-8xy+16y^2$

$48x^{5}:-3x^{2}$

$\frac{1}{1-\cos\left(x\right)}+\frac{1}{1+cos\left(x\right)}=\frac{2}{sin^2\left(x\right)}$

$\frac{dy}{dx}=\frac{xy}{x^2+11}$

$\tan\left(20\right)=\frac{\sin\left(20\right)}{1+\cos\left(20\right)}$