$x^2+21x-232\:\:\:x=3$

$\left(9-7f\right)\left(81-63f+49f^2\right)$

$\frac{dy}{dx}=\ln\left(x\right)-9x^2$

$\lim_{x\to\pi}\arctan\left(\frac{\sin\left(x\right)}{1+\cos\left(x\right)}\right)$

$125\cdot125$

$\frac{4}{x-4}=\frac{3x}{x+3}$

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