$\frac{\left(x^2+2x-63\right)}{\left(x+9\right)}$

$\lim_{x\to0}\left(\frac{12x+4}{e^x}\right)$

$\frac{d^2}{dx^2}\left(x\ln\left(x\right)^2\right)$

$\lim_{x\to\infty}\left(ln\left(4x\right)-ln\left(x+7\right)\right)$

$\lim_{x\to2}\left(\frac{x-2}{\sqrt{2}-\sqrt{x}}\right)$

$4xydx+\left(x^2+y^2\right)dy=0$