$\lim_{x\to9}\left(\frac{3-\sqrt{x}}{81-x^2}\right)$

$\int\frac{1}{\sqrt{9\:-\:16x\:-\:4x^2}}dx$

$49x^4+1-14x^2$

$\frac{1}{sin\left(t\right)}-cos\left(t\right)cot\left(t\right)$

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

$\frac{d}{dx}\left(x^2-xy+y^2=4\right)$

$x^2\:-\:14x\:+\:49\:=\:16$