$\left(x^2-y\right)dx-xdy=0\:$

$\ln\left(x\right)+\ln\left(7\right)$

$\sec\left(a\right)^2=\frac{\csc\left(a\right)}{\csc\left(a\right)-\sin\left(a\right)}$

$x^4-9x^2+16$

$sin^22\theta\:\left(cot^2\theta\:-tan^2\theta\:\right)=4\:cos\:2\theta\:$

$\lim_{x\to12}\left(x+\pi\right)cotx$

$x\left(5-3x\right)$