$x^2+y^2-3^2$

$\ln\left(\frac{x}{y}\right)$

$\lim_{x\to\infty}\left(\ln\left(\frac{x^2-1}{x^2+1}\right)^3\right)$

$\cos\left(x\right)\cdot\frac{\sin\left(x\right)}{\tan\left(x\right)}$

$\left(2xy\:-\:\tan\left(y\right)\right)dx\:+\:\left(x^2-x\left(\sec\left(y\right)^2\right)dy\right)\:=\:0$

$sen\left(x^2+2x+1\right)$

$\frac{x^2+x+4}{x-1}$