$5+\:\left(-16:\left(+21-13\right)-3\left(-7+15\right)\right)$

$f\left(x\right)=\ln\left(\frac{1+x}{1-x}\right)$

$\frac{9x-3}{4x}$

$-12\cdot2\cdot3$

$\lim_{x\to0}\left(\tan\left(7x\right)^x\right)$

$23x^2\cdot x$

$\left(x+6\right)^2\:\left(x\:+3\right)\left(x\:+5\right)\:-\:2\left(x+\:1\right)\left(x+\:9\right)$