$15-x^2-2x$

$3+\left|6-\left(-2\right)\right|$

$k2\:+\:16k\:=\:-37$

$\lim_{x\to0}\left(\frac{sin\left(x^2\right)}{\left(sin\left(x\right)\right)^2}\right)$

$\frac{sec\left(x\right)}{cos\:\left(x\right)}-\frac{tan\left(x\right)}{cot\left(x\right)}\:\left(x\right)=1$

$2x\left(x+5\right)+3\left(x+5\right)$

$\frac{6}{5}-\frac{9x}{5}$