$\left(k\:+\:7\right)\left(-8\right)$

$\frac{1}{1-\senz}-\frac{1}{1+\senz}=2\tan z\sec z$

$\frac{\left(2x+15\right)}{\left(5\cdot\left(x+3\right)\cdot7\right)}$

$\int\frac{\ln^2\left(x\right)}{x^{\frac{5}{3}}}dx$

$6x^3+7x^2-3x$

$\cos\frac{\pi}{3}\cos\frac{\pi}{6}+\sin\frac{\pi}{3}\sin\frac{\pi}{6}$

$\left(x+9\right)^2\:-\left(x-9\right)^2$