$\lim_{x\to\frac{\pi}{2}}\left(\frac{2\left(x\right)-\pi}{1\:+\:cos2\left(x\right)}\right)$

$\frac{dy}{dx}=5\left(y^2+25\right)$

$\left(-1-x\right)^2$

$\lim_{x\to0}\left(\frac{14-14\cos\left(x\right)}{7}\right)$

$4a^2+36ab+18b^2$

$\frac{dy}{dx}=\left(y+1\right)^{-3}$

$4.-15k\:-\:1\:+\:12\:+\:2k$