$x^4-2x^3+7x^2-5-8x-\left(-4-1-7x^2-x^3-2x^4\right)$

$6c^4-18bc=12bc^3$

$\lim_{x\to\frac{\pi}{4}}\left(sec^2u+csc^2u\right)$

$\lim_{x\to4}\left(\frac{4-x}{\sqrt{x}-2}\right)$

$\left(t^{2}+1\right)^{dy}dt=2y$

$\frac{-2}{x}+\frac{7}{\left(x-1\right)}$

$8ab3c\:+\:24ab\:-\:14ab2\:+\:bc\:-\:6ab3c\:$