$7+6\:.\:2-8\::\:\left(-4\right)+3\:-5\:$

$\left(-5x+19\right)^2$

$\frac{2}{\csc\left(x\right)+\cot\left(x\right)}+\frac{2}{\csc\left(x\right)-\cot\left(x\right)}=4\csc\left(x\right)$

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

$18xy^836xy^6and90xy^4$

$\left(2x+6\right)\left(2x-15\right)$

$\left(2\sqrt{a}+b\sqrt{b^3}\right)\left(2\sqrt{a}+b\sqrt{b^3}\right)$