$\left(a+\sqrt{15}\right)\left(a-\sqrt{15}\right)$

$2ab^2-4a^2b$

$4x^2-6x+81$

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

$\int\left(s^7\left(8+s^8\right)^4\right)ds$

$\int\frac{-4}{\left(x^2+4\right)\left(x^2+4\right)}dx$

$y^{'\:}=\frac{y\left(y-2\right)}{x\left(x-1\right)}$