$\frac{4a^{-2}b^4}{a^9b^3}$

$\frac{x^4-3x^3+2x^2-x+8}{x-1}$

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

$\frac{d^2}{dx^2}\ln\left(2x+3y\right)$

$\left(-\frac{2}{3}a+\frac{7}{3}b\right)^{2}$

$\left(-1\right)^nx^n+x^n$

$\sin\left(x\right)+\cot\left(x\right)\cos\left(x\right)=2\sin\left(x\right)$