$\frac{2x-3}{x^2-3x}$

$\left(10x^2+11\right)\left(10x^2-11\right)$

$\frac{\left(x^2+4\right)\left(x-2\right)}{\left(3x+6\right)\left(x+2\right)}$

$2+3^3+7$

$f\left(x\right)=\frac{1}{\left(1+x\right)^2}$

$\frac{49x^2y^3-14x^3y+21x^4y^3z}{7x^3y}$

$\frac{d^2}{dx^2}\left(\frac{1}{x^2+5}\right)$