$\frac{1-k}{1-\frac{1}{k}}$

$\left(\frac{9ax^3}{3yz^2}-\frac{7yz^2}{2ax^3}\right)^2$

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

$\frac{2}{2x^2+5x+3}+\frac{1}{2x^2-x-6}-\frac{3}{x^2-x-2}$

$f\left(x\right)=\left(x^2+2x-8\right)\cdot\left(x+1\right)$

$\frac{x^{-3}}{x^{-9}}$

$y'=2\frac{y}{x}+4\frac{x}{y}$