$8x\cdot x^2$

$9u^2-4x^2$

$\frac{9}{x^2\cdot\sqrt[2]{x^2-81}}$

$\frac{\frac{1}{\infty^2}\cdot\left(2\cdot\infty\right)}{\left(\frac{1}{\infty\:}\right)^2}$

$\frac{2}{2x}$

$\left(9x^{10}y^3\right)\left(-x^5+y^3\right)$

$\frac{dy}{dx}=tan\left(y\right)tan\left(x\right)$