$20ab^2-5ab-10a^3\:b$

$\left(2xy^2-7y^2\right)^3$

$\lim_{x\to0}\left(e^x-x\right)^{\frac{2}{x}}$

$\left(\frac{1}{2}x-\frac{\sqrt{3}}{2}y\right)^2$

$\cos\left(\frac{2\pi}{5}\right)\cdot\cos\left(\frac{\pi}{5}\right)$

$\left(3a+8xy\right)\left(3a-7x^2\right)$

$f\left(x\right)=-2x^4+2x^2$