$21x^2y^2+28x^2y-7xy$

$\lim_{x\to0}\left(\frac{2x\left(cos2x\right)-1}{sin\left(4x\right)-4x}\right)$

$\left(\sqrt[2]{5}+1\right)\left(\sqrt[2]{5}-1\right)$

$\lim_{x\to-\infty}\left(\frac{3x^2}{e^{-x}}\right)$

$\lim_{x\to0}\left(\frac{x^3}{x^2+x\:}\right)$

$-5\:+4\:-1+6\:-\:-3$

$\left(h-n^2\right)^2$