$21p^2qr^4\:+\:14p^3qr^2\:-\:28p^2r^3$

$x\left(2x\:+\:7\right)\:$

$3ab^3-\:6a^{3\:}b$

$\frac{1}{\cos\left(x\right)}-\frac{\cos\left(x\right)}{1+\sin\left(x\right)}=\tan\left(x\right)z$

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

$\frac{n^2}{1+n^3}\cdot\:\left(x-1\right)^n$

$324x^4y^2+288x^3y^3+64x^2y^4$