$\left(2xy+7\right)\cdot\left(2xy-7\right)$

$\frac{10x^{4}-29x^{2}+2x^{5}+51x-13x^{3}-18}{5x+x^{2}-3}$

$\frac{dy}{dx}=\left(x^2+3\right)\left(2y^2+9\right)$

$39x+3\cdot39x+3$

$\lim_{x\to\infty}\left(\frac{5x^2-3x+1}{x-3}\right)$

$4^6\cdot4^7$

$\frac{d}{dx}\left(\sqrt{\frac{x-3}{x+2}}\right)$