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

$\left(\frac{1}{3}x-7\right)\left(\frac{1}{3}x+7\right)$

$\frac{x^5-x^4+x^2-2}{x^2+1}1$

$\cot^2x=\left(\csc x-1\right)\left(\csc x+1\right)$

$a^3\left(b-c\right)+b^3\left(c-a\right)+c^3\left(a-b\right)$

$\frac{x^2-25}{x^2-9}.\frac{x+3}{x+5}$

$\int2x\left(x^2+3\right)dx$