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

$500\cdot40$

$\lim_{a\to0}\frac{\sin\left(a\right)\sin\left(2a\right)}{1-cos\left(a\right)}$

$\left(\frac{3}{7}m-\frac{6}{5}n^2\right)^2\left(\frac{3}{7}m-\frac{6}{5}n^2\right)$

$3\cos2x-5\cos x=1$

$\left(-3m+n\right)\left(-3m-n\right)$

$\left(3x^2\right)-\left(5x\right)^3$