$\lim_{x\to-\infty}\left(\frac{21x^5-9}{3x^5-4x^4}\right)$

$\left(x^2+4y\right)\left(x^2-4y\right)$

$\int_0^{\frac{\pi}{3}}\left(\frac{1}{\cos\left(x\right)^2}\right)dx$

$25x-3<30$

$\int\frac{1}{x\left(ax+1\right)}dx$

$y=\frac{4x+2}{\left(3-2x\right)^3}$

$\left(x+4\right)\left(x^2-8x+16\right)$