$\frac{12ax^3+4x^2}{4ax^2+6ax}$

$\int_{\frac{\pi}{2}}^{\frac{\pi}{2}}\frac{x^2\sin x}{1+x^6}dx$

$-16-4x^6$

$x^2+9x+20=156$

$\left(2x+3\right)^2-\left(x+4\right)^2-3\left(x+1\right)^2$

$-2x+8=-2$

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