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

$\frac{2x^3-4x^2+x}{2x+1}$

$\lim_{x\to\infty}\left(\frac{e^{\left(\frac{x^2}{4}\right)}}{\frac{x}{2}e^{\left(\frac{x^2}{4}\right)}}\right)$

$12+\left(-345\right)+\left(-162\right)$

$-4+-2^3$

$2x^4+9y=2x^2y+36$

$\frac{cos\left(x\right)}{1+sin\left(x\right)}-\frac{1}{cos\left(x\right)}=tan\left(x\right)$