$m ^ { 4 } - n ^ { 4 }$

$5\sqrt[4]{\frac{81}{9}a^6}b^9z$

$\left(x-2\right)\frac{dy}{dx}+xy=0$

$\int\frac{xarctan\left(x\right)}{\left(x^2+1\right)^2}dx$

$\frac{dx}{dt}.\:km\:x=-k\:x^2$

$\left(\frac{x-1}{x+3}\right)=\left(\frac{5x+20}{x^2-16}\right)$

$\sin\left(x-\pi\right)=\tan\left(x\right)$