$x^2-x^2+4^2-x^2+x^2y-xy^2+2-3x^2y$

$78=6\left(u+19\right)$

$-\left\{-\left[+8-8\left(7-3\right)+2\left(-5\right)\right]\right\}$

$-3+4-8+2+4$

$\cot\left(x-y\right)=\frac{1}{\tan\left(x-y\right)}$

$\int\frac{e^x}{\sqrt{1-e^x}}dx$

$\left(5c-3d\right)^2-\left(4a-1\right)^2$