$\frac{2+x}{-1-x}$

$81y^2+x^4+18yx^2$

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

$\cos\left(u\right)-\sin\left(u\right)=\cot\left(u\right)\cdot\cos\left(u\right)$

$\int\frac{\sin^3\left(x\right)}{\cos^2\left(x\right)}dx$

$\frac{d}{dy}\left(\ln\left(xy\right)=ax^2+by\right)$

$50\left(x-3\right)$