$\left(\cot a+1\right)^2$

$\frac{5x-11}{2x^2-x-6}$

$\:\:\frac{sen\:w}{sen\:w+cosw}$

$\lim_{x\to infinity}\left(\frac{2u}{e^u-1}\right)$

$13axy+39a^2x^3y^2-52a^3y^3+65a^4y^4$

$5a+3b+\left(-7a\right)+\left(-8b\right)$

$\frac{dy}{dx}+2xy=\left(3x^2+2x+1\right)e^{-x^2}$