$3m^2\:-\:\left(m\:+\:n\right)^2;\:m\:=\:2,\:n\:=\:-4$

$13t-9p-13t$

$0.2\cdot15$

$\frac{-\cos\left(x\right).\tan\left(x\right).\sin\left(x\right)}{\sin\left(-x\right).\tan\left(-x\right)}$

$\lim_{x\to0}\left(1+7x\right)^{\frac{1}{x}}$

$\lim_{x\to0}\left(\frac{\ln^2\left(1-x\right)}{cosx-1}\right)$

$5m\frac{2}{5}n\frac{3}{5}x\frac{4}{5}$