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

$\lim_{x\to0}\left(\frac{cosx-cos2x}{x-cosx}\right)$

$\left(-471\right)\left(8\right)$

$\left(3x^3-6\right)\left(x^3+1\right)$

$\frac{d}{dx}\left(arctan\left(-5x\right)\right)$

$\left(-cos\:\left(y\right)\right)dx\:+\:\left(xsen\left(y\right)-1\right)dy=0$

$49\cdot51$