$\lim_{x\to0}\left(tan\left(x\right)\cdot tan2x\right)$

$\frac{\sin\left(a\right)}{\cos\left(a\right)-1}=-\cot\left(\frac{a}{2}\right)$

$50\:-\:\left(-\:40\right)\:-\:\left(\:-20\right)$

$-5\left(2x+1\right)-2\left(3x+2\right)$

$\frac{1}{sen}$

$11.015723631\cdot10^7$

$4x^6+8x^8-16x^{10}$