$tan\frac{a}{2}=\frac{sec\left(a\right)}{secacsc\left(a\right)+csc\left(a\right)}$

$\frac{\frac{1}{0}}{\frac{1}{0}}$

$tanxsin2x$

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

$2\sin\left(x\right)^2=1$

$\lim_{t\to\infty}\left(\frac{10t}{t^2+1}\right)$

$\left(-2.500\right)-+2.500$