Если tg(a/2)= -2 , то sin(a) + 2cos(a) = ?..

[latex]tg\frac{a}{2}=-2\\\\sina+2cosa= \frac{2tg\frac{a}{2}}{1+tg^2\frac{a}{2}} +2\cdot \frac{1-tg^2\frac{a}{2}}{1+tg^2\frac{a}{2}} =\frac{2\cdot (-2)}{1+(-2)^2}+2\cdot \frac{1-(-2)^2}{1+(-2)^2} =\\\\= \frac{-4}{5}+2\cdot \frac{-3}{5} = \frac{-4-6}{5} =-2[/latex]