Question

Найти tg2α, если tgα=-2

Answer 1

$tg2a= \frac{2tga}{1-tg ^{2} a} = \frac{2*(-2)}{1-(-2) ^{2} } = \frac{-4}{1-4} = \frac{-4}{-3} =1 \frac{1}{3}$