Question

Вычислите

$1-cos2a$

если $sina=\frac{1}{\sqrt{5}}$

Answer 1

$1-Cos2 \alpha =2Sin ^{2} \alpha =2*( \frac{1}{ \sqrt{5} } ) ^{2}=2* \frac{1}{5}= \frac{2}{5} =0,4$