(1-cos a) (1+cos a) = tg a × cos a =

Question

(1-cos a) (1+cos a) =
tg a × cos a =

Answer 1

(1-cosα)(1+cosα)=1+cosα-cosα-cos²α=1-cos²α=sin²α;
tgαcosα=sinα/cosα*cosα=sinα.