Question

(sinα+cosα)²-sin2α=1
  
Тождество

Answer 1

(sina+cosa)²-sin2a=1
sin²a+2sinacosa+cos²a-sin2a=1  (sin²α+cos²α=1)
1+2sinαcosα-sin2α=1                 (2sinαcosα=sin2α)
1+sin2α-sin2α=1
1=1
ч.т.д.