(1-cosa)(1+cosa)=sin^2(a)
1+cosa-cosa-cos^2(a)=sin^2(a)
1-cos^2(a)=sin^2(a)
sin^2(a)= sin^2(a)
Тождество доказано.
(1-cosa)(1+cosa)=sin^2(a)
1+cosa-cosa-cos^2(a)=sin^2(a)
1-cos^2(a)=sin^2(a)
sin^2(a)= sin^2(a)
Тождество доказано.