по пропорции
(sina-cosb)*(sina+cosb)=(sinb+cosa)*(sinb-cosa)
sin^2a-cos^2d=sin^2b-cos^2a
представим sin^2a=1-cos^a
1-cos^2a-cos^2b=1-cos^2b-cos^2a
-cos^2a-cos^2b+cos^2b+cos^2a=1-1
0=0
по пропорции
(sina-cosb)*(sina+cosb)=(sinb+cosa)*(sinb-cosa)
sin^2a-cos^2d=sin^2b-cos^2a
представим sin^2a=1-cos^a
1-cos^2a-cos^2b=1-cos^2b-cos^2a
-cos^2a-cos^2b+cos^2b+cos^2a=1-1
0=0