а)y'(x)=(1/2sin2x)'=sin2x
sin^2 a + cos^2 a + sin^2 a = cos^2 a
sin^2 a + cos^2 a + sin^2 a - cos^2 a = 0
2sin^2 a = 0
sin a = 0
2 (A-2) + 2(2B) = 2A+4B-4