Question

вычислите sin2a и cos2a,если cosa=0,8 и a>π/3<π

Answer 1

sin2a = 2sinacosa
cos2a = cos^2a - sin^2a
sin^2a = 1 - cos^2a = 1 - 16/25 = 9/25
cos2a = 16/25 - 9/25 = 7/25
sin2a = 2*(3/5)*(4/5) = 24/25