Sin 2α, cos 2α, если sinα=4/5: 0

Question

Sin 2α, cos 2α, если sinα=4/5: 0<α<π/2

Answer 1

sinα=4/5

cosα= √{1-sin²α} = √{1-16/25} = √9/25 = 3/5

sin 2α = 2 sin α · cos α = 2*4/5 * 3/5 = 24/25

cos 2α = cos² α - sin² α = 9/25 - 16/25 = -7/25