найти cos x, cos 2x, sin 2x, если Sin x = 4/5, и pi/2 < x

cosx - ?

cos2x = cos²x - sin²x?

sin2x = 2sinxcosx?

Sinx = 4/5

cosx = - √ (1-sin²x) = - √ (1 - 16/25) = - √9/25 = - 3/5

cos2x = cos²x - sin²x = 9/25 - 16/25 = - 7/25

sin2x = 2sinxcosx = 2 * 4/5 * (-3/5) = - 24/25