Question

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

Answer 1

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