Question

помогите решить пожалуйста!)))

Answer 1

169cos(3π+β) *sin(7π/2 +β)  = - 169cosβ *(-cosβ) =169cos²β =169 *(1/13)² = 1.
********************************************************************************************
cos(3π+β)*sin(7π/2 +β)  =cos(2π+π+β)* sin(4π -(π/2 -β) =cos(π+β) *(-sin(π/2 -β))= = (- cosβ)*  (- cosβ) =cos²β.