Question

cos( 5pi/2+a)=-0.6 a принадлежит (0^ pi/2) Найти cos (5pi+a)

Answer 1

cos (5π/2 + α) = - 0.6  α - в 1-й четверти
Cos (5π/2 + α) = сos (π/2 + α) = -sin α = -0.6
sin α = 0.6
cos α = √1 - 0.36 = 0.8
Cos (5π + α) = cos (π + α) = - cos α = -0.8
Ответ: cos (5π + α) = -0.8