Решение на фото................................................
α=π/2+β
cos(α+β)=cos(π/2+β+β)=-sin2β=-2sinα*sinβ=-2*(1/2)=-1
Решение на фото................................................
α=π/2+β
cos(α+β)=cos(π/2+β+β)=-sin2β=-2sinα*sinβ=-2*(1/2)=-1