Question

cos(α +β)+2 sin α sinβ , если α-β=π

Answer 1

cos(α+β)+2*sinα*sinβ=cos(α+β)+2*1/2*(cos(α-β)-cos(α+β))=
=cos(α+β)+cos(α-β)-cos(α+β)=cos(α-β)=cosπ=-1