[وليد خليف]

المشاركة الأصلية كتبت بواسطة tamer mansour

ABC is a triangle in which a = b . Prove that : SinC = 2 SinA CosB

since a =b then A = B=Y(say) then C= 180-2Y
i.e. sin C= sin (180-2y) =sin2Y=2sinYcosY=2sinAcosB