IF A,B,C are angles of a triangle , Prove that `cos2A+cos 2B+cos 2C=-4cosAcosBcosC-1`

If A, B, C are angles of a triangle , prove that cos 2A - cos 2B + cos 2C =1 -4 sin A cos B sin C

If A, B, C are angles of a triangle , prove that cos 2A+cos 2B -cos 2C=1-4 sin A sin B cos C

If A,B,C are the angles of a triangle then prove that cosA+cosB-cosC=-1+4cos(A/2)cos(B/2)sin(C/2)

If A,B,C are the angles of a triangle then prove that cosA+cosB-cosC=-1+4cos(A/2)cos(B/2)sin(C/2)

If A, B, C are angles of a triangle , prove that sin 2A+sin 2B-sin 2C=4cos Acos B sin C

If A,B,C are the angles of a triangle then prove that cos A+cos B-cos C=-1+4cos((A)/(2))cos((B)/(2))sin((C)/(2))

If A+B+C = pi , prove that : cos2A +cos2B +cos2C =-1-4cosAcosBcosC .

If A+B+C = pi , prove that : cos2A +cos2B +cos2C =-1-4cosAcosBcosC .

If A+B+C=pi , prove that cos 2A +cos 2B +cos 2C=-1-4cos A cos Bcos C.

If A+B+C=pi , prove that cos 2A +cos 2B +cos 2C=-1-4cos A cos Bcos C.