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

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 sinBsinC

If A+B+C=pi , prove that : cos2A+cos2B-cos2C=1-4sinA sinB cosC

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

In DeltaABC , prove that: cos2A+cos2B-cos2C=1-4sinAsinBcosC

If A+B+C=pi , prove that : cosA + cosB-cosC=4cos(A/2) cos(B/2) sin(C/2) -1

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

If A + B + C = pi , prove that cos A cosec B cosec C + cos B cosec C cosec A + cos C cosec A cosec B = 2 .

In a /_ABC prove that cos2A+cos2B+cos2C=-1-4cos A cos B cos C

cos2B + cos2A-cos2C = 1-4sin A sin B cos C