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

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

If A+B+C=pi/2 prove the following (i) sin 2A+sin 2B +sin 2C=4 cos A cos B cos C (ii) cos 2A +cos 2B+cos 2C=1+4 sin A sin B sin C.

If A+B+C=90^(@) then (cos2A+cos2B+cos2C-1)/(sin A sin 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 = 270^@ , then cos 2A + cos 2B +cos 2C +4sin A sin B sin C=

If A+B+C=90^(@) then (cos 2A+cos 2B+cos 2C-1)/(sin A sin B sin C)=

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

If A+B+C=270^(@), then cos2A+cos2B+cos2C+4sin A sin B sin C=

If A+B+C=180^(@) then cos2A+cos2B+cos2C=1-4cos A cos B cos C 2.If A+B+C=0 then cos A+cos B+cos C=-1+4(cos A)/(2)(cos B)/(2)(cos C)/(2)