If `A+B +C=pi, ` then `cos 2A + cos 2B+ cos 2C=`

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

If A+B+C =pi, then cos ^(2) A+ cos ^(2)B + cos^(2) C is equal to

If A+B+C=(3pi)/2 . Then cos 2A +cos 2B+cos2C is equal to ................. A) 1-4 cos A cos B cos C B) 4 sin A sin B sin C C) 1+2 cos A cos B cos C D) 1-4 sin A sin B sin C

If A+B+C=3pi/2 then cos2A+cos2B+cos2C=1-4sinAsinBsinC

If A+B+C =pi and cos A = cos B cos C then cot B. cot C = ............. A) 1/3 B) 1 C) 2 D) 1/2

If 8 theta = pi, then cos 7 theta + cos theta is equal to ............ A) 0 B) 1 C) -1 D) 7

In triangleABC,A+B+C=pi ,show that cos^2A+cos^2B-cos^2C=1-2sinAsinBcosC

In triangleABC,A+B+C=pi ,show that cos2A+cos2B+cos2C=-1-4cosAcosBcosC

If A+B+C=pi then prove that cos^2 (A/2)+cos^2 (B/2)-cos^2 (C/2)=2cos(A/2)cos(B/2)sin(C/2)

In a triangle ABC If ( 2 cos A)/a + ( cos B)/b + (2 cos C)/c = a/(bc) + b/(ca) , find the angle A.