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

if A+ B + C = pi, and cos A = cos B cos C, show that 2 cot B cot C=1.

If A + B + C = pi then prove that cos A + cos B + cos C = 1 + 4 sin(A/2) .sin(B/2).sin(C/2)

In any DeltaABC , a cos A +b cos B + c cos C =

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

If three angles A, B, C are such that cos A+ cos B + cos C = 0 and if lambda cos A cos B cos C = cos 3A + cos 3B + cos 3C , then value of lambda is :

If A+B+C+D=2pi , show that : cosA-cosB+cosC-cosD=4sin( (A+B)/(2)) sin( (A+D)/(2)) cos( (A+C)/(2)) .

Prove that : (sin 2A+sin 2B + sin 2C)/(cos A + cos B + cos C-1) = 8 cos(A/2) cos( B/2) cos( C/2)

In any DeltaABC , prove that : a cos A + b cos B + c cos C = 2a sin B sin C

If A+B+C =(3pi)/(2) , then cos2A+cos2B+cos2C is equal to-

In any DeltaABC , prove that : (cos A)/(b cos C + c cos B) + (cos B)/(c cos A + a cos C) + (cos C)/(a cos B + b cos A) = (a^2 + b^2 + c^2)/(2abc)