If `cos(a-b) + cos(b-c) + cos(c-a) = -1.5`, then find `cos2a + cos 2b + cos 2c`

if A + B +C= pi/2 ,prove that cos(A - B - C)+ cos (B-C- A) + cos (C- A - B)= 4 cos A cos B cos C

If A+B +C =2S, prove that : cos^2 S + cos^2 (S- A) + cos^2 (S-B)+ cos^2 (S -C) = 2 +2 cos A cos B cos C .

If A+ B + C = pi, then cos^(2) A + cos ^(2) B + cos ^(2) C is equal to : A) 1 - cos A cos B cos C B) 1 - 2 cos A cos B cos C C) 2 cos A cos B cos C D) 1 + cos A cos B cos C

If : A+B+C=pi, "then" : 1-cos^(2) A-cos^(2)B-cos^(2)C= A) 2 cos A * cos B * cos C B) 2 sin A * cos B * cos C C) 2 cos A * sin B * cos C D) 2 cos A * cos B * sin C

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

In DeltaABC , if b(b +c) = a^(2) and c(c + a) = b^(2) , then |cos A.cos B. cos C| is______

In DeltaABC , if b(b +c) = a^(2) and c(c + a) = b^(2) , then |cos A.cos B. cos C| is______

In DeltaABC , if b(b +c) = a^(2) and c(c + a) = b^(2) , then |cos A.cos B. cos C| is______

In DeltaABC , if b(b +c) = a^(2) and c(c + a) = b^(2) , then |cos A.cos B. cos C| is______