cos(B-C)+cos(C-A)+cos(A-B)=-(3)/(2)" is true if and only if "

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

(c-b cos A)/(b-c cos A)=(cos B)/(cos C)

a(cos C-cos B)=2(b-c)cos^(2)(A)/(2)

If A+B+C=pi then prove cos( (A)/2) cos( (B-C)/2) + cos( B/2) cos((C-A)/2) + cos( C/2) cos( (A-B)/2) = sinA +sinB+sinC

In any triangle A B C , prove that: a^3cos(B-C)+b^3cos(C-A)+c^3cos(A-B)=3a b c

If cos(a-b)+cos(b-c)+cos(c-a)=-1, then find cos2a+cos2b+cos2c