If cos(a-b)+cos(b-c)+cos(c-a)=-3/... then prove that cosa+cosb+cosc=sina+sinb+sinc=0 and hence deduce that cos(a-b)=cos(b-c)=cos(c-a)=-1/2
If cos(a-b)+cos(b-c)+cos(c-a)=-3/... then prove that cosa+cosb+cosc=sina+sinb+sinc=0 and hence deduce that cos(a-b)=cos(b-c)=cos(c-a)=-1/2