" (ii) "a cos(A+B+C)-b cos(B+A)-c cos(A+C)=0

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

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 are the angles of a triangle, show that, (iii) (cos A cos C + cos (A + B) cos(B + C))/(cos A sin C - sin (A + B) cos (B + C)) = cot C .

Prove that cos (A + B) cos C - cos (B + C) cos A = sin B sin (C - A)

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

If A + B + C =180^@ , prove that : cos (-A+B +C)+cos(A-B+C)+ cos (A +B-C)=1+ 4cos A cos B cos C .

cos (B+C-A)-cos(C+A-B)+cos(A+B-C)- cos (A+B+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

( a cos A + b cos B + c cos C )/( a +b +c ) =