If `A+B+C=pi`. Then prove that `cosA=-cos(B+C)`

If A+B+C =pi prove that sin2A=-sin(2B+2C)

If A+B+C=pi prove that (cosA)/(sinBsinC)+(cosB)/(sinCsinA)+(cosC)/(sinAsinB)=2 .

If A+B+C=180^@ ,prove that cos^2A+cos^2B+cos^2C=1-2cos Acos B cos C .

In triangle ABC , prove that sinA=sin(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

For any DeltaABC , prove that a(b cos C -c cos B) = b^2 - c^2

If A , B , C ,D are angles of a cyclic quadrilateral , then prove that cosA + cosB+cosC+cosD=0.

For any DeltaABC , prove that (a+b)/c=cos((A-B)/2)/sin(c/2)

For any triangle ABC, prove that (a+b)/c=cos((A-B)/2)/sin(C/2)

If sinA=sinBand cosA=cosB , then prove that " sin "(A-B)/(2)=0 .