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

If A+B+C=180^0 , prove that : cos^2 A + cos^2 B + cos^2 C + 2cosA cosB cosC=1 .

If A+B+C=0 , Prove : cos^2 A + cos^2 B +cos^2 C=1+2cosA cosB cosC .

If A+B+C=180^0 , prove that : cos^2 A+cos^2 B-cos^2 C=1-2sinA sinB cosC

A + B + C = 2S then prove that cos (SA) + cos (SB) + cos (SC) + cos S = 4 (cos A) / (2) (cos B) / (2) (cos C) / (2)

If A+B+C=2pi , prove that : cos^2B+cos^2C-sin^2A-2cosA cosB cosC=0 .

If A+B+C=pi , prove that : cos2A+cos2B-cos2C=1-4sinA sinB cosC

If A+B+C=180, prove that cos^(2)A+cos^(2)B+cos^(2)C=1-2cos A cos B cos C

If A+B+C=pi , prove that : cosA + cosB-cosC=4cos(A/2) cos(B/2) sin(C/2) -1

Prove that a cos A+b cos B+c cos C<=s

If A+B+C=2 pi, then prove that cos^(2)B+cos^(2)C-sin^(2)A=2cos A cos B cos C