IF A+B+C=2S, then prove that
`cos(S-A)+cos(S-B)+cosC=-1+4cos""(S-A)/2cos""(S-B)/2cos""C/2`.

If A+B+C=2S, then prove that cos(S-A)+cos(S-B)+cos C=-1+4cos((S-A)/(2))cos((S-B)/(2))cos((C)/(2))

If A+B+C=2S then prove that the following: cos(S-A)+cos(S-B)+cosC =4cos((S-A)/2)cos((S-B)/2)cosC/2-1

If A+B+C = 2S , then prove that sin(S-A)+sin(S-B)+sinC = 4 cos ((S-A)/2) cos ((S-B)/2) sin C/2 .

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

IF A,B,C are angles in the triangle, then prove that cosA+cosB-cosC=-1+4cos""A/2.cos""B/2.sin""C/2

If A +B+C= 2S , then prove that (i) sin (S-A)+sin (S-B) + sin C=4 cos . (S-A)/(2) cos. (S-B)/(2) sin .(C)/(2) (ii) cos (S-A)+cos (S-B)+cos C=-1+4 cos. (S-A)/(2) cos.(S-B)/(2)cos. (C)/(2)

If A+B+C = 2S , then P.T cos(S-A)+cos(S-B)+cos(S-C)+cosS=4cos.(A)/(2)cos.(B)/(2)cos.(C)/(2)

If A+B+C=180^@ , then prove that cos2A + cos2B +cos2C=-1-4cosA cosB 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 = 180^(@) , prove that cos A + cos B - cos C = -1 + 4 cos (A)/(2) cos"" (B)/(2) sin"" (C )/(2)