Hellow guys, Welcome to my website, and you are watching If A + B + C = 2S, then prove that cos(S - A) + cos(S - B) + cos(S - C) = 4 cosA/2 cosB/2 cosC/2. and this vIdeo is uploaded by EDUTAINMENT ONLINE at 2020-10-16T07:33:29-07:00. We are pramote this video only for entertainment and educational perpose only. So, I hop you like our website.