Prove that

cos a +cos b +cos c + cos (a + b+ c) = 4 cos ((a+b)/2) ((b+c)/2) ((c+a)/2)

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- July 7th 2013, 11:45 AMsciencepalbasic trigo
Prove that

cos a +cos b +cos c + cos (a + b+ c) = 4 cos ((a+b)/2) ((b+c)/2) ((c+a)/2) - July 7th 2013, 12:07 PMsciencepalRe: basic trigo
Sorry it is

cos a +cos b +cos c + cos (a + b+ c) = 4 cos ((a+b)/2) cos ((b+c)/2) cos ((c+a)/2) - July 7th 2013, 09:22 PMibduttRe: basic trigo
please post the effort you have made on this question