Prove an identity using law of cosines

greatwhiteshark

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May 8, 2005
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Prove an identity using law of cosines:

A = alpha
B = Beta
C = Gamma

cosA/a + cosB/b + cosC/c = a^2 + b^2 + c^2/2abc
 
a^2 = b^2 + c^2 - 2bc*cos(A)
2bc*cos(A) = (b^2+c^2-a^2)/(2abc)

cosA/a + cosB/b + cosC/c =

(2bc*cosA + 2ac*cosB + 2ab*cosC)/2abc =

etc.

BTW You are getting careless with ()s again!
 
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