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cosA= 5/9 find cos1/2A



are you familiar with the half-angle formulas?
the one I would use here is
cos A = 2cos^2 (1/2)A - 1
5/9 + 1 =2cos^2 (1/2)A
14/9 =2cos^2 (1/2)A
cos (1/2)A = √(7)/3

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