Posted by **Anonymous** on Thursday, May 3, 2007 at 1:43pm.

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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