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posted by adil on Tuesday, December 1, 2009 at 6:00pm.
prove that (2cosx+1)(2cosx-1)= 1 +2cos2x
Using cos(2x)=cos²(x)-sin²(x) and cos²(x)=1-sin²(x) expand the right-hand-side to 4cos²(x)-1 which easily factorizes to the left-hand-side, namely: (2cosx+1)(2cosx-1)
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