trig
posted by adil .
prove that
(2cosx+1)(2cosx1)= 1 +2cos2x

Using
cos(2x)=cos²(x)sin²(x)
and cos²(x)=1sin²(x)
expand the righthandside to
4cos²(x)1
which easily factorizes to the lefthandside, namely:
(2cosx+1)(2cosx1)
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