trig

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prove that

(2cosx+1)(2cosx-1)= 1 +2cos2x

  • trig -

    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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