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Prove the identity. (must work with left side)


  • trig -

    Let x^2 = y
    What you have written is equivalent to
    1 - 2 sin y = cos y
    which is not a correct identity.

    It looks like you have put parentheses in the wrong places. The outside ones are unecessary.

    A correct version would be
    1 - 2 (sin x)^2 = cos 2x
    That is one of the double-angle identities

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