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Math Help - prooof!!

  1. #1
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    prooof!!

    can someone set me straight on this proof?

    tan3A=(3tanA-tan^3)/(1-3tan^2A)

    thanks a bunch
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  2. #2
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    Quote Originally Posted by ringer123 View Post
    can someone set me straight on this proof?

    tan3A=(3tanA-tan^3)/(1-3tan^2A)

    thanks a bunch
    Start from tan (A + 2A) and use the compound angle formula.

    Replace tan(2A) using the double angle formula.

    Simplify.
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