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Math Help - Lagrange identity

  1. #1
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    Lagrange identity

    Can someone please help me with this question,


    thank you.
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  2. #2
    MHF Contributor
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    Re: Lagrange identity

    to show it just multiply both sides by (1-z)

    to show the trig identity let

    $$z=e^{i\phi}$$

    and take the Real part of both sides

    yeah, there's some trig work to do on the right hand side but it's nothing magic
    Thanks from Tweety
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