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Homework Help: [cos nt - n.sin nt] rewrite as [cos (nt + tan^-1 n)]

  1. Jul 16, 2012 #1
    1. The problem statement, all variables and given/known data

    I am working through an example in fourier analysis and the author has rewritten [cos nt - n*sin nt] as [cos (nt + tan^-1 n)]. Can somebody show how he does this? ie. the steps involved.

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jul 16, 2012 #2


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    there's a factor missing :rolleyes:

    the RHS is cosnt*costan-1n - sinnt*sintan-1n

    = cosnt*costan-1n*(1 - sinnt*tantan-1n)

    = … ? :wink:
  4. Jul 17, 2012 #3
    I see what is going on now.
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