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Homework Help: Diffraction Gratings and Incident Light

  1. Nov 12, 2013 #1
    1. The problem statement, all variables and given/known data
    If light incident on a diffraction grating makes an angle η with respect to the normal of the grating, show that mλ=dsinθ becomes d( sin(θ-η) + sin(η) ) = mλ

    2. Relevant equations

    3. The attempt at a solution

    I haven't done any work with diffraction gratings in a long time so this has thrown me for a loop :/ I can't really start the problem because I don't quite understand where to begin
  2. jcsd
  3. Mar 14, 2015 #2
    This question just simply needs the knowledge of double angle formula in trigonometry. You just need to change from sin A to sin(A-n) + sin(n).
    So, what's the double angle formula for sin A?
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