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Interpolation problem

  1. Apr 18, 2013 #1
    Hi guys,

    I was solving this problem using backward interpolation
    https://dl.dropboxusercontent.com/u/49829206/1.PNG [Broken]

    and I got this solution

    https://dl.dropboxusercontent.com/u/49829206/3.PNG [Broken]

    but What I don't get is that how come is the the forth difference is constant while it not in real because forth difference of sin(x) will be either cos(x) or sin(x)

    Edit: images replaced with links, please don't post images wider than about 800 pixels.
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Apr 18, 2013 #2


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    Staff: Mentor

    The 4th difference is neither a cos nor a sin, but the 4th difference is small if you restrict the analysis to the range 25° to 45°. Therefore, the assumption that the 3th difference is constant gives a good approximation. This method is similar to a Taylor series.
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