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Math Help - acquiring a cubic equation from a data table

  1. #1
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    acquiring a cubic equation from a data table

    I'm not allowed to use a calculator on this one....
    I have to get a cubic equation from a set of points but they don't have a constant D3.
    I completely forget how to do this...
    the set of data are: left is x right is y
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  2. #2
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    Any cubic equation is of the form y= Ax^3+ bx^2+ cx+ d. One way to get a cubic equation from the data is to just pick three points and put their x and y values into that, so you have 3 equations to solve for a, b, and c. If I were doing this I would pick numbers at the beginning, center and end of the list.

    Or you might be expected to give the "least squares" cubic approximation. That's much harder.
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  3. #3
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    Quote Originally Posted by HallsofIvy View Post
    Any cubic equation is of the form y= Ax^3+ bx^2+ cx+ d. One way to get a cubic equation from the data is to just pick three points and put their x and y values into that, so you have 3 equations to solve for a, b, and c. If I were doing this I would pick numbers at the beginning, center and end of the list.

    Or you might be expected to give the "least squares" cubic approximation. That's much harder.
    I forget how to do that....sorry~
    but could you show me how to do it? just for like 2 equations and I'll be able to catch on.
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