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Math Help - MAth Cubics

  1. #1
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    MAth Cubics

    what is the cubic eqaution for the follwing coordinates
    and how do i deduce it?
    (1,10),(2,23)(3,38)(4,55)(5,74)(6,96)(7,120)(8,149 )
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  2. #2
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    Hello, amak!

    Are there typos in the problem?


    What is the cubic eqaution for the follwing coordinates?

    . . (1,10), (2,23), (3,38), (4,55), (5,74), (6,96), (7,120), (8,149)

    There is no cubic that passes through these points!


    In fact, the first five points lie on a parabola: . f(x) \;=\;x^2 + 10x - 1

    . . and the other three points are quite "close" to the parabola.

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  3. #3
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    Quote Originally Posted by amak View Post
    what is the cubic eqaution for the follwing coordinates
    and how do i deduce it?
    (1,10),(2,23)(3,38)(4,55)(5,74)(6,96)(7,120)(8,149 )
    You might try to use the equation:

    y=ax^3+bx^2+cx+d

    Pick 4 of your points, substitute them in 4 of these equations and solve the system for a, b, c, d.

    Using (1, 10): 10=a(1)^3+b(1)^2+c(1)+d
    Using (2, 23): 23=a(2)^3+b(2)^2+c(2)+d
    .
    .
    ...and so on.
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