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How to find coefficients to polynomials?

Posted 10 years ago

I would like to find coefficients to polynomials, for example,

f(x) = ax^2 + bx + c
f(0) = 3
f(1) = 4
f(2) = 7

should solve for a, b, c such that f(x) = x^2 + 3 (a=1, b=0, c=3).

Another example:

f(x)  =  ax^3 + bx^2 + cx + d
f(2)  =  5
f(0)  =  1
f'(2) = 22
f'(0) =  2

The solution is 5x^3 - 10x^2 + 2x + 1.

I can solve these kinds of problems by substituting x in the function or its derivative which will give me four linear equations with a, b, c and d, which in turn can easily be solved.

Is it possible to directly express this kind of problem using the WolframAlpha website, without writing down the intermediate manual steps?

POSTED BY: Arne Schirmacher
2 Replies

This link to Wolfram|Alpha shows one way to do the input.

enter image description here

POSTED BY: Daniel Lichtblau

that would work for the first example, but not for the second. Is there any way to include the derivatives into the query?

POSTED BY: Arne Schirmacher
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