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jmc

algebra senior

Problem

Let . For how many polynomials does there exist a polynomial of degree 3 such that ?
Solution
The polynomial has degree 6, so must have degree 2. Therefore is uniquely determined by the ordered triple . When , 2, or 3, we have It follows that is one of the 27 ordered triples , where , , and can be chosen from the set .

However, the choices , , , , and lead to polynomials defined by , and , respectively, all of which have degree less than 2. The other choices for yield non-collinear points, so in each case is a quadratic polynomial.
Final answer
22