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P(x) upon division by (x-a)(x-b)(x-c) when P(a)=a, P(b)=b, P(c)=c

Source: 1990 ITAMO p3

January 31, 2020
polynomialremainderalgebra

Problem Statement

Let a,b,ca,b,c be distinct real numbers and P(x)P(x) a polynomial with real coefficients. Suppose that the remainders of P(x)P(x) upon division by (xa),(xb)(x-a), (x-b) and (xc)(x-c) are a,ba,b and cc, respectively. Find the polynomial that is obtained as the remainder of P(x)P(x) upon division by (xa)(xb)(xc)(x-a)(x-b)(x-c).