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A polynomial ineq

Source: Indian IMOTC 2004 Day 5 Problem 2

September 23, 2005
algebrapolynomialalgebra unsolved

Problem Statement

Let P(x)=x4+ax3+bx2+cx+dP(x) = x^4 + ax^3 + bx^2 + cx + d and Q(x)=x2+px+qQ(x) = x^2 + px + qbe two real polynomials. Suppose that there exista an interval (r,s)(r,s) of length greater than 22 SUCH THAT BOTH P(x)P(x) AND Q(x)Q(x) ARE nEGATIVE FOR X(r,s)X \in (r,s) and both are positive for x>sx > s and x<rx<r. Show that there is a real x0x_0 such that P(x0)<Q(x0)P(x_0) < Q(x_0)