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4 integers wanted in a trinomial

Source: Austria Beginners' Competition 2011 p2

October 3, 2021
algebraquadratics

Problem Statement

Let pp and qq be real numbers. The quadratic equation x2+px+q=0x^2 + px + q = 0 has the real solutions x1x_1 and x2x_2. In addition, the following two conditions apply: (i) The numbers x1x_1 and x2x_2 differ from each other by exactly 1 1. (ii) The numbers pp and qq differ from each other by exactly 1 1. Show that then pp, qq, x1x_1 and x2x_2 are integers.
(G. Kirchner, University of Innsbruck)