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a segment d divides a segment s if there is a natural number n so s=nd ...

Source: Spanish Mathematical Olympiad 1986 P2

August 2, 2018
combinatoricscombinatorial geometry

Problem Statement

A segment dd is said to divide a segment ss if there is a natural number nn such that s=nd=d+d+...+ds = nd = d+d+ ...+d (nn times). (a) Prove that if a segment dd divides segments ss and ss' with s<ss < s', then it also divides their difference sss'-s. (b) Prove that no segment divides the side ss and the diagonal ss' of a regular pentagon (consider the pentagon formed by the diagonals of the given pentagon without explicitly computing the ratios).