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2016 Chandigarh RMO (ad + bc) divides each of a, b, c,d

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August 9, 2019
number theorydividesdivisor

Problem Statement

a,b,c,da, b, c, d are integers such that ad+bcad + bc divides each of a,b,ca, b, c and dd. Prove that ad+bc=±1ad + bc =\pm 1