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2020 Taiwan APMO Preliminary Problem 1

Source: 2020 Taiwan APMO Preliminary

July 23, 2020
Taiwanalgebratrigonometry

Problem Statement

Let ABC\triangle ABC satisfies cosA:cosB:cosC=1:1:2\cos A:\cos B:\cos C=1:1:2, then sinA=t\sin A=\sqrt{t}(sN,tQ+s\in\mathbb{N},t\in\mathbb{Q^+} and tt is an irreducible fraction). Find s+ts+t.