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2014 preRMO p3, ABCD with perp. diagonals, AB=20, BC=70, CD=90, DA=?

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August 9, 2019
geometryperpendiculardiagonals

Problem Statement

Let ABCDABCD be a convex quadrilateral with perpendicular diagonals. If AB=20,BC=70AB = 20, BC = 70 and CD=90CD = 90, then what is the value of DADA?