MathDB
Inscribed quadrilateral

Source: St Petersburg 2008 10th grade #2

July 28, 2011
trigonometrygeometry proposedgeometry

Problem Statement

Point OO is the center of the circle into which quadrilateral ABCDABCD is inscribed. If angles AOCAOC and BADBAD are both equal to 110110 degrees and angle ABCABC is greater than angle ADCADC, prove that AB+AD>CDAB+AD>CD.
Fresh translation.