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equal segments from perpendiculars and a diameter

Source: Nordic Mathematical Contest 1995 #1

October 4, 2017
geometryequal segments

Problem Statement

Let ABAB be a diameter of a circle with centre OO. We choose a point CC on the circumference of the circle such that OCOC and ABAB are perpendicular to each other. Let PP be an arbitrary point on the (smaller) arc BCBC and let the lines CPCP and ABAB meet at QQ. We choose RR on APAP so that RQRQ and ABAB are perpendicular to each other. Show that BQ=QRBQ =QR.