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**Jun** on
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2 circles C1 and C2 meet at the points A and B. Points C and Dare points on the circumferences of C1 and C2 respectively such that angle CAB = angle DAB. CD cuts C1 and C2 at the points Y and X respectively. if Z is the foot of the perpendicular from X to BY, prove that angle XBY = 2 angle ZXY