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Published online by Cambridge University Press: 20 January 2009
Let P1 and P1′ be images of each other with respect to a circle of radius a. (Fig. 13.) Draw AOB the diameter perpendicular to OP1′P1. If r1,r1′ represent respectively the distances of P1, and P1′ from 0, the centre of the circle, the condition is r1r1′ = a2.