An interediate step in the Gergonne solution of the problem of Apollonius.  The three given circles are <i>s1</i>, <i>s2</i> and <i>s3</i>, whereas <i>b1</i> and <i>b2</i> are one pair of solutions.  The line <i>r</i> is the radical axis of the two solutions.  The tangent lines at points <b>A</b> and <b>B</b> (the tangent points of <i>s2</i> with the solutions) intersect on the radical axis <i>r</i>.  The point <i>P</i> is the pole of the radical axis <i>r</i> in the circle <i>s2</i>.
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