Inside a circle there are circles , and which are tangent to at points , and correspondingly, which are all different. Circles and have a common point in the segment , circles and have a common point in the segment , and circles and have a common point in the segment . Prove that the circles , and intersect in the center of the circle .
Solution
Take a point on the common tangent to the circles and which lies on the other side of the line from the point . Then (Fig. 4). Consequently . Similarly and . If , then
to with the factor . Thus the radii of their circumcircles , and are equal to half of the radius of the circumcircle of the triangle . Since the circles and are tangent, the diameter of and the radius of , both drawn from the tangent point , coincide. Hence the circle goes through the center of the circle ; similarly the circles and go through the center of the circle .

Figure 4
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