Two Circles With Contact, Third Circle Inside One Of Them

Steps

1. We choose the reference circle for the inversion. Its center is chosen at the point of tangency of the given circles.
2. We apply the circular inversion to the given objects. The circles through the point of tangency are transformed into lines.
3. The solution circles are transformed into tangents to a circle parallel to the images of the given circles.
4. We invert the found tangents back using the same inversion.
5. The problem has two solutions.

Steps

1. The common point of tangency of the given circles will also be the point of tangency with the solution circles. Therefore, the centers of the solution circles will lie on the line passing through the centers of the given circles and the point of tangency.
2. The common tangent of the two touching circles will also be a tangent of the solution circles.
3. In the homotheties in which the outer given circle is mapped onto the solution circles, the common tangent of the two circles is mapped to tangents of this circle that are parallel to each other. The centers of these homotheties are the points of tangency between the outer given circle and the solution circles.
4. Since the common tangent of the two circles is mapped onto parallel tangents of the third given circle, the points of tangency of the tangents and the circles are also mapped onto each other. Therefore, the centers of the homotheties lie on lines passing through these points of tangency. They lie at the intersections of these lines with the given circle.
5. We have now found all points of tangency between the given circles and the solution circles. The centers of the solution circles lie on the perpendicular bisectors of the segments defined by these points of tangency.
6. The centers of the solution circles lie at the intersections of the found bisectors and the line passing through the centers of the circles and the point of tangency.
7. The problem has two solutions.