POINT • CIRCLE • LINE
Download GeoGebra file
Download GeoGebra file
Secant Line, Point on Line Inside Circle
Number of solutions: 2
GeoGebra construction
Steps
- Choose the circle of inversion so that the given point is its center.
- Apply circular inversion to the given circle. The given line remains invariant under this inversion, and the given point maps to infinity.
- The images of the solution circles are tangents to the image of the circle that are parallel to the given line.
- Invert the found tangents back to obtain the solution circles.
- The problem has two solutions.
GeoGebra construction
Steps
- The set of centers of all circles passing through a given point and tangent to a given circle forms an ellipse. Its foci are the given point and the center of the given circle. To construct the ellipse, we need one more point on it. Draw a line through the given point and the center of the circle. The point located halfway between the given point and the intersection of this line with the circle is a point on the ellipse.
- Construct the ellipse using the identified point.
- The centers of all circles tangent to the given line at the given point lie on the perpendicular line passing through that point.
- The centers of the desired solution circles are located at the intersections of the ellipse and the perpendicular line.
- The problem has two solutions.