English: The center of a dashed circle that intersects both given circles (solid black) orthogonally (that is, at right angles) must lie on the radical axis (red) of the two given circles. The tangent radii (blue) indicate that the blue point has the same power with respect to both circles, and therefore lies on the radical axis. Conversely, any point on the radical axis is the center of a unique circle that cuts both given circles orthogonally.