Perpendicular (Orthogonal) Circles

Perpendicular (Orthogonal) Circles If two circles intersect in two points, and the radii drawn to the points of intersection meet at right angles, then the circles are orthogonal, and the circles can be said to be perpendicular to each other. If the two radii of one circle meet at right angles also, then all four radii form a square, and the two circles are congruent. If the two radii of one circle form a straight angle, then what is the radius of the second circle?