Angles Formed By Lines Intersecting a Circle 1.Angles formed by two secants which intersect outside the circle : The measure of such an angle is equal to one-half the difference of the arcs intercepted by the secants 2.Angles formed by a tangent and a chord : This angle is one-half arc it cuts off 3.Angles formed by two chords: The angle formed by two chords is one-half the sum of the intercepted arcs [color=#c51414]Red dots are movable[/color] Reference 1. The Art of the Problem Solving by Sandor Lehoczky and Richard Rusczyk [color=#980002]228 [/color]2015