The Angle Formed by a Tangent and Chord Theorem Angle formed by a tangent and chord theorem: If a tangent to a circle and a chord intersect at a point c on the circle, then the measure of each angle they form is one-half the measure of its intercepted arc. mz = mAB This also means that ZEAB is going to be equal to the measure of its intercepted arc, BCA. B E A F