With the help of the previous theorem, this theorem can be easily proven. The triangles shown at the right are congruent by Hypotenuse Leg for Right Triangles. The radii of a circle are congruent (the legs), and the triangles share a side (the hypotenuses). The triangles have right angles at A and C since a radius drawn to the point of tangency is perpendicular to the tangent. By CPCTC, the tangents are congruent. 
