When encountering chords (when solving problems related to chords), it is often necessary to add the chord center distance, or reconnect the radius (or diameter) perpendicular to the chord or the radius of the chord end point. Function: ① Use the vertical diameter theorem; (2) Using the relationship between the central angle and its corresponding arc, chord and chord center distance; (3) Form a right triangle with half of the chord, the chord center distance and the radius, and calculate the related quantity according to Pythagorean theorem.