Two chords intersect at a point inside a circle that is not the center of the circle. Which statement must be true?

For two chords intersecting inside a circle, an angle’s measure is half the sum of the measures of the arcs intercepted by that angle and its vertical angle. The two vertical angles have equal measures, so their sum equals the sum of those two intercepted arc measures. Thus, the statement that the sum of each pair of vertical angles equals the sum of the intercepted arcs must be true.

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