(1) For example, in the circle O in the above figure, the central angle of arc AB is ∠AOB= 120 degrees, so the circular angle of this arc is ∠ m. 。

Therefore, the circumferential angle ∠M=( 1/2)∠AOB=60 degrees;

(2) In the above figure, the central angle ∠AOB subtended by chord AB is 120 degrees, and this chord AB subtends two arcs, namely, arc AMB and arc ANB, so the central angles subtended by chord AB are ∠M and ∠N, and ∠ m is already in (/kloc-0.

∠N= 120 degrees.

Summary of knowledge: an arc has a circumferential angle, while a chord has two circumferential angles.