As shown in the figure, AB=AC, O is the center of the circle, and P is the intersection of the circle and BC, that is, P is the midpoint of BC.

∫p is the intersection of a circle and∴ OA = OC = OPBC,

∴∠ 1=∠C and ∠ b =∠ c, ∴∠B=∠ 1,

And ∠C=∠C, ∴△ABC∽△OPC,

∴CO/CA=CP/CB, o is the midpoint of communication,

P is the midpoint of BC, which proves this point.