As shown in figure (3), make a chord BE⊥CD at point B, connect AE and CD at point P, and connect OB, OE, OA and PB.
∵BE⊥CD,
∴CD bisects BE, that is, point E and point B are symmetrical about CD.
∵AC? It's 60 degrees, point b is the midpoint of AC,
∴∠BOC=30,∠AOC=60,
∴∠EOC=30,
∴∠AOE=60 +30 =90,
∫OA = OE = 1,
∴AE=2OA=√2
The length of AE is the minimum value of BP+AP. ∴BP+AP=√2
(3) Expansion and extension
As shown in Figure (4), that is, point P is the symmetrical point E about straight line AB, point P is the symmetrical point F about straight line BC, and EF is connected to points M and N of AB and BC respectively.
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