△OEF,OE=OF=√2,EF=2。
∵(√2)? +(√2)? =2?
∴OE? +OF? =EF?
That is, △OEF is Rt△, ∠ EOF = 90.
∫ Point E is the midpoint of arc AC, and point F is the midpoint of arc AB.
∴ arc BC is: 90× 2 = 180.
BC is the diameter of this circle.
∴∠CAB=90
Namely: AC⊥AB