OC=√AC^2-AO^2=√5-1=2
∵∠BCO+∠ACO=90°
∠ACO+∠A=90°
∴∠BCO=∠A
∵∠B+BCO=90°
∴∠B=∠ACO
∵∠COB=∠COA=90°
∴△AOC∽△COB