解:若OC在∠AOB内部∵∠AOC:∠COB=2:3∴设∠AOC=2x,∠COB=3x∵∠AOB=40°∴2x+3x=40°得x=8°∴∠AOC=2x=2×8°=16°,∠COB=3x=3×8°=24°∵OD平分∠AOB∴∠AOD=20°∴∠COD=∠AOD﹣∠AOC=20°﹣16°=4°
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