证明：∵OA＝3OD，OB＝3OC∴ OA/OD= OB/OC且∠AOB=∠COD∴△AOB∽△COD∴ CD/AB= OD/OA=1/3∴此时AB=3CD O(∩_∩)O
：∵OA=30D，OB=3OC，∴ OA/OD= OB/OC，且∠AOB=∠COD．∴△AOB∽△COD．∴ CD/AB= OD/OA=1/3．∴此时AB=3CD
AB=3CD
