Who can work out some math problems in junior high school? Please ask for as much as possible.
As shown in the figure, straight line AB passes through point C on ⊙O, OA=OB, CA=CB, and ⊙O intersects straight line OB at E and D, connecting EC and CD.
(1) Verification: straight line AB is tangent to ⊙O;
(2) Try to guess the equivalence relation among BC, BD and BE, and prove it;
(3) If tan∠CED=? The radius ⊙O is 3. Find the length of OA.