From the tangent theorem: DB? DA=DC2, that is, DB(DB+BA)=DC2, and ∵∠A=∠BCD, ∴△DBC∽△DCA, ∴BCCA=DBDC, that is, 69 = DBDB? (DB+ 10)，

Solution: db = 8.

So the tangent DC2 = 8 (8+ 18) = 144.

∴DC= 12.

So the answer is: 12.