Angle OAB is a right angle, since line AB is tangent to the circle at A. Thus, triangle AOB is a right triangle.
Applying the Pythagorean Theorem: 5^2 + 12^2 = |OB|^2
Then |OB|^2 = 13^2, and |OB| = 13.
We find x by subtracting |OC| from 13: 13 - 5 = 8.
Line segment has length 8; x = 8.
