To the circle at point A, segment AB is tangent. In the circle of 5 units, the circumference has a length. If the radius of the circle is 12 units, then what is the length of the tangent KB? We can use the Pythagorean theorem to find KB because it's a right triangle. So the hypotenuse is (12^2 + 5^2) = (144 + 25) = 169. So KB = 13.