If a segment is perpendicular to a radius at its endpoint on a circle, then the segment is tangent to the circle. Therefore, to determine whether a tangent is shown on the diagram, it is enough to determine if $\overline{A B},$ which appears to be a tangent segment, forms a right angle with the radius of $⊙ C .$

Note that the length of the second radius is missing in the graph. Since in any circle the lengths of any radius are constant, the length of the missing radius is $20 .$

Now, we will use the Converse of the Pythagorean Theorem. We will substitute the given side lengths into the Pythagorean Theorem. If we obtain a true statement, the triangle is a right triangle. If we have a right triangle,