Answer:
AB is not tangent to the circle
Explanation:
You want to know if segment AB of length 9 is tangent to the circle with diameter 12 at point B given that the third side of the triangle is 13 units long.
Pythagorean triple
You know that the numbers {5, 12, 13} are a Pythagorean triple, so these lengths form a right triangle. The lengths (9, 12, 13) cannot form a right triangle, so AB will not be perpendicular to the diameter.
AB is not a tangent
Pythagorean theorem
The segments will form a right triangle if they satisfy the Pythagorean theorem, which requires the sum of the squares of the shorter sides equal the square of the longest side.
9² +12² = 13²
81 +144 = 169 . . . . . . false — not a right triangle
Form Factor
A "form factor" can be computed for the triangle to tell if the largest angle is acute, right, or obtuse. That is ...
f = a² +b² -c²
f = 81 +144 -169 = 56 . . . . . . . f > 0 means the triangle is acute
The measure of the largest angle can be found from ...
C = arccos(f/(2ab)) = arccos(56/216) ≈ 74.97°
This is further confirmation that AB is not tangent to the circle.
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Additional comment
The attached drawing is to scale. It shows AB has two points of intersection with the circle, so is not tangent.