Answer:
? = 9
Explanation:
You want the length of the segment marked ? in the given figure with a tangent of length 15 to a circle of radius 8.
Pythagorean triple
You recognize the triangle is a right triangle with sides 15 and 8, so you know from your knowledge of Pythagorean triples that the hypotenuse of the triangle is 17 units.
The unknown segment is 17 units less the radius of the circle:
? = 9 units
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Additional comment
If you don't remember the {8, 15, 17} Pythagorean triple, you can find the length of the hypotenuse using the Pythagorean theorem.
c² = a² +b²
c² = 8² +15² = 65 +225 = 289
c = √289 = 17
? = c -8 = 17 -8 = 9 . . . . . units