The radius of the circle is 9. If we imagine the distance to (8, sqrt 17) as a right triangle, where one leg is 8 and the other is square root 17, we can use the Pythagorean formula to solve this
8^2 (64) + sqrt 17^2 (17)= c^2
81=c^c
9=c
we can see that since the radius to the origin is 9, this point indeed lies on the circle.