Given two circles x2+y2=9 and x2+y2=25 find the difference between the radius of the large circle and the radius of small circle

Equation of a circle with center at the origin is given by x^2 + y^2 = r^2
First circle: x^2 + y^2 = 9 => x^2 + y^2 = 3^2 => radius is 3.
Second circle: x^2 + y^2 = 25 => x^2 + y^2 + 5^2 => radius is 5

Difference in radius = 5 - 3 = 2.

Do you need with the x value for the minimum? its always between the two intercepts for a parabola