Final answer:
The measure of the radius of the circle defined by x^2 + y^2 = 121 is 11 units.
Step-by-step explanation:
The equation x2 + y2 = 121 represents a circle.
By comparing this equation to the general equation of a circle (x - h)2 + (y - k)2 = r2, we can deduce that the center of the circle is (h, k) = (0, 0) and the square of the radius is 121, so the radius is √121 = 11.
Thus, the measure of the radius of the circle is 11 units.