Final answer:
The radius of the circle represented by the equation x² + y² = 121 is 11 units, as the equation is compared to the standard form of a circle's equation and the square root of 121 is calculated.
Step-by-step explanation:
The equation given, x² + y² = 121, represents a circle with its center at the origin (0,0) on the coordinate plane. To find the radius of the circle, we can compare the equation to the standard form of a circle's equation, which is (x - h)²+ (y - k)² = r², where (h,k) is the center of the circle, and r is the radius.
Since the given equation has no (h,k), we can infer that h=0 and k=0, indicating the circle is centered at the origin. The number on the right-hand side of the equation, 121, represents r². Therefore, the radius r is the square root of 121.
Calculating the square root of 121, we get r = 11. So, the radius of the circle given by the equation x² + y² = 121 is 11 units.