It is not true because the distance from (0, 0) to (2, 1) works out as the square root of 5 which is the circle's radius.
radius
radius
x2 + y2 = 25
x2 + y2 = 25
x2 + y2 =144
radius
radius
The circle of radius five centered at the origin.
If that equals 16 then the radius is 4
x2 + y2 = 25
x2 + y2= 16
x2 + y2 = 25
x2 + y2 = 36
17
x2 + y2 = 49
x2 + y2 =144
x2 + y2 = 400