What is the equation of a circle with center (6,4) that passes through the coordinate (2,1)?

First find the radius of circle by finding the length from center to the given point

well we  need the square of radius  r^2 = (6-2)^2 + (4-1)^2 = 25

equation of circle is (x - a)^2 + (y - b)^2 = r^2  where (a,b) is the center
so our circle is  
       (x - 6)^2 + ( y - 4)^2 = 25