As we know that the standard equation of circle is
, where r is the radius of circle and centre at (h,k)
Now , as the circle passes through (2,9) so it must satisfy the above equation after putting the values of h and k respectively
After raising ½ power to both sides , we will get r = +5 , -5 , but as radius can never be -ve . So r = +5
Now , putting values in our standard equation ;
This is the required equation of Circle
Refer to the attachment as well !