QUESTION 1
The given circle has equation:

We can rewrite to obtain;

This is equation is now in the form;

Where (h,k)=(0,0) is the center of the circle and
is the radius.
QUESTION 2
The center of the circle is at (1,1) and passes through the point (4,5).
The radius of this circle is given by;




units.
We substitute into the formula;



Expand if you wish;


