Question 1106620

The equation of a circle with center at (h,k) and radius r is:

         {{{  (x-h)^2 + (y-k)^2 = r^2 }}}


Since the circle is tangent to the coordinate axes, its center is at (r,r):

      {{{ (x-r)^2 + (y-r)^2 = r^2 }}}
      
Plugging in (x=1, y=2):
        {{{  (1-r)^2 + (2-r)^2 = r^2 }}}
        ….

Can you solve it from here?  (there are two solutions)