equation of circle touching x=0, y=0 and x=4 is ______

Suppose the centre is (h,k)
So the equation of circlle is (x-h)^2 + (y-k)^2 = r^2
Now this circle touches coordinate axis
so h=k=r
(x-r)^2 + (y-r)^2 = r^2

Also this circle touches x=4
Apply this condition and find r


that gives you eqn of circle

Thanks