Question 461758
The standard form of the equation of the circle is {{{(x-h)^2+(y-k)^2=r^2}}}

Since our circle is tangent to the x-axis its radius will be perpendicular to the 

the x-axis at the point (4, 0), and its radius will be:

{{{r^2=(4-4)^2+(0-8)^2=64}}}, and the equation of the circle is:

{{{(x-4)^2+(y-8)^2=64}}}.