Answer :

luana
[tex]Genereal\ formula\ for\ circle:\\(x-a)^2+(y-b)2=r^2\\Center\ of\ circle:\ S(a,b)\\r-radius\\\\x^2+y^2=4^2\\It's\ equation\ of\ circle,\ which\ has\ S(0,0)\ and\ radius\ 4.[/tex]