Question 771962
{{{x^2+y^2-4x+2y-4=0}}}

write it first in the standard form: {{{(x - h)^2 + (y-k)^2 = r^2}}} where {{{h}}} is x-coordinate and {{{k}}} is y-coordinate of the center ({{{h}}},{{{k}}}) and {{{r}}} is a radius


{{{(x^2-4x)+(y^2+2y)=4}}}...complete square


{{{(x^2-4x+_)+(y^2+2y+_)=4}}}

{{{(x^2-4x+4)-4+(y^2+2y+1)-1=4}}}

{{{(x-2)^2+(y+1)^2-5=4}}}

{{{(x-2)^2+(y+1)^2=9 }}}

so, the center is at ({{{h}}},{{{k}}})=({{{2}}},{{{-1}}})

and radius {{{r=3}}}

{{{drawing( 600, 600, -10, 10, -10, 10,
  grid( 1 ),circle(2,-1,0.1),
  green( circle( 2, -1, 3 ) ))}}}