Answer
$(x-2)^2+(y+1)^2=9$
Work Step by Step
Use standard form of equation of circles; $(x-a)^2+(y-b)^2=r^2$
Here, $r$ defines radius and $(a,b)$ defines center.
Then, $x^2+y^2-4x+2y-4=0$
or, $(x^2-4x+4)+(y^2+2y+1)=4+4+1$
or, $(x-2)^2+(y+1)^2=9$
