This equation depicts a circle with radious 3.
clc; clearvars;
syms x y
eq= x^2+y^2==9
fimplicit(eq, [-3 3]);
xlabel('x'); ylabel('y');
ax=gca;
ax.YAxisLocation='origin'; ax.XAxisLocation='origin' ;
ax.XLim=[-5 5]; ax.YLim=[-5 5];
clc; clearvars;
ci=@(x,y) x.^2+y.^2-9;
fimplicit(ci, [-3 3 -3 3]);
xlabel('x'); ylabel('y');
ax=gca;
ax.YAxisLocation='origin'; ax.XAxisLocation='origin' ;
ax.XLim=[-5 5]; ax.YLim=[-5 5];