Manipulate[Show[ContourPlot[(x1-3)^2+(x2-4)^2,{x1,-3,6},{x2,-3,6},Contours->Table[k,{k,0,maxf,4}],ContourShading->None],Graphics[Disk[{0,0},1]],Graphics[Disk[{3,4},.1]]],{maxf,0,40,4}]

f[x1_,x2_]:=(x1-3)^2+(x2-4)^2

f[3/5,4/5]

f[-3/5,-4/5]

Show[ContourPlot[(x1-3)^2+(x2-4)^2,{x1,-3,6},{x2,-3,6},Contours->{16,36},ContourShading->None],Graphics[Disk[{0,0},1]]]