How can draw one hyperbolic curve in 2D histogram?

[qq_pp]

How can draw one hyperbolic curve in 2D histogram?

[couet]

{
   TH2F *h1 = new TH2F("h1","",40,0,10,40,0,10);
   TF2 *f2 = new TF2("f2", "x*x+y*y",0.,10.,0.,10.);

   for (int i =0; i<10000; i++) {
      h1->Fill(gRandom->Gaus(6,1),gRandom->Gaus(6,1));
   }

   h1->SetMaximum(200);
   h1->SetMinimum(0);
   f2->SetMaximum(200);
   f2->SetMinimum(0);
   h1->Draw("LEGO1");
   f2->Draw("surf same");
}

[qq_pp]

@couet

f2->Draw(“surf same”);

I just want to draw one curve.

[couet]

May be this example ?