#include "TCanvas.h"
#include "TF1.h"
#include "TMath.h"

Double_t funz(Double_t *xx, Double_t *par){

  Double_t sq = 1/(TMath::Sqrt(par[0]));
  Double_t ar = sq*(TMath::Tan(xx[0]));
  return TMath::ATan(ar);

}

void Details(Double_t a = 1){
  
  TF1 *f = new TF1("f",funz,0,2*TMath::Pi(),1);
  f->SetParameter(0,a);

  TCanvas *c = new TCanvas("c","c");
  c->cd(1);
  f->Draw();
}