#include <iostream>
#include "TROOT.h"
#include "TSystem.h"
#include "TMath.h"
#include "TF1.h"
using namespace std; 
TF1 *f1, *f2,*f3;

Double_t fnc(Double_t *x,Double_t *par){
	return x[0]*x[0]+4;
}



double finter(double *x, double *par) 
{
    //return TMath::Abs(f1->EvalPar(x,par) - f2->EvalPar(x,par));
    return TMath::Abs(f3->EvalPar(x,par) - f2->EvalPar(x,par));
}
double fint(double start,double end) {                                
       TF1 *fint = new TF1("fint",finter,start,end,0);
       //double xint = fint->GetMinimumX();
       double xint = fint->Eval(8);
       return xint; 
}
void test2 ()
{
   f1=new TF1("f1","x^2 + 4",0,10);
   f2=new TF1("f2","x + 3",0,10);
   
   f3=new TF1("f3",fnc,0,10,0);
   
   cout << "x_int = " << fint(0,8) << endl; 
}