#include <iostream>
#include <cmath>

double f1(double x);
double f2(double x);
double rectangle(double a, double b, int kol, double (*f)(double x));

using namespace std;
int main(){
  cout << "1 = " << rectangle(0,M_PI,100,f1) << endl;
  cout << "2 = " << rectangle(0,1,200,f2) << endl;
  return 0;
}

double f1(double x){
  return (x*sin(x))/(1+(pow(cos(x),2)));
}
double f2(double x){
  return 1/(4-pow(x,2));
}
double rectangle(double a, double b, int kol, double (*f)(double x)){
  double x=a, h=(b-a)/kol,s=0;
  for (int i=1; i<kol; i++) {
    s+=f(x+(h/2));
    x+=h;
  }
  return s*h;
}