#include "stdafx.h"
#include <iostream>
#include"math.h"

using namespace std;
int main()
{
    #define pi 3,1415926
    setlocale(LC_CTYPE, "Rus");
    int n;
    double x;
    cout << "Введите x: ";
    cin >> x;
    cout << "Введите n: ";
    cin >> n;
    double fx = (pi / 2);
    for (int i = 1; i <= n; i++)
    {
        fx += pow(-1, i + 1) / ((2 * i + 1) * pow(x, 2 * i + 1));
    }
    cout << "actgx = " << atan(fx) << endl;
    system("pause");
    return 0;
}