#include <iostream>
#include <math.h>
using namespace std;

double Fact(int);
double Count1(int n);
double Count2(int n, float a);
double Count3(float a);

double Count1(int n)
{
    double S = 0;
    for (int i = 1; i <= n; i++)  S += 1 / Fact(i);
    return S;
}

double Count2(int n, float a)
{
    float P = 1;
    for (int i = 0; i <= n; i++)  P *= (a - i*n);
    return P;
}

double Count3(float a)
{
    int n;
    float x, x0;
    if (a <= 1)
    if (2 * a <= 0.95) x0 = 2 * a;
    else x0 = 0.95;
    else
    if (a<25) x0 = a / 5;
    else x0 = a / 25;
    n = 0; x = x0;
    cout << endl << "x0=" << x0;
    do
    {
        x0 = x;
        n = n + 1;
        x = 4 / 5 * x0 + a / (5 * pow(x0, 4));
    } while (5 / 4 * a*abs(x - x0) >= 0.000001);
    return x;
}
int main()
{
    setlocale(LC_ALL, "Russian");
    int n;
    cout << "Задача 1" << endl;
    cout << "Введите n:";
    cin >> n;
    cout << endl << "S=" << Count1(n);

    float a;
    cout << endl << endl << "Задача 2" << endl;
    cout << "Введите a: "; cin >> a; cout << "Введите n: "; cin >> n;
    cout << endl << "P=" << Count2(n, a);


    cout << endl << endl << "Задача 3" << endl;
    cout << "Введите a: "; cin >> a;
    cout << endl << "x(" << n << ") = " << Count3(a) << endl;
}


double Fact(int n)
{
    int i;
    double F = 1;
    for (i = 1; i <= n; i++)  F *= i;
    return F;
}