Bài 69

 Tính S(n) =

//========================================
//Cach 1

#include <stdio.h>
#include <conio.h>

void main()
{
 int n;
 printf("n = ");
 scanf("%d", &n);
 float S = 0;
 long M = 0;
 float dau = 1;
 for (int i=1; i<=n; i++)
 {
  M = M + i;
  S = S + dau*(float)1/M;
  dau = -dau;
 }
 printf("S = %f", S);
}

//========================================
//Cach 2

#include <stdio.h>
#include <conio.h>

float Tong(int);
void main()
{
 int n;
 printf("n = ");
 scanf("%d", &n);
 float kq = Tong(n);
 printf("S = %f", kq);
}

float Tong(int k)
{
 float S = 0;
 long M = 0;
 float dau = 1;
 for(int i=1; i<=k; i++)
 {
  M = M + i;
  S = S + dau*(float)1/M;
  dau = -dau;
 }
 return S;
}