#include <bits/stdc++.h>
using namespace std;
#define int long long
int gcd(int a,int b){
	if(b==0)return a;
	return gcd(b,a%b);//Thuat toan Euclid
}
int lcm(int a,int b){
	return a*b/gcd(a,b);
}
signed main(){
	int m,n;
	cin>>m>>n;
	cout<<"Sau it nhat "<<lcm(m,n)<<" ngay thi 2 ban lai cung truc nhat";
}

Bài 7:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const long long nmax = 1e6;
ll n, m;
int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);cout.tie(NULL);
  cin >> n >> m;
  cout << n * m / __gcd(n, m);
}

Bài 8:

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
const long long nmax = 1e6;
ll a, b, c, d;
int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);cout.tie(NULL);
  cin >> a >> b >> c >> d;

  ll e = a * d + b * c;
  ll e1 = b * d;

  ll e2 = a * c;
  ll e3 = b * d;

  ll h = __gcd(e, e1);
  ll h1 = __gcd(e2, e3);

  e /= h;
  e1 /= h;

  e2 /= h1;
  e3 /= h1;

  cout << "Tong la: " << e << " " << e1 << '\n';
  cout << "Tich la: " << e2 << " " << e3;
}