Bài 1:

#include <bits/stdc++.h>
using namespace std;
float h(float dt, float a){
    return 2*dt/a;
}
float dt(float a, float b, float c){
    float p = (a + b + c)/2;
    return sqrt(p*(p -a)*(p - b)*(p - c));
}
main(){
        float a, b, c, s;
        cin >> a >> b >> c;
        if (abs(b - c) < a && a < b + c){
            cout << "Tao thanh tam giac." << endl;
            s = dt(a,b,c);
            cout << "Dien tich: " << s << endl;
            cout << "Duong cao: " << h(s,a) << " " << h(s,b) << " " << h(s,c);
        } else {
            cout << "Khong tao thanh tam giac.";
        }
        
}
====================

Bài 2:

#include <bits/stdc++.h>
using namespace std;
main(){
 int a, b;
 cin >> a >> b;
 cout << "UCLN " << __gcd(a,b) << endl;
 cout << "BCNN " << (a*b)/__gcd(a,b);
}

cách khác:

#include <bits/stdc++.h>
using namespace std;
int gcd(int a,int b)
{
 while (a*b!=0)
 {
  a%=b;
  if(a!=0) b%=a;
 }
 return a+b;
}

main(){
 int a, b;
 cin >> a >> b;
 cout << "UCLN " << gcd(a,b) << endl;
 cout << "BCNN " << (a*b)/gcd(a,b);
}

#include <bits/stdc++.h>
using namespace std;
float dt(float a,float b,float c)
{
 float p=(a+b+c)/2;
 return sqrt(p*(p-a)*(p-b)*(p-c));
}
int main()
{
 float a,b,c;
 cin >> a >> b >> c;
 if (a+b+c>2*max(a,max(b,c)))
 {
  float d = dt(a,b,c);
  printf("%f %f %f la 3 canh cua tam giac\n",a,b,c);
  printf("Dien tich: %f\nCac chieu cao: %f %f %f\n",d,2*d/a,2*d/b,2*d/c);
 }
 else printf("%f %f %f khong phai la 3 canh cua tam giac",a,b,c);
 return 0;
}

=========================================================

#include <bits/stdc++.h>
using namespace std;
int ucln(int a,int b)
{
 while (a*b!=0)
 {
  a%=b;
  if(a!=0) b%=a;
 }
 return a+b;
}
int main()
{
 int a,b;
 cin >> a >> b;
 printf("Ucln: %d\nBcnn: %d\n",ucln(a,b),a*b/ucln(a,b));
}