题解

#include <bits/stdc++.h>
using namespace std;
int main(){
    double r ;
    cin >> r ;
    printf ("%.4f",2*r);
    cout << " " ;
    printf ("%.4f",2*3.14159*r);
    cout << " " ;
    printf ("%.4f",3.14159*r*r);
    return 0;
}

就这样