POJ 2242

 1 #include <iostream>
 2 #include <cmath>
 3 #include <iomanip>
 4 using namespace std;
 5 #define PI 3.141592653589793
 6 
 7 struct node
 8 {
 9     double x;
10     double y;
11 };
12 
13 node p_1;
14 node p_2;
15 node p_3;
16 
17 double a;
18 double b;
19 double c;
20 double give_len(node a,node b);
21 
22 int main()
23 {
24     //freopen("acm.acm","r",stdin);
25     double cos_c;    
26     double sin_c;
27     double s;
28     while(cin>>p_1.x>>p_1.y>>p_2.x>>p_2.y>>p_3.x>>p_3.y)
29     {
30         a = give_len(p_1,p_2);
31         b = give_len(p_1,p_3);
32         c = give_len(p_2,p_3);
33     //    cout<<"--- a"<<a<<endl;
34     //    cout<<b<<endl;
35     //    cout<<c<<endl;
36         cos_c = (a*a + b*b - c*c)/(2.0*a*b);
37         sin_c = sqrt((1 - cos_c*cos_c));
38         s = 0.5 * a*b*sin_c;
39         cout<<setiosflags(ios::fixed)<<setprecision(2)<<a*b*c*PI/(s*2.0)<<endl;
40     }
41 }
42 
43 double give_len(node a,node b)
44 {
45     return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y - b.y)*(a.y - b.y) );
46 }