海伦公式

 1 #include <cstdio>
 2 #include <cstring>
 3 #include <cmath>
 4 const int Pi=4*acos(-1.0);
 5 double r1,r2,r3;
 6 double a,b,c;
 7 double getarea(double a,double b,double c)
 8 {
 9     double p=a+b+c;
10     p/=2;
11     return sqrt(p*(p-a)*(p-b)*(p-c));
12 }
13 double gettarea(double a,double b,double c,double r)
14 {
15     double t=(a*a+b*b-c*c)/(2*a*b);
16     t=acos(t);
17     return t/2*r*r;
18 }
19 int main()
20 {
21     int T;
22     scanf("%d",&T);
23     for (int t=1;t<=T;t++)
24     {
25         scanf("%lf%lf%lf",&r1,&r2,&r3);
26         a=r1+r3;
27         b=r1+r2;
28         c=r2+r3;
29         double ans=getarea(a,b,c)-gettarea(a,b,c,r1)-gettarea(b,c,a,r2)-gettarea(a,c,b,r3);
30         printf("Case %d: %.9lf\n",t,ans);
31     }
32     return 0;
33 }