海伦公式

三角形三边边长a,b,c,则p=(a+b+c)/2;s=sqrt(p*(p-a)*(p-b)*(p-c));

 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 }

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