计算几何 求相交圆面积（余弦定理）

求任意两圆相交的面积
注意PI : 最好用公式表示，否则精度可能不够会一直wa

#include<bits/stdc++.h>  using namespace std;  #define PI acos(-1)  int main()  {      int T;      double x1,x2,y1,y2,r1,r2;      double a,b,s1,s2,d,sum;      cin >> T;      while(T--)      {          sum = 0;          cin >> x1 >> y1 >> r1 >> x2 >> y2 >> r2;          d = sqrt( (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2) );          if(r1 + r2 <= d)              puts("0.00");          else if(r2 >= r1 && d + r1 <= r2)          {              printf("%.2lf\n", PI * r1 * r1);          }           else if(r1 > r2 && d + r2 <= r1)          {              printf("%.2lf\n", PI * r2 * r2);          }          else          {              a = (r1 * r1 + d * d - r2 * r2) / (2.0 * r1 * d);              b = acos(a) * 2.0;              s1 = r1 * r1 * sin(b) / 2;              s2 = b / (2 * PI) * PI * r1 * r1;              sum = s2 - s1;              a = (r2 * r2 + d * d - r1 * r1) / (2.0 * r2 * d);              b = acos(a) * 2.0;              s1 = r2 * r2 * sin(b) / 2;              s2 = b / (2 * PI) * PI * r2 * r2;              sum += s2 - s1;              printf("%.2lf\n", sum);          }      }      return 0;  }