计算几何 求相交圆面积（余弦定理）

#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;
}