#include <bits/stdc++.h>
#define PI 2*acos(0)
using namespace std;
int main()
{
double d,l,D,L,i,r1,r2;
int tc;
double ans;
cin>>tc;
while(tc--)
{
cin>>D>>L;
d=D/2.0;
l=L/2.0;
r1=sqrt((L/2 * L/2) - (D/2 * D/2));
printf("%.3f\n",PI*r1*l);
}
return 0;
}
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