#include <bits/stdc++.h>
using namespace std;
int main() {
int t;
scanf("%d", &t);
while(t--)
{
int n, i;
long long int x1, y1, x2, y2;
double sum=0;
scanf("%d", &n);
scanf("%lld %lld", &x1, &y1);
x2 = x1; y2 = y1;
for(i=1; i<n;i++)
{
long long int x, y;
scanf("%lld %lld", &x, &y);
sum += (x1*y) - (y1*x);
x1 = x; y1 = y;
}
sum += (x1*y2) - (x2*y1);
if(sum < 0)
{
sum *= (-1);
}
printf("%.1lf\n", sum/2.0);
}
}
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