// Problem B. Polygon Area
// By Seksun Suwanmanee, Dept. of Computer Engineering, PSU Hatyai
// 10 July 2010

#include <stdio.h>
#define MX 100

int main()
{
    int np,n,i,j;
    float x[MX],y[MX], area[MX];
    scanf("%d",&np);

    for(i=0;i<np;i++)
    { 
      scanf("%d",&n);
      for (j=0;j<n;j++) scanf("%f %f",&x[j],&y[j]);  
      area[i] = 0.0;
      for (j=0;j<=n-2; j++) area[i]+=(x[j+1]+x[j])*(y[j+1]-y[j]) ;
      area[i] = (area[i]>=0)?area[i]/2.0:-area[i]/2.0;

    }
    for(i=0;i<np;i++) printf("%.2f\n",area[i]);      
    
    return 0;
}