QUADAREA.cpp

#include<bits/stdc++.h>

#define ll long long int
#define watch(x) cout << (#x) << " is " << (x) << endl  //watch function print variable and value for debugging
#define count_ones __builtin_popcountll                  // count_ones(9) is equal to 2 valid for ll also
#define fast_io ios_base::sync_with_stdio(false); cin.tie(NULL);
#define fo(i,n) for(ll i=0;i<n;i++)
using namespace std;
 
int main() {
 #ifndef ONLINE_JUDGE
	    freopen("input.txt", "r", stdin);
        freopen("output.txt", "w", stdout);
 #endif
       fast_io
 
       ll t;
       cin>>t;
       while(t--)
       {
         double a,b,c,d;
         cin>>a>>b>>c>>d;

         double sp=(a+b+c+d)/2;
         double area=sqrt((sp-a)*(sp-b)*(sp-c)*(sp-d));

         cout<<fixed<<setprecision(2)<<(double)area<<"\n";


       }


   return 0;
 }