HDU 1714 math

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<iomanip>
#include<math.h>
using namespace std;

int main()
{
int n;
double a, b, px, py;
cin >> n;
while(n--)
{
cin >> a >> b >> px >> py;
if (py < 0)
py = -py;
else if (py == 0)
{
cout << setprecision(2) << 0.00 << endl;
continue;
}
double jx, jy, k;
k = py * 1.0 / px;
jx = (a * a * b * b) / (b * b + a * a * k * k);
jx = sqrt(jx);
jy = k * jx;
double angle = atan(py * 1.0 / px);
double s1 = (0.5 * a * b * angle) - (0.25 * a * b * sin(2 * angle));
double s2 = 0.5 * jx * jy;
double s = s1 + s2;
cout << setprecision(2) << s << endl;
}
return 0;
}