OJ-Problems-Source/HDOJ/1714_autoAC.cpp

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#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
double a,b;
double x,y;
int n;
cin >> n;
while(n--&&cin >> a >> b >> x >> y)
{
y = y>0?y:-y;
double f = y/x;
double newx = sqrt(a*a*b*b/(b*b + f*f*a*a));
double newy = f*newx;
newx = newx/a*b;
newy /= b;
newx /= b;
double t = acos(newx);
double area = t * b * a / 2;
cout << fixed << setprecision(2) << area << endl;
}
}