#include<bits/stdc++.h>

using namespace std;

const double pi=acos(-1.0);

const double g=9.8;

const double eps=1e-;

int main()

{

    int t;

    scanf("%d",&t);

    while (t--)

    {

        double x,y,v;

        scanf("%lf%lf%lf",&x,&y,&v);

        double tant=v*v/g/x;

        double theta=atan(tant);

        double sint=sin(theta);

        double cost=cos(theta);

        double ymax=x*tant-g*x*x/2.0/v/v/cost/cost;

        if (ymax<y) printf("-1\n");

        else

        {

            double l=,r=theta;

            while (r-l>eps)

            {

                double mid=(l+r)/2.0;

                double tanm=tan(mid);

                double cosm=cos(mid);

                double ym=x*tanm-g*x*x/2.0/v/v/cosm/cosm;

                if (ym>=y) r=mid;

                else l=mid;

            }

            printf("%.6f\n",l);

        }

    }

    return ;

}