hdu 2298 二分+三分

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#define MS(x,y) memset(x,y,sizeof(x))
#define pi acos(-1.0)
using namespace std;
void fre(){freopen("t.txt","r",stdin);}
typedef long long LL;
typedef unsigned long long ULL;
const int maxn = 1000005;
const int inf = (1<<63)-1;
const double eps = 1e-8;
double x,y,v;
double calc(double n)
{
return x*tan(n) - 0.5*9.8*x*x/v/v/cos(n)/cos(n);
}
double three_div(double l,double r)
{
double m1,m2;
while(r - l > eps)
{
m1 = l + (r-l)/3;
m2 = r - (r-l)/3;
if(calc(m1) < calc(m2)) l = m1;
else r = m2;
}
return (l+r)/2;
}
double two_div(double x,double l,double r)
{
double m;
while(r - l > eps)
{
m = (l+r)/2;
if(calc(m) < x) l = m;
else r = m;
}
return (l+r)/2;
}
int main()
{
//  fre();
int t;
scanf("%d",&t);
while(t--)
{
scanf("%lf%lf%lf",&x,&y,&v);
double maxx = three_div(0,pi/2);
if(calc(maxx) < y) {printf("-1\n");continue;}
else printf("%.6lf\n",two_div(y,0,maxx));
}
return 0;
}