1004

题意：假设鲍勃是点(0,0),可以调整角度解决轨迹。帮助鲍勃摄水果在附近的树，并给出 一个点 x ，y 坐标，给出初速度。求从坐标原点以什么角度斜上抛运动可以达到那个点。

思路：根据以前所学物理学知识，写出运动轨迹方程,即：a=x*x*(9.8/(2*v*v)) 再根据二分法求出角度

#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstring>
using namespace std;
double PI=acos(1.0)

int main()
{
         double x,y,v,a,b,c,t,x1,x2;
         int n;
         cin>>n;
         cout.precision(6);
         while(n--)
         {
             cin>>x>>y>>v;
             if(x==0&&y==0)
               cout<<0<<endl;
             else
             {
                 a=x*x*(9.8/(2*v*v));
                 b=-1*x;
                 c=y+a;
                 t=b*b-4*a*c;
                 if(t<0)
                    cout<<-1<<endl;
                 else
                 {
                     x1=(-1*b-sqrt(t))/(2*a);
                     x2=(-1*b+sqrt(t))/(2*a);
                     if(x1>=0)
                     {
                         if(x2>=0)
                             x1=min(x1,x2);
                         cout << fixed << atan(x1) << endl;
                     }
                     else if(x2 >=0)
                        cout << fixed << atan(x2) << endl;
                     else
                         cout<<-1<<endl;
                 }
             }
         }
         return 0;
}