专题二1004

*简单题意：
　　从（0,0）处射箭，给出坐标（x， y）以及初速度，求射到目标的tan角度。
*解题思路：
　　一道高中物理题目，用解方程的方法求解。
*AC源码
#include <iostream>

#include <cstdio>

#include <cmath>

using namespace std;

int main()

{

int t;

double a, b, c;

double x, y, v, tep;

cin >> t;

while(t--)

{

cin >> x >> y >> v;

if(x == 0 && y == 0)

cout << "0" << endl;

else if(x == 0 && y > 0)

cout << "90" << endl;

else

{

a = 9.8 * x * x / (2 * v * v);

b = - x;

c = y + a;

tep = b * b - 4 * a * c;

double jiao;

if(tep < 0)

cout << "-1" << endl;

else

{

double x1 = (- b + sqrt(tep))/(2 * a);

double x2 = (- b - sqrt(tep))/(2 * a);

if(x1 >= 0)

jiao = atan(x1);

if(x2 >= 0)

jiao = atan(x2);

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

if(x1 < 0 && x2 < 0)

cout << "-1" << endl;

}

}

}

return 0;

}

Toxophily

Time Limit : 3000/1000ms (Java/Other) Memory Limit : 32768/32768K (Java/Other)

Total Submission(s) : 98 Accepted Submission(s) : 52

Problem Description

The recreation center of WHU ACM Team has indoor billiards, Ping Pang, chess and bridge, toxophily, deluxe ballrooms KTV rooms, fishing, climbing, and so on.<br>We all like toxophily.<br><br>Bob is hooked on toxophily recently. Assume that Bob is at point (0,0)
and he wants to shoot the fruits on a nearby tree. He can adjust the angle to fix the trajectory. Unfortunately, he always fails at that. Can you help him?<br><br>Now given the object's coordinates, please calculate the angle between the arrow and x-axis at
Bob's point. Assume that g=9.8N/m. <br>

Input

The input consists of several test cases. The first line of input consists of an integer T, indicating the number of test cases. Each test case is on a separated line, and it consists three floating point numbers: x, y, v. x and y indicate the coordinate of
the fruit. v is the arrow's exit speed.<br>Technical Specification<br><br>1. T ≤ 100.<br>2. 0 ≤ x, y, v ≤ 10000. <br>

Output

For each test case, output the smallest answer rounded to six fractional digits on a separated line.<br>Output "-1", if there's no possible answer.<br><br>Please use radian as unit. <br>

Sample Input

3<br>0.222018 23.901887 121.909183<br>39.096669 110.210922 20.270030<br>138.355025 2028.716904 25.079551<br>

Sample Output

1.561582<br>-1<br>-1<br>

Source

The 4th Baidu Cup final

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