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7479: Kindergarten Physics

内存限制：128 MB 时间限制：1 S
题面：传统 评测方式：Special Judge 上传者：
提交：5 通过：0
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题目描述

Zhang3 a participant of IPhO (Immortal Physics Olympiad). The 0th problem in the contest is as follows.

There are two balls that weigh a kg and b kg respectively. They can be regarded as particles in this problem, as they are small enough. At the very beginning (i.e. t=0), the distance between two balls is d km, and both of them are not moving.

Assuming that only gravitation works in this system (no other objects or other forces considered). The two balls has started moving since t=0. Your task is to calculate the distance between them when t=t0 (s).

Help Zhang3 solve the problem!



The following information might help when solving the problem.

- Universal gravitation formula: F=G⋅m1⋅m2/r2

- Gravitational constant: G=6.67430×10−11m3/(kg⋅s2)

输入格式

The first line of the input gives the number of test cases T(1≤T≤100). Ttest cases follow.
For each test case, the only line contains four integers a,b,d,t0(1≤a,b,d,t0≤100), representing the mass of the two balls, the initial distance between them, and how much time the balls move.
It is guaranteed that two balls will not collide within (t0+1)seconds.

输出格式

For each test case, print a line with a real number x, representing that the distance is xkm.
Your answers should have absolute or relative errors of at most 10−6.

输入样例 复制 

3
1 2 3 4
7 73 7 68
100 100 1 100

输出样例 复制 

2.99999999999999999982
6.99999999999999974807
0.99999999999993325700

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