地址：http://acm.split.hdu.edu.cn/showproblem.php?pid=6206
题目：
Apple
Time Limit: 1000/1000 MS (Java/Others) Memory Limit: 65535/32768 K (Java/Others)
Total Submission(s): 530 Accepted Submission(s): 172
Problem Description
Apple is Taotao's favourite fruit. In his backyard, there are three apple trees with coordinates (x1,y1), (x2,y2), and (x3,y3). Now Taotao is planning to plant a new one, but he is not willing to take these trees too close. He believes that the new apple tree should be outside the circle which the three apple trees that already exist is on. Taotao picked a potential position (x,y) of the new tree. Could you tell him if it is outside the circle or not?
Input
The first line contains an integer T, indicating that there are T(T≤30) cases.
In the first line of each case, there are eight integers x1,y1,x2,y2,x3,y3,x,y, as described above.
The absolute values of integers in input are less than or equal to 1,000,000,000,000.
It is guaranteed that, any three of the four positions do not lie on a straight line.
In the first line of each case, there are eight integers x1,y1,x2,y2,x3,y3,x,y, as described above.
The absolute values of integers in input are less than or equal to 1,000,000,000,000.
It is guaranteed that, any three of the four positions do not lie on a straight line.
Output
For each case, output "Accepted" if the position is outside the circle, or "Rejected" if the position is on or inside the circle.
Sample Input
3
-2 0 0 -2 2 0 2 -2
-2 0 0 -2 2 0 0 2
-2 0 0 -2 2 0 1 1
Sample Output
Accepted
Rejected
Rejected
Source
思路：
这题关键是找圆心，如果圆心知道了，后面的都好做了。
圆心坐标公式，来自维基：
这题精度要求高，直接用double or long double都会挂。
做法有俩个：
1.保留除法运算，那就只能用java的BigDecimal（好像叫这个）
2.进行公式化简：
所以这时只需要比较分子就好了，只需要大数模板。
然而我知道怎么做还是wa一下午，依旧没过，不会java，用c++的大数模板写又写挂了。。。gg，心痛。
这题还可以圆的反演做。
没有代码贴了。