湘大oj题目地址：传送门
Cycloid
时间限制：1000 ms | 内存限制：65536 KB
Description
A cycloid is the curve traced by a point on the rim of a circular wheel as the wheel rolls along a straight line. It is an example of a roulette, a curve generated by a curve rolling
on another curve.
--from wikipedia
Please calculate the area of an arch of a cycloid generated by a circle of radius r.
You may define pi as acos(-1.0).
Input
The first line of the input consists of a single integer K (1 <= K <= 1,000), denoting the number of test cases. Then K lines follow, each contains a real number r (0.0 < r < 1e3), indicating
the radius of circle.
Output
For each test case, output a line containing one real number with exactly three digits after the decimal point, indicating the area of an arch.
Sample Input
2
1.0
3.5
Sample Output
9.425
115.454
==================================傲娇的分割线=================================
题目意思：求圆走过的那一部分弧线所围成的面积，这个有一个公式，摆线留下的面积等于圆的三倍
#include <stdio.h>
#include<iostream>
#include<math.h>
using namespace std;
int main(){
int n;
double r;
scanf("%d",&n);
while(n--){
cin>>r;
double x=3*acos(-1.0)*r*r;
printf("%.3f\n",x);
}
}