oval-and-rectangle HDU - 6362

概率论
题目：
Patrick Star find an oval.

The half of longer axes is on the x-axis with length aa.

The half of shorter axes is on the y-axis with length bb.

Patrick Star plan to choose a real number cc randomly from [0,b][0,b], after that, Patrick Star will get a rectangle :

1. The four vertexes of it are on the outline of the oval.

2. The two sides of it parallel to coordinate axis.

3. One of its side is y=cy=c.

Patrick Star want to know the expectations of the rectangle’s perimeter.
Input
The first line contain a integer TT (no morn than 10), the following is TT test case, for each test case :

Each line contains contains two integer a, b (0 Output
For each test case output one line denotes the expectations of the rectangle’s perimeter .

You should keep exactly 6 decimal digits and ignore the remain decimal digits.

It is guaranted that the 7-th decimal digit of answer wont be 0 or 9.
Sample Input
1
2 1
Sample Output
8.283185
题意：椭圆里建立矩形，高等数学解一下。。

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define ll long long
using namespace std;
int main()
{
    int n,d,t;
    double s1,s2,a,b,dis[100],len[100],v[100],z;
    int cnt=1;double tt=0.0000005;
    cin>>t;//cout<
    //s1=3;s2=2;cout<
    while(t--){
    	cin>>a>>b;
    	s1=2*b+a*acos(-1);
		cout<<fixed<<setprecision(6)<<s1-tt<<endl;
	}
    return 0;
}