HDU1724 Ellipse

Math is important!! Many students failed in 2+2’s mathematical test, so let's AC this problem to mourn for our lost youth.. 
Look this sample picture:

A ellipses in the plane and center in point O. the L,R lines will be vertical through the X-axis. The problem is calculating the blue intersection area. But calculating the intersection area is dull, so I have turn to you, a talent of programmer. Your task is tell me the result of calculations.(defined PI=3.14159265 , The area of an ellipse A=PI*a*b )

InputInput may contain multiple test cases. The first line is a positive integer N, denoting the number of test cases below. One case One line. The line will consist of a pair of integers a and b, denoting the ellipse equation , A pair of integers l and r, mean the L is (l, 0) and R is (r, 0). (-a <= l <= r <= a).OutputFor each case, output one line containing a float, the area of the intersection, accurate to three decimals after the decimal point.Sample Input

2
2 1 -2 2
2 1 0 2

Sample Output

6.283
3.142

几何

simpson积分强行搞

 #include<iostream>
 #include<cstdio>
 #include<algorithm>
 #include<cstring>
 #include<cmath>
 using namespace std;
 const double eps=1e-;
 const int mxn=;
 int read(){
     int x=,f=;char ch=getchar();
     while(ch<'' || ch>''){if(ch=='-')f=-;ch=getchar();}
     while(ch>='' && ch<=''){x=x*-''+ch;ch=getchar();}
     return x*f;
 }
 int a,b;
 inline double f(double x){
     return b*sqrt((double)-(x*x/(double)a/a));
 }
 inline double sim(double l,double r){
     return (r-l)/*(f(l)+*f((l+r)/)+f(r));
 }
 double solve(double l,double r){
     double mid=(l+r)/;
     double res=sim(l,r);
 //    printf("l:%.3f  r:%.3f  res:%.3f\n",l,r,res);
     if(fabs(sim(l,mid)+sim(mid,r)-res)<=eps)return res;
     return solve(l,mid)+solve(mid,r);
 }
 int main(){
     int T=read();
     double l,r;
     while(T--){
         a=read();b=read();
         l=read();r=read();
         double ans=solve(l,r);
         printf("%.3f\n",*ans);
     }
     return ;
 }