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
22 1 -2 22 1 0 2
Sample Output
6.2833.142
几何
simpson积分强行搞
1 #include2 #include 3 #include 4 #include 5 #include 6 using namespace std; 7 const double eps=1e-9; 8 const int mxn=100010; 9 int read(){10 int x=0,f=1;char ch=getchar();11 while(ch<'0' || ch>'9'){ if(ch=='-')f=-1;ch=getchar();}12 while(ch>='0' && ch<='9'){x=x*10-'0'+ch;ch=getchar();}13 return x*f;14 }15 int a,b;16 inline double f(double x){17 return b*sqrt((double)1-(x*x/(double)a/a));18 }19 inline double sim(double l,double r){20 return (r-l)/6*(f(l)+4*f((l+r)/2)+f(r));21 }22 double solve(double l,double r){23 double mid=(l+r)/2;24 double res=sim(l,r);25 // printf("l:%.3f r:%.3f res:%.3f\n",l,r,res);26 if(fabs(sim(l,mid)+sim(mid,r)-res)<=eps)return res;27 return solve(l,mid)+solve(mid,r);28 }29 int main(){30 int T=read();31 double l,r;32 while(T--){33 a=read();b=read();34 l=read();r=read();35 double ans=solve(l,r);36 printf("%.3f\n",2*ans);37 }38 return 0;39 }