hdu 1724 辛普森积分

思路：求积分。

辛普森公式 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#define eps 1e-8
using namespace std;
double a,b;
double F(double x)
{
    return 2.0*b*sqrt(1.0-x*x/(a*a));
}
double simpson(double l,double r)
{
    double mid=l+(r-l)/2.0;
    return (r-l)*(F(l)+4.0*F(mid)+F(r))/6.0;
}
double inte(double l,double r,double sum)
{
    double mid=l+(r-l)/2.0;
    double ls=simpson(l,mid);
    double rs=simpson(mid,r);
    if(abs(ls+rs-sum)<=eps)return sum;
    else return inte(l,mid,ls)+inte(mid,r,rs);
}
int main()
{
    double l,r;
    int t;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%lf%lf%lf%lf",&a,&b,&l,&r);
        double ans=inte(l,r,simpson(l,r));
        printf("%.3f\n",ans);
    }
    return 0;
}