函数求值

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<cmath>
typedef long long ll;
using namespace std;
int p,q,r,s,t,u;
const double eps=1e-7;
//p?e?x + q?sin(x) + r?cos(x) + s?tan(x) + t?x2 + u = 0
double f(double x)
{
    return p*exp(-x)+q*sin(x)+r*cos(x)+s*tan(x)+t*x*x+u;//单调递减函数
}
int main()
{
    while(scanf("%d%d%d%d%d%d",&p,&q,&r,&s,&t,&u)!=EOF)
    {
        double l=0,r=1;
        if(f(0)*f(1)>0)
            printf("No solution\n");
        else
        {
            while(abs(f(r)-f(l))>eps)
            {
                double mid=(r+l)/2;
                if(f(mid)<0)//也可以写成if(f(l)*f(mid)<=0)
                    r=mid;
                else
                    l=mid;
            }
            printf("%.4lf\n",(l+r)/2);
        }
    }
    return 0;
}