循环-08. 二分法求多项式单根(20)

 1 #include<iostream>
 2 #include<cmath>
 3 #include<iomanip>
 4 using namespace std;
 5 double a3,a2,a1,a0;
 6 double f(double x){
 7     return a3*pow(x,3)+a2*pow(x,2)+a1*x+a0;
 8 }
 9 int main(){
10     double a,b,t=0.001;
11     cin>>a3>>a2>>a1>>a0;
12     cin>>a>>b;
13     while(b-a>t){
14         if(f((a+b)/2)==0){
15             cout<<setiosflags(ios::fixed)<<setprecision(2)<<(a+b)/2<<endl;
16             break;
17         }
18         else if(f((a+b)/2)*f(a)>0)
19             a=(a+b)/2;
20         else
21             b=(a+b)/2;
22     }
23     if(f((a+b)/2)!=0)
24         cout<<setiosflags(ios::fixed)<<setprecision(2)<<(a+b)/2<<endl;
25     return 0;
26 }

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