calculateRoot

求下面方程的一个根：根：f(x) = x 3 -5x 2 +10x-80 = 0。若求出的根是若求出的根是a ，则要求 |f(a)| <= 10 -6

 1 #include <iostream>
 2 #include <stdio.h>
 3 #include <math.h>
 4 using namespace std;
 5 double EPS = 1e-6;
 6 double findValue(double x) {
 7     return x*x*x - 5*x*x +10*x -80;
 8 }
 9 
10 int main() {
11     double first = 0, second = 100;
12     double midX = first + (second - first)/2.0;
13     double midVlaue = findValue(midX);
14     while( fabs(midVlaue) > EPS) {
15         if(midVlaue > 0) {
16             second = midX;
17         } else {
18             first = midX;
19         }
20         midX = first + (second - first)/2.0;
21         midVlaue = findValue(midX);
22 
23     }
24     printf("%.8lf", midX);
25     return 0;
26 }