问如何找到x1和x2的二分法？

EN

#include <iostream>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <random>


using namespace std;

double x1, x2, c, d, eps = 0.0001, b = 10, a=0;
int attempts=20;

double f(double x){

    return c *(x * x) + 2 * x - d;
}


int main() {

    mt19937 rnd(time(NULL));
    uniform_real_distribution <double> random(2.00, 8.99);
    c = random(rnd);
    cout << "Random c is equal to : " << c << endl;
    cout << "Enter d [real number from 5.00 -> 14.99]: ";
    cin >> d;

    while (d > 14.99 || d < 5.00) {

        cout << attempts << " Attempts left: ";
        cin >> d;
        attempts--;
        if (attempts == 0) {
            exit(1);
        }
    }

    while (abs(b - a) >= eps) {
        x1 = (a + b) / 2;
        if (f(x1) == 0.0) break;
        else if (f(x1) * f(a) <= 0) b = x1;
        else a = x1;
    }



    cout << "x1: " << x1 << endl;
    /*cout << "x2: " << x2 << endl; - how to get this number?*/
    return 0;
}