二分法求n次方根

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
int main(void)
{
    double l = -10000, r = 10000;
    double x;
    int n;
    cin >> x;
    cin >> n;
    while (r - l > 1e-8)
    {
        double mid = (l + r) / 2;
        if (pow(mid,n) >= x)
        {
            r = mid;
        }
        else
        {
            l = mid;
        }
    }
    printf("%.3lf", l);
    return 0;
}