tpa rec3

#include <stdio.h>
#define TOL 1e-6

double root(double a, double b, double(*f)(double)) {
  double mid = (a + b) / 2;
  if ((b - a)/2 <= TOL) {
    return mid;
  }
  if (f(a) * f(mid) < 0) {
    return root(a, mid, f);
  }
  return root(mid, b, f);
}

double f(double x) {
  return 2*x*x*x - 6*x - 1;
}

int main() {
  printf("%g\n", root(1, 2, f));
  return 0;
}