#include <bits/stdc++.h>
using namespace std;
int main() {
  int T, n;
  cin >> T;
  double R1, R2, R3;
  while (T--) {
    scanf("%lf%lf%d", &R1, &R2, &n);
    R3 = R1 - R2;
    double k1 = -1 / R1;
    double k2 = 1 / R2;
    double k3 = 1 / R3;
    double k4 = k1 + k2 + k3;
    double ans;
    for (int i = 1; i <= n; i++) {
      double R4 = 1 / k4;
      ans = R4;
      double k5 = 2 * (k1 + k2 + k4) - k3;
      k3 = k4;
      k4 = k5;
    }
    printf("%0.10lf\n", fabs(ans));
  }
  return 0;
}
