#include <bits/stdc++.h>
using namespace std;
const int MAX = 200;
int main(){
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);
  cout << fixed << setprecision(20);
  int T;
  cin >> T;
  for (int i = 0; i < T; i++){
    int N;
    double x;
    cin >> N >> x;
    cout << (complex<double>(0, -0.5) * (pow(complex<double>(x, -1), -(N + 1)) - pow(complex<double>(x, 1), -(N + 1)))).real() * pow(x * x + 1, (double) N / 2 + 1) * pow(-1, N) << endl;
  }
}