#define _CRT_SECURE_NO_WARNINGS

#include <bits/stdc++.h>
using namespace std; 

int main() {
	int T;
	cin >> T;

	while (T--) {
		int n; double x;
		cin >> n >> x;

		complex<double> xp(x, 1), xn(x, -1), I(0, 1);
		
		auto res = (pow(xn, -n - 1) - pow(xp, -n - 1)) / (2. * I);
		res *= pow(x * x + 1, n / 2. + 1);

		cout << fixed << setprecision(5) << res.real() << endl;
	}
}