import math
import scipy.misc

T = int(input())

def f(x):
    return 1 / (x*x + 1)

for _ in range(T):
    n, x = input().split()
    n = int(n)
    x = float(x)

    res = scipy.misc.derivative(f, x, 1.0E-6, n, order=(n+1)//2*2+1)
    res *= (x*x + 1)**(n/2 + 1) / math.factorial(n)
    print(res)