boom.py

import numpy as np
from scipy.optimize import curve_fit

x, y = np.loadtxt("2a.txt", delimiter=";").T

def test_func(x, n):
    alpha = (2 * np.pi / 360) * x
    n_sq = n ** 2

    cosine = np.cos(alpha)
    sine = np.sin(alpha)
    
    root_delta = np.sqrt(n_sq - sine ** 2)
    n_sq_cosine = n_sq * cosine

    return (n_sq_cosine - root_delta) / (n_sq_cosine + root_delta)


params, params_covariance = curve_fit(test_func, x, y)

print(params)
print(params_covariance)