I have fitted data (from a pandas dataframe) to a function

def cutoff(x, A):
    ff = 1/(1+(2 * np.pi * A * x)**2)**0.5
    return  ff
                     
xdata = data["X"]
ydata = data["CH1"]
popt, pcov=scipy.optimize.curve_fit(cutoff,xdata,ydata , p0 = [0.1e-3])

Now I want to output the x-value, where the y-value of the fit equals 1/2**0.5

Since I am new to python, I have no idea how to do this. Help would be much appreciated.

I didn’t include my previous attempts, as they were all just wild guesses / copied code I didn’t understand.