If x1001 + 1/(x^1001) = 15 Find x1001 - 1/(x^1001) = ?

Formula → If x + \(\frac{1}{x}\) = a

Then,  x - \(\frac{1}{x}\) = \(\sqrt {a^2 - 4}\)

Given, x¹⁰⁰¹ + \(\frac{1}{x^{1001}}\) = 15

So, x¹⁰⁰¹ - \(\frac{1}{x^{1001}}\) = \(\sqrt {(15)^2 - 4}\) = \(\sqrt {221}\)