Answer each of the following questions in one word or one sentence or as per exact requirement of the question:

If x < 0, y < 0 such that xy = 1, then write the value of tan^{–1} x + tan^{–1} y.

Given if x < 0, y < 0 such that xy = 1

Also given tan^{-1} x + tan^{-1} y

We know that

= -π + tan^{-1} (∞)

1