a) cot x = 1 ⇔ cot x = cot \({\pi \over 4}\) ⇔ x = \({\pi \over 4}\) + kπ, k ∈ Z
b) cot x = -1 ⇔ cot x = cot \( - {\pi \over 4}\) ⇔ x = \( - {\pi \over 4}\) + kπ,k ∈ Z
c) cot x = 0 ⇔ cot x = cot \({\pi \over 2}\)⇔ x = \({\pi \over 2}\) + kπ, k ∈ Z
