Cotangent reciprocal identity: cot θ = 1 / tan θ
Cotangent is the reciprocal of tangent, so cot θ = 1/tan θ. The reciprocal form and the quotient form cot θ = cos θ / sin θ agree everywhere both are defined, but the quotient form is the safer one to use at angles where tan θ is zero or undefined.
Related Reciprocal identities
Practise it
Reading a formula is not the same as recalling it under time pressure. The workspace drills Reciprocal questions in the quiz, and the triangle solver shows a worked solution for any triangle you type in.
Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.