Cofunction identity: tan(π/2 − θ) = cot θ

\tan(\tfrac{\pi}{2} - \theta) = \cot\theta

Tangent and cotangent are cofunctions: tan(π/2 − θ) = cot θ. The same complementary-angle relationship holds for every function-and-cofunction pair - sine/cosine, tangent/cotangent, secant/cosecant.

Related Cofunction identities

sin(π/2 − θ) = cos θ cos(π/2 − θ) = sin θ

Practise it

Reading a formula is not the same as recalling it under time pressure. The workspace drills Cofunction questions in the quiz, and the triangle solver shows a worked solution for any triangle you type in.

Practise Cofunction Open the triangle solver

Or browse all 45 identities in the full reference, or read the trigonometry guides for the method behind them.