Pythagorean identity with cotangent: 1 + cot²θ = csc²θ
Dividing sin²θ + cos²θ = 1 through by sin²θ gives 1 + cot²θ = csc²θ. It is the cotangent-cosecant counterpart of the tangent-secant form, and the one to use when an expression is written in terms of sines rather than cosines.
Related Pythagorean identities
Practise it
Reading a formula is not the same as recalling it under time pressure. The workspace drills Pythagorean 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.