Given the task definition and input, reply with output. In this task your given a passage in Catalan. you must ask a question in Catalan, that is relevant to the passage. A question that is constructed should be precise and based on factual information from the passage. A constructed question should be: (a) unambiguous (b) be directly answerable from the passage (c) have a unique answer (d) have an answer that is a continuous span of text from the passage. Try to avoid formulating questions that (a) can be answered without referring to the passage, or (b) use exactly the same words or questions given in the passage. Try to make the question fluent in the language used. You have to create exactly one question.

Cas de l'angle obtus. Aquesta demostracio fa servir directament el teorema de la potencia d'un punt, sense els triangles auxiliars obtinguts per a construir una tangent o una corda. Es construeix un cercle amb centre B i radi a (vegeu Figura 9), el qual interseca la secant que passa per A i C en els punts C i K. La potencia del punt A respecte del cercle es igual simultaniament a AB2 BC2 i a ACAK. Per tant,
Per on passa la secant?