Putnam 2011 B3

Session B

Let $f$ and $g$ be (real-valued) functions defined on an open interval containing $0$ , with $g$ nonzero and continuous at $0$ . If $fg$ and $f/g$ are differentiable at $0$ , must $f$ be differentiable at 0?

Curated text Kedlaya Putnam archive. Quoted with source.

Solutions

Human solution Solution 1 by Kiran Kedlaya and Lenny Ng

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