Is there an example of sequence of functions $f_n$ that are differentiable and converge uniformly to $|x|$ on $[-1,1]$?
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The inequality $\lvert x \rvert \le \sqrt{x^2 + \frac 1 {n^2} }\le \lvert x \rvert + \frac 1 n$ shows that $$f_n(x) = \sqrt{x^2 + \frac 1 {n^2}}, \hspace{3mm} x \in [-1,1], \hspace{3mm} n \in \mathbb N $$ works.
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