\( \definecolor{colordef}{RGB}{249,49,84} \definecolor{colorprop}{RGB}{18,102,241} \)
Show that the function \(f(x)=\begin{cases} 0 & \text{for } x<0 \\ x & \text{for } x\ge 0 \end{cases}\) is not differentiable at \(x=0\).

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