## Differentiality: a function is differentiable at a point if it has a derivative there, in other words: the function f is differentiable at x if lim as h approaches 0 (f(x+h)-f(x))/h exists. thus the graph of f has a non-vertical tangent line at (x, f(x)).the value of the limit and the slope of the tangent line are the derivatives of f at x0. show that absolute value function is not differentiable at x=0. f(x)=|x|.

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