## Pure Theory of One-Variable Calculus:

thread #1:

definition of a critical point

Definition: If f is a function, then x is said to be a critical point of f fif x is in the domain of f and (f is differentiable at x implies f'(x) = 0).

Notice that, by

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Notice that, by

**material implication**, if x is a point in the domain of f at which f is not differentiable, then x is a critical point of f.(end of page)