Question
Explain where the fact that a differentiable function must be continuous was assumed in the proof of the product rule for derivatives.
Step 1
If we have a function $f(x) = g(x) \cdot h(x)$, then the derivative of $f$ with respect to $x$ is given by: \[f'(x) = g'(x) \cdot h(x) + g(x) \cdot h'(x)\] Show more…
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Show that if a function $f$ is differentiable at $x=a$, then $f$ must be continuous at $x=a$ Hint: Write$$f(x)-f(a)=\left[\frac{f(x)-f(a)}{x-a}\right](x-a)$$ Use the product rule for limits and the definition of the derivative to show that $$\lim _{x \rightarrow a}[f(x)-f(a)]=0$$
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Show that if a function $f$ is differentiable at $x=a,$ then $f$ must be continuous at $x=a$ Hint: Write $$f(x)-f(a)=\left[\frac{f(x)-f(a)}{x-a}\right](x-a)$$ Use the product rule for limits and the definition of the derivative to show that $$\lim _{x \rightarrow a}[f(x)-f(a)]=0$$.
Prove or Disprove: "All differentiable functions are continuous but not all continuous functions are differentiable".
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