Proving differentiability for a function from the definition

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SUMMARY

The discussion centers on proving the differentiability of a function using its definition, specifically addressing the assumption that the derivative exists at a point. The key equation referenced is the limit definition of the derivative, ##f'(a) = \lim_{x \to a} \frac{f(x) - f(a)}{x - a}##. The assumption of differentiability is justified by the initial condition stating that the function ##f## is differentiable. This foundational understanding is crucial for correctly applying the limit definition in calculus.

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Homework Statement
Please see below
Relevant Equations
Please see below
For this problem,
1715475811269.png

The solution is,
1715475847832.png

However, does someone please know why we allowed to assume that the derivative exists for f i.e ##f'(a) = \lim_{x \to a} \frac{f(x) - f(a)}{x - a}##?

Thanks!
 
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ChiralSuperfields said:
Homework Statement: Please see below
Relevant Equations: Please see below

For this problem,
View attachment 345049
The solution is,
View attachment 345050
However, does someone please know why we allowed to assume that the derivative exists for f i.e ##f'(a) = \lim_{x \to a} \frac{f(x) - f(a)}{x - a}##?

Thanks!
Because of the first sentence: Let ##f## be a differentiable function.
 
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