Find the derivative of $f(x)=x$.

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Lesson Parent: 
Differentiation II: The Gory Details of Calculating Derivatives
Problem: 

Prove that when $f(x)=x$ then $df/dx=1$.

Answer: 

1

SAMPLE SOLUTION

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Solution: 

Recall that

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Now let's construct the function

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In this particular problem we have

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Now the derivative is

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But we know that

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and therefore

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