Finding a derivative from the limit definition

In summary, To find the derivative of f(x)=x1/3 using the limit definition, you can use the formula (a - b)(a2 + ab + b2) = a3 - b3, modified for cube roots, to simplify the numerator and cancel out the h in the denominator.
  • #1
Jimmy25
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Homework Statement



Find the derivative of f(x)=x1/3 using the limit definition of a derivative.

Homework Equations





The Attempt at a Solution



I am stuck once I plug the numbers into the limit definition equation. How can I simplify the numerator in such a way the the h in the denominator will cancel when both the numbers in the number are cube roots?
 
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  • #2
Show us what you have and where you're stuck.

You're going to want to use this idea : (a - b)(a2 + ab + b2) = a3 - b3. This formula can be modified to work with cube roots, like so. (a1/3 - b1/3)(a2/3 + a1/3b1/3 + b2/3) = a - b.
 
  • #3
Edit: Don't worry, Mark got it better than me
 

FAQ: Finding a derivative from the limit definition

1. What is the limit definition of a derivative?

The limit definition of a derivative is the mathematical formula that represents the instantaneous rate of change of a function at a specific point. It is expressed as the limit of the difference quotient as the change in the input value approaches 0.

2. Why is finding a derivative from the limit definition important?

Finding a derivative from the limit definition is important because it allows us to calculate the precise rate of change of a function at any point, which is essential in many fields of science and engineering. It also helps us understand the behavior of a function and make predictions about its future values.

3. What are the steps to finding a derivative from the limit definition?

The steps to finding a derivative from the limit definition are as follows:

  1. Write out the limit definition of a derivative using the given function.
  2. Simplify the difference quotient by factoring and canceling out common terms.
  3. Take the limit as the change in the input value approaches 0.
  4. Solve the limit to find the derivative of the function at the given point.

4. Can you give an example of finding a derivative from the limit definition?

Yes, for example, if we have the function f(x) = x^2 and we want to find the derivative at x = 2, we would use the limit definition as follows:

lim(h → 0) [f(2+h) - f(2)] / h

= lim(h → 0) [(2+h)^2 - 2^2] / h

= lim(h → 0) [4 + 4h + h^2 - 4] / h

= lim(h → 0) (4h + h^2) / h

= lim(h → 0) (4 + h)

= 4

Therefore, the derivative of f(x) = x^2 at x = 2 is 4.

5. Are there any other methods for finding a derivative besides the limit definition?

Yes, there are other methods for finding a derivative such as the power rule, product rule, quotient rule, and chain rule. These methods are often easier and more efficient than using the limit definition, but they are based on the same fundamental concept of finding the instantaneous rate of change of a function.

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