Finding antiderivative without integration

In summary, an antiderivative is a function that, when differentiated, gives back the original function. It is useful to find antiderivatives without integration as it can be a quicker and more efficient method, especially for complex functions. This is done by using the rules of differentiation in reverse. However, not all functions have a simple antiderivative that can be found without using integration, and there may be limitations to this method such as accuracy and applicability to all functions. It is important to verify the solution by taking the derivative of the antiderivative to ensure it matches the original function.
  • #1
PhizKid
477
1

Homework Statement


f'(u) = 1 / (1 + u^3)
g(x) = f(x^2)
Find g'(x) and g'(2)

Homework Equations





The Attempt at a Solution


So the derivative of function f at u is: 1 / (1 + u^3)
That means g'(x) would be f'(x^2), but to find the general derivative of f at u is 1 / (1 + u^3) so can I just plug in x^2 for u so I get: 1 / (1 + x^6) ?
 
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  • #2
Your subject has nothing to do with this problem. There are no antiderivatives here. You need to use the chain rule to compute g'(x). It is NOT true that g'(x) = f'(x^2).
 
  • #3
Don't you need to find f(u) which would be going backwards from 1 / (1 + u^3), which is an antiderivative?

And why is g'(x) != f'(x^2)? I just took the derivative of both functions on each side with respect to x
 
  • #4
PhizKid said:
Don't you need to find f(u) which would be going backwards from 1 / (1 + u^3), which is an antiderivative?

And why is g'(x) != f'(x^2)? I just took the derivative of both functions on each side with respect to x

No, you don't need to find f(u). Regarding why g'(x) != f'(x^2), please apply the chain rule to differentiate both sides of g(x) = f(x^2).
 
  • #5
We learned the Chain Rule but not sure how to apply it here. My best guess would be:

g'(x) = f'(x) * 2x
 
  • #6
PhizKid said:
We learned the Chain Rule but not sure how to apply it here. My best guess would be:

g'(x) = f'(x) * 2x
Since g(x) = f(x2), then g'(x) = f'(x2) * 2x
 
  • #7
Sorry, that's what I meant. I write it down on paper but I'm not very good at typing

So for g'(x) I have f'(x^2) * 2x
Do I have to somehow use f'(u) = 1 / (1 + u^3) in order to find the values for 'x' for f'(x^2) * 2x ? Do I need to use the Chain Rule again? If so, how would I apply it in this situation?
 
  • #8
PhizKid said:
Sorry, that's what I meant. I write it down on paper but I'm not very good at typing

So for g'(x) I have f'(x^2) * 2x
Do I have to somehow use f'(u) = 1 / (1 + u^3) in order to find the values for 'x' for f'(x^2) * 2x ? Do I need to use the Chain Rule again? If so, how would I apply it in this situation?
You don't need to use the chain rule again. If f'(u) = 1/(1 + u^3) then what is f'(x^2)? Just substitute u = x^2. You are simply evaluating the function defined by f'(u) = 1/(1 + u^3) at the particular value u = x^2.
 
Last edited:
  • #9
How do you know that u = x^2 ?
 
  • #10
PhizKid said:
How do you know that u = x^2 ?

What does f'(x^2) mean? It means "evaluate the function f' at x^2." We have a formula for f'(u), i.e. a formula to "evaluate the function f' at u." If I want to evaluate f'(5), then I replace u with 5. If I want to evaluate f'(x^2), then I replace u with x^2.
 

1. What is an antiderivative?

An antiderivative is the inverse operation of taking a derivative. It is a function that, when differentiated, gives back the original function.

2. Why would you want to find an antiderivative without integration?

One reason is that integration can be a time-consuming process, especially for complex functions. Finding an antiderivative without integration can be a quicker and more efficient method in some cases.

3. How do you find an antiderivative without integration?

The most common method is to use the rules of differentiation in reverse. This involves identifying the function's derivative and working backwards to find the original function.

4. Can all functions be solved for their antiderivatives without integration?

No, not all functions have a simple antiderivative that can be found without using integration. Some functions may require more advanced techniques or may not have an antiderivative at all.

5. Are there any limitations to finding antiderivatives without integration?

Yes, there are limitations. This method may not work for all functions, and it may not always give the most accurate result. It is important to check the solution by taking the derivative of the antiderivative to ensure it matches the original function.

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