Find the second derivative of F (x)

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Homework Help Overview

The problem involves finding the second derivative of a function defined by an integral, specifically F(x) = ∫[a,x] (t-x)² f(t) dt. The context suggests a focus on calculus, particularly the application of the Fundamental Theorem of Calculus and the Leibniz integral rule.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster expresses confusion about evaluating the integral and finding the second derivative, noting difficulty with the concept of derivatives in this context. Some participants suggest using the Fundamental Theorem of Calculus to find the first derivative and then differentiate again for the second derivative. Others mention applying the Leibniz integral rule and highlight that there are terms in the integral that need differentiation.

Discussion Status

Participants are exploring different methods to approach the problem, with some providing guidance on using the Fundamental Theorem of Calculus and the Leibniz rule. There is an ongoing exchange of ideas, with no clear consensus yet on the best approach, as some participants are still seeking clarification on the concepts involved.

Contextual Notes

The original poster has indicated a lack of familiarity with the Leibniz integral rule and is uncertain about how to handle the function f(t) within the integral. This suggests a need for foundational understanding before proceeding with the problem.

~Sam~
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Homework Statement



Assuming sufficient differentiability, find second derivative of F(x) = integ[a,x] (t-x)2 f(t) d(t)

Homework Equations



Probably Fund.Thm of Calculus and some properties


The Attempt at a Solution



I really have no idea..I tried evaluating but with t=x but I get zero..I have never done second derivative so I'm somewhat clueless. Anyone care to help and explain?
 
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The second derivative is the derivative of the first derivative. E.g., if f(x) = x^2, f'(x) = 2x, and f''(x) = d/dx(f'(x)) = d/dx(2x) = 2.

The Fundamental Theorem of Calculus can help you get F'(x), so take a careful look at this theorem and any examples that show how to use it. After that, just take the derivative of what you got for F'(x).
 
Use the Leibniz integral rule twice. Besides the term that you found equal to zero, there's another term that involves differentiating the integrand. That part is not necessarily zero.
 
I don't quite understand? I've never learned the leibniz rule. Can you exemplify it with this question? The f(t) part also confuses me.
 
Last edited:
Don't worry about the f(t) part. Your answer will be in terms of f(t). http://en.wikipedia.org/wiki/Leibniz_integral_rule Here's an easy example. Take F(x) to be the integral from a to x of x*t*dt. You only have to deal with the first and third terms in the rule. The first term you get just from putting t=x in the integrand, so x^2. That's the one you know. The last term says you should differentiate inside the integral. That gives you the integral from a to x of t*dt. Or x^2/2-t^2/2. Adding the two you get F'(x)=3*x^2/2-a^2/2. Compare that with what you get by actually integrating and then differentiating. Now try doing that with your example. What's F'(x)?
 

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