If f(a)=g(a) and f(b)-g(b), prove they will have parallel tan lines

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Homework Help Overview

The problem involves proving that two differentiable functions, f and g, have parallel tangent lines at some point in the interval [a,b], given specific conditions about their values at the endpoints of the interval. The discussion also explores a variation of the problem where the conditions are relaxed.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the Mean Value Theorem and consider the implications of the conditions f(a)=g(a) and f(b)=g(b). There is an exploration of how to relate the derivatives of the functions at a point in the interval.

Discussion Status

Some participants have suggested applying the Mean Value Theorem to a new function H(x) = f(x) - g(x) as a potential approach. There is an ongoing exploration of how to rigorously prove the statement, with hints being provided to guide the discussion.

Contextual Notes

Participants have noted the importance of the conditions given in the problem and are considering how relaxing these conditions might affect the proof. There is an acknowledgment of the need for a rigorous approach rather than relying solely on graphical intuition.

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Homework Statement


(a) If f and g are differentiable functions on the interval [a,b] with f(a)=g(a) and f(b)=g(b), prove that at some point in the interval [a,b], f and g have parallel tangent lines.

(b) Prove that the result of part a holds if the assumptions f(a)=g(a) and f(b)=g(b) are relaxed to requiring f(b)-f(a)=g(b)-g(a).


Homework Equations





The Attempt at a Solution

 
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You know the rules. What have you tried?
 
I haven't, really. I know that by graphing specific examples I can intuitively confirm that it is true. But I'm struggling on how to rigorously prove it.
 
Judging from your recent posts you have recently studied a theorem that has expressions like f(b)-f(a) in it haven't you?
 
Mvt?
 
Yes. Here's my last hint before hitting the sack: Try applying that theorem to H(x) = f(x) - g(x).
 
Should I use f'(c)=(f(b)-f(a))/(b-a) and g'(c)=(g(b)-g(a))/(b-a)? Then how should i relate them to each other? Set them equal?
 
You've already said "f(a)=g(a) and f(b)=g(b)" so it is not necessary to "set them equal", they are equal!
 

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