Prove that this equation has at least one real root

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Homework Help Overview

The problem involves proving that the equation f'(x) + λf(x) = 0 has at least one real root between any pair of roots of the function f(x) = 0, where f is a continuous and differentiable function and λ is a real number. The discussion centers around the implications of Rolle's Theorem and the properties of continuous functions.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between the roots of f(x) and the behavior of its derivative f'(x) in the context of the additional term λf(x). There are attempts to clarify the definitions and implications of the problem statement, as well as to explore the connection to differential equations.

Discussion Status

Participants are actively engaging with the problem, raising questions about the assumptions made regarding the continuity and differentiability of f. Some hints and suggestions have been offered, including the use of the Intermediate Value Theorem and considerations of the function's behavior at its roots. There is a recognition of the complexity involved in applying Rolle's Theorem directly to the modified function g(x).

Contextual Notes

There is a discussion about the clarity of the problem statement and the implications of differentiability. Some participants express uncertainty regarding the assumptions about the function f and its roots, particularly in relation to the continuity of f' and the nature of the differential equation presented.

  • #31
I gave that hint about adjacent roots but I should have thought more about the question first, because it (the question as well as my hint) was a little misleading. Dick (as usual, I'm pleased to say) led us directly to the best way to look at it, a geometric argument.
 
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  • #32
verty said:
I gave that hint about adjacent roots but I should have thought more about the question first, because it (the question as well as my hint) was a little misleading. usual, I'm pleased to say) led us directly to the best way to look at it, a geometric argument.
Thanks for clearing that up, verty. (I still like my eλx method.)
 
  • #33
haruspex said:
Thanks for clearing that up, verty. (I still like my eλx method.)

I like it too. It's elegant and does use pure Rolle's theorem, not the MVT. But I like the MVT approach because I think it's easier to discover graphically, without the extra bit of cleverness. Tough call really.
 
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