Prove that this equation has at least one real root

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SUMMARY

The discussion centers on 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 λ is a real number. Participants emphasize the application of Rolle's Theorem and the Intermediate Value Theorem to establish the existence of roots. The conversation highlights the importance of continuous differentiability of f and suggests using the function g(x) = f'(x) + λf(x) to analyze sign changes between roots. The conclusion is that if g changes sign between two roots of f, then g must have a root in that interval.

PREREQUISITES
  • Understanding of Rolle's Theorem
  • Familiarity with the Intermediate Value Theorem
  • Knowledge of continuous and differentiable functions
  • Basic concepts of differential equations
NEXT STEPS
  • Study the application of the Intermediate Value Theorem in real analysis
  • Explore the implications of Rolle's Theorem in proving the existence of roots
  • Investigate the properties of continuous and differentiable functions
  • Learn about differential equations and their solutions, particularly in relation to roots
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Mathematics students, educators, and anyone interested in the analysis of real-valued functions and the application of theorems in calculus.

  • #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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