How Does the Derivative Change the Multiplicity of a Zero?

  • Thread starter Thread starter ehrenfest
  • Start date Start date
Click For Summary
SUMMARY

The discussion focuses on proving that if a function f(t) has a zero t_0 of multiplicity n, then its derivative f'(t) has a zero at t_0 of multiplicity exactly n - 1. The proof utilizes the representation of f(t) as f(t) = (t - t_0)^n g(t), where g(t_0) is non-zero. The derivative is then expressed as f'(t) = (t - t_0)^(n - 1)k(t), with k(t) defined as k(t) = ng(t) + (t - t_0)g'(t), confirming that k(t_0) is non-zero, thereby establishing the multiplicity of f' at t_0 as n - 1.

PREREQUISITES
  • Understanding of polynomial functions and their properties
  • Knowledge of derivatives and differentiation techniques
  • Familiarity with the concept of multiplicity of roots
  • Basic understanding of continuity and limits in calculus
NEXT STEPS
  • Study the implications of the Rolle's Theorem in relation to multiplicity
  • Explore the relationship between higher-order derivatives and root multiplicity
  • Learn about Taylor series expansions and their applications in root analysis
  • Investigate the behavior of functions near their critical points
USEFUL FOR

Students studying calculus, particularly those focusing on polynomial functions and their derivatives, as well as educators looking for clear explanations of root multiplicity concepts.

ehrenfest
Messages
2,001
Reaction score
1

Homework Statement


How do you show that if f(t) has a zero t_0 of multiplicity n, then f'(t) has a zero at t_0 of multiplicity EXACTLY n -1?

I can prove that the multiplicity is at least n-1 but I am having trouble with the exactly part...


Homework Equations





The Attempt at a Solution

 
Physics news on Phys.org
if f(t) has a root of multiplicity n, then we can write f(t) = (t - t_0)^n g(t) where g(t_0) != 0. Then f'(t) = (t-t_0)^(n-1)k(t) where k(t) = ng(t) + (t-t_0)g'(t) and k(t_0) = ng(t_0) != 0, so f' has a root of multiplicity n-1.
 

Similar threads

Replies
2
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
Replies
6
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 10 ·
Replies
10
Views
10K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 15 ·
Replies
15
Views
2K
  • · Replies 0 ·
Replies
0
Views
2K