Find x- and y- Intercepts....4

  • Context: MHB 
  • Thread starter Thread starter mathdad
  • Start date Start date
Click For Summary

Discussion Overview

The discussion revolves around finding the x- and y-intercepts of the polynomial function y = 2x^5 - 5x^4 + 5. Participants explore methods for determining these intercepts, particularly focusing on the challenges associated with solving polynomial equations of degree 5.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested, Mathematical reasoning

Main Points Raised

  • One participant calculates the y-intercept as (0, 5) by substituting x = 0 into the polynomial.
  • Another participant expresses doubt about the existence of roots for the equation 0 = 2x^5 - 5x^4 + 5 that can be expressed in terms of elementary functions.
  • A participant comments on the general solvability of polynomials, noting that while polynomials of degree 4 and lower have guaranteed solutions, degree 5 polynomials may not, and suggests that the current polynomial likely does not have a simple solution.
  • Another participant mentions reliance on numeric root-finding techniques for polynomials of degree 3 or higher when rational roots are not applicable.
  • A later reply indicates an understanding that finding "nice" roots may require advanced techniques, which the participant is not yet familiar with.

Areas of Agreement / Disagreement

Participants generally agree on the complexity of finding roots for the given polynomial, particularly noting the challenges associated with degree 5 polynomials. However, there is no consensus on the specific methods or techniques that should be employed to find the x-intercepts.

Contextual Notes

The discussion highlights the limitations of elementary functions in expressing roots for higher-degree polynomials and the reliance on numerical methods when analytical solutions are not feasible.

Who May Find This Useful

This discussion may be useful for students or individuals interested in polynomial functions, root-finding techniques, and the challenges associated with higher-degree equations in mathematics.

mathdad
Messages
1,280
Reaction score
0
Find the x- and y-intercepts.

y = 2x^5 - 5x^4 + 5

Let x = 0

y = 2(0)^5 - 5(0)^4 + 5

y = 5

The y-intercept is y = 5 and it takes place at the point (0,5).

Let y = 0 to find the x-intercept.

0 = 2x^5 - 5x^4 + 5

I am stuck here.
 
Physics news on Phys.org
I don't think $0 = 2x^5 - 5x^4 + 5$ has roots that can be expressed in terms of elementary functions.
 
More "nice" roots, right?
 
There's always a solution(s) for polynomials of degree 4 and lower (if one includes complex-valued results). Once we reach a degree of 5 we are, in general, out of luck (so to speak) but there are some quintics (polynomials of degree 5) that are solvable. I don't think the one we have here is, though.

A useful online tool is W|A (Wolfram Alpha). I will suggest that you familiarize yourself with this tool as it can aid insight into problems that may be difficult. :D
 
For any polynomial of degree 3 or more that doesn't succumb to the rational roots theorem to get down to a combination of linear/quadratic factors, I rely on numeric root finding techniques to approximate the real roots (and those are the only roots we need for finding intercepts). :D
 
You are saying that "nice" roots in this case require advanced techniques. I am not there yet. I get it now.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 20 ·
Replies
20
Views
4K
  • · Replies 9 ·
Replies
9
Views
3K
  • · Replies 3 ·
Replies
3
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 3 ·
Replies
3
Views
1K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K