Factoring Polynomial z^4-4z^3+6z^2-4z-15 =0

  • Context: Undergrad 
  • Thread starter Thread starter Fabio010
  • Start date Start date
  • Tags Tags
    Factoring Polynomials
Click For Summary

Discussion Overview

The discussion revolves around the factoring of the polynomial equation z^4-4z^3+6z^2-4z-15 = 0, with participants seeking methods to find its solutions. The scope includes mathematical reasoning and problem-solving techniques related to polynomial factorization.

Discussion Character

  • Mathematical reasoning, Homework-related, Exploratory

Main Points Raised

  • One participant inquires about factoring the polynomial and expresses difficulty in proceeding after applying Ruffini's rule.
  • Another participant suggests continuing with Ruffini's rule, indicating that there is likely another root and that the remaining factor will be quadratic.
  • A participant claims to have found the solutions as -1, 3, and 1 +/- 2i, but expresses uncertainty in applying Ruffini's rule again.
  • One participant points out a potential error in the quotient, suggesting that the leading term should be z^3 instead of -z^3.
  • A participant acknowledges understanding after correcting their approach and mentions factoring the polynomial as (z^3-5z^2+11z-15)/(z-3).
  • Another participant advises to apply Ruffini's rule again with the divisors of -15.

Areas of Agreement / Disagreement

The discussion reflects a lack of consensus on the correct application of Ruffini's rule and the factorization process, with participants expressing differing levels of understanding and success in finding solutions.

Contextual Notes

There are indications of missing assumptions regarding the application of Ruffini's rule and the identification of roots, as well as unresolved steps in the factorization process.

Fabio010
Messages
84
Reaction score
0
z^4-4z^3+6z^2-4z-15 =0

How can i factor this polynomial in order to find the solutions??


I tried with the ruffini' rule.

and i reached the following equation [(z+1)(-z^3-5z^2+11z-15)] =0

now how can i factor (-z^3-5z^2+11z-15) ?

i tried it, but i can not solve it... :/
 
Mathematics news on Phys.org
Proceed with Ruffini. You'll find another root (because the problem is easy) and the remaining factor is quadratic, whose solutions you get with the formula.
 
the solutions are

-1; 3; 1+/-2i

i am going to try with ruffini again.
 
i cant. Even knowing the solutions, i can not proceed with ruffini's rule.
Maybe something is escaping me.
 
Redo the quotient (z^4-4z^3+6z^2-4z-15)/(z+1), since the leading term must be z^3, not -z^3.
 
ok it now makes sense.

now i factor it


(z^3-5z^2+11z-15)/(z-3)



...

but without the solution i would never be able to discover that i should divide (z^3-5z^2+11z-15) by (z-3)
 
Do Ruffini again: try with the divisors of -15 of both signs.
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 11 ·
Replies
11
Views
3K
  • · Replies 4 ·
Replies
4
Views
1K