Solve the problem involving Rings

Click For Summary

Discussion Overview

The discussion revolves around solving polynomial equations within the context of ring theory, particularly focusing on the polynomial expressions involving ##(x+1)^n## and their transformations. Participants explore various polynomial forms, their factorizations, and implications in the structure of rings and fields.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant proposes using the polynomial ##(x+1)^3## and questions whether it leads to the expression ##(2x-2)+ x+3## or requires a polynomial with ##x^2+1##.
  • Another participant provides a detailed expansion of ##(x+1)^3##, showing it equals ##2\cdot (x-1)## and identifies ##x^2=-1##.
  • A subsequent reply expresses confusion over a specific transformation in the calculations and clarifies their understanding by introducing a variable ##m## to aid in the manipulation of the equation.
  • Further, a participant calculates ##(x+1)^4##, confirming it equals ##-4## through two different approaches, including polynomial expansion and substitution.
  • Another participant discusses the polynomial ##x^3+4##, expressing it in terms of ##x(x^2)+4## and deriving the expression ##4-x## through substitution.
  • Lastly, a participant notes that the ring ##\mathbb{R}[x]## is an integral domain, and the ideal generated by ##x^2+1## is both prime and maximal, leading to the conclusion that ##\mathbb{R}[x]/\langle x^2+1 \rangle## forms a field, specifically the complex numbers.

Areas of Agreement / Disagreement

Participants express various viewpoints and calculations regarding polynomial transformations and their implications in ring theory. There is no clear consensus on the interpretations or methods, indicating ongoing debate and exploration of the topic.

Contextual Notes

Some calculations and transformations depend on specific assumptions about polynomial forms and their properties within ring theory. The discussion includes unresolved steps and varying interpretations of polynomial identities.

chwala
Gold Member
Messages
2,828
Reaction score
425
TL;DR
Kindly see attached (reference is highlighted part)
1690385428932.png


Its a bit clear; i can follow just to pick another polynomial say

##(x+1)^3## are we then going to have ##(2x-2)+ x+3##?

or it has to be a polynomial with

##x^2+1## being evident? cheers...
 
Physics news on Phys.org
Let's see ...
\begin{align*}
(x+1)^3&=(x+1)^2\cdot (x+1)=2x\cdot (x+1)=2x^2+2x=2\cdot (x^2+1) -2+2x=2x-2=2\cdot (x-1)\\
&\text{crosscheck}\\
(x+1)^3&=x^3+3x^2+3x+1=x\cdot (-1)+3\cdot (-1)+3x+1=2x-2=2\cdot(x-1)
\end{align*}
We identify ##x^2=-1.##
 
  • Informative
Likes   Reactions: chwala
...I was getting a bit lost on this line:

$$2x^2+2x=2\cdot (x^2+1) -2+2x=2x-2=2\cdot (x-1)$$

...but i now i got it by letting,

##x^2+x=x^2+1+m##

therefore

##m=x-1##

other steps follow well.
 
...which means that

##(x+1)^4=(x+1)^2 (x+1)^2 =2x ⋅2x=4x^2=4(-1)=-4##

Cross check:

##(x+1)^4=x^4+4x^3+6x^2+4x+1=1-4x-6+4x+1=-4##
 
Lastly on this just to get the drift of things, if we have a polynomial say;

##x^3+4##

then this becomes,

##x(x^2)+4=x(-1)+4=4-x##

...
 
chwala said:
Lastly on this just to get the drift of things, if we have a polynomial say;

##x^3+4##

then this becomes,

##x(x^2)+4=x(-1)+4=4-x##

...
Right. The ring ##\mathbb{R}[x] ## is an integral domain, the ideal ##\langle x^2+1 \rangle## is prime and maximal. This makes ##\mathbb{R}[x]/\langle x^2+1 \rangle ## a field, the complex numbers. So ##x= \mathrm{i}.##

Here we have ##x^3+4= \mathrm{i}^3+4=-\mathrm{i} +4 =4-x.##
 
  • Like
Likes   Reactions: chwala

Similar threads

  • · Replies 6 ·
Replies
6
Views
1K
  • · Replies 24 ·
Replies
24
Views
1K
  • · Replies 0 ·
Replies
0
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 6 ·
Replies
6
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 12 ·
Replies
12
Views
5K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 55 ·
2
Replies
55
Views
7K