Theory of cubic equation question

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    Cubic Theory
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Homework Help Overview

The discussion revolves around finding a polynomial whose roots are the squares of the roots of the cubic equation \(x^3 - 4x^2 + x - 1 = 0\). Participants are exploring the relationship between the roots of the original polynomial and the new polynomial formed from their squares.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss various methods to derive the new polynomial, including substituting \(y = x^2\) and manipulating the original equation. There are questions about the validity of certain algebraic steps and the definitions of polynomials.

Discussion Status

The conversation is ongoing, with participants providing hints and corrections regarding algebraic manipulations. Some participants suggest alternative methods involving symmetric polynomials, while others express confusion about the algebraic process.

Contextual Notes

There is a noted emphasis on ensuring that the expressions formed are valid polynomials, and some participants highlight the importance of careful algebraic handling, particularly when squaring terms.

  • #31
lionely said:
sighh sigh sighj sigh sigh sigh sigh why didn't i see that ...

(1+4x)^2 = 1 + 8x + 16x^2...

VERY GOOD. Finally. OK, now just simplify and group the terms.

Remember to expand the LHS correctly too. :smile:

BTW, if you're working in the variable 'y', you should use that throughout, otherwise it's confusing (and actually wrong).
 
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  • #32
it is x3 -14x2+x-1
 
  • #33
lionely said:
it is x3 -14x2+x-1

Not quite. Every coefficient is right except the one for the x term. You must have made a mistake, show your exact work.

A bit of a cheat, but you can test your answer here: http://www.gyplan.com/eqcubic_en.html

And, not to belabour the point, what you wrote is still not an equation! You MUST put the '=0'.
 
  • #34
lol... x^3 -14x^2-7x-1
 
  • #35
lionely said:
lol... x^3 -14x^2-7x-1

Still not an equation. Just an expression. But all the coefficients are right.
 
  • #36
looooooool OKAY HERE IT IS x^3 -14x^2-7x-1 = 0!
 
  • #37
lionely said:
looooooool OKAY HERE IT IS x^3 -14x^2-7x-1 = 0!

GREAT!:biggrin:
 

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