Theory of cubic equation question

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    Cubic Theory
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The discussion centers on finding the polynomial whose roots are the squares of the roots of the cubic equation x3 - 4x2 + x - 1 = 0. Participants clarify that the correct approach involves using symmetric polynomials and correctly manipulating algebraic expressions. The final polynomial derived from the discussion is x3 - 14x2 - 7x - 1 = 0, which is confirmed as the correct answer after addressing algebraic errors and ensuring proper equation formatting.

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  • #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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