Is this cublc polynomial function solvable?

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Discussion Overview

The discussion revolves around the solvability of two specific cubic polynomial equations: x^3 - x - 2 = 0 and x^3 + 9x - 1 = 0. Participants explore methods for determining their solvability, including algebraic and graphical approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant presents the cubic polynomial x^3 - x - 2 = 0 and questions its solvability.
  • Another participant mentions a similar polynomial x^3 + 9x - 1 = 0, asserting that both are solvable but expresses uncertainty about finding solutions algebraically or graphically.
  • Some participants suggest testing for divisibility by specific binomials as a method to explore the solvability of the polynomials.
  • One participant proposes using synthetic division as a technique to evaluate the polynomials.
  • Another participant asserts that every cubic equation is solvable and references the cubic root algorithm, specifically Cardano's method.
  • A later reply identifies (x-2) as a binomial that yields a zero remainder for the first polynomial, leading to a quotient of (x+1)^2.

Areas of Agreement / Disagreement

Participants express differing views on the methods for solving the cubic equations, with some advocating for synthetic division while others suggest evaluating the polynomials directly. There is no consensus on the best approach or on the specific solutions to the equations.

Contextual Notes

Some participants reference techniques like synthetic division and Cardano's method without fully resolving the implications of these methods for the specific polynomials discussed. The discussion includes assumptions about the solvability of cubic equations but does not clarify the conditions under which these methods apply.

davedave
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Here is a very difficult cubic polynomial.

x^3 - x - 2 = 0

I am wondering whether it is solvable or not. Please think about it.
 
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I need help with this too I posted a similar one and haven't got a response... mine was x^3 + 9x -1=0...They are solvable, but I don't know how to get an answer algebraically or graphically.
 
EDIT: Deleted totally misleading answer. Ignore if you read it.
 
Last edited:
davedave said:
Here is a very difficult cubic polynomial.

x^3 - x - 2 = 0

I am wondering whether it is solvable or not. Please think about it.

aew782 said:
I need help with this too I posted a similar one and haven't got a response... mine was x^3 + 9x -1=0...They are solvable, but I don't know how to get an answer algebraically or graphically.

Are they solvable? Let's have a guess: The first one can be tested for divisibility by x+1, x-1, x+2, and x-2. The second one can be tested for divisibility by x+1 and x-1. The results may be faster if you know synthetic division.
 
symbolipoint said:
Are they solvable? Let's have a guess: The first one can be tested for divisibility by x+1, x-1, x+2, and x-2. The second one can be tested for divisibility by x+1 and x-1. The results may be faster if you know synthetic division.

Thank you that's all I needed!
 
You can use synthetic division, but isn't it simpler to just evaluate the polynomial and see if the equation is satisfied?
 
The first binomial rendering zero remainder is (x-2). The quotient is x^2+2x+1 which is (x+1)^2. No need to use Cardano's or Vietas substitution for this cubic (micromass gave a good reference Wikipedia article).
 

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