Finding Values for k in f(x) = 2x^3+7x-3

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Discussion Overview

The discussion revolves around finding values for k in the polynomial function f(x) = 2x^3 + 7x - 3, specifically when this function is divided by (2x - k) and results in a remainder of -8. The scope includes polynomial division and the application of the division algorithm for polynomials.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant asks how to find values for k given that f(x) divided by (2x - k) yields a remainder of -8.
  • Another participant interprets the question as needing to solve for k as a function of x, suggesting a misunderstanding.
  • A different participant explains that dividing polynomials involves long division and that the remainder can be expressed as a cubic function in k, leading to three possible values for k.
  • Another participant clarifies that the division algorithm can be used to express f(x) in terms of (2x - k) and a polynomial, allowing for simultaneous equations to find k.
  • There is a note of confusion regarding the interpretation of the remainder, with participants acknowledging different understandings of the problem.
  • One participant emphasizes the importance of equating coefficients from both sides of the polynomial equation to solve for k.

Areas of Agreement / Disagreement

Participants express differing interpretations of the problem, particularly regarding the nature of the remainder and how to approach the division. There is no consensus on a single method or interpretation, indicating multiple competing views remain.

Contextual Notes

Some assumptions about the interpretation of the remainder and the structure of the polynomial division are not fully resolved, leading to different approaches suggested by participants.

chris_tams
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If i have f(x) = 2x^3 + 7x -3

And when f(x) is divided by (2x-k) I have -8

How do i find values for k?
 
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I might be misunderstanding your question, but are you saying that

\frac{2x^3+7x-3}{2x-k}=-8

and you wish to solve for k as a function of x?
 
How do you actually divide 2 polynomials ? Do the long division ...you'll find the remaider to be R = f(k), where f is a cubic in k. Equate this to -8 and you have the 3 values of k.
 
Yes and no there's no need to solve as a function of x: he's saying that if we write

2x^3+7x-3 = (2x-k)(x^2+ax+b)-8

what is k?

It's a division algorithm for polynomials question; by comparing coeffs on each side you ought to be able to solve a set of simulatneous equations to find k (and a and b)
 
I'm assuming you mean the remainder is -8. It's not clear, and evidently, TALewis has interpreted differently.

And Matt's way is much easier.
 
Last edited:
Ah, if you mean the remainder is -8, that makes much more sense.
 
yes, what i mean is that when, 2x^3+7x-3/(2x-k) This equals some polynomial funtion with a remainder of -8. How do i work out what the polynomial is?
 
Last edited:
Look at matt's post again.

Expand the RHS and equate coefficients of the different powers of x, between the LHS and RHS. For instance, "Is there an x^2 term in the LHS ?...No !" So you equate the coefficient in the RHS to zero...and so on. Solving from these equations gives you k.
 
Yes youth. Cheers !
 

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