Can matrices be used to solve systems with different degree variables?

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Discussion Overview

The discussion revolves around the possibility of using matrices to solve a system of equations that includes the same variable raised to different degrees. The equations presented involve quadratic terms and linear terms, prompting questions about the applicability of matrix methods in this context.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asks whether it is possible to use a matrix to solve a system of equations with the same variable at different degrees, providing specific equations as examples.
  • Another participant acknowledges the matrix representation of the equations but emphasizes the need to understand the implications of the results.
  • Some participants point out that there are three equations but only two variables, suggesting that this typically leads to no solution unless one equation is redundant.
  • Concerns are raised about the potential for misinterpreting false solutions if constraints are ignored in the matrix approach.
  • There is a discussion about the definition of a square matrix and its relevance to solving systems of equations with independent variables.
  • Some participants express skepticism about the feasibility of applying linear algebra to the problem, while others encourage further exploration of the topic.

Areas of Agreement / Disagreement

Participants generally agree that the system as presented is problematic due to the mismatch in the number of equations and variables. However, there is disagreement about the potential for using matrices in this context, with some asserting it cannot work and others suggesting there may be ways to apply matrix methods.

Contextual Notes

The discussion highlights limitations related to the number of independent variables versus the number of equations, as well as the implications of using matrix algebra in this scenario.

woodne
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Hello! First post here.

My question is, is it possible to use a matrix to solve a system where you have the same variable, but a different degree. i.e.

2x^2 + 2x + y = 2
-3x^2 - 6x + 2y = 4
4x^2 + 6x - 3y = 6

Now, I know this is possible other ways, but seeing as each of those would have multiple solutions, is it possible to solve using a matrix?
 
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woodne said:
Hello! First post here.

My question is, is it possible to use a matrix to solve a system where you have the same variable, but a different degree. i.e.

2x^2 + 2x + y = 2
-3x^2 - 6x + 2y = 4
4x^2 + 6x - 3y = 6

Now, I know this is possible other ways, but seeing as each of those would have multiple solutions, is it possible to solve using a matrix?
There are lots of ways you can use a matrix... I imagine, though you meant solving the matrix equation

<br /> \left(<br /> \begin{array}{ccc}<br /> 2 &amp; 2 &amp; 1 \\<br /> -3 &amp; -6 &amp; 2 \\<br /> 4 &amp; 6 &amp; -3<br /> \end{array}<br /> \right)<br /> \left(<br /> \begin{array}{c}<br /> x^2 \\ x \\ y<br /> \end{array}<br /> \right)<br /> =<br /> \left(<br /> \begin{array}{c}<br /> 2 \\ 4 \\ 6<br /> \end{array}<br /> \right)<br />

Well, this is a matrix equation, so you can apply matrix algebra to do whatever you wanted to it. Just make sure you understand what your results mean.
 
too much information …

Hi woodne! Welcome to PF! :smile:

You have three equations, but only two variables. :frown:

So there won't normally be a solution (unless one of the equations is redundant).

If you ignored one equation, you'd only have a 2x3 matrix …
 
That's what i was thinking, that it shouldn't be possible to solve that by a matrix, but my physics teacher swears there's a way to use a matrix for everything.
 
tiny-tim said:
So there won't normally be a solution (unless one of the equations is redundant).

If you ignored one equation, you'd only have a 2x3 matrix …
Er, if there is no solution then there is no solution. All ignoring a constraint achieves is vastly increasing the likelyhood you will mistakenly interpret a 'false solution' as being an actual solution.



P.S. have either of you seriously consider how one might apply linear algebra to this problem? Or did you just think "oh, it can't work" and stop thinking?
 
Last edited:
woodne said:
That's what i was thinking, that it shouldn't be possible to solve that by a matrix, but my physics teacher swears there's a way to use a matrix for everything.

Ask your teacher whether he/she means a square matrix - if so, ask how that can work if there aren't enough independent variables! :smile:

Oh, and be tactful … :rolleyes:
 
Isn't the team "square matrix" used when the dimensions are equal? (let y equal a dimension, such as y x y)
 
razored said:
Isn't the team "square matrix" used when the dimensions are equal? (let y equal a dimension, such as y x y)

Yes, that's right - so a square matrix could only be useful for solving independent variables.

If there are three variables, of which only two are independent (such as x^2 x and y), there won't normally be a solution for more than two equations involving them - which would only give enough numbers for a 3 x 2 matrix! :smile:
 

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