Question about using matrices for differential equations

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Discussion Overview

The discussion revolves around solving a system of differential equations using matrices, specifically focusing on finding the general solution and determining coefficients based on initial conditions. The scope includes mathematical reasoning and homework-related queries.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a system of differential equations and seeks help in calculating coefficients for the solution using eigenvalues and eigenvectors.
  • Another participant asks for the general solution of the system, indicating a potential misunderstanding of the problem.
  • A different participant mentions using eigenvectors to form a matrix and attempts to solve for coefficients but encounters discrepancies with expected results.
  • Some participants express dissatisfaction with the responses received, indicating they do not address their questions.
  • There is a suggestion that the solution might simply be the matrix A, although this is not elaborated upon.
  • One participant inquires about the course material and the textbook being used, suggesting a lack of foundational knowledge in differential equations.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the method for solving the differential equations or the interpretation of the responses given. Multiple competing views and uncertainties remain regarding the correct approach and calculations.

Contextual Notes

Some participants express uncertainty about the coefficients and how to apply initial conditions, indicating potential gaps in understanding or missing steps in their reasoning. There is also a mention of differing results from a website, suggesting possible confusion in the solution process.

Who May Find This Useful

This discussion may be useful for students studying differential equations or matrix algebra, particularly those seeking clarification on solving systems of equations and applying initial conditions.

EtherNohow
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Let x(t)=
[x1(t)
x2(t)]
be a solution to the system of differential equations:

x′1(t)=−2x1(t)+2x2(t)
x′2(t)==−6x1(t)+9x2(t)

If x(0)=
[4
-2]
find x(t).

I got the eigenvalues to be -6 and -5, but I don't know how to calculate the coefficients in front of the exponents. For lambda=-6 I get the vector (1, -2) and for lambda=-5 I get the vector (2, -3). I think these would be the coefficients, but I'm not sure, and I don't know how to use the initial values for x(0). Thanks for your help!
 
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Given a system of equations ##\dot{\mathbf{x}}(t) = A \mathbf{x}(t)##, what is the general solution of this problem?
 
micromass said:
Given a system of equations ##\dot{\mathbf{x}}(t) = A \mathbf{x}(t)##, what is the general solution of this problem?
I put the vectors eigenvectors from into a matrix and put 4 and -2 on the right and solved for the two variables. I got -8 and 6 but the website says only -8 is right, and in don't know where to get the other two coefficients?
 
That doesn't answer my question at all.
 
micromass said:
That doesn't answer my question at all.
Wouldn't it just be A? Since other than that both sides are the same?
 
In your course, what does it tell you about systems of differential equations? What book are you reading?
 
micromass said:
In your course, what does it tell you about systems of differential equations? What book are you reading?
I haven't taken differential equations yet. I'm in matrix algebra using Elementary Linear Algebra 7e by Larson.
 

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