Linear Algebra - Find a subspace

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Homework Help Overview

The problem involves finding a subspace W of R³ such that R³ is the direct sum of a given subspace V, defined by two linear equations. The original poster expresses confusion about how to approach this type of exercise, noting a lack of examples from their teacher.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants discuss the nature of the equations defining subspace V, noting that each equation represents a plane and questioning the intersection of these planes. Some participants attempt to solve the system of equations to find a representation of the subspace.

Discussion Status

The discussion is ongoing, with participants exploring the characteristics of the subspace V and its representation. There is a suggestion that W could be a plane perpendicular to the line represented by V, but no consensus has been reached on the exact approach to finding W.

Contextual Notes

Participants are working under the constraints of the problem as posed, with an emphasis on understanding the concepts of direct sums and subspaces without specific examples provided by the instructor.

cristina89
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Homework Statement



V is a subspace of the vector space [itex]R^{3}[/itex] given by:
V = {(x, y, z) E [itex]R^{3}[/itex] / x + 2y + z = 0 and -x + 3y + 2z = 0}
Find a subspace W of [itex]R^{3}[/itex] such that [itex]R^{3}[/itex] = V[itex]\oplus[/itex]W

I'm really lost in this. My teacher didn't give any example of how to solve this kind of exercise... Can anyone help me how to start and develope this?
 
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each of those equations defines a plane - what is the intersection of two planes?
 
lanedance said:
each of those equations defines a plane - what is the intersection of two planes?

A straight line?

Well, if I solve this system:

x = -2y + z
y = -3/5z --> x = -11/5z
 
Last edited:
To start with, do you know what your looking for ? Do you know what is the direct sum of two subspaces?
 
So the subspace V is a line through the origin, and can be represented by the span of a single vector parallel to that line.

Now onto Dansure's question...
 
W will be a plane perpendicular to that line, containing the origin.
 

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