- #1
BiGyElLoWhAt
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Homework Statement
A:
Let ##T## be the linear function ##T####:\mathbb{R}^3→\mathbb{R}^1## defined as ##T####(x,y,z) = x-3y+z##.
The nullspace of T is a 2 dimensional subspace of ##\mathbb{R}^3## (a plane through the origin). Give an example of the basis of this subspace ##\{ \vec{u},\vec{v} \}##
B:
Give an example of a vector ##\vec{w} \in \mathbb{R}^3## so that ##\{ \vec{u},\vec{v},\vec{w} \} ## is a basis for ##\mathbb{R}^3##
u and v are from part a.
Homework Equations
Not sure what to put here in this case...
The Attempt at a Solution
So, the nullspace of T is all vectors so that ##T(\vec{x})=\vec{0}##.
So ##\left [ \begin{array}{ccc}
1 & -3 & 1 \\ \end{array} \right ]## ## \left [ \begin{array}{c} x \\ y \\ z \\ \end{array} \right ] = \left [ \begin{array}{c}
0 \\ \end{array} \right ]##
which, it's pretty obvious without even working through anything that my plane is simply ## x - 3y +z = 0##
So I guess my question here, is this: when I need to setup a basis, can I treat this similar to a calc 3 problem? Both for part a and part b. So for part a, can I say that a basis is (upon solving for z)
##\{ \left [ \begin{array}{c} -1 \\ 0 \\ \end{array} \right ] \ \text{,}\ \left [ \begin{array}{c} 0 \\ 3 \\ \end{array} \right ] \}##
But through a few scalar multiplications, this can be:
##\{ \left [ \begin{array}{c} 1 \\ 0 \\ \end{array} \right ] \ \text{,}\ \left [ \begin{array}{c} 0 \\ 1 \\ \end{array} \right ] \}##
Or also, should this be in 3 dimension?
##\{ \left [ \begin{array}{c} 0 \\ -1 \\ 0 \\ \end{array} \right ] \ \text{,}\ \left [ \begin{array}{c} 0 \\ 0 \\ 3 \\ \end{array} \right ] \}##
And then for b, I probably shouldn't do it this way, as we never covered the cross product, but could I just cross my 2 bases to get a 3rd orthogonal (I guess it only needs to be linearly independant of the other 2) vector as a basis for my ##\mathbb{R}^3## ? Noted that this only works because we're working in R^3 and subspaces thereof, but work smart not hard, right?