Finding the Span of u1 & u2 in R^3

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In summary, the span of the vectors u1 and u2 in R^3 is the x-z plane, as the first and third entries of the vectors are equal and can be described by the equation x=z. To solve for all vectors perpendicular to u1 and u2, one can use Gaussian elimination or consider (1/2)(u1-u2) and (1/2)(u1+u2) to better understand the pattern.
  • #1
physicsss
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I'm stuck on the following problem:

Describe the span of the vectors u1 and u2 in R^3, where
u1 = (1, 1, 1), u2 = (1, −1, 1)

I know that the span is a(u1)+b(u2), which becomes (a+b,a-b,a+b), but I don't know where to go from here.

TIA.
 
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  • #2
do you know gaussian elimination, reduction for matrices?

i.e. how to solve for all vectors perpendicular to both of those?

or you could just look at your general vector, since it satisfies an obvious equation.
 
  • #3
physicsss said:
I'm stuck on the following problem:

Describe the span of the vectors u1 and u2 in R^3, where
u1 = (1, 1, 1), u2 = (1, −1, 1)

I know that the span is a(u1)+b(u2), which becomes (a+b,a-b,a+b), but I don't know where to go from here.

TIA.
Consider (1/2)(u1-u2)=(0,1,0) and (1/2)(u1+u2)=(1,0,1)
It will then be easier to see what is happening.
 
  • #4
Is it the x-z plane in R^3?
 
  • #5
have you noticed that the first and third entries of your vectors are equal? what does that tell you about an equations characterizing these vectors?
 
  • #6
The main diagonal line in x-z plane
 
  • #7
i.e. x=z describes all of these vectors.
 

What is the span of u1 and u2 in R^3?

The span of u1 and u2 in R^3 refers to the set of all possible linear combinations of the vectors u1 and u2 in three-dimensional space.

How do you find the span of u1 and u2 in R^3?

To find the span of u1 and u2 in R^3, you can create a matrix using the coefficients of the linear combination and use Gaussian elimination to determine the pivot columns. The vectors corresponding to the pivot columns will form a basis for the span of u1 and u2.

Why is finding the span of u1 and u2 in R^3 important?

Finding the span of u1 and u2 in R^3 allows us to understand the range or column space of a linear transformation defined by these vectors. It also helps us determine if the vectors are linearly independent or if they span the entire space.

Can the span of u1 and u2 in R^3 be a plane or a line?

Yes, it is possible for the span of u1 and u2 in R^3 to be a plane or a line. This will depend on the linear combination of the two vectors. For example, if one vector is a scalar multiple of the other, the span will be a line. If the two vectors are linearly independent, the span will be a plane.

Can the span of u1 and u2 in R^3 be the entire space?

No, the span of u1 and u2 in R^3 cannot be the entire space. This is because the two vectors are only two-dimensional and cannot span a three-dimensional space. The span will always be a subspace of R^3.

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