PLEASE HELP How to Cross Product Two 3x3 matrices

[dellatorre]

How do I take the cross product of Two 3x3 Matrices.

For example what is cross product of:
[-1 0 0]
[0 1 0]
[0 0 1]
x
[0 -1 0]
[1 0 0]
[0 0 1]

thanks,
Della

 

[Hurkyl]

The cross product isn't an operation on matrices -- your question doesn't make sense as given. Can you provide more information?

 

[dellatorre]

ok, maybe its not the cross product I need to do then.

The problem I'm struggling with is this:
"Show that matrix
[0 -1 0]
[-1 0 0]
[0 0 1]
for a reflection about line y=-x
is equivalent to a reflection relative to the y-axis followed by a counter-clockwise rotation of 90 degrees."

So for my answer, first I have for the reflection relative to the y axis, I have the matrix:
[-1 0 0]
[0 1 0]
[0 0 1]

and for the counter-clockwise rotation of 90 degrees, I have the matrix:
[0 -1 0]
[1 0 0]
[0 0 1]

but then I don't know what my next step should be.

Do you know how to do this?

thanks,
Della

 

[Edgardo]

Multiply both matrices with each other.
For matrix multiplication see here:
https://www.physicsforums.com/showpost.php?p=1500534&postcount=12
http://www.colorado.edu/engineering/cas/courses.d/IFEM.d/IFEM.AppB.d/IFEM.AppB.pdf

 

[Fredrik]

So for my answer, first I have for the reflection relative to the y axis, I have the matrix:
[-1 0 0]
[0 1 0]
[0 0 1]

That one changes the x coordinate of the vector it acts on, not the y coordinate.

but then I don't know what my next step should be.

Multiply the matrices.

 

[dellatorre]

thank you all :-))