# Unit of the Determinant of a 2-space Matrix

1. May 12, 2007

### Hendrick

Do determinants of a 2-space matrix have a unit of [units]^2?
Also, does A_parallelogram = || u x v|| have a unit of [units]^2 too?
This has confused me as Area has a unit of [units]^ 2 but the examples from the Contemporary Linear Algebra (Anton and Busby) text book does not state any units at all.

2. May 12, 2007

### HallsofIvy

Staff Emeritus
The area of a parallelogram has units of "u2" where u is whatever unit is being used to measure area. That is a specific application of norm and does NOT say that norm of the cross product of a vector has any units at all! Are you assuming that there is some form of "measurement" so that the vectors in whatever vector space you are talking about have a specific unit? And that raises the question, are you thinking of some specific vector space?

3. May 12, 2007

### Hendrick

Well, yeah. Finding the area of a unit square 'ABCD' that is represented by a 2x4 M matrix =
[ 0 1 1 0 ]
[ 1 1 0 0 ]
which has been multiplied by a 2x2 matrix N =
[ -2 0 ]
[ 0 -2 ]

I had to calculate the area of N.M and the determinant of the N matrix.
And I was just wondering since it's the area (found by Aparallelogram = || u x v||) do I just write [units]^2?
Also since I'm meant to find out that the determinant is the area of the parallelogram, should I write [units]^2 or leave it blank?

-- So there is an application of the norm of the cross product of two adjacent vectors in 2-space (Aparallelogram = || u x v||), in this situation should I put [units]^2 in the answer? I deduce that I'm not meant to know about det(N) being the area of N.M so I guess I won't write any units for that.

Last edited: May 12, 2007
4. May 12, 2007

### HallsofIvy

Staff Emeritus
What units are you told the length is measured in? If you are not given any measurements for a length, then I would not write any units for the area.

5. May 12, 2007

### Hendrick

No units, it just says calculate the area of N.M and calculate det(N).
I just want to cover my bases as it asked for area and I thought I should just put a unit of 'units^2' at the end...