A good answer might be:


1  0  0
0  1  0
0  0  1
T = 

1  0  0
0  1  0
0  0  1

Transpose of I

For any dimension: IT = I.

IT = I

Another useful property is the following. Actually, this is really just an application of the definition of I.

AIB = AB

Another easy application of the definition:

II = I, or I2 = I

These are all obvious; you should not have to memorize anything here. But it does help to look them over.

QUESTION 6:

Compute the following: 


0.5  0.0  0.0
0.0  0.5  0.0
0.0  0.0  0.5


2    4    6
0  -12   -8
4    0    4
=

Hint: you don't actually need to multiply matrices.