1 0 0 0 1 0 0 0 1

For any dimension:

I^{T}=I

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

A I B=A B

Another easy application of the definition:

I I=I, orI^{2}=I

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

Compute the following:

0.5 0.0 0.0 0.0 0.5 0.0 0.0 0.0 0.52 4 6 0 -12 -8 4 0 4=

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