A good answer might be:

(2I)(0.5I) = I


Product Yields I

It is clear that (2I)(0.5I) = 2 (0.5)I = 1I = I. But, just for practice, mentally multiply out these matrices the long way: 


2   0   0
0   2   0
0   0   2


1/2   0    0
 0   1/2   0
 0    0   1/2

The rows from the first matrix "match" the columns of the second so that the dot product is 1 only for the major diagonal. All other dot products are 0. The resulting matrix is I.

QUESTION 8:

Say that ax = b for real numbers a and b and real variable x. Solve for x.