A good answer might be:

YES   x(AB) == (xA)B for scalar x.


Scalar Factor

Recall that xA means that every element of A is multiplied by x. Here is a demonstration of the rule:

Often a matrix-matrix multiplication can be simpified by factoring one of the matrices. See the question.

QUESTION 10:

Compute the following:


10   0  20
20  40  10
 0  20  10

-2   2 
 1   1
 2  -2