# Question #4ca6c

##### 1 Answer

Oct 24, 2016

#### Explanation:

Let

Using the properties of matrix multiplication, we know that

#= a_11b_11+a_12b_21+a_13b_31#

#=4(9)+1(-6)+3(1)#

#=36-6+3#

#=33#

Similarly, we know that

#=a_21b_12+a_22b_22+a_23b_32#

#=5(3)+2x(2)+(-3)(4)#

#=15+4x-12#

#=4x+3#

Notice that we didn't need to do all the multiplication. We only needed to multiply rows and columns to get equations containing our variables.

(Also, as a side note, if we *did* do the full multiplication, we'd find that the book has a mistake, in that