Answer
-2A=[-4 0 2 ; -8 10 -4]
B-2A=[3 -5 3 ; -7 6 -7]
AC is undefined
CD=[1 13 ; -7 -6]
Work Step by Step
I will express matrices as ( A B C ; D E F ), where the entries listed go across columns and then break to a new row and column one after each ";".
We want to find:
-2A=-2(2 0 -1 ; 4 -5 2)=(-4 0 2 ; -8 10 -4)
B-2A=[7 -5 1 ; 1 -4 -3[+[-4 0 2 ; -8 10 -4]=[3 -5 3; -7 6 -7]
AC=undefined. The reason for this is that the # of columns of A must be equal to the # of rows in C, because of the law for matrix multiplication. 3 is not equal to 2.
CD=[1 2 ; -2 1][3 5 ; -1 4]=[3*1-1*2 5*1+4*2 ; 3*-2+1*-1 -2*5+1*4]=[1 13 ; -7 -6]
