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1 2 3 01 0 1 0 0 1-2 6 01 0 1 -3 0 1 0 0 01 1-2 -3 0 6, LetA=10010 2 1 0 0 B= 10

ID: 3145006 • Letter: 1

Question

1 2 3 01 0 1 0 0 1-2 6 01 0 1 -3 0 1 0 0 01 1-2 -3 0 6, LetA=10010 2 1 0 0 B= 10310 0 0 0 1 J 0 0 01 Lo 0 0 0 1 J Determine which of the following is TRUE. (a) AB = 4 (b) AC = 14 (c) AD = 14 (d) BC = 4 (e) none of these 7. Determine which of the following is FALSE, where all matrices are is n by n (a) If A is invertible then the elemetary row operations that reduce A to I, also reduce In to A-1 (b) If A is row equivalent to In then A is invertible. (c) (AB)--B-A-1 if A and B are invertible (d) BA CA implies B-C. (e) none of these 8. To find inverse of a matrix E we need to use row operations to reduce the matrix [E L.] Now suppose that [E 12] has been reduced to a certain form. Then we can read off E 1221|and A=101 ,D=102 Determine which of the following is E-1 (a). A (b). B (c). C(d). D (e). none of these

Explanation / Answer

A = [ 1 2 3 0 ; 0 1 0 0 ; 0 0 1 0; 0 0 0 1];
>> A

A =

     1     2     3     0
     0     1     0     0
     0     0     1     0
     0     0     0     1

>> B =[1 -2 6 0 ; 0 1 -3 0 ; 0 0 1 0; 0 0 0 1];
>> C =[1 0 0 0 ; 2 1 0 0 ; 0 3 1 0 ; 0 0 0 1];
>> D = [1 -2 -3 0 ; 0 1 0 0 ; 0 0 1 0 ; 0 0 0 1];

B

B =

     1    -2     6     0
     0     1    -3     0
     0     0     1     0
     0     0     0     1

>> C

C =

     1     0     0     0
     2     1     0     0
     0     3     1     0
     0     0     0     1

>> D

D =

     1    -2    -3     0
     0     1     0     0
     0     0     1     0
     0     0     0     1

>> A*B

ans =

     1     0     3     0
     0     1    -3     0
     0     0     1     0
     0     0     0     1

>> A*C

ans =

     5    11     3     0
     2     1     0     0
     0     3     1     0
     0     0     0     1

A*D

ans =

     1     0     0     0
     0     1     0     0
     0     0     1     0
     0     0     0     1

>> B*C

ans =

    -3    16     6     0
     2    -8    -3     0
     0     3     1     0
     0     0     0     1

since AD = I

option C) is correct

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