If X = bmatrix x \ y \ z bmatrix is a solution of the system of equations AX = B, where adj A = bmatrix 4 & 2 & 2 \ -5 & 0 & 5 \ 1 & -2 & 3 bmatrix and B = bmatrix 4 \ 0 \ 2 bmatrix, then |x + y + z| is equal to :
- 3
- 2
- 32
- 1
Answer
(2) 2
Solution
|adj A| = 4(0 + 10) - 2(-15 - 5) + 2(10 - 0) = 40 + 40 + 20 = 100
|adj A| = |A|2 |A| = 10
X = A-1B = 1|A|(adj A)B
(adj A)B = bmatrix 16 + 0 + 4 \ -20 + 0 + 10 \ 4 + 0 + 6 bmatrix = bmatrix 20 \ -10 \ 10 bmatrix
x + y + z = 20 - 10 + 10 10 = 2
|x + y + z| = 2
Answer: (2)