Let \(\begin{array}{l}A+2B=\begin{bmatrix} 1&2 &0 \\ 6&-3 &3 \\ -5&3 &1 \end{bmatrix}\end{array} \) and \(\begin{array}{l}2A-B=\begin{bmatrix} 2&-1 &5 \\ 2&-1 &6 \\ 0&1 &2 \end{bmatrix}\end{array} \). If Tr(A) denotes the sum of all diagonal elements of the matrix A, then Tr(A) – Tr(B) has value equal to:
a. 0
b. 1
c. 3
d. 2
Solution:
Answer: (d)
tr (A + 2B) ≡ tr (A) + 2 tr (B) = –1 …..(1)
and tr (2A – B) ≡ 2tr (A) – tr (B) = 3 …..(2)
On solving (1) and (2) we get
tr (A) = 1, tr(B) = –1
tr (A) – tr(B) = 1 + 1 = 2