Let A = bmatrix 2 & -1 \ 1 & 1 bmatrix. If the sum of the diagonal elements of A13 is 3n, then n is equal to .
Answer
7
Solution
A2 = bmatrix 3 & -3 \ 3 & 0 bmatrix = 3B, where B = bmatrix 1 & -1 \ 1 & 0 bmatrix
B2 = bmatrix 0 & -1 \ 1 & -1 bmatrix, B3 = B B2 = bmatrix -1 & 0 \ 0 & -1 bmatrix = -I
A12 = (A2)6 = 36 B6 = 36 (B3)2 = 36 I
A13 = 36 A = bmatrix 2 36 & -36 \ 36 & 36 bmatrix
Sum of diagonal elements = 2 36 + 36 = 37
n = 7
Answer: 7