Let the matrix A = bmatrix 1 & 0 & 0 \ 1 & 0 & 1 \ 0 & 1 & 0 bmatrix satisfy An = An-2 + A2 - I for n 3. Then the sum of all the elements of A50 is :
- 44
- 39
- 52
- 53
Answer
(4) 53
Solution
An - An-2 = A2 - I for n 3
Putting n = 50, 48, , 4 (24 equations) and adding:
A50 - A2 = 24(A2 - I)
A50 = 25A2 - 24I
A2 = bmatrix 1 & 0 & 0 \ 1 & 0 & 1 \ 0 & 1 & 0 bmatrix bmatrix 1 & 0 & 0 \ 1 & 0 & 1 \ 0 & 1 & 0 bmatrix = bmatrix 1 & 0 & 0 \ 1 & 1 & 0 \ 1 & 0 & 1 bmatrix
Sum of elements of A2 = 5; sum of elements of I = 3
Sum of elements of A50 = 25 5 - 24 3 = 125 - 72 = 53
Answer: (4)