For all integers n \geq 1, which of the following is divisible by 9?
(a) 8^n+1
(b) 4^n-3n-1
(c) 3^2^n+3n+1
(d) 10^n+1
(a) 8^n+1
(b) 4^n-3n-1
(c) 3^2^n+3n+1
(d) 10^n+1
The easiest way I think is to put the lowest value of n to see which one doesn't satisfy the criteria.
If you put n = 1, you can then eliminate (c) and (d)
for n = 2, you can eliminate (a)
Only option left is (b) which should be the answer.
