I think it’s a because the other ones don’t make sense
Covert the problem into and equation using formulas
@Konrad509's answer was fantastic.
What you first need to know is this. 3 consecutive natural numbers multiplied by each other, for instance: (1*2*3) or (2*3*4) or (3*4*5) or (4*5*(2*3)) can be described using the abstract expression:
(n-1)n(n+1)
-------------
Now:
A=n(n²+11),
and:
n(n²+11)
=n(n²-1+12)
=n³-n+12n
=n(n²-1)+12n
=n(n+1)(n-1)+12n
=(n-1)n(n+1)+(4*3)n
-------------------------
So:
A=(n-1)n(n+1)+(4*3)n
Therefore, A is divisible by 3.
