The question is:

For all positive integers x, let x▲ be defined to be (x-1)(x+1). Which of the following is equal to 6▲-5▲?

A) 2▲ +1▲

B) 3▲+2▲

C) 4▲+3▲

D) 5▲+4▲

E) 6▲+5▲

I was under the impression that if I substituted (x-1)(x+1) for ▲ and worked the problem, I could come up with the answer, but I must be missing something. I am aware that the minus sign in the original problem is the subtraction of a binomial, but that did not help.