Carcass wrote:
If x is not equal to 1 and \(y = \frac{1}{x−1}\), then which one of the following cannot be the value of y ?
(A) 0 
(B) 1 
(C) 2 
(D) 3 
(E) 4
We might first recognize that, 
if a/b = 0, then it MUST be the case that a = 0ASIDE: Some students may believe that, if a/b = 0, then it could also be the case that b = 0. This, however, is not true. 
A fraction with zero in the denominator is undefined (e.g., 3/0 is undefined), which means it does not evaluate to be an actual number. 
Given all of this, we can see that \(\frac{1}{x−1}\) can never equal zero. 
Answer: A
If you're not convinced, let's see what happens when y = 0
We get: \(0 = \frac{1}{x−1}\)
Multiply both sides by \((x-1)\) to get: \(0 = 1\)
This makes no sense!!
Answer: STILL A!
Cheers, 
Brent