Find the product of all x such that the expression (x^2 - 4)/(x^2 - 1) is undefined.
It's undefined when x^2 -1 = 0
So
x^2 -1 = ( x - 1) (x + 1) = 0
Setting both factors = 0 and solving for x produces x = 1 or x = -1
The product of these = 1 * -1 = -1
