The answer is not necessarily 0.

Even though one of the terms will be (x-x) which is 0, and the product of any number multiplied by 0 is 0, there is the case in which one of the terms may not be an actual number, per se, but may be undefined? In such a case, despite the existence of one of the terms being equal to 0, the product itself will be undefined.  Suppose, for example, that a is given as 10/9, b = 9/8, c = 8/7, etc. In this sequence x then would be -13/-14, which is the same as 13/14, and (x - x) would be (13/14 - 13/14) which is 0. Yet the tenth term, (j - x), will be (1/0 - 13/14), which is undefined.