Pragmatist engineers will say that y/y is always equal to 1, so x(y/y) will always equal x.

Mathematicians will say that such reasoning has been known to lead to contradictory conclusions, and the form (y/y) is always equal to 1, except when y=0, inwhich case it is indeterminate.

You need to choose which universe you live in, and how paranoid you have to be.