The distance from (x, y) to (-1, 0) is and the distance from (x, y) to (1, 0) is / Saying that the product of those two distances is equal to 1 means that .
That means that
I don't see how you can get your formula from that. It is, in any case, NOT "a curve in ". It is, just as the problem says, a subset of , not .