In Egyptian mythology, Hatmehit was a fish-goddess, wife of Banebdjetet and mother of Har-pa-khered. The center of her cult was in Mendes.
Alternative: Hatmehyt
... on x) to the expression to the left of "=", that will make it a perfect square trinomial of the form x2 + 2xy + y2. Since "2xy" in this case is (b/a)x, we must have y = ...