# The rings \$ F[x,y]/ (y^{2} – x) \$ and \$F[x,y]/( y^{2} – x^{2}) \$ for any field F

The rings $$F(x,y)/ (y^{2} – x)$$ and $$F(x,y)/( y^{2} – x^{2})$$ are not isomorphic for any field F.