Ugh, I shouldn't try and post at stupidly late hours. In case you're still reading, in the first paragraph x is NOT also a function of y, as x = +- sqrt(5/y), a

Ugh, I shouldn't try and post at stupidly late hours. In case you're still reading, in the first paragraph x is NOT also a function of y, as x = +- sqrt(5/y), and we have the choice of signs to deal with. The rest is ok.