This equation tells us that the hydronium ion concentration will be the same as the nominal concentration of a strong acid as long as the solution is not very dilute. As the acid concentration falls below about 10–6 M, however, the second term predominates; [H+] approaches √Kw, or 10–7 M. The hydronium ion concentration can of course never fall below this value; no amount of dilution can make the solution alkaline!
Notice that Eq 6 is a quadratic equation; in regular polynomial form it would be