E556  De criteriis aequationis \(fxx + gyy = hz^2\), utrum ea resolutionem admittat nec ne?
(On the criteria of whether equation \(fxx + gyy = hz^2\) admits a resolution or not)
Summary:
Euler's motivating example is that \(xx + yy = 2zz\) has solutions but that \(xx + yy = 3zz\) has no solutions. The question is, what values of those letters \(f\), \(g\) and \(h\) give equations that have solutions? He shows, given an \(f\), a \(g\) and three values of \(h\) for which there are solutions, how to construct a fourth value of \(h\), and calls it (section 12) a "most elegant theorem."
According to the records, it was presented to the St. Petersburg Academy on December 7, 1772.
Publication:

Originally published in Opuscula Analytica 1, 1862, pp. 211241

Opera Omnia: Series 1, Volume 4, pp. 1  24
 Reprinted in Commentat. arithm. 2, 1849, pp. 556569 [E556a]
Documents Available:
 Original Publication: E556
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