Legendre's equation

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In mathematics, Legendre's equation is the Diophantine equation

ax^2+by^2+cz^2=0.

The equation is named for Adrien Marie Legendre who proved in 1785 that it is solvable in integers x, y, z, not all zero, if and only if −bc, −ca and −ab are quadratic residues modulo a, b and c, respectively, where a, b, c are nonzero, square-free, pairwise relatively prime integers, not all positive or all negative .

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