History of Hindu Mathematics: A Source Book v2.c17.s14.76

v2.c17.s14.76

Thus we have, in general, if x=α, y=β be a solution of the equation $Nx² ± k = y²,$ x=α/m, y=β/m is a solution of the equation $Nx²± k/m²=y²;$ and x=na, y=nβ is a solution of the equation $Nx²± n²k=y²,$ where m, n are arbitrary rational numbers.