\( x^2 + xy = n-y \) quadr. Erg.
\( x^2 + xy + \frac{y^2}{4} = n-y + \frac{y^2}{4} \)
\( (x + \frac{y}{2})^2 = n-y + \frac{y^2}{4} \)
\( x + \frac{y}{2} = \sqrt { n-y + \frac{y^2}{4} } \)
oder \( x + \frac{y}{2} = -\sqrt { n-y + \frac{y^2}{4} } \)
==>
\( x = - \frac{y}{2} + \sqrt { n-y + \frac{y^2}{4} } \)
oder \( x = - \frac{y}{2} -\sqrt { n-y + \frac{y^2}{4} } \)