We have, (−4,5) is one vertex of the square and equation of diagonal is 7x−y+8. Diagonals of square are perpendicular to each other ∴ Equation of other diagonal which is perpendicular to 7x−y+8=0 is x+7y=λ It passes through (−4,5) ∴ −4+35=λ⇒λ=31 Hence, equation of diagonal is, x+7y=31