If (-4, 5) is one vertex and 7x-y+8=0 is one diagonal of a square, then the equation of the second diagonal is

Let A (-4,  5) and  Equation BD  is  7x –y + 8=0

Slope of BD = -7/-1 = 7

m= Slope of AC = -1/Slope of BD = -1/7

$\begin{array}{l}\therefore Equationof\overline{AC}isy-5=\frac{-1}{7}\left(x+4\right)\\ \Rightarrow 7y-35=-x-4\\ \Rightarrow x+7y-31=0\end{array}$