The extremities of the diagonal of a square are (1,1) & (-1,-1).Obtain two vertices and equation of diagonal.

Question

$\begin{array}{1 1}(a)\;(-1,1),(1,-1),y=-x\\(b)\;(1,1),(1,1),y=x\\(c)\;(-2,1),(1,-2),y=-2x\\(d)\;(2,1),(1,-2),y=-3x\end{array}$