let the points be A,B,C,D.
distance between points under root (x2-x1) whole square+(y2-y1)whole square
so distance of AB=under root 20
distance of BC= " " 80
" " CD= " " 20
" " DA= " " 80
THAT MEANS THAT opp sides are equal then diagonals must also be equal then
AC=10 and BD=10 as diagonals and opp sides are equal they are vertices of rectangle