vertices -3,1 1,4 4,0 0,-3 ABCD are these vertices of a square

ryan15

you can just plot these points on a piece of paper by your common sense and check whether it forms a square by applying the distance formula

sqroot of ((y2-y1)(y2-y1) + (x2-x1)(x2-x1)

and check if they are equal or not and also it will be visibly clear from the diagram that sides are perpendicular or not.