What are the possible values of K? (1 Viewer)

[fabl]

y= 2x+1 , y=2x -1 , y =3-1/2x , y =k-1/2x

What are the possible values of K if the lines enclose a square?

 

[braintic]

I can do this, but only in a very messy way.
To assist me in finding a neat method, can you tell me what exercise this came under.
Was it perpendicular distance, k-method, properties of quadrilaterals, .......... ?

 

[fabl]

The overall heading of the exercise is gradients of intervals and lines. This chapter covers the perpendicular distance.

It hints saying that the distance between two intercepts of one pair of lines must equal the distance between the y inc on other pair?