They are perpendicular.
For example, if we have the point E (1, 2) and E' (2, 1)
we can get the slope as follows
m' = (yE' - yE) / (xE' - xE)
⇒ m' = (1 - 2)/(2 - 1) = -1 / 1 = -1
Now we have the slope of the line y = x, which is m = 1
we can apply
m*m' = (1)*(-1) = - 1
we can say that they are perpendicular.
They are perpendicular. Not sure.
the correct answer is that they are perpendicular.