Do we know anything about the angle between y and x?
Lines y and z are parallel if x ⊥ y.
Practice makes perfect
In this case, we know that z and x are perpendicular.
However, we know nothing about the relation between the lines y and x. We need to know the angle between y and x as well in order to say that y and z are parallel by the Lines Perpendicular to a Transversal Theorem. Therefore, we should modify the statement to be as follows.
Lines y and z are parallel if x ⊥ y.
