Consider the diagram. Planes M and N intersect at line d. Lines a, b, and e are on plane M. Line a is vertical and forms a right angle with line d. Line b is diagonal and goes up and to the right. Line e is at the top of the plane and is close to being horizontal. Line c is on plane N and is goes slightly up and to the right. Lines e and c can be described as intersecting. parallel. perpendicular. skew.