Yes. Take a look at the corner of your room,where two walls meet the floor.
No, never. Perpendicular lines cross each other at right angles. To be parallel two lines must never cross each other.
Two lines are perpendicular when the cross product of their director vectors is equal to one. Example A = (1,0,0) B= (0,1,0) A x B = 1 then A is perpendicular to B
yes but they have to meet at a 90 degree angle to be perpendicular.
Form right angles