Question

Are two lines with the same slope and different y-intercepts always, sometimes, or never perpendicular?

Answer 1

They are never perpendicular. They will be parallel and will never meet!  

Answer 2

Never perpendicular

Explanation:

Two lines with the same slope and different y-intercepts on the Cartesian Plane, behave like that graph below. Since they do not form a 90º angle and do not have any common point, then they are neither perpendicular nor concurrent. So these are parallel lines.

Notice that parallel lines share the value for the slope. In this case, m=3