What are some real world examples of perpindicula r lines?

Answer 1

-- Look around. You'll see a pair of them at every place on the floor

of your room where two edges of the floor meet.

-- At the same places, you'll also see a vertical line ... where two walls meet ...

that's perpendicular to both edges of the floor that meet there.

So, just in the room where you're sitting now, there are 12 pairs of perpendicular lines

at the 4 corners of the floor.

And another 12 pairs at the 4 corners of the ceiling.

Is that real enough for you ?