Counting Perpendicular Lines: Finding All Line Pairs in a Square

Question

How many pairs of perpendicular lines are there in the square below?

00:00 How many perpendiculars are there in the drawing?

00:03 All angles in the square are right angles

00:07 A perpendicular creates a right angle at the intersection point between the lines

00:13 Let's mark and count all the right angles

00:19 And this is the solution to the question

Let's remember that perpendicular lines are lines that form a right angle of 90 degrees between them.

Our right angles are:

$ABC,BCD,CDA,DAB$

The lines that form angle ABC are: AB+BC

The lines that form angle BCD are: BC+CD

The lines that form angle CDA are: CD+DA

The lines that form angle DAB are: DA+AB

Since in a rectangle we have 4 marked angles of 90 degrees, we must have 4 pairs of perpendicular lines.