Parallel and Intersecting Lines
Perpendicular lines
Find out whether two crossing lines can make four equal angles.
Can you draw two crossing lines so that all four angles are equal? What would each angle be?
Use the linear pair rule. Two side-by-side angles add to 180°. If they are equal, each is half of 180°, which is 90°: a right angle.
Or think of the whole turn: the four angles together go all the way round, 360°. Four equal parts: 360° ÷ 4 = 90°.
Two lines that cross at right angles (90°) are called perpendicular lines. We say l is perpendicular to m.
In drawings, a right angle is shown with a tiny square in the corner, instead of writing 90°. Look out for it.
Perpendicular lines are everywhere: the two edges at a corner of a page, the corner of a table, where a wall meets the floor.
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