27
Parallel and perpendicular lines
Textbook: Part 1, lesson 27, pp. 84–86
GoalRecognise parallel and perpendicular lines and know their properties.
New words
parallel · parallelperpendicular · perpendikularintersect · kesishadiright angle · to‘g‘ri burchak
Explanation
Parallel lines never meet and the distance between them is the same everywhere. We write a ∥ b. Perpendicular lines cross at a right angle (90°). We write a ⊥ b. In a rectangle the opposite sides are parallel and the adjacent sides are perpendicular.
Worked examples
In rectangle ABCD, AB ∥ CD and BC ∥ AD; AB ⊥ BC.
The ruled lines of a notebook are parallel to each other, and the margin line is perpendicular to them.
Class activity
“Lines in the classroom”: children find parallel and perpendicular lines in the room (window, board and desk edges) and test right angles with a set square or a folded sheet of paper.
Practice
1
How many pairs of parallel sides does a rectangle have?
2
2
At how many corners of a square do perpendicular sides meet?
4
3
a ⊥ c and b ⊥ c (in one plane). How are the lines a and b placed relative to each other?
Parallel
4
A rectangle measures 12 cm by 5 cm. How many cm apart are the two long sides?
5