Right Angles, Squares and Rectangles
Primary 1 · Mathematics
Right Angles, Squares and Rectangles
Lesson 1 of 5
12 min
Let's begin
Uwase sits at her desk. The classroom door stands open.
She looks at the corner of the door frame. It looks like the corner of her exercise book.
Are they really the same? Today you will test corners with your own hands.
Take two straight sticks. Lay them on the floor.
Let one end of each stick touch. That meeting place is a corner.
Another name for a corner is an angle.
Now move one stick slowly. The corner gets wider. Move it back. The corner gets narrower.
One special corner has its own name. It is the right angle.
Pick up your exercise book. Look at one corner of the cover.
That corner is a right angle. People also call it a square corner.
Your book is now your tester. Take it with you.
Here is the test. Do it the same way every time.
Step 1 Hold the corner of your book into the corner you want to test.
Step 2 Push it in gently.
Step 3 Look for a gap.
No gap at all? It is a right angle.
A gap? It is not a right angle.
Careful! Do not look at a corner and guess. Some corners look square but open a little too wide. Your book knows the truth.
A wide corner lets your book slip in. It leaves a gap.
A narrow corner is too small. Your book will not go in at all.
| Corner | Right angle? |
|---|---|
| Corner of the door frame | yes |
| Corner of a window | yes |
| Where the wall meets the floor | yes |
| The sharp point of a pencil | no, too narrow |
| A book lying half open | no, too wide |
Turn your exercise book around. Test the same door corner again.
It still fits with no gap. It is still a right angle.
A right angle can lie on its side. It is still a right angle.
When you find a right angle, draw a tiny square inside the corner.
That small square says: I tested this one. It is a right angle.
A short look at right angles.
Tip
No gap means right angle
Your book corner goes everywhere with you.
Push it in. Look for light in the gap. No gap, no doubt.
Do each one, then tap Show answer to check.
Test the corner of your desk with your book. Is it a right angle?
Answer: yes on most desks. The book corner fits with no gap.
A corner is very wide. Your book leaves a big gap. Is it a right angle?
Answer: no. A gap means it is not a right angle.
You turn a right angle on its side. Is it still a right angle?
Answer: yes. Turning never changes a right angle.
Which one has a right angle? A window corner, or a pencil point?
Answer: the window. The pencil point is far too narrow.
Walk around your home. Find 3 right angles and test each one.
Answer: a door frame, a window, the top of a table all work.
What you learned today
Quick check
You push your book into a corner. No gap. It is...
