Right Angles, Squares and Rectangles
Primary 1 · Mathematics
Right Angles, Squares and Rectangles
Lesson 2 of 5
12 min
Let's begin
Mugisha is drawing his house in his exercise book.
He draws the door by eye. One corner comes out wide, like an open book.
His door leans over. Today you will draw corners that stand up straight.
A set square is a flat piece of plastic. It has a square corner in it.
Put your book corner against that corner. No gap. It is a true right angle.
The set square keeps the corner for you. Your hand cannot keep it.
Careful! Do not draw a corner by eye. It comes out nearly square, and nearly is not enough.
Do these four steps in this order, every time.
Step 1 Lay the set square flat on your page.
Step 2 Hold it down hard with one hand.
Step 3 Draw a line along one edge.
Step 4 Do not move it. Now draw a line along the other edge.
The two lines meet. You have drawn a right angle.
Careful! Most wrong corners come from a set square that slipped. Keep that hand pressing down until both lines are drawn.
Lift the set square off. Take your exercise book.
Push the book corner into the corner you drew.
No gap? Good work. Draw a tiny square inside the corner.
A gap? Rub it out and draw it again. Everyone does this.
You can make a right angle from any plain paper.
Step 1 Fold the paper once, any way you like. Press the fold flat.
Step 2 Fold it again. Lay the first fold exactly on top of itself.
Step 3 Press it flat and open it a little.
The corner where the two folds meet is a right angle.
Test it on your book corner. No gap!
Now hold the folded paper still and draw along both folds. That works just like a set square.
One hand holds the set square. The other hand draws.
No set square? Fold a square corner from paper.
Tip
Hold it still. Then draw twice
One hand presses. The other hand draws.
If the set square moves between your two lines, the corner is spoiled. Start again.
Get a pencil and your book. Then tap Show answer to check.
Which tool has a right angle in it: a set square or a rope?
Answer: the set square. A rope bends any way it likes.
How many lines do you draw to make one right angle?
Answer: 2. One along each edge of the set square.
Fold a plain paper twice to make a square corner. How many folds?
Answer: 2. The second fold lies on top of the first one.
You drew a corner. Your book corner leaves a gap. What went wrong?
Answer: the corner is too wide. The set square slipped, or you drew by eye.
Draw a right angle. Test it. Mark it with a small square.
Answer: no gap means you did it. If there is a gap, draw it again.
What you learned today
Quick check
Which tool has a right angle in it?
