Grade 1 · Maths · Lessons
What makes a triangle
🔺triangle⬜not a triangle🔄turned📐3 sides
Triangles.The big ideaThree straight sides, closed all round. Colour, size and tilt don't matter.
How it works
A triangle has three straight sides and is closed all round.
Colour, size and tilt don't matter.
If it has a gap or a curve, it is not a triangle.
Example 1: Check the sides
- Count the sides: 3 straight sides.
- Check it is closed with no gaps.
- It is a triangle.
Example 2: A gap
- A shape has 3 sides but one side has a gap.
- It is not closed all round.
- It is not a triangle.
Example 3: Bigger or turned
- Make a triangle bigger, or turn it on its side.
- It still has 3 straight sides.
- It is still a triangle.
Words to know
- triangle
- A shape with 3 straight sides.
- side
- A straight edge of a shape.
Watch out
- Count the sides and check they are straight.
- A turned triangle is still a triangle.
- A round corner means it is not a triangle.
Try it
- How many sides does a triangle have?
- Is a triangle still a triangle when it is turned?
- Is a shape with a curved side a triangle?
- Is a shape with a gap in it a triangle?
Answers: 1. 3 · 2. yes · 3. no · 4. no
For grown-upsHunt for triangles at home: a slice of pizza, a sandwich cut corner to corner, a road sign.