Investigate the shapes made when rectangles are cut on the diagonal | Maths

Starter quiz

Which of these shapes are rectangles?
- a ✓
- b ✓
- c
- d ✓
Which of these shapes are squares?
- a
- b ✓
- c
- d ✓
Why is this shape not a rectangle?
- It does not have 4 straight sides.
- It does not have any sides of equal length.
- It does not have 4 right angles. ✓
- It is not a quadrilateral.
Match the description to the type of shape.
- Rectangle
  
  ⇔
  
  A four-sided polygon with 4 right angles. ✓
- Quadrilateral
  
  ⇔
  
  Any four-sided polygon. ✓
- Square
  
  ⇔
  
  A four-sided polygon with 4 right angles and 4 equal sides. ✓
5. Match each line to the correct name.
- a
  
  ⇔
  
  diagonal ✓
- b
  
  ⇔
  
  vertical ✓
- c
  
  ⇔
  
  horizontal ✓
Look at this pattern. How many rectangles are there altogether?
- '9' ✓

Exit quiz

Aisha cuts this rectangle in half using a vertical line. What shape will both halves be?
- Squares
- Rectangles ✓
- Triangles
Aisha cuts this rectangle in half using a diagonal line. What shapes will both halves be?
- Squares
- Rectangles
- Triangles ✓
Aisha cuts this square into two triangles using one diagonal line. Which of these statements is true?
- Both triangles have one right angle. ✓
- One triangle is larger than the other.
- Both triangles have two sides of equal length. ✓
Laura uses two diagonal lines, cutting from each vertex at the top of the square to each at the bottom. How many triangles would the rectangle be cut up into?
- '4' ✓
Aisha cuts a rectangle into four triangles. This is one of the triangles. How many angles inside the shape are smaller than a right angle?
- '2' ✓
Which statements are always true? When you make two diagonal cuts through any rectangle…
- …each triangle will have at least two sides the same length. ✓
- …all of the triangles are identical.
- …you always end up with four triangles. ✓
- …all of the triangles will have right angles.

Worksheet

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Presentation

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Lesson Details

Key learning points

An angle can be exactly a right angle.
An angle can be less than or greater than a right angle.
When you cut a square using two diagonal lines, you get four identical triangles.
When you cut a rectangle that is not a square using two diagonal lines, you get two pairs of identical triangles.

Common misconception

Pupils may find it hard to recognise when an angle is greater than a right angle.

You can model this by trying to move the obtuse angle (though pupils don't need to know the term yet) within a right angle checker. They should be able to see that it is too large to fit.

Keywords

Diagonal - A straight line connecting one vertex to another, but is not the side or edge.