New
New
Year 3

Investigate the shapes made when rectangles are cut on the diagonal

I can describe the shapes made when rectangles are cut on the diagonal.

New
New
Year 3

Investigate the shapes made when rectangles are cut on the diagonal

I can describe the shapes made when rectangles are cut on the diagonal.

Lesson details

Key learning points

  1. An angle can be exactly a right angle.
  2. An angle can be less than or greater than a right angle.
  3. When you cut a square using two diagonal lines, you get four identical triangles.
  4. 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.

Encourage pupils to draw as accurately as possible. They can also cut out shapes to check that they are the same shape and size. Ask questions that allow pupils to make generalisations (e.g. when you divide squares using two diagonal lines, you get 4 right-angled triangles.)
Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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6 Questions

Q1.
Which of these shapes are rectangles?
An image in a quiz
Correct answer: a
Correct answer: b
c
Correct answer: d
Q2.
Which of these shapes are squares?
An image in a quiz
a
Correct answer: b
c
Correct answer: d
Q3.
Why is this shape not a rectangle?
An image in a quiz
It does not have 4 straight sides.
It does not have any sides of equal length.
Correct answer: It does not have 4 right angles.
It is not a quadrilateral.
Q4.
Match the description to the type of shape.
Correct Answer:Rectangle ,A four-sided polygon with 4 right angles.

A four-sided polygon with 4 right angles.

Correct Answer:Quadrilateral,Any four-sided polygon.

Any four-sided polygon.

Correct Answer:Square,A four-sided polygon with 4 right angles and 4 equal sides.

A four-sided polygon with 4 right angles and 4 equal sides.

Q5.
5. Match each line to the correct name.
An image in a quiz
Correct Answer:a,diagonal

diagonal

Correct Answer:b,vertical

vertical

Correct Answer:c,horizontal

horizontal

Q6.
Look at this pattern. How many rectangles are there altogether?
An image in a quiz
Correct Answer: 9

6 Questions

Q1.
Aisha cuts this rectangle in half using a vertical line. What shape will both halves be?
An image in a quiz
Squares
Correct answer: Rectangles
Triangles
Q2.
Aisha cuts this rectangle in half using a diagonal line. What shapes will both halves be?
An image in a quiz
Squares
Rectangles
Correct answer: Triangles
Q3.
Aisha cuts this square into two triangles using one diagonal line. Which of these statements is true?
An image in a quiz
Correct answer: Both triangles have one right angle.
One triangle is larger than the other.
Correct answer: Both triangles have two sides of equal length.
Q4.
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?
An image in a quiz
Correct Answer: 4, Four
Q5.
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?
An image in a quiz
Correct Answer: 2, Two
Q6.
Which statements are always true? When you make two diagonal cuts through any rectangle…
Correct answer: …each triangle will have at least two sides the same length.
…all of the triangles are identical.
Correct answer: …you always end up with four triangles.
…all of the triangles will have right angles.

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