Starter quiz
- What is the sum of internal angles of a triangle?
- '180' ✓
- Which of these is a property of an isosceles triangle?
- All angles are always equal
- Two angles are always equal ✓
- All sides are different lengths
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- Which of these is a property of a right angled triangle?
- ✓
- All sides are equal in length
- They cannot be isosceles.
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- What are the sizes of the internal angles of a regular triangle?
- 60ᵒ ✓
- 50ᵒ
- 90ᵒ
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What type of triangle is this?- Scalene ✓
- Right angled
- Equilateral
- Isosceles
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- Match the angle types
- Acute⇔< 90ᵒ ✓
- Right angle⇔90ᵒ ✓
- Obtuse⇔>90ᵒ and <180ᵒ ✓
- Reflex⇔>180ᵒ ✓
- Straight line⇔180ᵒ ✓
Exit quiz
Which of the following statements is true for these triangles?- The triangles are similar. ✓
- The triangles are not similar.
- It is not possible to know whether the triangles are similar or not.
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For this pair of triangles, can you determine whether they are similar without using side lengths?- Yes, because their three angles correspond. ✓
- No because you only know two angles.
- No, because you always need a side and two angles.
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Would a triangle ABC with sides AB = 8cm, BC = 6cm, AC = 10cm be similar to the one shown in the diagram?- Yes ✓
- No
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- Which of these statements accurately describes mathematical similarity in shapes?
- Their only difference is their angles. Their sides are in the same proportions.
- Their only difference is their size. Their sides are in the same proportions. ✓
- Their only difference is their sides. Their area is exactly the same.
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- Which statement is true?
- A triangle with the same perimeter as the one shown would always be similar.
- A triangle with the same area as the one shown would always be similar.
- A triangle with the same area as the one shown would not always be similar. ✓
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What is the value of ?- 1 ✓
- 1.5
- 2
- 2.5
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- An enlargement means a change in size.
- The lengths of the lines may change when enlarged.
- The angles inside an object do not change when enlarged.
- When an object is enlarged, the image is similar.
Common misconception
You need to know all the lengths or all of the angles in a pair of triangles to know that they are similar.
Remind pupils that they do not necessarily need to know all of the length and angles to determine whether two triangles are congruent, so they don't all need to be known to determine similarity.
Keywords
Similar - Two shapes are similar if the only difference between them is their size. Their side lengths are in the same proportions.
Enlargement - Enlargement is a transformation that causes a change of size.
Scale factor - Scale factor is the multiplier between similar shapes that describes how large one shape is compared to the other.
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