Starter quiz
- What is half of 36?
- '18' ✓
- What does congruent mean?
- Exactly the same size and shape. ✓
- Completely different in all ways.
- Exactly the same shape but smaller or bigger.
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- How many of the side lengths are the same in a scalene triangle?
- '0' ✓
- How do you calculate the area of a rectangle?
- Base × perpendicular height ✓
- Base + perpendicular height
- Length × width ✓
- Add the side lengths together.
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- How do you calculate the area of a parallelogram?
- Base × perpendicular height ✓
- Base + perpendicular height
- Length × width
- Add the side lengths together.
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- 15 × 14 = ______
- '210' ✓
Exit quiz
Which of the dotted lines shows the perpendicular height of the triangle?- Line a ✓
- Line b
- Line c ✓
- Line d ✓
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- How do you calculate the area of a triangle?
- Multiply the base by the perpendicular height.
- Multiply the base by the perpendicular height and halve it. ✓
- Multiply the base by the perpendicular height and double it.
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- Which of these show the correct formula for calculating the area of a triangle?
- Area = base + perpendicular height × 2
- Area = base × perpendicular height ÷ 2 ✓
- Area = perpendicular height × base ÷ 2 ✓
- Area = base ÷ perpendicular height × 2
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Calculate the area of the triangle. ______ cm².- '10' ✓
Calculate the area of the triangle. ______ cm².- '42' ✓
- Calculate the area of a triangle with a base of 14 cm and a perpendicular height of 9 cm. ______ cm².
- '63' ✓
Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- The area of a triangle is half the area of a parallelogram with same base and perpendicular height.
- The area of a triangle can be calculated using the formula area = base × perpendicular height ÷ 2
Common misconception
Pupils often over-generalise the word 'base' and do not recognise that the base is not always horizontal or the 'bottom' part of the shape.
Take time to identify that the base is related to the perpendicular height and show that one triangle can have a different base dependent on where the measurement is taken from. Pupils should consider efficiency when selecting a base.
Keywords
Parallelogram - A parallelogram is a quadrilateral with two pairs of parallel and equal sides.
Base - The base is the side which is perpendicular to the shape’s height.
Perpendicular - Two lines are perpendicular if they meet at a right angle.
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