Explain how to calculate the area of a triangle
Lesson details
Learning outcome
I can explain how to calculate the area of a triangle.
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
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.
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.
Teacher tip
Show triangles where the base is identified but not horizontal and model rotating the triangle until the base is horizontal, then reposition again. Reinforce that it was still the base regardless of its orientation.
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.What is half of 36?
Q2.What does congruent mean?
Q3.How many of the side lengths are the same in a scalene triangle?
Q4.How do you calculate the area of a rectangle?
Q5.How do you calculate the area of a parallelogram?
Q6.15 × 14 =
Assessment exit quiz
6 Questions
Q1.Which of the dotted lines shows the perpendicular height of the triangle?
Q2.How do you calculate the area of a triangle?
Q3.Which of these show the correct formula for calculating the area of a triangle?
Q4.Calculate the area of the triangle. cm².
Q5.Calculate the area of the triangle. cm².
Q6.Calculate the area of a triangle with a base of 14 cm and a perpendicular height of 9 cm. cm².
To help you plan your 6 maths lesson on: Explain how to calculate the area of a triangle, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your 6 maths lesson on: Explain how to calculate the area of a triangle, download all teaching resources for free and adapt to suit your pupils' needs.
The starter quiz will activate and check your pupils' prior knowledge, with versions available both with and without answers in PDF format.
We use learning cycles to break down learning into key concepts or ideas linked to the learning outcome. Each learning cycle features explanations with checks for understanding and practice tasks with feedback. All of this is found in our slide decks, ready for you to download and edit. The practice tasks are also available as printable worksheets and some lessons have additional materials with extra material you might need for teaching the lesson.
The assessment exit quiz will test your pupils' understanding of the key learning points.
Our video is a tool for planning, showing how other teachers might teach the lesson, offering helpful tips, modelled explanations and inspiration for your own delivery in the classroom. Plus, you can set it as homework or revision for pupils and keep their learning on track by sharing an online pupil version of this lesson.
Explore more key stage 2 maths lessons from the Area, perimeter, position and direction unit, dive into the full primary maths curriculum, or learn more about lesson planning.