Myths about teaching can hold you back
- Year 8
Constructing triangles
I can use intersecting circles to construct triangles from given lengths.
- Year 8
Constructing triangles
I can use intersecting circles to construct triangles from given lengths.
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Lesson details
Key learning points
- A construction is an accurate drawing made using geometrical properties.
- A scalene triangle can be constructed using intersecting circles with different radii.
- An equilateral triangle can be constructed using intersecting circles with equal radii.
- An isosceles triangle can be constructed using intersecting circles.
Keywords
Scalene triangle - Scalene triangles have three different-sized angles and three edges of different lengths.
Isosceles triangle - Isosceles triangles have two equal-sized angles. Two of the edges are equal in length.
Equilateral triangle - Equilateral triangles have three equal-sized angles and three edges of equal length. They are regular triangles.
Radius - The radius is any line segment that joins the centre of a circle to any point on its circumference.
Common misconception
Pupils may avoid using the pair of compasses and opt for a ruler instead.
Emphasise the efficiency and accuracy of using compasses instead of a ruler in the construction of their triangles.
To help you plan your year 8 maths lesson on: Constructing triangles, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 8 maths lesson on: Constructing triangles, 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.
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Explore more key stage 3 maths lessons from the Constructions unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
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Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.Match the angle size to the type of angle.
$$12^\circ$$ -Â
acute angle
$$90^\circ$$ -Â
right angle
$$138^\circ$$ -Â
obtuse angle
$$305^\circ$$ -Â
reflex angle
Q2.Which of these sketched triangles are definitely isosceles?
Q3.Lucas has used a centimetre ruler to draw a line of 8.2 cm. Which image shows his line?
Q4.Which of these shows the best set up of a pair of compasses?
Q5.An arc of a circle is part of the circle’s .
Q6.A triangle has a perimeter of 65 mm. Two of the edges are 23 mm and 26 mm respectively. How long is the third edge of the triangle?
Assessment exit quiz
6 Questions
Q1.Which description matches this sketch?
Q2.When constructing a triangle from three edge lengths, we use a pair of compasses to draw circles.
Q3.Which of the following shows a partial construction of an equilateral triangle?
Q4.Which of the following lengths could be the edge lengths of a triangle?
Q5.Which of the points C, D or E when connected to AB would create a triangle with three edges of different lengths?
Q6.Triangle ABE is an triangle.