Constructing a triangle given three side lengths using compasses
I can construct a triangle given the three required side lengths.
Constructing a triangle given three side lengths using compasses
I can construct a triangle given the three required side lengths.
These resources will be removed by end of Summer Term 2025.
Lesson details
Key learning points
- The first side can be drawn accurately with a ruler
- A pair of compasses should be used to indicate potential positions for the other sides, by drawing arcs
- Where the two remaining sides intersect is where the two sides should be drawn to
- All triangles with the same measurements are congruent
Keywords
Pair of compasses - A pair of compasses is a tool which can be used to draw circles and arcs. A pair of compasses is sometimes referred to just as a compass.
Radius - The radius is any line segment that joins the centre of a circle to any point on its circumference.
Congruent - If one shape can fit exactly on top of another using rotation, reflection or translation, then the shapes are congruent.
Arc - An arc is part of a curve. An arc of a circle is part of the circle’s circumference.
Common misconception
Pupils may try to draw the triangle using only a pencil and ruler, rather than construct it using a pair of compasses.
Remind pupils that if the task is to 'construct' then they must use their geometry equipment.
To help you plan your year 11 maths lesson on: Constructing a triangle given three side lengths using compasses, download all teaching resources for free and adapt to suit your pupils' needs...
To help you plan your year 11 maths lesson on: Constructing a triangle given three side lengths using compasses, 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 4 maths lessons from the Loci and construction unit, dive into the full secondary maths curriculum, or learn more about lesson planning.
Equipment
Pair of compasses, ruler, protractor.
Licence
Starter quiz
6 Questions


Angle AOB -
45°
Angle BOD -
135°
Angle COD -
90°
Reflex angle BOD -
225°
Reflex angle BOC -
315°



Exit quiz
6 Questions




AB -
6.4 cm
CA -
7.2 cm
BD -
9.1 cm