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.
Equipment
Pair of compasses, ruler, protractor.
Licence
Starter quiz
6 Questions
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Angle AOB -
45°
Angle BOD -
135°
Angle COD -
90°
Reflex angle BOD -
225°
Reflex angle BOC -
315°
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Exit quiz
6 Questions
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AB -
6.4 cm
CA -
7.2 cm
BD -
9.1 cm