Constructing Triangles: SSS, SAS and AAS — Interactive Lesson (Ages 11–14)

☆☆☆☆☆ Add your review • Year 7–9 • 🎓 Interactive Lesson & Activities

A 31-slide interactive KS3 lesson on constructing triangles with a ruler, compasses and protractor, covering equilateral, SSS, SAS and AAS constructions.

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Can your students build a triangle from three lengths? This 31-slide interactive lesson guides them step by step through constructing triangles with a ruler, compasses and protractor.

Mastering Constructing Triangles in Year 7–9 Maths

Students begin with a starter on finding missing angles, then learn to construct an equilateral triangle using arcs. They construct triangles given three sides (SSS), such as 8 cm, 7 cm and 6 cm, and discover that the two shorter sides must add up to more than the longest. They go on to constructions from two angles and a side (AAS), and from two sides and an angle (SAS), then measure the results.

What’s Included

31-slide interactive lesson on constructing triangles
Step-by-step equilateral and SSS constructions with a compass
AAS and SAS constructions with a protractor
A possible-or-not question on the triangle inequality
Practice constructions and a plenary with several triangles

Key Benefits for Students

Builds accurate compass and protractor skills
Explains when a triangle can and cannot be constructed
Links construction to measuring lengths and angles
Clear numbered steps to follow

Why Teachers Love It

No prep — ready for whole-class teaching on an interactive whiteboard
Steps are shown one at a time for modelling
Self-marking questions support independent practice
Pairs well with real geometry equipment
Includes a plenary with a range of triangles

Love this? You’ll love…

A dependable addition to a KS3 geometry topic, giving students hands-on practice with accurate constructions. These skills support work on angles, congruence and loci.

Build accurate geometry skills today — Add to Basket.

FAQ

What year group is this for? KS3 — Years 7–9 (ages 11–14).

What equipment do students need? A ruler, a pair of compasses and a protractor.

Which constructions are covered? Equilateral, SSS, SAS and AAS triangles.

Year Groups	Year 7–9
Resource Type	🎓 Interactive Lesson & Activities
Format	Digital Only
Curriculum	England & Wales — KS3 (Years 7–9)
Added	4 March 2026