Angles in triangles (age 10+)

Find unknown angles in triangles, quadrilaterals, and regular polygons using angle sum properties

How to tell they’ve got it

Tick these off as you see them — no test required.

Find a missing angle in a triangle given two angles (using angle sum = 180°)
Calculate a missing angle in a quadrilateral (angle sum = 360°)
Calculate the interior angle of a regular hexagon from the angle sum formula

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Try this together

If your child knows that angles in a triangle always add up to 180°, and two angles in a triangle are 55° and 70°, can they work out the third angle without measuring it?

Where this sits on the map

Stuck here? Check the skills it builds on first. Confident? Here’s what it unlocks.

Builds on

Types of angles (age 8+)ages 8–12Finding unknown angles in polygons requires reading diagrams where known angles are marked with arcs and tick marks

Angle Sum Rulesages 9–10Finding unknown angles builds on Y5 angle sum facts (180°, 360°)

Classifying shapes by propertiesages 10–11Finding angles in polygons requires knowing shape properties

Angles in triangles (age 10+)this skill · ages 10–11

Unlocks

Angle sums in triangles and polygonsages 11–14Extends KS2 angle sums in triangles and quadrilaterals to general polygons

Constructing mathematical argumentsages 10–11Angle-based proofs draw on angle sum knowledge

Generalising with repeated reasoningages 10–11Generalising polygon angle sums exemplifies repeated reasoning

solid = must come firstdashed = helps

Curriculum alignment

Candidate matches to official curriculum codes — machine-suggested, unreviewed (v0.1).

Show candidate curriculum codes · 3 ACARA · 2 NSW · 3 VIC

Australian Curriculum v9 candidate

AC9M6M04low confidenceYear 6 · Measurement

identify the relationships between angles on a straight line, angles at a point and vertically opposite angles; use these to determine unknown angles, communicating reasoning

AC9M5M04low confidenceYear 5 · Measurement

estimate, construct and measure angles in degrees, using appropriate tools including a protractor, and relate these measures to angle names

AC9M4M04low confidenceYear 4 · Measurement

estimate and compare angles using angle names including acute, obtuse, straight angle, reflex and revolution, and recognise their relationship to a right angle

NSW syllabus codes & stages only

MA2-GM-03low confidenceMathematics K-10 · Stage 2

MA3-GM-03low confidenceMathematics K-10 · Stage 3

Victorian Curriculum 2.0 codes & levels only

VC2M5M04low confidenceMathematics · Level 5 · Measurement strand

VC2M4M04low confidenceMathematics · Level 4 · Measurement strand

VC2M6M04low confidenceMathematics · Level 6 · Measurement strand

These are candidate alignments generated by semantic matching — machine-suggested and unreviewed (v0.1), not official or verified mappings. For official curriculum content see australiancurriculum.edu.au, curriculum.nsw.edu.au and f10.vcaa.vic.edu.au. Don’t rely on them for registration or compliance purposes.

Nearby on the map

2-D shapes (age 10+)ages 10–11 3-D shapes (age 10+)ages 10–11 Classifying shapes by propertiesages 10–11 Coordinates (age 10+)ages 10–11

All Geometry skills →