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Angle sums in triangles and polygons

PROCEDURAL
MathematicsGeometry|Ages 11—14|ID: mt_J03RFlVdas

Derive and use the angle sum in a triangle (180°), use it to deduce the angle sum in any polygon ((n−2) × 180°), and calculate interior and exterior angles of regular polygons

Mastery Evidence

  • Calculate a missing angle in a triangle by subtracting the known angles from 180°
  • Find the sum of interior angles in a hexagon by dividing it into triangles
  • Calculate each interior and exterior angle of a regular polygon given the number of sides

Assessment Prompt

“If [child] knows two angles of a triangle are 50° and 70°, can they work out the third? And can they figure out the angles inside a regular pentagon?”

Curriculum Standards2 alignments

8.G.5Common Core State Standards for Mathematics
Angle arguments and similarity

Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.

G
KS3.Maths.Geo.12The national curriculum in England
Sum of Angles in Polygons

derive and use the sum of angles in a triangle and use it to deduce the angle sum in any polygon, and to derive properties of regular polygons

Mathematics · Key Stage 3

Prerequisites3

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Unlocks1