Classifying Triangles by Sides and Angles

Solving Problems with Triangles

The Sum of Angles in a Triangle

Exterior Angles of a Triangle

Classifying Quadrilaterals

Classifying Triangles

Describe, sort and classify triangles by their sides and angles, including equilateral, isosceles, scalene, acute-angled, right-angled and obtuse-angled triangles.

Solving Triangle Problems: Missing Angles

Determine missing angles in triangles using the angle sum of 180°, isosceles and equilateral properties, and simple algebra.

Interior Angles of a Triangle

Demonstrate that the interior angles of a triangle sum to 180° and use the angle sum with parallel lines to calculate unknown angles.

The Exterior Angle Theorem

Identify interior and exterior angles of a triangle and apply the exterior angle theorem: an exterior angle equals the sum of the two opposite interior angles.