Angles in triangles and polygons
Pages
Types of triangle
Equilateral, isosceles, scalene and right-angled triangles.
The angle sum of a triangle
Why the three angles sum to 180°.
Base angles of an isosceles triangle
The angles facing the equal sides are equal.
The exterior angle of a triangle
An exterior angle equals the sum of the two interior angles opposite it.
Interior angles of a polygon
Splitting an n-sided polygon into n − 2 triangles to find its angle sum.
Exterior angles of a polygon
Why the exterior angles of any polygon sum to 360°.
Angles in regular polygons
Each interior and exterior angle of a regular polygon.
Practice
Practice
The angle sum of a triangle
Why the three angles sum to 180°.
PracticeBase angles of an isosceles triangle
The angles facing the equal sides are equal.
PracticeThe exterior angle of a triangle
An exterior angle equals the sum of the two interior angles opposite it.
PracticeInterior angles of a polygon
Splitting an n-sided polygon into n − 2 triangles to find its angle sum.
PracticeExterior angles of a polygon
Why the exterior angles of any polygon sum to 360°.
PracticeAngle rules review
Parallel lines and polygons, stating the reason each time.