Geometry of a Straight Line
Gr 9

The Grade 9 Geometry of a Straight Line module develops the essential angle–relationship skills learners need to handle more advanced geometry in later grades. This chapter focuses on understanding how angles behave when points, lines, and transversals interact, and teaches learners how to apply these rules accurately in diagrams and problem-solving contexts.

The lessons cover fundamental concepts such as adjacent angles, complementary and supplementary angles, vertically opposite angles, and angles on a straight line. Learners also explore transversals, parallel lines, corresponding angles, alternate angles, and co-interior angles. Each rule is introduced with clear explanations and worked examples, allowing students to recognise patterns and justify their reasoning.

By the end of this module, learners will be able to identify angle relationships quickly, calculate unknown angles with confidence, and apply geometric reasoning effectively—skills that are vital for success in senior-phase geometry and analytical problem solving.