The study explored the effect of the activity-based approach (ABA) on grade 11 learners' performance in solving two-dimensional (2D) trigonometric problems. A sequential explanatory design was used, starting with the quantitative, followed by the qualitative method. The experimental group (EG) and the control group (CG) were facilitated using ABA, while CG was taught using traditional teaching approach. A 2D trigonometry test was used as a pre- and posttest to measure learners' performance. EG's experiences of using ABA were captured through focus group interviews. The study findings reveal significant differences between EG and CG posttests [t(100)=0.3. 95; p=0.05] with Cohen d=0.79. Also, ABA did not segregate between boys and girls. Despite ABA being time-consuming, learners in EG developed collaborative skills, trigonometry vocabulary, the ability to solve trigonometric problems, and learning autonomy, which improved their performance. The study recommends ABA to improve learners' performance.