Education and mathematics competencies and skill have become the most central elements that impact on the development of any nation, particularly in science and technology. The fundamental importance of mathematics to humans could be explained in terms of the interrelationship between mathematics and the development of humans to advance the cause of humans. In this paper we report on a qualitative study which explored the mental constructions made by grade 12 learners (n = 30) when solving triangles in trigonometry. The study was carried out at a school in KwaZulu-Natal in South Africa. The data was collected from written responses of students to a structured activity sheet, consisting of questions on three dimensional problems. The data were analysed using APOS theory. Findings emanating from the data analysis informed a modification of the initial genetic decomposition, which raised some didactical implications for basic education, specifically for the learning and teaching of trigonometry