Abstract
Trigonometric function transformation, governed by the parameters in f(x) = A sin(Bx + C) + D, is widely reported as a persistent source of student misconceptions because interpreting it requires the simultaneous coordination of several abstract parameters. This pilot case study describes the conceptual understanding demonstrated by one mathematics education student regarding the parameters of amplitude, period, phase shift, and vertical shift after completing a GeoGebra-assisted exploration task structured around a four-stage Project-Based Learning (PjBL) model. A qualitative document analysis was conducted on the participant's worksheets, which contained observation tables, GeoGebra screenshots, written analyses, and reflections for each parameter, following an approach that isolated a single parameter before requiring the combination of all parameters. The participant's responses were compared against commonly reported misconception indicators for trigonometric transformation drawn from the literature, including confusion between the sign and magnitude of the amplitude, treating the period-frequency relationship as directly rather than inversely proportional, errors in the direction of the phase shift, and failure to divide the phase constant by the frequency coefficient when combining parameters. The analysis showed that the participant correctly identified all four parameter-graph behavior relationships, including the phase-by-frequency division step that is most frequently reported as a source of student error, and no clear misconception was found in this case. These findings tentatively suggest that staging GeoGebra exploration from single parameters toward combined parameters within a PjBL structure may support the construction of accurate concepts, although the limited scope of a single participant constrains the generalizability of the findings. This study was primarily intended to pilot the worksheet design and analytical framework in preparation for a broader study involving a larger number of participants.