<![CDATA[ABSTRACT Mathematical problem-solving ability in plane geometry remains characterized by a wide range of errors that are influenced not only by students’ conceptual understanding but also by their confidence in their own capabilities (self-efficacy). This condition highlights the need for an analytical perspective that simultaneously considers cognitive and affective dimensions in students’ mathematical performance. Accordingly, this study aims to identify the characteristics of students’ problem-solving errors in plane geometry based on the SOLO Taxonomy by considering different levels of self-efficacy. A descriptive qualitative approach supported by quantitative data was employed. Data were collected through a self-efficacy questionnaire, a mathematical problem-solving test, and semi-structured interviews involving six eighth-grade students at SMP Negeri 2 Lamongan selected through purposive sampling, representing high, moderate, and low self-efficacy categories. The data were analyzed using the interactive analysis model consisting of data reduction, data display, and conclusion drawing. The findings indicate that differences in self-efficacy are associated with variations in students’ cognitive structures as described by the SOLO Taxonomy. Students with high self-efficacy demonstrated more advanced levels of thinking and committed relatively minor technical errors, whereas those with moderate self-efficacy exhibited inconsistencies during the reflective stage. In contrast, students with low self-efficacy experienced conceptual, procedural, and reflective errors throughout almost all stages of problem-solving. Integrating the SOLO Taxonomy with self-efficacy provides a more comprehensive framework for mapping students’ error characteristics and offers an empirical basis for designing mathematics instruction that is more responsive to students’ cognitive characteristics and learning needs. ABSTRAK Kemampuan problem solving matematis pada materi bangun datar masih memperlihatkan beragam karakteristik kesalahan yang tidak hanya berkaitan dengan penguasaan konsep, tetapi juga dipengaruhi oleh keyakinan siswa terhadap kemampuannya sendiri (self-efficacy). Situasi tersebut mendorong perlunya analisis yang mampu memotret keterkaitan antara dimensi kognitif dan afektif secara terpadu. Penelitian ini diarahkan untuk mengidentifikasi karakteristik kesalahan problem solving siswa pada materi bangun datar berdasarkan Taksonomi SOLO dengan meninjau tingkat self-efficacy. Pendekatan deskriptif kualitatif yang didukung data kuantitatif diterapkan melalui pemberian angket self-efficacy, tes problem solving, dan wawancara mendalam terhadap enam siswa kelas VIII SMP Negeri 2 Lamongan yang dipilih menggunakan purposive sampling, masing-masing mewakili kategori self-efficacy tinggi, sedang, dan rendah. Data dianalisis secara terpadu menggunakan model analisis interaktif melalui proses reduksi data, penyajian data, dan penarikan simpulan. Temuan penelitian memperlihatkan bahwa perbedaan tingkat self-efficacy berkaitan dengan variasi kualitas struktur berpikir berdasarkan Taksonomi SOLO. Siswa dengan self-efficacy tinggi mampu mencapai level berpikir yang lebih kompleks dengan kesalahan yang relatif bersifat teknis, sedangkan kelompok sedang masih menunjukkan ketidakkonsistenan pada tahap refleksi. Di sisi lain, kelompok self-efficacy rendah mengalami kesalahan konseptual, prosedural, dan reflektif pada hampir seluruh tahapan penyelesaian masalah. Integrasi Taksonomi SOLO dan self-efficacy menghasilkan pemetaan karakteristik kesalahan yang lebih komprehensif sehingga dapat dimanfaatkan sebagai landasan dalam merancang pembelajaran matematika yang lebih adaptif terhadap karakteristik berpikir siswa.]]>
