Penelitian ini bertujuan untuk menganalisis kemampuan penalaran siswa kelas IX MTs Negeri Tarakan. Jenis penelitian adalah kualitatif deskriptif. Subjek penelitian adalah siswa kelas IX sebanyak empat siswa yang dipilih secara purposive sampling. Pengumpulan data dilakukan dengan tes, wawancara dokumentasi dan triangulasi, kemudian dianalisis menggunakan reduksi data, penyajian data, dan penarikan kesimpulan. Berdasarkan hasil penelitian dari empat subjek yang tergolong dalam kemampuan penalaran kategori tinggi dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel, kemampuan penalaran kategori sedang dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel, dan kemampuan penalaran kategori rendah dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel menunjukkan bahwa, subjek yang memiliki kemampuan penalaran kategori tinggi dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel mampu memenuhi keempat indikator penalaran yaitu melakukan manipulasi matematika, menyajikan pernyataan matematika secara lisan dan tertulis, menyusun dan memberi alasan terhadap kebenaran solusi serta menarik kesimpulan pernyataan secara logis. Kemudian subjek yang memiliki kemampuan penalaran kategori sedang dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel mampu memenuhi tiga indikator kemampuan penalaran, yaitu melakukan manipulasi matematika, menyajikan pernyataan matematika secara lisan dan tertulis serta menyusun dan memberi alasan terhadap kebenaran solusi. Sedangkan subjek yang memiliki kemampuan penalaran kategori rendah dalam menyelesaikan soal cerita matematika pada materi sistem persamaan linear dua variabel mampu memenuhi satu indikator kemampuan penalaran, yaitu melakukan manipulasi matematika.

Kata Kunci: Kemampuan Penalaran, Soal Cerita Matematika, Sistem Persamaan Linear Dua Variabel, Kualitatif Deskriptif

This research aimed to analyze the reasoning abilities of grade IX students at MTs Negeri Tarakan. This research was classified into a descriptive-qualitative study. The research subjects were 4 grade IX students selected through a purposive sampling technique. The research data were collected through test, interview, documentation and triangulation. The collected data were then processed through data reduction, data presentation, and conclusion drawing. Based on the research results, those four research subjects were respectively classified into high, medium and low categories related to their reasoning ability in solving the mathematical story questions on two-variable linear equation system materials. The research subjects in high category on their reasoning abilities in solving the mathematical story problems on the two-variable linear equation system materials were able to meet four reasoning indicators: performing the mathematical manipulations, presenting the mathematical statements in both spoken and written forms, composing and giving reasons to show the correct solution, and logically drawing conclusions. Meanwhile, the subjects in medium category on their reasoning abilities in solving the mathematical story problems on the two-variable linear equation system materials were able to meet three reasoning indicators: performing the mathematical manipulations, presenting the mathematical statements in both spoken and written forms, as well as composing and giving reasons to show the correct solution. Furthermore, the subjects in low category on their reasoning ability in solving the mathematical story problems on two-variable linear equation system materials were only able to fulfill one reasoning indicator: performing the mathematical manipulations. Keywords: Reasoning ability, mathematical story problems, two-variable linear equation system, descriptive-qualitative.