<![CDATA[ABSTRAK Tujuan penelitian ini adalah mengetahui peningkatan kemampuan komunikasi matematis siswa yang diajar dengan menggunakan model pembelajaran kooperatif tipe Group Investigation pada materi Bangun Ruang Sisi Lengkung di kelas IX. Jenis penelitian ini adalah penelitian tindakan kelas (Classroom Action Researh). Subjek dari penelitian ini adalah siswa kelas IX-A yang berjumlah 32 orang sedangkan objek penelitian ini adalah kemampuan komunikasi matematis siswa dengan menggunakan model pembelajaran kooperatif tipe Group Investigation pada materi Bangun Ruang Sisi Lengkung. Instrumen penelitian ini melalui tes kemampuan komunikasi dan observasi. Soal tes hasil belajar berbentuk uraian, disetiap akhir siklus diberikan tes kemampuan komunikasi matematis yang terdiri dari empat soal. Sebelum tes diujikan, terlebih dahulu soal-soal divalidkan.Penelitian ini dilaksanakan dalam 2 siklus yang masing-masing terdiri dari 3 pertemuan. Dari tes kemampuan komunikasi matematis pada siklus I diperoleh 17 siswa (53,125%) yang memenuhi kemampuan komunikasi matematis (nilainya ≥ 70) dan 15 siswa (46,875%) yang belum memenuhi kemampuan komunikasi matematis dengan rata-rata kelas 66,32. Pada siklus II diperoleh 28 siswa (87,5%) yang memenuhi kemampuan komunikasi matematis dan 4 siswa (12,5%) yang tidak memenuhi tingkat kemampuan komunikasi matematis dengan rata-rata kelas 77,64. Dari siklus I ke siklus II diperoleh peningkatan jumlah siswa yang memenuhi kemampuan komunikasi matematis sebanyak 11 siswa dan rata-rata kelas meningkat sebesar 11,32. Berdasarkan rata-rata hasil observasi yang dilakukan oleh observer, diperoleh pengelolaan pembelajaran yang dilakasanakan oleh guru (peneliti) mengalami peningkatan sebesar = 18,94%, rata-rata observasi guru siklus I = 73,86% (kategori cukup baik), sedangkan pada siklus II rata-rata hasil observasi guru = 92,80% (kategori sangat baik) dan rata-rata hasil observasi siswa juga mengalami peningkatan sebesar 20,83%, rata-rata observasi siswa siklus I = 70,83% (kategori cukup baik) sedangkan rata-rata observasi siswa siklus II = 91,66% (kategori sangat baik).Karena telah memenuhi kriteria kemampuan komunikasi matematis siswa (Indikator keberhasilan dalam penelitian telah tercapai) dan mengalami peningkatan dari siklus I ke siklus II maka dapat disimpulkan bahwa model pembelajaran kooperatif tipe Group Investigation dapat meningkatkan kemampuan komunikasi matematis siswa pada materi Bangun Ruang Sisi Lengkung. Kata Kunci: Kemampuan komunikasi matematis, Pembelajaran Group Investigation. ABSTRACTThe aimed of this research was to know the improvement of the students’ ability in mathematical communication that being taught by using cooperative learning method with the type Group Investigation in side of the arch solidsmaterial at the 3rd grade of SMP Swasta Gajah Mada Medan of the year 2017/2018. The type of this researh is Clasroom Action Research . The subject of this research is the third grade students, class 9-A that consisits of 32 students while the object of this research is the students ability in mathematical communication by using cooperative learning method typeGroup Investigationin side of the arch solids.The instrument of this reseach was done by testing the students skill in communication and doing observations. The type of the test is in form of essay-test, at the end of each cycle the students were given a mathematical communication ability test that consists of four questions. The questions of the test being validated first before it given to the students.This research was done into two cycles that consists of three meetings in each cycle. Based on the mathematics communication ability test in cycle 1, there are 17 students (53,125%) who pass the mathematical communication ability test (the scores ) and there are 15 students (53,125%) who could not pass the mathematical communication ability test with the average score 66,32. In cycle 2 there are 28 students (87.5%)who can pass the mathematical communication ability test and there are 4 students who cannot pass themathematical communication ability test with the average score (77.64). From cycle 1 up to cycle 2, there are 11 students who can improve in terms of mathematical communication ability and thestudents average score improved up to 11.32 point. Based on the result of observation sheets that being collected by the observer, it showed that the teaching and learning process that had been conducted by the teacher (researcher) made animprovement (18.94%). The teacher observation sheets in cycle 1 is 73.86% (good level) while in the cycle 2 the teacher observation sheet become 92.80% (very goodlevel) and the result of the students observation sheet also improved up to 20.83%, the average of the students observation sheet in cycle 1 is 70.83% (good level) while the average score of the students observation sheets in cycle 2 is 91.66% (very good level).Since the results of the students ability in matematical communication had been revealed (it had been reached the minimum criteria) and as it stated that there is an improvement from cycle 1 up to cycle 2, so it can be concluded that Cooperative method type Group Investigation can improve the students’ mathematical communication ability in side of the arch solidsmaterial. Keyword: Mathematical comunication ability, Group Investigation learning.]]>
