Penelitian ini bertujuan untuk mengetahui pengaruh model pembelajaran kooperatif tipe Group Investigation terhadap kemampuan penalaran matematis siswa kelas VIII SMP Negeri 5 Tarakan. Penelitian ini dilakasanakan pada semester ganjil tahun ajaran 2017/2018 di SMP Negeri 5 Tarakan.
Jenis penelitian ini adalah quasi exsperimental research dengan desain posttest only control design. Populasi dalam penelitian ini adalah seluruh kelas VIII SMP Negeri 5 Tarakan. Sampel penelitian ini adalah kelas VIII-10 sebagai kelas eksperiemen dan VIII-9 sebagai kelas kontrol. Sampel penelitian diambil dengan teknik simple random sampling. Teknik pengumpulkan data dalam penelitian ini menggunakan tes. Teknik analisis data menggunakan analisis deskriptif dan analisis inferensial. Analisis deskriptif meliputi rata-rata hitung dan simpangan baku. Analisis inferensial mmenggunakan analisis uji t (independent sample t-test) pihak kanan.
Hasil analisis deskriptif menunjukkan bahwa skor rata-rata kemampuan penalaran matematis siswa kelas eksperimen adalah 66,07 dan skor rata-rata kemampuan penalaran matematis siswa kelas kontrol adalah 48,89 sedangkan berdasarkan hasil uji independent sample t-test dengan taraf signifikan 5% (? = 0,05) diperoleh nilai signifikan (1-tailed) sebesar 0. Sehingga dapat dilihat bahwa 0< 0.05. Dengan demikian Ho ditolak dan Ha diterima, sehingga dapat disimpulkan bahwa model pembelajaran kooperatif tipe Group Investigation berpengaruh terhadap kemampuan penalaran matematis siswa.

Kata Kunci: Model Pembelajaran Kooperatif Tipe Group Investigation, Penalaran Matematis

The objective of this research was to determine the effect of Group Investigation type cooperative learning model on mathematical reasoning ability of eighth grade students of SMP Negeri 5 Tarakan. This research was conducted in the odd semester of the 2017/2018 academic year at SMP Negeri 5 Tarakan. The type of this research is quasi experimental research with posttest only control design. The population of this research was all the eighth grade students of SMP Negeri 5 Tarakan. The sample of this research was class VIII-10 as an experimental class and VIII-9 as a control class. The research sample was taken by simple random sampling technique. The technique of data collection used by the researcher was tests. The technique of data used descriptive analysis and intferential analyis. Descriptive analysis includes mean of calculation and standard deviaton. Inferential analysis used independent sample t-test analysis. The results of descriptive analysis showed that the mean score of students' mathematical reasoning ability in the experimental class was 66.07 and the mean score of the mathematical reasoning ability of the control class students was 48.89 while based on the results of the independent sample t-test with a significant level of 5% (? = 0.05) obtained a significant value (1-tailed) of 0. So it can be seen that 0 < 0.05. Thus Ho is rejected and Ha is accepted, so it can be concluded that the Group Investigation type cooperative learning model influences of students' mathematical reasoning abilities. Keywords: Group Investigation Type Cooperative Learning Method, Mathematical Reasoning