Peningkatan Kemampuan Penalaran Matematis Melalui Model Pembelajaran Problem Based Learning berbasis Numbered Heads Together (PTK pada Siswa Kelas VII H Semester Gasal SMP Negeri 2 Mojolaban Tahun Pelajaran 2017/2018)

The purpose of this study is to improve students' mathematical reasoning abilities through Problem Based Learning based learning model of Numbered Heads Together on VIIH grade students Semester gasal SMP Negeri 2 Mojolaban academic year 2017/2018. The type of research used is classroom action research. Implementation of the action is carried out in two cycles consisting of 2 meetings each cycle. Data collection techniques use observation sheets, tests, field note sheets, and documentation. Data analysis techniques use data collection, data reduction, data display, and conclusions. The results showed an increase in mathematical reasoning with the following indicators: 1) The ability of the students to submit the assumption before the action as much as 5 people (16,67%), in cycle I 10 person (33,33%), and on cycle II 20 people (62,5%). 2) students' ability to present mathematical statements through writing before the actions of 14 people (46,67%), in cycle I 21 person (70%), and on cycle II 28 people (93,33%). 3) The ability of students to manipulate mathematics before the actions of 9 people (40%), on the cycle I 13 person (40%), and on cycle II 18 people (60%). 4) The ability of students to draw conclusions before the actions of 6 people (20%), on the first cycle there are 8 people (26,67%), and in cycle II 13 people (63,33%)