This qualitative research aimed to find out the students' mathematical reasoning
skills reviewed from cognitive systematic and cognitive intuitive style on the
subject matter of polyhedrons. The subjects of this research were 6 students from
Class VIII C who were taken using the questionnaire of cognitive systematic and
intuitive of Cognitive Style Inventory (CSI). The subjects were then categorized
into 3 students for the group of cognitive systematic style and 3 students for the
group of cognitive intuitive style. The data were collected using a questionnaire,
written test, interview, and documentation. The results showed that students with
cognitive systematic style were able to master all indicators of mathematical
reasoning skill in finishing mathematical questions including proposing a notion,
doing a mathematics manipulation, drawing a conclusion, compiling evidence,
giving reasons toward solutions, checking the validity of an argument, and finding
a pattern of characteristic from mathematics symptoms to generalize, while the
student with cognitive intuitive style was able to master three indicators of
mathematical reasoning skill including proposing a notion, checking the validity
of an argument, and finding a pattern or characteristic from mathematics
symptoms to generalize. So, the group of students with cognitive systematic style
had better mathematical reasoning skills.