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Someone is said to reason if they do a logical thinking process to get a conclusion or judgment in solving a problem. The purpose of this study is to obtain a picture of student reasoning at carrying out the plan in solving geometry problems. This research is a descriptive exploratory study with a qualitative approach. Methods of collecting data through problem-solving tasks, interviews, and documentation. The subject of this study was a male student at UHO Primary School who had a mathematical ability level in the medium category. The data obtained were analyzed qualitatively through five steps, namely 1) data classification; 2) data reduction 3) data presentation; 4) interpretation of data, and 5) concluding. The results of this study indicate that 1) the subject has carried out problem-solving according to the plan and its logical arguments; 2) the subject uses the concepts and principles that will be used in solving problems and their logical arguments; 3) the subject computes (calculations) correctly and logically; 4) the subject makes a conclusion from the calculation correctly and logically; 5) the subject uses the interpretation of the results of calculations correctly and logically.

reasoning; problem solving geometry; polya stage; Carrying out the Plan