This research is a Classroom Action Research (CAR) conducted at SMA Negeri 1 Nangapanda with class X language and culture research subjects. The subject matter that will be studied is trigonometric comparisons in right triangles. Factors to be studied are learning outcomes and student activities in learning activities. This research was conducted in two cycles with planning, implementation, observation and evaluation, and reflection. Sources of data in this study are the results of observations by the observer and the results of a written test at the end of the cycle of class X Babu students of SMA Negeri 1 Nangapanda. The type of data is quantitative data in the form of an assessment of the results of written tests at the end of the cycle and qualitative data in the form of data from observations of student activities and teacher activities. The results showed that 19 out of 23 (82%) students had met the minimum completeness criteria. Meanwhile, the results obtained from the comparison in cycles one and 2 showed an increase in the achievement of students' mastery results in this classroom action research. The average increase in student learning outcomes from 77.39 in cycle 1 increased by 13.31 points to 91.30 in the average result of cycle 2. These results indicate an increase in learning outcomes with the application of Problem Based Learning.