This research aims at describing errors as well as knowing the factors causing students to make an error in solving problems in the material of the Two-Variable Linear Equation System (SPLDV). This research involved 31 students from grade eight students of Indonesian junior high school. To collect the data, tests, observation, and interview methods were used. The data validity was triangulation in which it required a comparison of data with interviews. The technique of data analysis was in three stages, starting from data reduction, data presentation, and conclusion. The analytical framework was developed based on the Newman error category. The results obtained are three types of errors, namely error understanding problems, transformation errors, and process skills errors. Factors causing these errors, in general, are students who find difficulties to acknowledge the meaning of the questions, students have a low level of understanding and creativity in identifying problems into mathematical models, and students' carelessness in process skills.

In line with pedagogical competencies, the purposes of this study are (1) to determine and measure the capability of Content Knowledge (CK), Pedagogical Knowledge (PK), and Pedagogical Content Knowledge (PCK) for prospective Indonesian language teacher in preparing lesson plan based on 2013 curriculum in academic year 2017/2018, and (2) to describe the implementation of the lesson plan prepared by prospective Indonesian language teachers in teachinglearning process for academic year 2017/2018. This type of research is descriptive qualitative by using the documentation method. The results showed that the Indonesian language teachers' capability of CK was 79.11% (good), the capability of PK was 80.41% (good), and the capability of PCK was 83.2% (good). Then in the applied Learning, the