The purpose of the study: This paper aimed at describing the teachers' competence in the acquisition and use of the language of mathematics at public and private senior high schools all over Malang City, Malang Regency, and Batu City, Indonesia. Methodology: Qualitative descriptive research design was employed by means of content analysis on the results of the interview and documents of mathematic instructions designed by 30 teachers who also served as the research subjects, spiral analysis on the qualitative data by Creswell was applied to analyze the data, with the support of NVivo 12 plus software. Main Findings: This research has revealed that the teachers have acquired and used the language of mathematics, with some errors and fallacies in the use of mathematics vocabularies, grammar, and the explanation of mathematical symbols. The teachers' competence in the acquisition and use of the language of mathematics was influenced by the knowledge about mathematical concepts, presentations, and instructions. Applications of this study: The findings of this study are expected to add new knowledge about the competency of the mathematics language of the teacher so that it can be used as a reference for colleges producing teacher candidates in developing the curriculum. Theoretically, these results can be used as a reference and contribute to assessing the mathematical language competence of teachers. Novelty/Originality of this study: This current research, is based on their educational qualifications, and to identify factors that influence the teachers' competence in the acquisition and use of the language of mathematics which is less explored by the earlier researcher.

One of the basic concepts of geometry and measurement, which is learned from elementary to higher education, is area and volume. This study aims to describe and explore the process of the students in generalizing the concept of volume and surface area of a rectangular prism. The teaching experiment method was carried out to nineteen secondary school students as the subject of the study. The data was collected through observation, class discussion, and semi-structured interviews, which were then analyzed using interactive models: data reduction, data presentation and verification, and conclusions. The results of the analysis showed that the process of generalizing among students to the concept of volume and surface area was through constructing and determining the obtained dimensions of geometry, specialization, and symbolic use.

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This paper aimed at analyzing the use of guided worksheet in mathematics learning at Madrasyah Aliyah Muhammadiyah 1 Malang, especially in the students' activities and responses. This study was conducted by means of descriptive design with qualitative approach. The data were obtained through classroom observation and questionnaires distributed to the students in Grade X and XI of Social Science Stream, MA Muhammadiyah 1 Malang. The data were subsequently analyzed descriptively. The findings of this study have showed that the students were actively engaged in learning activities through peer discussion, reading, and questioning the concepts delivered by the teacher through the guided worksheet. Moreover, this study indicated the positive responses from the students in which they felt more motivated, eager to actively engage, and more triggered to think critically during the learning process.