• Education of Primary School Mathematics
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• v.21 no.1
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• pp.75-91
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• 2018

This study examines the educational meaning of the sum of the angles of a triangle in elementary school mathematics and discusses the introduction and explanation methods to convey the meaning faithfully. First, we investigated how to introduce the sum of the angles of a triangle in the Korean national mathematics curriculums from the past to the present and surveyed the experiences and opinions of the teachers. The results of the survey are summarized and discussed in three parts: The context of 'arranging angles activities' and 'measuring angles activities', the methods to convey the meaning of the sum of the angles of a triangle as an invariance, and other details.

• Communications of Mathematical Education
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• v.35 no.4
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• pp.425-444
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• 2021

In this study, under the assumption that the goal pursued in measurement area can be reached through the composition of the measurement activity considering the mathematical process, the method of summing the interior angles of a triangle using the measurement error was applied to the 4th grade class of the elementary school. Results of the study, first, students were able to recognize the possibility of measurement error by learning the sum of the interior angles of a triangle using the measurement error. Second, the discussion process based on the measurement error became the basis for students to attempt mathematical justification. Third, the manipulation activity using the semicircle was recognized as a natural and intuitive way of mathematical justification by the students and led to generalization. Fourth, the method of guiding the sum of the interior angles of a triangle using the measurement error contributed to the development of students' mathematical communication skills and positive attitudes toward mathematics.

• Education of Primary School Mathematics
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• v.16 no.2
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• pp.183-192
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• 2013

This study points out that the angle sum of a triangle and the property of parallel lines are taught without showing any relations between them on elementary school mathematics textbooks. This study looks into the structure of Euclid Elements so that it discusses about the contents of current Korean textbooks. The property of the alternate angles and the corresponding angles of parallel lines are inherent in many subjects in Elementary school mathematics, and have meaning that must be thought with the angle sum of triangles in the structure of Euclid Elements. With this consideration, this study makes a conclusion that these two subjects should be taught by presenting relations between them.

• Communications of Mathematical Education
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• v.13 no.2
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• pp.693-700
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• 2002

대학수학(미분적분학의 이해, 생활과 수학)수업에서, 공간좌표 단원과 도형편을 지도할 때, 구체적인 모델을 들고 또, 구체적인 예- 쌍곡기하에서는, i)삼각형의 세 내각의 크기의 합은 180도 보다 작다 ii) 피타고라스 정리가 성립하지 않는다. iii) 세 내각의 크기가 90도이고 한 내각의 크기가 90도 보다 작은 사각형이 존재한다. 는 예를 들어 유클리드 기하와 쌍곡기하에 대해 비교 설명하며 수업에 흥미를 불러 일으키고, 새로운 세계에 대한 생각을 할 수 있는 기회를 제공한다.

• School Mathematics
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• v.5 no.4
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• pp.401-420
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• 2003

We have many problems in the teaching and learning of proof, especially in the demonstrative geometry of middle school mathematics introducing the proof for the first time. Above all, it is the serious problem that many students do not understand the meaning of proof. In this paper we intend to show that teaching the meaning of proof in terms of historic-genetic approach will be a method to improve the way of teaching proof. We investigate the development of proof which goes through three stages such as experimental, intuitional, and scientific stage as well as the development of geometry up to the completion of Euclid's Elements as Bran-ford set out, and analyze the teaching process for the purpose of looking for the way of improving the way of teaching proof through the historic-genetic approach. We conducted lessons about the angle-sum property of triangle in accordance with these three stages to the students of seventh grade. We show that the students will understand the meaning of proof meaningfully and properly through the historic-genetic approach.