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四、关于“角”与“平行和相交”本册教材在直观认识线段的基础上,学习射线和直线,体会两点确定一条直线和两点间所有连线中线段最短。在二年级(下册)直观认识角、比较角的大小和辨认直角、锐角、钝角的基础上,继续认识角。学习用量角器量指定角的度数,学习周角、平角的概念以及它们与钝角、直角、锐角之间的大小关系,最后学习用三角尺或量角器画指定度数的角。在“平行和相交”单元,结合具体情境,了解平面上的平行和相交(包括垂直),学习画已知直线的平行线和垂线。教材在编写时主要考虑了下面几个问题。
Four, on the “angle” and “parallel and intersect,” the textbook on the basis of intuitive understanding of the line, learn the ray and straight line, experience two points to determine a straight line and the connection between the two points in the shortest line segment. In the second grade (second volume) intuitive understanding of the angle, the angle comparison of the size and angle recognition, acute angle, obtuse angle, based on the continued recognition. Learn the angle of the angle Specified angle degree, learning angle, angle and the concept of their relationship with the obtuse angle, right angle, acute angle between the size, and finally learn to use a ruler or protractor to draw the specified degree angle. In the “parallel and intersect” units, understand the parallelism and intersection (including vertical) in the plane, learn the parallel lines and vertical lines of the known straight line according to the specific situation. Teaching materials in the preparation of the main consideration of the following questions.