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几何初步知识是小学数学基础知识的重要部分,概念复杂,学生不易辨析。对此,笔者对容易混淆的概念,编拟若干错例,并加以辨析,供同仁参考。 1.平角实际上是一条直线。辨析角的两边成一条直线,这时所成的角叫做平角。 2.不相交的两条直线叫做平行线。辨析在同一平面内,不相交的两条直线叫做平行线。 3.三角形按边分类,可分为不等边三角形,等腰三角形和等边三角形。辨析应是两类,即不等边三角形和等腰三角形。因为等边三角形是特殊的等腰三角形。 4.梯形的下底大于上底辨析梯形的底边水平放时有上下底之分。在上面的一条叫上底,在下面的一条叫下底。下底不一定大于上底。如果梯形的底边不是水平放置,就不要分上底、下底,只是说梯形的两底。
Initial knowledge of geometry is an important part of the basic knowledge of elementary mathematics, the concept of complex, difficult to identify students. In this regard, I confused the concept of confusion, the preparation of a number of wrong examples, and to be identified for my colleagues reference. The angle is actually a straight line. Discerning the two sides of the corner into a straight line, then the angle formed by the angle is called a flat angle. 2. The two lines that do not intersect are called parallel lines. Discrimination in the same plane, the two lines do not intersect is called parallel lines. 3. Triangles by edge classification, can be divided into unequal triangle, isosceles triangle and equilateral triangle. Discrimination should be two categories, namely, inequilateral triangles and isosceles triangles. Because the equilateral triangle is a special isosceles triangle. 4. trapezoidal lower than the bottom of the trapezoidal discrimination at the bottom horizontal when the upper and lower end of the sub. In the top one is called the bottom, the bottom one is called bottom. Bottom not necessarily greater than the top. If the bottom of the trapezoid is not placed horizontally, do not sub-top, bottom, just say that the two trapezoidal.