This lesson comes from the first volume of the fourth grade of the primary school mathematics education edition. Learning content and knowledge structure diagram: The content of this lesson is based on students' extensive contact with corners in their lives and their full perceptual knowledge of corners. Teaching can make students know straight corners and rounded corners with the help of folding fan materials.

Through observation and hands-on practice, explore and master the relationship among acute angle, right angle, obtuse angle, right angle and rounded corner, so that students can feel that the content of mathematics learning is realistic and meaningful. So as to experience the fun of "learning mathematics" and "doing mathematics".

corner

As a quantifier, "jiao" is not limited to the reference of drinks. For example, cutting a piece from a cake is called "ten cents" and one tenth of a dollar is called "ten cents". However, this quantifier usage of "Jiao" has another source. Animal horns are sharp at one end and huge at the other.

It should be said that there are many things in this form in life, and horns can often be their names: water chestnut, soap horn, table horn, mountain horn, and cape of good hope (that is, headland-a sharp place extending into the sea).

Obviously, these "horns" have the morphological characteristics of animal horns in detail or abstractly. As a common form, "jiao" naturally becomes a quantifier of jiao. The reason why "jiao" is the name of monetary unit is nothing more than this: "jiao" is opposite to "yuan (circle)". If a circle is divided into several parts according to the center of the circle, it is naturally also a number of "jiao".

"angle" can also mean the meaning of actor class, pronounced jué. Can represent the role, that is, the "corner" of the "protagonist" and "supporting role"; It can also refer to business, such as the "corner" of "clown" and "Dan Jiao". From this, the meaning of "actor" is derived, such as "corner" of "famous corner".

The semantic category of "horn" is not created out of thin air. Before classical Chinese, the "corner" could represent the positions of several vertex areas in the space, but in this space of the stage, actors with different roles and occupations are generally on different "corners", hence the name "corner".