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An angle larger than a right angle and smaller than a fillet is called an optimal angle.

[Right angle, acute angle, obtuse angle, upper angle, lower angle]

Half a right angle is called a right angle, which is represented by "┓" when drawing. The right angle is 90 degrees. An angle smaller than a right angle is called an acute angle, and an acute angle is greater than 0 and less than 90. An angle greater than a right angle and less than a right angle is called an obtuse angle, and the obtuse angle is greater than 90 and less than 180. An angle smaller than a right angle is called a bad angle, and acute angle, right angle and obtuse angle are all bad angles. An angle larger than a right angle and smaller than a rounded corner is called an optimal angle, and the optimal angle is larger than 180 and smaller than 360.

Teaching: (1) Generally, primary schools only give names such as acute angle, right angle, obtuse angle, right angle and rounded corner. These names can be understood on the basis of measuring angles. Measure the right angle (90) first, and then lead to other angles.

(2) Through the demonstration and measurement of the activity model, students can know the degree range of various angles and their relationships. You can also let students know the relationship between right angles and right angles and between rounded corners and right angles by origami.

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