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1、人教版四年级上册数学,角的分类,教师 石旭蓉,一、复习旧知尝试分类（下面的角各是什么角，并把这些角分类。）,二、探究新知用量角器测一测直角的度数,90的角，是直角。,直角,1直角=90,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成
2、才路,角可以看作由一条射线绕着它的端点，从一个位置旋转到另一个位置形成的图形。,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,一条射线绕它的端点旋转半周，形成的角叫做平角。,认识平角,状元成才路,状元成才路,状元成才路,状元成
3、才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,平角的两条边在同一条直线上。,你会画平角吗？,（1）,（2）,小结：通过角的定义我们知道：角是从一个顶点引出的两条射线所组成的图形。一个角必须满足有一个顶点和两条边这两个条件。,试着测一测平角的度数吧!,方法一：用量角器量,1平角=1
4、800,180,方法二：用三角板拼,180,1平角=2直角,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,一条射线绕它的端点旋转一周，形成的角叫做周角。,认识周角,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状
5、元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,状元成才路,你会画周角吗？,1周角=3600,方法一：用三角板拼,1周角2平角4直角,重新认识锐角,小于90度的角，叫做,锐角,重新认识和钝角,大于90度,而小于180度的角，,叫做钝角,再次对角分类,小于900,等于900,小于1800,大于900,等
6、于1800,等于3600,锐角直角钝角平角周角,他们之间有什么关系？,仔细读题，判断下面说法正确吗？1、平角就是一条直线。（ ）2、当角的两条边成一条直线时，这样的角就是平角。（ ）3、周角就是一条射线。（ ）4、一条射线就是一个周角。（ ）5、一条射线绕着它的端点转一周和它本身重合后，就形成一个周角。（ ）,三、巩固运用,巩固运用,说说每个钟面上的时针和分针各组成了什么角？,5,105,20,90,150,91,45,180,39,89,360,179,锐角,直角,钝角,平角,周角,5,20,45,39,90,105,150,179,180,360,89,91,分一分，填一填。,巩固运用,能力提升,说说下面这些图形的名称？,1= 700,2= （ ）,200,200,这节课你又有了哪些收获？,