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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,30,、,45,、,60,、,90,、,15,、,75,、,105,、,120,、,135,、,150,、,165,、,180,3,、请你试用一对三角尺根据刚才学过的角的和差,知识拼出所有的特殊角。,B,做一做,O,C,A,从一个角的顶点出发，把这个角分成相等的两个角的射线叫做这个角的,角平分线。,在一张纸上画出一个角,AOC,并剪,下，将这个角对折，使其两边重,合，折痕记作,OB,，它与角两边所,成的两个角的大小有什么关系？,OB,平分,AOC,（已知）,AOB=BOC=,1/2,AOC,或,AOC=2 AOB=2 BOC,（角平分线定义）,A,B,C,D,O,如图 ,AOB,BOC,COD,，,则,OB,是,的平分线，,AOC,，,BOD,BOC,AOC,BOC,BOC,AOD,BOD,AOD,此时,OB,、,OC,叫,AOD,的三等份线,练一练,A,B,C,D,E,AD,是,BAC,的平分线,=,ABC=2 ABE,平分,（角平分线的定义）,BAD,CAD,BE,ABC,（角平分线的定义）,练一练,角的度量单位：度、分、秒,.,度,分,秒,60,60,3600,60,3600,60,1,的,60,分之一为,1,分，记作“,1”,，即,1,60,1,的,60,分之一为,1,秒，记作“,1”,，即,1,60,复习回顾一、角的度量单位,例,1,：填空,（,1,）,34.5,0,=,0,/,（,2,）,112.27,0,=,0,/,/,解：（,1,）,34.5,0,=34,0,+0.5,0,=34,0,+0.5,60,/,=34,0,+3 0,/,=34,0,30,/,（,2,）,112.27,0,=112,0,+0.2760,/,=112,0,+16.2,/,=112,0,+16,/,+0.260,/,=112,0,16,/,12,/,34,30,112,16,12,题型一：角度的换算,例,2,、把下列各题结果化成度,72,0,36,/,(2)37,0,14,/,24,/,解,:(1)72,0,36,/,=72,0,+36,/,=72,0,+(3660),0,=72,0,+0.6,0,=72.6,0,(2)37,0,14,/,24,/,=37,0,+14,/,+24,/,=37,0,+14,/,+(24,60),/,=37,0,+14,/,+0.4,/,=37,0,+14.4,/,=37,0,+(14.460),0,=37,0,+0.24,0,=37.24,0,例,3,、加减法计算,解,:(1),原式,=(12+45),0,+(36+24),/,+(56+35),/,=57,0,+60,/,+91,/,=57,0,+61,/,+31,/,=58,0,+1,/,+31,/,=58,0,1,/,31,/,题型二：角度的加减法运算,(1)12,0,36,/,56,/,+45,0,24,/,35,/,(2)79,0,45,/,61,0,48,/,49,/,(2)79,0,45,/,61,0,48,/,49,/,解,:,原式,=79,0,44,/,60,/,61,0,48,/,49,/,=78,0,104,/,60,/,61,0,48,/,49,/,=(78-61),0,(104-48),/,(60-49),/,=17,0,56,/,11,/,例,4,、乘除法运算,(3)21,0,31,/,27,/,3 (4)63,0,21,/,39,/,3,(5)106,0,6,/,25,/,5,解,:,原式,=(213),0,(313),/,(273),/,=63,0,93,/,81,/,=63,0,94,/,21,/,=64,0,34,/,21,/,题型三：角度的乘除法运算,(4)63,0,21,/,39,/,3,解,:,原式,=(633),0,(213),/,(393),/,=21,0,7,/,13,/,(5)106,0,6,/,25,/,5,解,:,原式,=(1065),0,(65),/,(255),/,=21,0,(,66,5),/,(255),/,=21,0,13,/,(,85,5),/,=21,0,13,/,17,/,题型三：角度的乘除法运算,例,5,：计算,例题讲解,=825936,解（,1,）,=3738+4521.6,=3738+452136,解,=3236,=4660-1424,=,（,46-14,）,（,60-24,）,=,（,37+45,）,（,38+21,）,36,例,1,：如图,O,是直线,AB,上一点,AOC=5317BOC,度数,A,O,B,C,解：,BOC=AOB-AOC=180-5317,=12643,例题讲解,例,2,：把一个周角,7,等分,每一份角是多少度,?,（精确到分）,解,:,3607=,51+,37,=51+,180 7,51+,26,即,5126,A,B,D,C,A,B,D,C,应用新知,解决问题,3.,已知,OB,是,AOC,的平分线，,OD,是,COE,的平分线。,（,1,）如果,AOB,40,，,DOE,30,那么,BOD,是多少度？,（,2,）如果,AOE,140,，,COD,30,那么,AOB,是多少度？,30,30,40,40,2.,如图,AOC=40,COB=70,ON,、,OM,分别 平 分,AOC,、,COB,求：,MON,的度数,.,N,C,M,B,O,A,解,:,因为,ON,平分,AOC,所以,NOC=0.5AOC=20,因为,OM,平分,COB,所以,COM=0.5COB=35,=20+35,=55.,20,35,所以,MON=NOC+COM,2,、如图，,AOC,和,BOD,都是直角。,若,DOC,=28,，说出,AOB,的度数。,A,B,C,D,O,3,.(2008,呼和浩特中考,),将一副三角板按图示方法放置（直角顶点重合）,C,O,A,D,B,则,AOB+DOC=,_,看谁反应快,:,比一比,29,H,180,小结与归纳,1,度、分、秒都是,60,进制，逢,60,进,1,；,加减法要将度与度、分与分、秒与秒分别加减，,分秒相加逢,60,要进位，相减时要借,1,当作,60,；,（借,1,作,60,；借,1,作,60,）,3,乘法运算度分秒同时分别乘；,除法先从度开始除，除不尽转化为分，再,除不尽转化为秒，直到精确到要求的位数为止；,
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