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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,*,分数的大小比较,倒数比较法,3,吨,3,8,吨,10,3,25,吨,9,11,千克,10,11,千克,7,11,千克,3,8,吨,3,25,吨,3,10,吨,分母相同的两个分数,分子大的分数值越大,分子小的分数值越小。,分子相同的两个分数,分母越大分数值越小,分母越小分数值越大。,10,11,千克,9,11,千克,7,11,千克,复习题:比较分数大小:,7,12,41,60,和,4,321,6,531,和,【12,,,60】=60,7,12,=,125,75,=,60,35,因为,35,41,7,12,41,60,所以,技法回顾:,通,分母,分数比较大小方法:,1.,找分母的最小公倍数,2.,通分母,3.,比分子,4.,得结果,(,写原分数,),比较分数大小:,4,321,6,531,和,【4,,,6】=12,4,321,=,12,963,6,531,=,12,1062,因为,963,1062,所以,4,321,6,531,通,分子,分数比较大小方法:,1.,找分子的最小公倍数,2.,通分子,3.,比分母,4.,得结果,(,写原分数,),教学目标:,1.,使学生理解和掌握用倒数法比较异分母分数的大小。,(教学重点),2.,自主探究用倒数比较法解题的特征及方法。,(教学难点),3.,培养学生的动手操作能力,观察比较和对比总结的能力。,777,7777,7777,77777,比较分数大小:,777,7777,7777,77777,和,777,7777,的倒数是,7777,777,=,10,111,1,7777,77777,的倒数是,77777,7777,=,10,1111,1,所以,777,7777,7777,77777,因为,10,111,1,10,1111,1,判断方法:,倒数越大,原分数越小;,倒数越小,原分数越大。,比较分数大小:,33,333,333,3333,和,33,333,的倒数是,333,33,=,10,11,1,333,3333,的倒数是,3333,333,=,10,111,1,所以,33,333,333,3333,因为,10,11,1,10,111,1,5551,5555,的倒数是,5555,5551,5551,=,1,4,4563,4567,的倒数是,4567,4563,=,1,4563,4,比较分数大小:,5551,5555,4563,4567,9215,9219,9215,9219,的倒数是,9219,9215,=,1,9215,4,因为,5551,4,4563,4,9215,4,5551,5555,4563,4567,9215,9219,所以,把下面的分数按照从大到小的顺序排列。,5,9,10,19,15,37,30,61,1,5,4,1,10,9,15,2,7,2,30,1,9,5,19,10,37,15,61,30,倒数:,5,9,10,19,15,37,30,61,把下面的分数按照从大到小的顺序排列。,5,9,10,19,15,37,30,61,【5,10,15,30】=30,5,9,=,=,=,30,54,10,19,30,57,30,74,15,37,30,61,5,9,10,19,15,37,30,61,小探究:,什么样的题采用倒数法解题比较简单?,777,7777,7777,77777,和,5551,5555,4563,4567,9215,9219,技法小结:,在比较分数的大小时,如果分子、分母的差相等或分母是分子的几倍加(减)几,那么它们就能应用倒数比较法比较大小。,用倒数法比较时,倒数越大,原分数越小;倒数越小,原分数越大。,温馨小提示:,收获的果实,作业布置:,4567,4587,9876,9896,和,比较分数大小:,234,335,2134,2235,789,890,作业布置:,5551,5555,4563,4567,9215,9219,思考题:,感谢各位领导、,同事莅临指导!,
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