巧“换元”解难题
江苏省如东县大豫镇社区教育中心 陈 耀
当常规的方法很难有效解决问题时,我们往往会想到用“换元”的方法,使原本比较复杂的问题变得稍为简单一些.“换元”的巧妙程度直接决定了你解题的难易程度,本文介绍几个“数与字母互换”的例题,供大家欣赏.
例1.比较大小
(第
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解:设
则
,上面两数之比为
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例2(第六届全国部分省市联赛题)若
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(C)
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解:由题意,设
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例3.计算:
(第七届美国邀请赛试题)
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解:设
,
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