含绝对值的不等式解法练习题及答案.pdf
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1、学习必备欢迎下载例 1 不等式|83x|0 的解集是 A BRCx|x D8383分析,即|83x|083x0 x83答选 C例 2 绝对值大于2 且不大于5 的最小整数是 A 3 B 2 C 2 D 5 分析列出不等式解根据题意得2|x|5从而 5x 2 或 2x5,其中最小整数为5,答选 D例 3不等式 4|13x|7 的解集为 _分析利用所学知识对不等式实施同解变形解原不等式可化为4|3x1|7,即 43x17 或 7 解之得 或 ,即所求不等式解集为 或 3x14x2x1x|2x1x53835383例 4已知集合Ax|2|62x|5,xN,求 A分析转化为解绝对值不等式解2|62x|5
2、 可化为2|2x6|5 即 ,或,52x652x622x62即,或,12x112x82x4解之得 或 4xx211212因为 xN,所以 A0,1,5 说明:注意元素的限制条件例 5 实数 a,b 满足 ab0,那么 -第 1 页,共 5 页精品p d f 资料 可编辑资料-学习必备欢迎下载A|ab|a|b|B|ab|ab|C|ab|ab|D|ab|a|b|分析根据符号法则及绝对值的意义解a、b 异号,|ab|ab|答选 C例 6 设不等式|xa|b 的解集为 x|1 x2,则 a,b 的值为 A a1,b 3 Ba 1,b3 Ca 1,b 3 Dab,1232分析解不等式后比较区间的端点解由
3、题意知,b0,原不等式的解集为x|a bx ab,由于解集又为x|1x 2 所以比较可得ab1ab2ab ,解之得,1232答选 D说明:本题实际上是利用端点的位置关系构造新不等式组例 7 解关于 x 的不等式|2x1|2m 1(m R)分析分类讨论解 若 即,则 恒不成立,此时原不等2m10m|2x1|2m112式的解集为;若 即,则 ,所以2m10m(2m1)2x12m11m12xm综上所述得:当时原不等式解集为;当时,原不等式的解集为mm1212x|1 mxm 说明:分类讨论时要预先确定分类的标准例解不等式8 3212|xx分析一般地说,可以移项后变形求解,但注意到分母是正数,所以能直接
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10、:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1文档编码:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1文档编码:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1文档编码:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1文档编码:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1文档编码:CW8Z1C5H2R9 HD6D6S9P2H10 ZG6R3A10I7I1学习必备欢迎下载解注意到分母|x|20,所以原不等式转化为2(3|x|)|x|2,整理得|x|xx|x,
11、从而可以解得,解集为 4343434343说明:分式不等式常常可以先判定一下分子或者分母的符号,使过程简便例 9 解不等式|6|2x1|1分析以通过变形化简,把该不等式化归为|ax b|c 或|axb|c 型的不等式来解解事实上原不等式可化为6|2x1|1 或6|2x1|1 由得|2x1|5,解之得 3x2;由得|2x1|7,解之得x3 或 x 4从而得到原不等式的解集为x|x 4 或 3x2 或 x3 说明:本题需要多次使用绝对值不等式的解题理论例 10已知关于x 的不等式|x2|x3|a 的解集是非空集合,则实数 a的取值范围是 _分析可以根据对|x2|x3|的意义的不同理解,获得多种方法
12、解法一当 x 2 时,不等式化为x2 x3a 即 2x1a 有解,而2x15,a5当 2x3 时,不等式化为x2 x3a 即 a5当 x3 是,不等式化为x2x3a 即 2x1 a有解,而 2x 15,a5综上所述:a 5 时不等式有解,从而解集非空解法二|x2|x3|表示数轴上的点到表示2 和 3 的两点的距离之和,显然最小值为3(2)5故可求 a 的取值范围为a5解法三利用|m|n|mn|得|x2|x3|(x2)(x3)|5所以 a 5时不等式有解说明:通过多种解法锻炼思维的发散性例 11 解不等式|x1|2x分析一对 2x 的取值分类讨论解之解法一原不等式等价于:或 2x0 x12xx1
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