2022英语周报二十八期答案

局二一轮复习·新咼考第二节One possible versionDear Sir/madamI' m writing to complain about a Kindle that I pur-chased from your website on May i stAfter one week of its purchase, I found it didnt workas expected. The battery didn't last long after beingrecharged, perhaps merely half a day. Worse than that, thewords on the screen were not distinct enough, which i thinkis damaging to my eyesighthave been a devoted customer of your company and: Ihope you will look into the matter seriously and replace thefaulty Kindle with a new one as guaranteed. Thank youYours sincerelyLi Hua

2x-7,x≥423.解析:(1)当a=4时,f(x)=x=3 x-4={13x<4(1分)2x-7≤2≤27-2x≤2故f(x)≤2等价于或或3≤x<4x<3解得:4≤x≤或3≤x<4或二≤x<3(3分)综上所述:不等式(x)52的解集为25分)(2)∵不等式f(x)≤a2-3的解集非空x∈R使得x-3 x-al≤a2-3a成立而x-3 x-2(x-3)-(x-a)=-3(6分)2a-3≥0即3a-a2≤a-3≤a2-3aa2-4a 3≥0a≥3或a≤-1解得(8分)a≥3或a≤1故a的取值范围为(一,-1[3, ∞)(10分)

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