2＝2±3．
x1＝2＋3，x2＝2－3． ·················································································· 6分
18．（本题6分）
解：解不等式①，得x＜2． ·························································································· 2分
解不等式②，得x≥－1． ······················································································· 4分 所以不等式组的解集是－1≤x＜2． ·········································································· 5分 所以不等式组的整数解是－1，0，1． ······································································· 6分
7
19．（本题6分）
a2－4a2＋2a2
解：(2－)÷ a－4a＋4a－2a－2
(a＋2)(a－2)a(a＋2)2＝[]÷ ··········································································· 3分 2－ (a－2)a－2a－2
a－2a
＝· ································································································ 5分
a－2a(a＋2)1
＝． ··········································································································· 6分
a＋2
20．（本题8分）
解：（1）因为24÷20%＝120(份)，所以本次抽取了120份电子小报． ··································· 2分 条形统计图中80分的份数是42，扇形统计图中80分的百分比是35%． ···················· 4分 （2）900×(30%＋10%) ··························································································· 6分
＝360(份)． ··································································································· 7分 所以估计该校学生比赛成绩达到90分以上（含90分）的电子小报有360份．
····································································································································· 8分
21．（本题8分）
解：（1）作图正确． ·································································································· 3分
（2）CF⊥AB．
理由如下：连接CD、CE、FD、FE． ··································· 4分 由作图知CD＝CE，FD＝FE． ············································ 5分 A
方法一：所以点C、F都在线段DE的垂直平分线上．
········································································ 7分
D ·P F
E B C 所以CF是线段DE的垂直平分线，即CF⊥AB． ······································ 8分
方法二：因为CF＝CF，所以△CDF≌△CEF． ···················································· 6分 所以∠DCF＝∠ECF． ········································································· 7分 又因为CD＝CE，所以CF⊥AB． ·························································· 8分
22．（本题8分）
1解：（1）．············································································································· 2分
3（2）分别转动两个转盘一次，所有可能出现的结果有：（1，4）、（1，5）、（1，
6）、（2，4）、（2，5）、（2，6）、（3，4）、（3，5）、（3，6），共有9种，它们出现的可能性相同．由于指针指向歌曲“3”时，该歌手就选择自己最擅长的歌曲“1”，所以所有的结果中，该歌手演唱歌曲“1”和“4”（记为
2
事件A）的结果有2种，所以P（A）＝． ······························································· 8分
9
8
（说明：通过枚举、画树状图或列表得出全部正确情况得4分；没有说明等可能性扣1分．）