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2019年福州市质检理科数学(解析版)
试卷第 1 页,总 20 页 2019 年 福 州 市 普 通 高 中 毕 业 班 质 量 检测 理科数学 第 Ⅰ卷 一、选择题:本大题共 12 小题,每小题 5 分,共 60 分.在每小题给出的四个选项中,只有一项是符合题 目要求的. 1.设复数 z 满足i 1 iz ,则 z 的共轭复数为( ) A. 1 i B.1 i C. 1 i D.1 i 解析:因为 1 i 1 iiz ,所以 1+iz ,故选 A. 2.已知集合 22 1 3 , 2 0A x x B x x x ,则 A B =( ) A.{ |1 2}x x B.{ | 1 1}x x C.{ | }2 1, 1x xx 或 D.{ | 1}x x 解析:因为 1 , 1 2A x x B x x ,所以 1A B x x ,故选 D. 3.中国传统文化是中化民族智慧的结晶,是中化民族的历史遗产在现实生活中的展现.为弘扬中华民族 传统文化,某校学生会为了解本校高一 1000 名学生的课余时间参加传统文化活动的情况,随机抽取 50 名 学生进行调查.将数据分组整理后,列表如下: 参加场数 0 1 2 3 4 5 6 7 参加人数占调查人数的百分比 8% 10% 20% 26% 18% m% 4% 2% 以下四个结论中正确的是( ) A. 表中 m 的数值为 10 B. 估计该校高一学生参加传统文化活动次数不高于 2 场的学生约为 180 人 C. 估计该校高一学生参加传统文化活动次数不低于 4 场的学生约为 360 人 D. 若采用系统抽样方法进行调查,从该校高一 1000 名学生中抽取容量为 50 的样本,则分段间隔为 25 解析: A 中的 m 值应为 12; B 中应为 380 人; C 是正确的; D 中的分段间隔应为 20,故选 C. 4.等比数列{ }na 的各项均为正实数,其前 n 项和为 nS .若 3 2 64, 64a a a ,则 5S ( ) A.32 B.31 C.64 D.63 解析:解法一:设首项为 1a ,公比为 q ,因为 0na ,所以 0q ,由条件得 2 1 5 1 1 4 64 a q a q a q ,解得 1 1 2 a q , 所以 5 31S ,故选 B. 解法二:设首项为 1a ,公比为 q ,由 2 2 6 4 64a a a ,又 3 4a ,∴ 2q ,又因为 2 1 4a q 所以 1 1a , 所以 5 31S ,故选 B. 5. 已知sin π 1 6 2 ,且 π0, 2 ,则 3os πc ( ) 试卷第 2 页,总 20 页 A.0 B. 1 2 C.1 D. 3 2 解析:解法一:由 π 1sin 6 2 ,且 π0, 2 得, π 3 ,代入 πcos 3 得, πcos 3 = cos 0 1 ,故选 C. 解法二:由 π 1sin 6 2 ,且 π0, 2 得, π 3cos 6 2 , 所以 π π π π π π πcos cos cos cos sin sin 13 6 6 6 6 6 6 ,故选 C. 6.设抛物线 2 4y x 的焦点为 F ,准线为l , P 为该抛物线上一点, PA l , A 为垂足.若直线 AF 的 斜率为 3 ,则 PAF△ 的面积为( ) A. 2 3 B. 4 3 C.8 D.8 3 解析:解法一:设准线与 x 轴交于点 Q ,因为直线 AF 的斜率为 3 , 2FQ , 60AFQ , 4FA ,又因为 PA PF ,所以 PAF△ 是边长为 4 的等边三角形, 所以 PAF△ 的面积为 2 23 3 4 =4 34 4FA .故选 B. 解法二:设准线与 x 轴交于点Q , , )P m n( ,因为直线 AF 的斜率为 3 , 2FQ , 60AFQ , 所以 2 3AQ ,所以 2 3n ,又因为 2 4n m ,所以 3m , 又因为 4PA PF , 所以 PAF△ 的面积为 1 1 4 2 3=4 32 2PA n .故选 B. 7.如图,网格纸上的小正方形的边长为 1,粗实线画出的是某几何体的三视图,则该几何体的体积为( ) A.32 B.16 C. 32 3 D. 80 3 第 7 题 试卷第 3 页,总 20 页 解析:由三视图知,所求几何体的体积为直三棱柱的体积减去三棱锥的体积 3 21 1 804 4 2=3 2 3 1 2 .故 选 D. 8.已知函数 ( ) 2sin( )f x x 0, 图象的相邻两条对称轴之间的距离为 ,将函数 ( )f x 的图象向左平移 3 个单位长度后,得到函数 ( )g x 的图象.若函数 ( )g x 为偶函数,则函数 ( )f x 在区间 0, 2 上的值域是( ) A. 1 ,12 B.( 1,1) C.(0, 2] D.( 1,2] 解析:由图象的相邻两条对称轴之间的距离为 ,所以T ,又因为 0 ,所以 2 ,解得 =2 . 0, 2 ,将函数 ( )f x 的图象向左平移 3 个单位长度后,得到函数 2( ) 2sin 2 3g x x 的 图象.因为函数 ( )g x 为偶函数, 所以 2 ,3 2k k Z ,由 ,解得 = 6 ,所以 ( ) 2sin 2 6f x x . 因为0 2x ,所以 1 sin 2 12 6x ≤ ,所以函数 ( )f x 在区间 0, 2 上的值域是( 1,2] ,故选 D. 9.已知 ( )g x 为偶函数, ( )h x 为奇函数,且满足 ( ) ( ) 2xg x h x .若存在 [ 1,1]x ,使得不等式 ( ) ( ) 0m g x h x ≤ 有解,则实数 m 的最大值为( ) A. 1 B. 3 5 C.1 D. 3 5 解析:由 ( ) ( ) 2xg x h x ,及 ( )g x 为偶函数, ( )h x 为奇函数,得 2 2 2 2( ) , ( )2 2 x x x x g x h x - .由 ( ) ( ) 0m g x h x ≤ 得 2 2 4 1 212 2 4 1 4 1 x x x x x x xm -≤ ,∵ 21 4 1xy 为增函数,∴ max 2 31 4 1 5x ,故选 B. 10.如图,双曲线 2 2 2 2 1( 0, 0)x yC a ba b : 的左、右焦点分别为 1 2,F F ,过 2F 作线段 2F P 与C 交于点Q , 试卷第 4 页,总 20 页 且Q 为 2PF 的中点.若等腰△ 1 2PF F 的底边 2PF 的长等于C 的半焦距,则C 的离心率为( ) A. 2 2 15 7 B. 2 3 C. 2 2 15 7 D. 3 2 解析:连结 1QF ,由条件知 1 2QF PF ,且 2 2 cQF .由双曲线定义知 1 2 2 cQF a ,在 1 2Rt FQF△ 中, 2 2 22 22 2 c ca c ,解得C 的离心率 2 2 15 7e ,故选 C. 11.如图,以棱长为 1 的正方体的顶点 A 为球心,以 2 为半径做一个球面,则该正方体的表面被球面所 截得的所有弧长之和为( ) A. 3 4 B. 2 C. 3 2 D. 9 4 解析:正方体的表面被该球面被所截得的弧长有相等的三部分,例如,与上底面截得的弧长是以 1A 为圆心, 1为半径的圆周长的 1 4 ,所以弧长之和为 2 33 4 2 .故选 C. 12. 已知数列{ }na 满足 1 1a , 2 1 2 2 ( 1) 2 4 n n n n n aa a na n ,则 8a ( ) A. 64 8 9 2 B. 32 8 9 2 C. 16 8 9 2 D. 7 8 9 2 解析:因为 2 1 2 2 ( 1) 2 4 n n n n n aa a na n ,所以 2 2 2 1 2 41 ( 1) n n n n a na n a n a , 第 10 题图 第 11 题图 试卷第 5 页,总 20 页 所以 22 2 2 1 2 41 4 2n n n n n n a na nn n n a a a a , 所 以 2 1 1 2 2 n n n n a a , 令 2n n nb a , 则 2 1n nb b , 两 边 取 对 数 得 1lg 2lgn nb b , 又 1 1 1lg lg 2 lg3b a ,所以数列 lg nb 是首项为lg 3 ,公比为 2 的等比数列. 所以 11 2lg lg3 2 lg 3 nn nb ,所以 123 n nb ,即 1232 n n n a ,从而 123 2nn na ,将 8n 代入,选 A. 法二、因为 2 1 2 2 1 2 4 n n n n n aa a na n ,所以 2 2 2 1 2 41 1 n n n n a na n a n a , 所以 22 2 2 1 2 41 4 2n n n n n n a na nn n n a a a a , 所以 2 1 1 2 2 n n n n a a ,令 2n n nb a ,则 2 1n nb b ,因为 1 3b ,所以 2 2 3b ,所以 22 4 3 3 3b , 所以 24 8 4 3 3b ,…,所以 72 64 8 3 9b 。所以 8 8 8 2b a ,所以 8a 64 8 9 2 ,故选 A。 第Ⅱ卷 本卷包括必考题和选考题两部分.第 13~21 题为必考题,每个试题考生都必须作答.第 22 、23 题为选考题,考生根据要求作答. 二、填空题:本大题共 4 小题,每小题 5 分,共 20 分. 13.已知两个单位向量 ,a b ,满足 3a b b ,则 a 与b 的夹角为__________. 解析:因为 ,a b 是单位向量, 3a b b , 2 2 2 1= 3 2 cos , 2 2cos , 1, cos , , ,2 3 2 a b a a b a b b a b a b a b ( ), . 14. 已知点 (0, 2)A ,动点 ( , )P x y 的坐标满足条件 0x y x ≥ ≤ ,则 PA 的最小值是 . 解析: PA 的最小值转化成点 A 到直线 y x 的距离 2 2 2 d -= , 15. 2 5(1 ) (1 )ax x 的展开式中,所有 x 的奇数次幂项的系数和为-64,则正实数 a 的值为__________. 解析:设 2 5 2 3 4 5 6 7 0 1 2 3 4 5 6 7(1 ) (1 )ax x a a x a x a x a x a x a x a x , 令 1x 得 0 1 2 3 4 5 6 70 a a a a a a a a ①, 试卷第 6 页,总 20 页 令 1x 得 2 5 0 1 2 3 4 5 6 7(1 ) 2a a a a a a a a a ②, ②-①得: 2 5 1 3 5 7(1 ) 2 2( + )a a a a a ,又因为 1 3 5 7+ 64a a a a , 2 5(1 ) 2 128a ,解得 3 1a a 或 (舍). 16.已知函数 2 e( ) ln(2 ) e x f x a x 有且只有一个零点,则实数 a 的取值范围是__________. 解析:解法一:由当 1 2x 时,显然 1 2x 不是该函数的零点;当 1 2x 时,由 2 e( ) ln 2 e 0 x f x a x ,分离参数得 2 ee ln 2 x a x ,令 2 ee( ) ln 2 x p x x , 函数 2 e( ) ln 2 e x f x a x 有且只有一个零点,等价于直线 y a 与函数 2 ee( ) ln 2 x p x x 有且只有一个零点。 利用导数,可判断并得出 ( )p x 的图象如图所示, 因为直线 y a 与函数 ( )p x 的图象的交点个数为 1, 由图可知,实数 a 的取值范围是 ( ,0) { }e . 解法二:由 2 e( ) ln 2 e x f x a x 得 2 e2( ) ln ee xxf x a a .令 2 0e xt t , 则 ( ) ln etg t a t a .当 1 et 时, 1 e1 e 0eg ,所以 1 et 不是函数 ( )g t 的零点; 当 1 et 时,令 ( ) ln e 0tg t a t a ,分离参数得 e ln 1 t a t , 试卷第 7 页,总 20 页 所以 2 e( ) ln e x f x a x a R 的零点个数问题,等价于直线 y a 与函数 e 1( ) 0ln 1 e t p t t tt 且 的图象的交点个数的问题.利用导数,可判断并得出 ( )p t 的图象如图所示, 因为直线 y a 与函数 e 1( ) 0ln 1 e t p t t tt 且 的图象的交点个数为 1, 由图可知,实数 a 的取值范围是( ,0) { }e . 三、解答题:解答应写出文字说明、证明过程或演算步骤. 17. (12 分) ABC△ 的内角 A , B ,C 的对边分别为 a ,b ,c .若角 A , B ,C 成等差数列,且 3 2b . (1)求 ABC△ 的外接圆直径; (2)求 a c 的取值范围. 【解析】(1)由角 A 、 B 、C 成等差数列, 所以 2 +B A C ,···················································································· 1 分 又因为 + + =A B C , 所以 3B ,·························································································· 2 分 根据正弦定理得, ABC△ 的外接圆直径 3 22 = 1πsin sin 3 bR B . ····················· 4 分 (2)解法一:由(1)知, 3B ,所以 2 3A C ,所以 20 3A , ··········· 5 分 试卷第 8 页,总 20 页 由(1)知 ABC△ 的外接圆直径为 1,根据正弦定理得, 1sin sin sin a b c A B C , ······································································ 6 分 ∴ 2sin sin sin sin 3a c A C A A ··············································· 8 分 3 13 sin cos2 2A A 3 sin 6A . ······································································ 9 分 ∵ 20 3A ,∴ 5 6 6 6A ∴ 1 sin 12 6A ≤ , ·········································································11 分 从而 3 3 sin 32 6A ≤ , 所以 a c 的取值范围是 3 , 32 . ························································12 分 解法二:由(1)知, 3B ,根据余弦定理得, 2 2 2 2 cosb a c ac B ··········································································· 6 分 2( ) 3a c ac ··················································································· 7 分 2 2 21( ) 3 ( )2 4 a ca c a c ≥ ,(当且仅当 a c 时,取等号)················· 9 分 因为 3 2b , ∴ 2( ) 3a c ≤ ,即 3a c ≤ ,······························································10 分 又三角形两边之和大于第三边,所以 3 32 a c ≤ ,································11 分 所以 a c 的取值范围是 3 , 32 . ································································12 分 18. (12 分) 试卷第 9 页,总 20 页 如图,四棱锥 P ABCD , //AB CD , 90BCD , 2 2 4AB BC CD , PAB△ 为等边三角形, 平面 PAB 平面 ABCD , Q 为 PB 中点. (1) 求证: AQ 平面 PBC ; (2)求二面角 B PC D 的余弦值. (1)证明:因为 //AB CD , 90BCD , 所以 AB BC , 又平面 PAB 平面 ABCD ,且平面 PAB 平面 ABCD AB , 所以 BC ⊥平面 PAB ,············································································· 1 分 又 AQ 平面 PAB ,所以 BC ⊥ AQ ,························································ 2 分 因为Q 为 PB 中点,且 PAB△ 为等边三角形,所以 PB ⊥ AQ ,······················· 3 分 又 PB BC B , 所以 AQ 平面 PBC . ········································································ 4 分 (2)解法一:取 AB 中点为O ,连接 PO ,因为 PAB△ 为等边三角形,所以 PO⊥ AB , 由平面 PAB ⊥平面 ABCD ,因为 PO 平面 PAB ,所以 PO ⊥平面 ABCD ,········· 5 分 所以 PO ⊥OD ,由 2 2 4AB BC CD , 90ABC , 可知 //OD BC ,所以OD AB . 以 AB 中点O 为坐标原点,分别以 , ,OD OB OP 所在直线为 , ,x y z 轴,建立如图所示的空间直角坐标系 O xyz . ··································································································· 6 分 所以 (0, 2,0), (2,0,0),A D (2,2,0), (0,0, 2 3), (0, 2,0)C P B , 则 2,2,0 , ( 2,0,2 3), (0, 2,0)AD DP CD , 因为Q 为 PB 中点,所以 (0,1, 3)Q , 由 (1) 知,平面 PBC 的一个法向量为 (0,3, 3)AQ .······································· 7 分 设平面 PCD 的法向量为 ( , , )n x y z ,由 0, 0 n CD n DP 得 2 0 2 2 3 0 y x z ,取 1z ,则 ( 3,0,1)n ,·················································· 9 分 由 2 3 1cos , 43 3 3 1 AQ nAQ n AQ n .··············································11 分 x y z O 第 18 题 试卷第 10 页,总 20 页 因为二面角 B PC D 为钝角, 所以,二面角 B PC D 的余弦值为 1 4 .·······················································12 分 解法二: 取 AB 中点为O ,连接 PO ,因为 PAB△ 为等边三角形,所以 PO⊥ AB , 由平面 PAB ⊥平面 ABCD ,所以 PO ⊥平面 ABCD ,········································· 5 分 所以 PO ⊥OD ,由 2 2 4AB BC CD , 90ABC , 可知 //OD BC ,所以OD AB . 以 AB 中点O 为坐标原点,分别以 , ,OA OD OP 所在直线为 , ,x y z 轴,建立如图所示的空间直角坐标系 O xyz . ···································································································· 6 分 所以 (2,0,0), (0, 2,0), ( 2, 2,0),A D C (0,0, 2 3), ( 2,0,0)P B , 所以 ( 2, 2,0), (0, 2, 2 3),AD DP (2,0,0)CD , 由(1)知,可以 AQ 为平面 PBC 的法向量, 因为Q 为 PB 的中点, 所以 ( 1,0, 3)Q , 由(1)知,平面 PBC 的一个法向量为 ( 3,0, 3)AQ ,········································ 7 分 设平面 PCD 的法向量为 ( , , )n x y z , 由 0, 0 n CD n DP 得 2 0 2 2 3 0 x y z , 取 1z ,则 (0, 3,1)n ,············································································· 9 分 所以 2 3 1cos , 43 3 3 1 AQ nAQ n AQ n ···············································11 分 因为二面角 B PC D 为钝角, 所以,二面角 B PC D 的余弦值为 1 4 .·······················································12 分 解法三:过点 B 作 PC 的垂线 BH ,交 PC 于点 H ,连结 DH .由解法一或二知 PO ⊥平面 ABCD ,CD 平面 ABCD ,所以 PO CD .由条件知OD CD , 又 PO OD O ,所以CD ⊥平面 POD , 又 PD 平面 POD ,所以CD PD⊥ , 又CD CB ,所以 Rt PDC Rt PBC△ ≌ △ , 所以 DH PC⊥ ,由二面角的定义知,二面角 B PC D 的平面角为 BHD . x y z O 第 18 题 H O 试卷第 11 页,总 20 页 ·················································································································· 7 分 在 Rt PDC△ 中, 4, 2PB BC , 2 5PC , 由 PB BC BH PC ,所以 4 2 4 5 52 5 PB BCBH PC . ······························· 8 分 同理可得 4 5 5DH , ·················································································· 9 分 又 2 2BD .在 BHD△ 中, 2 2 2 cos 2 BH DH BDBHD BH DH ∠ ···································································10 分 2 2 24 5 4 5 2 25 5 1 44 5 4 52 5 5 . 所以,二面角 B PC D 的余弦值为 1 4 .·······················································12 分 19.(12 分) 最近,中国房地产业协会主办的中国房价行情网调查的一份数据显示,2018 年 7 月,大部分一线城市的房 租租金同比涨幅都在 10%以上.某部门研究成果认为,房租支出超过月收入 1 3 的租户“幸福指数”低,房租 支出不超过月收入 1 3 的租户“幸福指数”高.为了了解甲、乙两小区租户的幸福指数高低,随机抽取甲、乙 两小区的租户各 100 户进行调查.甲小区租户的月收入以 0 3, , 3 6, , 6 9, , 9 12, , 12 15, (单 位:千元)分组的频率分布直方图如下: 月收入/千元0 3 6 9 12 15 0.030 0.0600.070 0.160 频率 组距 乙小区租户的月收入(单位:千元)的频数分布表如下: 月收入 [0,3) [3,6) [6,9) [9,12) [12,15] 试卷第 12 页,总 20 页 户数 38 27 24 9 2 (1)设甲、乙两小区租户的月收入相互独立,记 M 表示事件“甲小区租户的月收入低于 6 千元,乙小区 租户的月收入不低于 6 千元”.把频率视为概率,求 M 的概率; (2)利用频率分布直方图,求所抽取甲小区 100 户租户的月收入的中位数; (3)若甲、乙两小区每户的月租费分别为 2 千元、1 千元.请根据条件完成下面的 2 2 列联表,并说明 能否在犯错误的概率不超过 0.001 的前提下认为“幸福指数高低与租住的小区”有关. 幸福指数低 幸福指数高 总计 甲小区租户 乙小区租户 总计 附:临界值表 P(K2≥k) 0.10 0.010 0.001 k 2.706 6.635 10.828 参考公式: 2 2 ( ) ( )( )( )( ) n ad bcK a b c d a c b d . 【解析】(1)记 A 表示事件“甲小区租户的月收入低于 6 千元”,记 B 表示事件“乙小区租户的月收入不低 于 6 千元”, 甲小区租户的月收入低于 6 千元的频率为(0.060+0.160) 3=0.66 , 故 ( )P A 的估计值为0.66 ;·············································································· 1 分 乙小区租户的月收入不低于 6 千元频率为 24 9 2 =0.35100 , 故 ( )P B 的估计值为0.35; ·············································································· 2 分 因为甲、乙两小区租户的月收入相互独立, 事件 M 的概率的估计值为 ( )= ( ) ( ) 0.66 0.35=0.231P M P A P B .························ 4 分 (2)设甲小区所抽取的 100 户的月收入的中位数为t , 则 0.060 3+( 3) 0.160=0.5t ,····································································· 6 分 解得 5t . ·································································································· 7 分 (3)设 0 :H 幸福指数高低与租住的小区无关, 幸福指数低 幸福指数高 总计 甲小区租户 66 34 100 乙小区租户 38 62 100 总计 104 96 200 试卷第 13 页,总 20 页 ·················································································································· 9 分 根据 2 2 列联表中的数据, 得到 2K 的观测值 2200(66 62 38 34) 15.705 10.828104 96 100 100k , ·······················11 分 所以能在犯错误的概率不超过 0.001 的前提下认为“幸福指数高低与租住的小区”有关. …………12 分 20. (12 分) 已知圆O : 2 2 2x y r ,椭圆 2 2 2 2: 1 0x yC a ba b 的短半轴长等于圆O 的半径,且过C 右焦点的 直线与圆O 相切于点 1 3,2 2D . (1)求椭圆C 的方程; (2)若动直线l 与圆O 相切,且与C 相交于 ,A B 两点,求点O 到弦 AB 的垂直平分线距离的最大值. 【解析】(1)解法一:由条件知 22 2 1 3 12 2r , ····································· 1 分 所以 1b .·································································································· 2 分 过点 D 且与圆O 相切的直线方程为: 3 3 1 2 3 2y x , 即 3 2 0x y .······················································································· 3 分 令 0y 得, 2x ,由题意知, 2c ,从而 2 2 2 5a b c ································ 4 分 所以椭圆C 的方程为: 2 2 15 x y .································································· 5 分 解法二:由条件知 22 2 1 3 12 2r , ······················································· 1 分 所以 1b .·································································································· 2 分 设椭圆右焦点坐标为( ,0)c ,过该点与圆O相切于点 1 3,2 2D 的直线方程为: 3 3 12 ( )12 2 2 y x c , 化简得: 2 3 2(1 2 ) 2 3 0x c y c ,··························································· 3 分 圆O到直线的距离等于半径 1,即 2 2 2 3 1 (2 3) ( 2(1 2 )) c c , 解得 2c . 从而 2 2 2 5a b c , ··················································································· 4 分 试卷第 14 页,总 20 页 所以椭圆C 的方程为: 2 2 15 x y .································································· 5 分 解法三:如图,设椭圆的右焦点为 F ,由于直线l 与圆O 相切于点 D,所以三角形 FOD 是以 ODF 为 直角的直角三角形. ······················································································ 1 分 因为切点的坐标为 1 3,2 2D ,所以 60DOF .··········································· 2 分 由条件知 22 2 1 3 12 2r ,所以圆的半径 1r . ······································· 3 分 所以在 Rt FOD△ 中, 2OF .从而 2 2 2 5a b c .······································· 4 分 所以椭圆C 的方程为: 2 2 15 x y .································································· 5 分 (2)解法一:设点O 到弦 AB 的垂直平分线的距离为 d , ①若直线l x 轴,弦 AB 的垂直平分线为 x 轴,所以 0d ;若直线l y 轴,弦 AB 的垂直平分线为 y 轴, 所以 0d .································································································· 6 分 ②设直线l 的方程为 ( 0)y kx m k ,因为l 与圆O 相切, 所以 2 1 1 m k ,即 21m k .································································· 7 分 由 2 2 15 y kx m x y ,消去 y 得 2 2 2(1 5 ) 10 5 5 0k x kmx m . 设 1 1 2 2( , ), ( , )A x y B x y ,由韦达定理知: 1 2 1 2 1 22 2 10 2, ( ) 21 5 1 5 km mx x y y k x x mk k . ······································ 8 分 所以 AB 中点的坐标为 2 2 5 ,1 5 1 5 km m k k , 所以弦 AB 的垂直平分线方程为 2 2 1 5 1 5 1 5 m kmy xk k k , 试卷第 15 页,总 20 页 即 2 4 01 5 kmx ky k . ················································································· 9 分 所以 2 2 4 1 5 1 km kd k . ···················································································10 分 将 21m k 代入得, 2 22 4 4 4 4 2 51 5 11 5 52 51 5 km kkd kk kk ≤ , (当且仅当 5 5k , 30 5m 时,取等号).·················································11 分 综上所述,点O 到弦 AB 的垂直平分线距离的最大值为 2 5 5 .······························12 分 解法二:设点O 到弦 AB 的垂直平分线的距离为 d , ①若直线l x 轴,弦 AB 的垂直平分线为 x 轴,所以 0d ;若直线l y 轴,弦 AB 的垂直平分线为 y 轴, 所以 0d .································································································· 6 分 ②设 1 1 2 2( , ), ( , )A x y B x y , AB 中点坐标为 0 0( , )M x y ,由点 ,A B 在椭圆上得, 2 21 1 2 22 2 1,5 1,5 x y x y ① ② , 由①-②得, 1 2 1 2 1 2 1 2 1 05 x x x x y y y y , 即 01 2 1 2 1 2 1 2 0 1 5 5AB xy y x xk x x y y y ,··························································· 7 分 所以直线l 的方程为: 0 0ABy y k x x ,化简得 2 2 0 0 0 05 5 0x x y y x y . ····· 8 分 因为直线l 与圆O 相切,所以 2 2 0 0 2 2 0 0 5 1 25 x y x y ,化简得 2 2 2 2 0 0 0 05 25x y x y , ·················································································································· 9 分 又因为弦 AB 的垂直平分线方程为 0 0 0 0 5yy y x xx ,即 0 0 0 05 4 0y x x y x y ,10 分 所以,点O 到弦 AB 的垂直平分线的距离为: 试卷第 16 页,总 20 页 d 0 0 0 0 2 22 2 0 0 0 00 0 0 0 4 4 4 4 2 5 5 55 2 525 x y x y x y x yx y y x ≤ , 当且仅当 2 2 0 05x y 时,取等号. ···································································11 分 所以点O 到弦 AB 的垂直平分线距离的最大值为 2 5 5 .·······································12 分 21. (12 分) 已知函数 ( ) ln(1 ) ( )1 xf x a x ax R , 2 m 1 2e e( ) xg x x . (1)求函数 ( )f x 的单调区间; (2)若 0a , 1 2, [0, ]x x e ,不等式 1 2( ) ( )f x g x≥ 恒成立,求实数 m 的取值范围. 【解析】(1)因为 ( ) ln(1 ) ( 1)1 xf x a x xx , 所以 2 2 1 1( ) ( 1) 1 ( 1) a ax af x x x x , ······················································· 1 分 当 0a ≤ 时, ( ) 0f x ,所以函数 ( )f x 的单调递增区间为( 1, ) . ···················· 2 分 当 0a 时,由 ( ) 0 1 f x x ,得 11 1x a ; 由 ( ) 0 1 f x x ,得 11x a ; ········································································ 3 分 所以函数 ( )f x 的单调递增区间是 11, 1 a ;递减区间是 11 ,a . ············ 4 分 综上所述,当 0a ≤ 时,函数 ( )f x 的单调递增区间为( 1, ) . 当 0a 时,函数 ( )f x 的单调递增区间是 11, 1 a ;递减区间是 11 ,a . ·················································································································· 5 分 (2)若 0a , 1 2, [0, ]x x e ,不等式 1 2( ) ( )f x g x≥ 恒成立, 等价于“对任意 [0, ]x e , min( ) ( )maxf x g x≥ 恒成立”. ······································· 6 分 当 0a 时,由(1)知,函数 ( )f x 在[0, ]e 单调递增, 所以 min( ) 0 0f x f . ·············································································· 7 分 试卷第 17 页,总 20 页 mx+1 2 1 mx+1( ) 2 e + e ( 2)emxg x x x m x mx , (i)当 0m≥ 时,由0 ex≤ ≤ ,得 ( ) 0g x ≥ ,知函数 ( )g x 在[0, ]e 单调递增, 所以 e 3 2 max( ) (e) e e 0mg x g ,不符合题意. ·········································· 8 分 当 0m 时,令 ( ) 0g x 得, 20,x x m 或 . (ii)当 2 0e m ≤ ,即 2 em ≥ 时,在[0, ]e 上 ( ) 0g x ≥ ,所以 ( )g x 在 [0, ]e 上单调递增,所以 e 3 2 max ( ) (e) e emg x g ,只需满足: e 3 2e e 0m ≤ ,即 1 em ≤ , 所以 2 1 e em ≤ ≤ .···················································································· 9 分 (iii)当 2 em ,即 20 em 时, 在 20, m 上 ( ) 0g x ≥ ,所以 ( )g x 在 20, m 单调递增; 在 2 ,em 上 ( ) 0g x ≤ ,所以 ( )g x 在 2 ,em 单调递减, 所以 2 max 2 2 4( ) ( ) e 0eg x g m m ≤ , 所以 2 3 4 em ≥ , 得 3 4 em ≤ ,又因为 3 4 2 e e ,所以 2 em .··················11 分 综上所述,实数 m 的取值范围为 1, e . ·····················································12 分 (二)选考题:共 10 分.请考生在第 22、23 题中任选一题作答.如果多做,则按所做第一个题目计分. 22. [选修 4 4 :坐标系与参数方程] (10 分) 在直角坐标系 xOy 中,直线l 的参数方程为 1 2 3 2 x t y a t (t 为参数,aR ).以坐标原点为极点,x 轴 正半轴为极轴建立极坐标系,曲线C 的极坐标方程为 4cos ,射线 03 ≥ 与曲线C 交于 ,O P 两点,直线l 与曲线C 交于 ,A B 两点. (1)求直线l 的普通方程和曲线 C 的直角坐标方程; (2)当 AB OP 时,求 a 的值. 试卷第 18 页,总 20 页 【解析】(1)将直线l的参数方程化为普通方程为 3 0x y a . ························ 2 分 由 4cos ,得 2 4 cos ,··································································· 3 分 从而 2 2 4x y x ,即曲线C 的直角坐标方程为 2 24 0x x y . ························· 5 分 (2)解法一:由 4cos 03 ≥ ,得 2, 3P . 所以 2OP , ····························································································· 6 分 将直线l的参数方程代入圆的方程 2 24 0x x y ,得 2 2(2 3 ) 0t a t a 由 0 ,得 2 3 4 2 3 4a ·································································· 8 分 设 A、B 两点对应的参数为 1 2,t t , 则 2 2 1 2 1 2 1 2AB 4 4 4 3 2t t t t t t a a ····································· 9 分 解得, 0a 或 4 3a . 所以,所求 a 的值为0 或 4 3 . ······································································10 分 解法二:将射线 ( 0)3 ≥ 化为普通方程为 3 0 ( 0)x y x ≥ ,···················· 6 分 由(1)知,曲线C : 2 2( 2) 4x y 的圆心 (2,0)C ,半径为 2 , 由点到直线距离公式,得C 到该射线的距离为: 2 3 3 3 1 d , 所以该射线与曲线C 相交所得的弦长为 2 22 2 ( 3) 2OP .·························· 7 分 圆心C 到直线l 的距离为: 2 3 2 3 23 1 a a , ·············································· 8 分 由 2 2 2 2 3 1 22 a ,得 2(2 3 ) 12a ,即 2 3 2 3a ,····················· 9 分 解得, 0a 或 4 3a 所以,所求 a 的值为0 或 4 3 . ······································································10 分 23.[选修 4 5 :不等式选讲] (10 分) 已知不等式 2 1 2 1 4x x 的解集为 M . 试卷第 19 页,总 20 页 (1)求集合 M ; (2)设实数 ,a M b M ,证明: 1ab a b ≤ . 【解析】(1)解法一:当 1 2x 时,不等式化为: 2 1 1 2 4x x ,即 1x , 所以 11 2x ;························································································ 2 分 当 1 1 2 2x ≤ ≤ 时,不等式化为: 2 1 2 1 4x x ,即 2 4 , 所以 1 1 2 2x ≤ ≤ ; ······················································································ 3 分 当 1 2x 时,不等式化为: 2 1 2 1 4x x ,即 1x , 所以 1 12 x ; ···························································································· 4 分 综上可知, { 1 1}M x x .······································································ 5 分 解法二:设 ( ) 2 1 2 1f x x x , 则 14 , ,2 1 1( ) 2, ,2 2 14 , 2 x x f x x x x ≤ ≤ ··········································································· 2 分 函数 ( )f x 如下图所示, ·················································································································· 4 分 因为 ( ) 4f x ,由上图可得, 1 1x 试卷第 20 页,总 20 页 所以 1 1M x x .··············································································· 5 分 解法三:不等式 2 1 2 1 4x x , 等价于 1 2 2 1 1 2 4 x x x 或 1 1 2 2 2 1 2 1 4 x x x ≤ ≤ 或 1 2 2 1 2 1 4 x x x ;··············· 3 分 解得 1 1x , 1 1M x x .·················································································· 5 分 (2)证法一:因为 ,a M b M ,所以 1, 1a b ≥ . ······································· 6 分 而 1 1ab a b ab a b ······························································· 7 分 = 1 1 0a b ≤ ······················································································ 9 分 所以 1ab a b ≤ . ·················································································10 分 证法二:要证 1ab a b , 只需证: 1 0a b a b ≤ ,······································································ 6 分 只需证: 1 1 0a b ≤ , ········································································ 8 分 因为 ,a M b M ,所以 1, 1a b ≥ , ··························································· 9 分 所以 1 1 0a b ≤ 成立. 所以 1ab a b ≤ 成立. ···········································································10 分查看更多