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高三数学参考答案
2023.11
题号 1 2 3 4 5 6 7 8 9 10 11 12
答案 C A C B A B D C AD AB ACD BD
题号 13 14 15 16
答案 3
第1页(共6页)
f ( x ) s in ( 2 x
3
)
2 0 ,
4
2 7
17.【答案】(1) 因为 f ( x
1
) 0 , f ( x
2
) 0 ,且 x
1
x
2
的最小值为
2
,所以
T
2 2
,
则 T
2
,所以 2,············································································ 2分
T
又 f ( 0 ) 2 3 ,所以 4 s in 2 3 ,
又 | |
2
,所以
3
,
所以 f ( x ) 4 s in ( 2 x
3
)
. ················································································· 3分
令
2
2 k 2 x
3 2
2 k
,解得
5
1 2
k x
1 2
k , k Z ,
所以函数 f(x)的单调递增区间为
5
1 2
k ,
1 2
k , k Z .
··································· 5分
(2) 由题可知 f ( ) 4 s in ( 2
3
)
1 2
5
3
,则sin(2 ) ,
3 5
因为 (
1 2
,
2
)
,所以 2
3
(
2
,
4
3
)
,
所以 c o s ( 2
3
) 1 (
3
5
) 2
4
5
, ································································· 7分
所以sin2sin[(2 ) ]sin(2 )cos cos(2 )sin
3 3 3 3 3 3
3
5
1
2
(
4
5
)
2
3
3
1
4
0
3
. ·····························································10分
18.【答案】(1) 证明:连接 A B
1
, A
1
B 交于点 E ,连接 A C
1
, A C1 交于点 F ,连接 E F ,
则平面ABC 和平面ABC交线为EF,
1 1 1
因为ABCABC 为直三棱柱,所以
1 1 1
A B B
1
A
1
,ACC A 为平行四边形,
1 1
所以 E 为AB 中点,
1
F 为AC 中点,所以EF BC , ·········································· 4分
1 1 1
又 E F 平面ABC ,BC 平面ABC ,
1 1 1 1 1 1 1 1
所以EF 平面ABC ,即l 平面
1 1 1
A
1
B C1
1
. ························································ 6分
(2) 直三棱柱 A B C A
1
B C1
1
中, B A B C ,所以BA,BC,BB 两两垂直.
1
以 BA,BC,BB 为单位正交基底,建立如图所示的空间直角坐标系Bxyz,
1
则C(0,1,0),C (0,1,1),A(1,0,1). ···································································· 7分
1 1
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}第2页(共6页)
A
1
A
x
E
B
z
1
B
F
C
C
1
y
设 Q ( 0 , 0 , t ) ,则 Q C
1
( 0 ,1 ,1 t ) , C A
1
(1 , 1 ,1 ) ,
所以 c o s Q C
1
, C A
1
Q
Q
C
C
1
1
C
C
A
A
1
1
1 (1
t
t ) 2 3
3
3
·····································10分
解得 t
1
2
,所以线段 B Q 长为
1
2
. ··································································12分
1a
19.【答案】(1) 方法一:因为f (x)是奇函数,所以f (0)=0,即 0,解得a1, ···· 2分
22
2x 1
此时, f(x) ,
2x12
f ( x )
2
2
x
x
1
1
2
(
( 2
2
x
x
1
1
2
) 2
) 2
x
x
2
1
2
2
x
x
1
f ( x ) ,
则 f ( x ) 是奇函数.
故 a 1 . ····································································································· 4分
方法二:因为f (x)是奇函数,
所以 f ( x ) f ( x )
2
2
x
x
1
a
2
2
2
x
x 1
a
2
2
2
x
x
1
a
2
1
2
a
2
2
x 1
x
0 ,
即 ( a 1 ) ( 2 x 1 ) 0 对 x R 恒成立,
所以a1. ···································································································· 4分
-2x+1 1 1
(2) 由(1)知f (x)= =- + ,则f (x)在R上为减函数, ·························· 6分
2x+1+2 2 2x+1
又f (x)是奇函数,
由 f ( 3 s in c o s ) f ( k c o s 2 ) 0 得: f ( 3 s in c o s ) f ( k c o s 2 ) f ( k c o s 2 ) ,
所以 3sincoskcos2,
即 3sincoscos2k在
4
, 0
上有解, ············································· 9分
记 g ( ) 3 s in c o s c o s 2 ,则 g ( )
2
3
s in 2
1 c o
2
s 2
s in 2
6
1
2
2
因为 ,0 ,则2 , ,
4 6 3 6
1
所以sin2
1,
,所以
6 2
g ( )
3
2
, 1
,
所以
3
2
k
3
,即k . ··············································································12分
2
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}20.【答案】(1) 提出假设
第3页(共6页)
H
0
:该品牌方便面中 C 卡片所占比例与方便面口味无关.
2
( a b ) (
n
c
( a d
d ) (
b
a
c 2 )
c ) ( b d )
1 5 0
9
(
5
2 0
5 5
4 5
3 0
1 0
1 2
7
0
5 ) 2 7 5
4 1 8
0 .1 8 6 .6 3 5
, ··········· 3分
又 P ( 2 0 .0 1 0 ) 6 .6 3 5 ≥ ,
所以没有99%的把握认为“该品牌方便面中 C 卡片所占比例与方便面口味有关”. ······ 4分
(2) ①记“小明一次购买3袋该方便面,中奖”为事件A,
P ( A )
2
5
2
5
1
5
A 33
1
2
2
4
5
. ·············································································· 8分
② 记“小明一次购买3袋该方便面,未获得 C 卡”为事件 B .
P ( B A ) (
4
5
) 3
1
6
2
4
5
, ····················································································10分
P ( B | A )
P
P
( B
(
A
A
)
)
1
1
6 4
2 52
1 2
4
5
6 4
1 0 1
.
64
答:①小明中奖的概率为 ;②小明为中奖,未获得
125
C 卡的概率为
6 4
1 0 1
. ·············12分
21.【答案】(1) 由题可知ABc, A C 3 c ,BC2c,
在 △ A B C 中,由余弦定理得 c o s A B C
B A 2
2
B
B
C
A
2
B C
A C 2
c 2 ( 2
2
c
2 )
c
(
2 c
3 c ) 2
1
2
,
又 A B C ( 0 , ) ,所以 A B C
3
, ································································· 2分
又 D 为 B C 的中点,所以 B D
1
2
B C c ,则 B D B A ,
所以 △ A B D 为等边三角形,又 A D 1 ,
所以AB1, B C 2 ,
所以 S
△ A B C
1
2
B A B C s in A B C
1
2
1 2
2
3
2
3
. ·········································· 4分
(2) 方法一:由题可知 A B c , A C 3 c , A D 1 , B D D C
a
2
,
设ABC2, D A C , A D B ,则ADC,
在 △ A B D 中,由正弦定理得
s in
A
B
A D B
s in
A
D
A B D
c 1
,即 ,
sin sin2
在 △ A D C
DC AC
中,由正弦定理得 ,即
sinDAC sinADC s
a
2
in s in (
3 c
)
,
1 a
所以 ,则
sin2 2 3sin
a
c o
3
s
,① ···························································· 6分
在△ABD和 △ A D C 中,由余弦定理得
a a
12 ( )2 c2 12 ( )2 ( 3c)2
2 2
cosADBcosADC 0,
a a
2 1 2 1
2 2
所以a2 48c2,② ······················································································ 8分
在△ADC中,由余弦定理得DC2 AD2 AC2 2ADACcosDAC,
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}即
第4页(共6页)
(
a
2
) 2 1 2 ( 3 c ) 2 2 1 3 c c o s ,即 c o s
1 3 c
2
2
3 c
1
4
a 2
,③ ························10分
将 a 2 8 c 2 4 代入得 c o s
c
2
2
3
2
c
,④
由①④得 (
a
3
) 2 (
c
2
2
3
2
c
) 2 ,即
8 c
3
2 4
( c 2
1
2 c
2
2
) 2
,即 9 c 2 ( 2 c 2 1 ) ( c 4 4 c 2 4 ) ,
即 2 c 6 7 c 4 5 c 2 4 0 ,即 ( c 2 1 ) ( 2 c 2 1 ) ( c 2 4 ) 0 ,
因为 c 0 ,所以 c 2 1 ,则 a 2 8 c 2 4 4 ,所以 a 2 .
故BC的长为2. ····························································································12分
B
2 θ
A
α
θ
D
π - α
C
方法二:作 A B C 的角平分线,交 A C 与 M .
设 A B C 2 , D A C ,则 A B M C B M ,
在 △ A B M 和 △ C B M
AB AM
,
sinAMB sin
中,由正弦定理可得
BC CM
,
sinBMC sin
又AMBBMC,所以 s in A M B s in ( B M C ) s in B M C ,
所以
A
B
B
C
A
C
M
M
.
A
θ M
2θ
B D C
由题可知ABc,AC 3c,BC a,所以
A
C
M
M
c
a
, C M
c
3
a c
a
. ······················ 7分
在 △ A C D 和 △ B C M 中, C A D C B M ,ACDBCM ,
AC BC
所以△ACD∽△BCM ,所以 ,
CD CM
3c a
则 ,即a2 ac6c2 0,即
a 3ac
2 ca
( a 3 c ) ( a 2 c ) 0 ,
所以 a 3 c (舍)或 a 2 c . ·············································································· 9分
在 △ A B D 和△ADC中,由余弦定理得
a a
12 ( )2 c2 12 ( )2 ( 3c)2
2 2
cosADBcosADC 0,
a a
2 1 2 1
2 2
所以a2 48c2, ························································································ 11分
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}则
第5页(共6页)
a 2 4 2 a 2 ,解得 a 2 .
故 B C 的长为2. ····························································································12分
方法三:延长CB到 E ,使 E B B A ,连接 E A .
由题可知ABc, A C 3 c , B C a , B D D C
a
2
,
设 A B C 2 , D A C ,则 B E A B A E ,
在 △ A C D 和 △ E C A 中, A E C D A C , A C D E C A ,
所以 △ A C D ∽ △ E C A ,所以
A
C
C
D
E
A
C
C
,则 A C 2 C D E C , ·································· 7分
所以 ( 3 c ) 2
a
2
( a c ) ,
即 a 2 a c 6 c 2 0 ,即(a3c)(a2c)0,
所以 a 3 c (舍)或 a 2 c . ·············································································· 9分
在△ABD和 △ A D C 中,由余弦定理得
c o s A D B c o s A D C
1 2
2
(
a
2
)
a
2
2
1
c 2
1 2 (
a
2
2
)
2
a
2
(
1
3 c ) 2
0 ,
所以 a 2 4 8 c 2 , ························································································ 11分
则 a 2 4 2 a 2 ,解得 a 2 .
故 B C 的长为2. ····························································································12分
A
θ θ
θ 2θ
E B D C
22.【答案】(1) 因为 f ( x ) x 2 a x a 2 ln x ( x 0 ) ,
a2 2x2 axa2 xa2xa
则 fx2xa , ········································· 1分
x x x
令 f ( x ) 0 ,则 x
a
2
或 x a .
1°若a0,当 x 0 , a , f x 0 , f x 单调递减;当 x a , , f x 0 , f x 单调递增.
所以 f(x) f aa2lna0,解得a1; ···················································· 3分
min
2°若a0,当 x
0 ,
a
2
, f x 0 , f x 单调递减;
当 x
a
2
,
, fx0, f x 单调递增.
a a2 a2 a 3 a
所以 f(x) f a2ln 0,即 ln ,解得
min 2 4 2 2 4 2
a 2 e
34
.
3
综上,a的值为1或2e4. ·············································································· 5分
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}(2) 若
第6页(共6页)
a 0 时, f x x x a 2 a ln x ,
当 0 x m in a 2 ,1 时, x a 2 0 , a ln x 0 ,则 f x 0 不满足条件. ··················· 6分
若 a 0 时,由 f 1 1 a 2 0 可得 0 a 1 . ······················································· 8分
下面证明其充分性,即证当0a1时, f x x 2 a 2 x a ln x 0 恒成立.
思路一:关于 a 的函数haxa2 alnxx2,0a1是一段开口向下的抛物线.
只要证
h
h
0
1
x
2
x
0
ln
① ,
x x 2 0 ② .
其中 ① 式显然成立.
令 ( x ) x 2 x ln x ,则 ( x ) 2 x 1
1
x
2 x 2
x
x 1 ( 2 x 1 )
x
( x 1 )
,
所以当x(0,1)时,(x)0,(x)单调递减;当x(1,)时,(x)0,(x)单调递增.
所以(x)(1)0,②式得证.
所以,当0a1时, f xx2 a2xalnx0恒成立.
综上, a 的取值范围是 [ 0 ,1 ] . ···········································································12分
思路二:令 h x x 1 ln x ,则 h x 1
1
x
x
x
1
0 .
当 x ( 0 ,1 ) 时, h ( x ) 0 , h ( x ) 单调递减;当 x (1 , ) 时, h ( x ) 0 ,h(x)单调递增.
所以h(x)h(1)0,则 x 1 ln x .
由 ln x x 1 ,得 a [ 0 ,1 ] 时, x 2 a 2 x a ln x x 2 a 2 x a x 1 x 2 a 2 a x a ,
又当 a [ 0 ,1 ] 时,方程x2 (a2 a)xa0的(a2 a)2 4aa[a(a1)2 4]0,
所以 x 2 a 2 x a ln x 0 对x(0,)恒成立.
所以, a [ 0 ,1 ] 均满足.
综上, a 的取值范围是 [ 0 ,1 ] . ···········································································12分
{#{QQABRYYAggCoAABAAAhCEwFCCAIQkBGCCCoOwBAIoAAAABFABCA=}#}