内容正文:
!复习专号
!
高中数学北师大(选修
!"!
)
!"# $"% &" "#
参考答案
书书书
12.
!"
f′(x)= abe
ax,
#$
k= ab,%&'"y-
1
b =
a
bx,(
a
bx-y+
1
b =0,!"&'
a
bx-y+
1
b =0)*x
2
+y2 =1
+&
,
#$
1
b
a2
b2
+槡 1
=1,
(
a2+b2 =1,
#$
a2+
b2≥2ab,#$ab≤ 12,#$(a+b)
2=a2+2ab+b2=1+
2ab≤2.(a+b≤槡2.
!
、
"#$
13.(2,+∞); 14.y=1,9x-2y-16=0;
15.-3e; 16.103.
%&
:
13.f′(x) = 2x - 2 - 4x =
2x2-2x-4
x =
2(x2-x-2)
x (x>0),,f′(x)>0,-x>2.
14.
./0
(2,1)
1&0231&04567
.
15.f′(x)= 1x+
m
x2
=x+m
x2
,
89
x=-m
":;
f(x)
<=>?0
.
@
-m≤1,(m≥-1A,fmin(x)=f(1)=-m=4,-
m=-4(
!"
);
@
1<-m<e,
(
-e<m<-1
A
,f(x)
min
=f(-m)=
ln(-m)+1=4,
-
m=-e3(
!"
);
@
-m≥e,(m≤-eA,fmin(x)=f(e)=lne-
m
e =
1-me =4,-m=-3e.
16.
BC89
,
DEFGHC#I-<JK
f(x)=(x-
2) 10
x-2+4(x-6)[ ]2 =4x3-56x2+240x-278(2<x<6),
L
f′(x)=12x2-112x+240,
,
f′(x)=0,
-
x=103Mx=
6,
NO 2,10( )3 P,f′(x) >0,:; f(x)QRST;O
10
3,( )6P,f′(x)<0,:;f(x)QRSU,#$x=
10
31:
;
f(x)
O
(2,6)
V<=W?0
,
X1YW?0
,
#$@
x=103
A
,
:;
f(x)
Z-YW?
.
'
、
()$
17.
(
:f′(x)=x2-4=(x+2)(x-2).
,
f′(x)=0,
-
x=-2
M
x=2.
[
f(x)
<T\]"
(-∞,-2)2(2,+∞),U\]"
(-2,2).
(1)
@
x=-2
A
,f(x)
Z=W?
,
[
f(-2)=-83 +8+m=
28
3,-m=4.
(2)
B
(1)
-
,f(x)= 13x
3-4x+4,
#$@
x=2
A
,f(x)
^=>?
f(2)=-43.
18.
(
:(1)f(x)=(x2+x+1)ex,f′(x)=(2x+1)ex+
(x2+x+1)ex =(x2+3x+2)ex,
@
f′(x)>0
A
,
_-
x<-2
M
x>-1,
@
f′(x)<0
A
,
_-
-2<x<-1,
#$:;<QRT\]"
(-∞,-2),(-1,+∞);QR
U\]"
(-2,-1).
(2)f(x)=(2x+a)ex+(x2+ax+a)ex
=[x2+(2+a)x+2a]ex
=(x+a)(x+2)ex =0,
#$
x=-a,x=-2,
!"
a≤2,#$ -a≥-2.L`abc:
x (-∞,-2) -2 (-2,-a) -a (-a,+∞)
f′(x) + 0 - 0 +
f(x) #$% #&%
Ba89
f
=W
(x)=f(-2)=(4-2a+a)e-2 =3,
_-
a=4-3e2≤2,#$dOe;a,ff(x)<=W?"3.
19.
(
:(1)
%ghij
n
klm
,
L
(n+1)x=m,
(
n=
m
x -1,#$ y=f(x) =256n+(n+1)(2 槡+ x)x=
256 m
x-( )1+
m
x 2 槡( )+ xx=
256m
x 槡+m x+2m-256(0<
x≤m).
(2)
B
(1)
9
f′(x) =- 256m
x2
+ 12mx
-12 =
m(x
3
2 -512)
2x2
.
,
f′(x)=0
-
,x
3
2 =512,
#$
x=64.
@
0<x<64
A
,f′(x)<0,f(x)
O\]
(0,64)
V"U
:;
;
@
64<x≤640A,f′(x)>0,f(x)O\](64,640]V
"T:;
.
#$
f(x)
O
x=64
nZ-Y>?
,
oA
n=mx-1=
640
64
-1=9.
[gij
9
klmpqf
y
Y>
.
20.
(
:(1)f′(x) = 1x -
a(x+1)-a(x-1)
(x+1)2
=
(x+1)2-2ax
x(x+1)2
=x
2+(2-2a)x+1