Page 1 Fддмо May 06, 2014 answer sheet provided. ИEГНEИ True

管 院 微 積 分 聯 合 教 學 段 考 五 May 06, 2014
考 試 時 間 l20分 鐘 , 題目卷 為三張紙 ,共五頁 ,滿分120分。所有 題目的答
案 都請依題 號順序依序寫在答案卷上,而是非與填充題必須寫在第一頁。答案
卷 務必寫學 號、姓名 ,題目卷不 必繳回。 考試開始 30分鐘後不得入場,開始
40分鐘內不 得離場。 考試期間禁 止使用字 典、計算 機及任何通訊器材,監試
人 員不得回 答任何關 於試題的疑 問。Quest
ions
are
to be an
swer
ed o
n th
e
answer sheet provided.
是 非 題 True or False (20 poLnts), 請 答 T(Tue)或 F(False)。 每 題 2分 。
( 不 需 詳列 過 程 , 請依 題 號 順 序依 序 寫 在 答案 卷 第 一 頁上 。 )
F ’ , 玨 y=/(x)h a solution ofa first-order diiferential equation, then,=c.,(x)
is also a solution of址 lefirst-order diferential equation, whEre C id any real
number.
F。 , 9: c、乎 f'j
(Sol)
二 c, ( ; 化 ’ r3x+仁 ,
手 , g、 6。njf d's. 丫 咎‘-占勺十歹
宁 身 ’ =c、 ( e, 1:r5夕 丰 6x于夕
争clg二fefc于F,d咒
宁齧二3咒’f多咒+
舌,幸:。‘。“弘*
”亡
州 几/ 彤 >9, 1
-r 2. If y = eTt satisfies the differential equation y"
- y' - 3
0y = 0
, th
en the
va
lue
of
'r is 6 0r -5.
(Sol)
yn _ y' _ 30y = (r2 _ r - 30)ert = (r - 6)(r + 5)ert
T 3.Ⅱ J =/y. dA
, wh
ere D is
the
dis
k {X2
+y2
< 1
6},
then I =14 43.
23
(Sol) (jD xfi了(了 ,dA =the volume of the upper half ba
with radius 4 and center at (0,0,0).
1
b
4. For any function f, if f(x)dx = 1, then f must be a probability density
function on [a, bl.
(Sol)
-
Co
\
o
e
队 P
YO
b
O
\
D
'
l
'
tA
 ̄
U
.
v
\
ct
,
o
v
k
.
于 \
m
O
k
S
I b
乏 y
i
o\
i
-
Y
l
p
 ̄
o'
t
'
x
'
Q
.
一 5.The differential equation ydx -(蠶十 : r:2y)dy=o is separable
(Sol)
化[
1
+亿l
呵)
dx二寸“乎
十 h巳化 , 净teYp1
5。幻r
be
LH
S c。n
n
。亡b
f se
P,Y
O,
t‘翻
6. A deposit of ¥10, 000 is made into a bank account a
nd the
ac
cou
nt e
arn
s i
nte
res
t
at a rate of 3.2% per year, compounded continuously. The balance, B, in the
account in
t year
s s
ati
sfi
es the
di
ffe
rent
ial
eq
uat
ion
dB
/dt
= 10, 000
+ 0.0
32B
.
(Sol)
dBldt = 0.032B with B(O) - 10000.
7
. The me
di
an
(中位數)of
a
no
rm
al
d
is
tr
ib
ut
io
n is
n
e
ve
r at
z
er
o.
(S
ol
)
Ik
k、肌乏d下队n
。干 SC
d订O
[0
1
Y爿 n
。rr
”q
O
I
Ts
C
V
7
b
“t7
。n
;j
。、
/下頁還有 試題)
2
I
f
d
Q/
d
t
=
5
Q
-
2
0
0
t
h
e
n
w
h
e
n
Q
=
1
0,
t
h
e
q
u
a
n
t
i
t
y
Q
w
i
l
l
b
e
d
e
c
r
e
a
s
i
n
g
(
S
ol
)
dQ
/d
t
lo
=i
o
=
(
5
Q - 2
00
)1
0
=i
o =
- 1
50
<
0
H
en
c
e Q i
s de
c
re
as
i
ng
w
h
en
Q
= 10
.
F 9.
For an iter
ate
d i
nte
gra
l, one can
al
way
s s
wit
ch the
ord
er of int
egr
ati
on.
(Sol)
10.
The
wait
ing tune
in hour
s fo
r stu
dent
s in
Cal
culu
s t
ea
ch
e
r'
s o
伍c
e
i
s
an e
xpone
ntia
lly c te
d
T
an
d
om
v
a
ri
ab
l
e X w
it
h a
ss
oc
i
at
ed
pr
ob
a
bi
li
t
y
densityfunctioYf()r-面 而 e-丽 .thentheaveragewaitingtimeis10000
h
ours
.
(Sol)
If a continuous random va
riab
le X
is e
xpon
enti
ally
dis
trib
uted
with the probability density function
f(x) = ke— 缸 (0兰 x < oo)
. then the expected value E (X) is equal to llk.
(下 頁還有試題)
3
填 充 題 Short answer questions (40 points), 每 題 5分 。
( 不 需詳 列 過 程 ,僅將答 案依題號順序 依序寫在答案 卷第一頁上即可 。)
1.Let R be a region bounded by 0三 z兰 l,0≤ y≤ 1
Then xyeT2dA = -
.t e I
Answe
r :
-
戽
(Sol) 1i J { 'x A e‘ t'd,d3
= l-l {j [IJ xe dX] dl
= l' d[兰 l' e, dul dg
e-i .芒 I:二 e芋\
= 15 ̄[e-i)d J = -.-2 4
2. Let f (x) = k .
xye
-(r
2+Y
2) be a j
oin
t p
roba
bil
ity
de
nsi
ty fun
cti
on o
n
D = {0 < x < oo,0 < y < oo}, then le
Answer: 斗 . -
cs
。l
’卡 5
:j
:化 各电‘ 卉“》 仪d
子
= l
-(
(:仅e'
z"
y-
)(
5:芯{9
dg
)
二 幸(兰 f
'1
:) (圭亡 ’I
:、
: 芸I
。 —,、 c
。 —、,=姜=1
争 阜二斗
)e
a
n
or
ma
l ra
a.
b
le
w
it
h me
an
1
00
a
nd
v
ar
i
an
c
e
4
0
0
.I
f
i
t
i
s
given that P(Z < 1.25) = 0.8944, then P(X < 75) =
Answer : 0, / o厂 占 .
‘ s。 : ’ P f欠 +呷 , , 二 P c霉 t尘 -’ ,
=P c罢 : 宅 },
二 P[暑 (一 I、 2亨 )
二 P[星 >“ ) 多 )
= / -0, 占 ? 毕 中
: 。1
/0
多b
(下頁還有試題)
4
4. Use ELder's method with n = 4 to obtain an approximation of the initial value
problem y' = 1十 2xy,y(0) = 0 at x = 1. Round the answers to the nearest
hundredth.
Answer : y(l)≈
|、≤。
(Sol)告 = 1 + 2xy , Exact solution is: { 2LJn erf(x)ex'}
The exact solution is
y = gJ; erf(x)eX2 = 21(寺 只 e_r2dt)eX2 = (joe_t2dt)eX2
Indeed,
尝 =吾 ([o e_'2dt)eX2 = e_X2eX2十 (£ o e_t2dt)2xeT2
= 1十 2xy
and
y(0) = ([o e叫 2dt)eX2lX=o = 0.
The exact value of y(l) is
y(l) =00 e_"dt)eX2I肛 , = 2. 030 1
W
e no
w ap
p
ro
xi
ma
te
t
he
v
a
l
ue
o
f
t
h
e s
o
l
u
t
i
o
n y
a
t
x
=
1
b
y
Eu
l
e
r
'
s
m
et
h
o
d
h = '4
0 = 0
.2
5,
F
(x
,y
) = 1+
2x
y
xo
=
O
,x
i =
0
.2
5,
x2
=
0
.5
,X
3 = 0.
75
,
X4
=
1
Y
o =0
Yi = Yo十 hF(xo,yo) = 0 + 0.25(1十 2 x o x 0) = 0.25
Y2 = Yi十 hF(xi,yi) = 0.25十 0.25(1十 2 x 0.25 x 0.25) = 0.53
y3 = Y2十 hF(x2,Y2) = 0. 53十 0.25(1
+ 2 x
0.5 x 0.53) = 0.
91
y4 = y3十 hF(X3,y3) = 0.91 + 0.25(1 + 2 x 0.75 x 0.91) = 1. 50
Wel
l,
as
y
ou
c
an
s
ee
t
he
a
pp
r
o
x
i
m
a
t
io
n
i
s
t
ol
e
r
a
b
l
e
(下頁還有試題)
5
5. Suppose that x measures the time (
in hou
rs)
it
ta
kes
fo
r a stu
den
t t
o c
omp
let
e
an exam. All students are done within two hours and the probability density
function
for
x is f (
x) =譬 if 0 < x <
2.
Wh
at is the
av
erag
e t
une
fo
r s
tud
ent
s
to complete the exam?
Answer'圣 二h二
(Sol)
E㈤ =6 xf(x)dx=/: x譬 dx=÷hr
6. As you know, when a course ends, students start to forget the material they
have learned. One model assumes that the rate at which a student forgets
material is proportional to the differenc
e b
etw
een
th
e m
ate
ria
l cu
rre
ntl
y r
e-
membered and some positive constant, a. Let y = f (t) b
e t
he frac
tio
n o
f t
he
original material remembered t weeks after the course has ended. Set up a
. differential equ
atio
n f
or y, usi
ng k a
s a
ny c
ons
tan
t o
f p
rop
ort
ion
alit
y y
ou may
need (let k > 0) Your equati
on wil
l c
ont
ain two
co
nst
ant
s; the
co
nsta
nt A(a
lso
positive) is l n y for all t.
A_nswer iis ̄_t_ _' ̄C d-辟, 。卞 . o,吣, fYq勾 =To ̄
(Sol)
Let Q(t) denote the amount of material remembered t weeks after the course
has ended. Then
7Q = -k(Q - a), k > 0, where a represents the material which will never be
dt
forgotten.
Write y(t) = 9《o) = the
frac
tion
of the orig
inal
mate
rial
rem
embe
red t we
eks a
fter
the course has ended.
D
ivid
i
ng
t
hr
ou
gh
t
he
e
qu
at
io
n鲁 = -k(Q
- a
) by
Q
(
O)
, we
h
av
e
詈=
—尼殄 —爿),尼>o
,w
he
re
A= a
( 下頁 還有試題)
6
7. While taking a walk along the road where you live
, y
ou acc
iden
taL
ly dro
p y
our
glove, but you don't know where. The probability density function f(x) for
having dropped the glove x kilometers from home (along the road) is
f (x) = 2e-2' for x > 0
. W
hat
is
th
e pr
oba
bil
ity
th
at you
dr
oppe
d i
t w
ith
in 1
kilometer of home?
Answer: \-e-z
(Sol)
P(O三X兰 1) =/: 2e-2xdx = 1 - e-2  ̄ 0.864 66
8. Suppose that Congress enacts(國 會 制 定 ) a one-time-only 10% tax rebate(折
扣 ) that is expected to infuse(注 A) ¥y billion, 5 < y < 7 , into the econ-
omy. If every person and every corporation is expected t
o s
pend
a pro
por
tio
n
x, 0.6 < x < 0.8, of each doll
ar rec
eiv
ed, the
n, by the
mu
lti
pli
er p
rin
cip
le in
economics, the total amount o
f s
pen
dmg
S (
血 b
ilj
ion
s o
f d
oll
ars)
ge
ner
ate
d b
y
this tax rebate is given by S(x,y) =丁兰 百 What is the a
ver
age
to
tal
am
oun
t
. of spending for the indicated rana'es of the values of x and y?
Answer:  ̄O又yl 2
(Sol)
The a
ver
ag
e va
lue
o
fc
on
R
=<
(x
,y)
:o
.6
<x
<0.
8,
5三夕兰7>
is
丽赤而堪只击办出二20. 794 b
illion.
= 20_QY
) 2 (=-30卫h圭)
(下 頁還有試題)
7
計 算 問 答 證 明 題 Please show all your work (60 points), 每 題 10分 , 請 依 題 號 順
序 依 序 寫 在 答案 卷 上 , 可 以 用 中 文或 英 文 作 答 。 請 詳列 計 算 過 程 , 否 則不予計 分。需
標 明 題 號 但 不必 抄 題 。
2 4
1. (10 points) Evaluate xey2 dyd:r:
(Sol)
/ : / : : xey:dydx=/ / xxey2 dA,whereR is the region
月 ={( x, 少 ) : x2三 y≤ 4, o三 x三 2}
=<(x, y): O<x<fl, o三 y至 4>
Consequently,/ : 丘 42 xeY2dydx = (o/ ; yxeY2dxdy =/ : (孚 ey2)1三 fydy
= : 2 eY2dy =÷ ey2矚 = 41eI6 -÷ .
( 下頁還有試題)
8
2. (10 points) The resale value of a
ce
rta
in mac
hin
e de
cre
ase
s a
t a
ra
te pro
port
ion
al
to the machine's current value. The machine was purchased at ¥50,000 and 2 yr
later was worth ¥32,000.
a. Find an expression for the resale value of the machine at any time t.
b. Find the value of the machine after 5 yr.
(Sol)
鲁 = -kA, A(O)=500
00, A(2)=32
000, k>o
Th
e so
lut
io
n is A(
t)
=C
e-k
t.
A(
O)
=5
000
0劃C=
50
000
32
0
00
=
A
(
2)
=
5
0
00
0
e
-
2k
=
;e
-
2
k=
立呈业旦-
上旦
50
000
15
;尼=专(h
16
-
ln2
5)
=I
n5 - Ln
4
a.
A(
t)
=5
000
0e
-(
h5-
ln
4)
t
b.
A(5)=50000e-On5 ̄4)x5=50000em(4)-5
= 5000045= 50000 x酱等=16384 dolla
rs.
(下 頁還有試題)
9
3. (10 points) The popul
ati
on dens
ity
of
a cer
tai
n c
ity
is giv
en by the
fu
nct
ion
/(z,g)=
so: OOOl
xyl
十20)(y
2+36
)
where the origin (0, 0) gives the location of the
go
ver
nme
nt cen
ter.
Fi
nd the
po
p-
ulation inside the rectangular area described loy
R = {(x,y)l - 15 < x < 15; -20 < y < 20}
:五,
艾艾
S-e,oooK爸
(2l+lo)[旨 ‘+j; )
U
20 争
=4( 知 ooo) - 1
。 蹿 , ‘ j
如
Ⅵ
= 200000. 。
锣l十;占
舷%
旷
。
云
√苫J r
/:夕
硅乎乎
1C
咒‘斗"
:枷。 。。. 陪纠9、;;I川I兰厶I Yl+2。l
200000
吹x
1
l习
奴 穆 ‘ —人 ; 占 ) .(及 a华f -从l。):
4
=掣帆筹)(人祟)一‘。‘。弘等),F
l争)
/;C
乏 3/ l辞, f
( 下賈 選有試題一
4. (10 points) The scores on an economics examination are normal
ly出stri
but
ed wit
h
a mean of 72 and
a sta
nda
rd d
evi
ati
on of 16.
If
th
e in
str
uct
or ass
ign
s a
gr
ade of A
to top lOVo of the class, what is the
ap
pro
xim
ate low
est
sc
ore
a stu
den
t ma
y h
ave
and still
1.28 1 ::2 .x
obtain an A? (了 乔e- 2 dx≈ 0.4)
(Sol)
T ̄ 巨髟: 72乱彳 磁谢 Kag/=2夕 吕.
Jpr i#e必 w钥才 子 ‘‘uX.t、”。、fIh-岔
猙d。群,
/.e.
于( 丫 三 义)‘。, l
BcJ广 尸(X;i: 9‘、,P( 父 : 2: i, >三 主 三 1
/s 一 /占 /
P(孑2
竽夕
: ~ 厄嗵 罢手品似氏s如棚菇√儿 ’b。吠
4《勿 4, : J斩 芹J, 、 ,
争 乙 拿 二 +l-9
/ ‘
弓咒;72+,占C,.1矿)‘尹‘,华},
口 /,2d
5。+露弘才删詹泊六.c厶好+J9; s
奴Je
df,”“d才
 ̄d;}√:I'hf} 户,伞护.
(下 買遺有 試题)
11
5. (10 points) T
he l
ife
sp
an (in
ye
ars
) o
f a cer
tai
n m
ake
of
ca
r b
atte
ry is an exp
one
n-
tia
lly
di
str
ibu
ted ran
dom
va
ria
ble
wi
th an e
xpe
cte
d v
alu
e o
f 5
. F
ind the
pr
oba
bil
ity
that the life span of a battery is
a. more than 6 yr.
b. between 2 and 4 yr.
(Sol)
f
(x
) = ke
-h
(0
兰 x
<
0
0)
f
(x
) = 0.
2e
-0
.
2x
a.
P(
X > 6)
=
'0
.
2e
-0
.2
xd
x = li
mb
+ (_
e-
0.
2
',
1盞
6
= lj
IU
b_
m(
_e
-0
2b
十 e
-1
2
) = e-
1.
2 =
0
.
30
1 19
b.
P(
2
<
X
<
4
)
=
j2
0
.
2
e
-
0.
2
Y
d
x
=
(_
e
-
0
;
2
x
,1
爱 =
(
e-
0
4
_
e
-
0.
8
)
=
0
.2
2
0
9
9
(下 頁還有試題)
12
6. (10 points) A container that has a constant cross section A is皿 ed wit
h w
ater
to
height H. The wat
er js dis
cha
rge
d th
rou
gh an ope
nin
g o
f c
ross
se
cti
on B a
t t
he bas
e
of
th
e c
ont
aine
r. By usi
ng Tor
ric
ell
i's Law
, i
t c
an be sho
wn that
th
e h
eig
ht h o
f t
he
water at time t satisfies the initial-value problem (1 ft = 12 in )
d九 B一
面 =一 百 √ : 而 危 (o)=H
a. Find an expression for h.
b. Find the time T it takes for the tank to empty.
c. Find T if A=4(ft2), B=l(jn.2), H = 1
6(f
t),
an
d g
=32
(ft
/sec
2).
(Sol)
渤今汐左二‘
/ *亙星 =_ tTB历砭 (A’  ̄le4 +,(e白 。J ,s _eA7t7 ̄,
弓云 d
茫 一和万 转
守‘ 2
厉 二普沔 手+
乙.
5h睫 散 。 , 二 ㈠ 弓 2
河,。‘ f
-c-
.、 ,书, I
兰I
—氟 可士+
2
\
f
fi
-
J
J
=卜芽居 廾历/‘ .
、, ,O
二/-
芋 压T
十 同;
; y二 矗
序 d q
— 丛生 丛
3 d}
刚 I符 二 , : : q守 l ffl, L, ; j'ft -{万 共 :
’ T二 士 ・ 胆 二 聊 肛 二 批 喲
J4牛 ~
(試 題結束 1