BQ
GIAO
Dl)C
& DAO
HOC
QUOC
GIA
TP. HO
CHi
MINH
TRUONG
HOC
KINH
TE
·
HOANG
NGQC
QUANG
NHU'NG
M0
HiNH
Du'
TRU'
•
' -
vOI nONa
c.Au
NGA.u
NHIEN
,.
CHUYEN NGANH : TOAN

THUOC
E>AI
HOC QUOC GIA
. . . . .
THANH
PHO HO
CHI
MINH

NGU'OI
HU'ONG
DAN KHOA HOC:
PGS-
PTS:
LEVAN
HOT

-
PHAN BII;N 1: .

-
PHAN BII;N 2: .
an
se
du<;jc
bao v$ t9i
H(>i
dong cham
an Nha nude hop t9i Truong
E>9i

So
lu'<;5c
lich
sll'
ly
thuye't
quan
ly
dt!
tn1'
.
-
Cac
khai
co
ban
.
-
Cac
loc;ti
chi
phi
.
-
Cach
xay
dtfng
mo
hlnh
.

-
d€
I .
-
d€
II .
B. Tru'ongh<;1p
yeu
xua't
khi
thie'u
hang
dt!
tn1'
thl
cho
.
C.
Truong
h<;1p
ma't
yeu
khi
yeu
khong
du'<;jc
dap
ung
.
Chu'ong III

ung
ngay
se
cho
.
C.
Mieu
ta
xa'p
xi
<Q,r>-
Mo
hlnh
bi
ma't
nhung
nhu
khong
du'QC
dap
ung
ngay
.
D.
Phan
tich
mo
hlnh
va
thi

.
2.
Stj
6n
dinh
.
3.
St! phl.l thu()c
cua
(Q*,
r*)
vao
'A,
TI,
I, C .
·
Trang
1
3
3
3
4
7
9
9
12
13
15
20
23

20 voi cong thuc
Wilson xac dinh kh6i
lu'<;lng
hang h6a
b6
sung cho tung
d<;lt.
Nhung ly
thuye't quan ly
dl,i
tru
voi
cac
lu'<;lng
nhien chi
du'QC
phat
me sau the' chie'n II. Be'n nay cung voi slf phat cua
ky
vi tinh,
quan ly
dl,i
tru
du'<;lc
phat
me
v€ ly thuye't cling nhu' trong ung
dl,ing.
Nhung ly thuye't toan
hQc

khai
ni<$m
co ban,
phan
tich cac chi phi va each xay
dl,ing
mo
hlnh.
Chu'ong II : Trinh
bay
m()t
s6
mo hlnh quan ly dlf
tru
voi
cac
lu'<;lng
xac dinh.
- Mo hlnh don
gian
( cong thuc Wilson)
-
Mo hlnh voi
yeu
CllU
se
cho khi thie'u hang
dl,i
tru.
- Mo hlnh voi

Xet
sv
t5n duy nha't
nghi<$m
cling nhu' tinh
6n
dinh cua
mo
hlnh
xet
d chu'ong III.
Trong 3 chu'ong d'au chung toi t6m nhii'ng ke't qua
v'e
ly thuye't
quan
ly dlf trii' duqc trinh
bay
trong
cac
tai
lil$u
(vi
dv
nhu
trong
sach
chuyen khao
cua
Hadley-Whitin (Analysis
of

nghil$m cua
hi$
tren kha vi
theo
cac
tham
s6
A.,
TI,
I, C.
Nhii'ng ke't qua d6 giup chung ta
ra'"t
nhi'eu khi giai quye't nhii'ng
bai
toan
tht;t'c
te'.
*****
Trang 2
I ,

M()
1),:\U -
C:AC:
1\tiAI
f:(}
.

se mat m(lt ph'an
1<;1i
va uy tin cua ta d6i voi khach hang hi giam di,
anh hu'dng de'n kinh doanh lau dai con nhung nguyen nhan khac nua
cling khong kern ph'an
quan
trQng.
Thi dv nhu' gia nguyen nao d6
thay
d6i dang k€ theo mua, khi gia nguyen d6 tha'p, tat nhien ta c6
1<;1i
ne'u
mua dt! tru cho san xuat cho nhung thoi di€m gia nguyen
len cao. So qua m(lt vai nguyen nhan, ta thay dt! tru nguyen la
c'an
thie't.
Trong cong quan ly dt! tru chung ta phai tra loi hai cau hoi sau:
1,
Thoi di€m h6 sung
dv
tru.
2,
Kh6i
lu<;1ng
hang h6a h6 sung
dv
tru la hao nhieu.
Trong
chu'ong nay chung ta se
c6

ta c6
dQ
tv
do nha't djnh, d€ quye't dinh
v'e
thoi di€m va kh6i
lu'<;1ng
hang h6a (thie't hi)
c'an
h6 sung.
Stl'
dvng cac phu'dng phap toan
hQC
ta se chi ra cac quy quan ly
dv
tru, ta phai mieu ta th6ng quan ly dlj tru ngon
ngu
toan
hQC.
mo
Trang 3
ta m9t
thO'ng
ngon ngu tmin h9c thu'ong
du'cjc
g9i la mo hlnh h6a
toan h9c cua
thO'ng
d6. Nhu'ng the' gioi
th\l'c

do Ford Harros rut ra vao narn 1915 thu'ong
du'cjc
g9i la cong thuc ddn gian xac djnh kh6i
lu'cjng
b6 sung hay cong
Wilson. Quy€n sach d'au tien vie't
v"e
va'n
d"e
quan ly
dv
tru
la do rn9t c9ng
tac vien cua
H9c Massachuset F.F Raymond vie't vao narn 1931. Nhu'ng
chi
vao cu6i nhung narn cua The' chi€n II, khi nghien cliu chie'n
lu'cjc
phat tri€n r'arn r9 thl cong nghien cliu quan ly dlf tru rnoi
du'cjc
chu
y.
Quy€n sach cua Whitin vie't narn 1953 la quy€n sach vie't tie'ng Anh
xem
xet
rn9t each
c;Jn
ke
rno hlnh quan ly dt! tru nhien. De'n nay
nghien

tru
san ph§rn c6 ra't
nhi"eu
chi phi. C6 nhung
chi phi khong thay d6i du ta thay d6i each thuc quan ly. Nhung chi phi
d6 ta
se
khong
d"e
toi. Chung ta chi
d"e
toi nhung chi phi thay d6i khi
ta thay
d6i cung each
di"eu
hanh.
Cl;l
th€ c6 5 chi phi sau:
1.
Chi phi lien quan d€n hang (chi phi ti€p
2.
Chi phi lien quan de'n bao quan san ph§rn (con g9i chi phi htu
kho).
3.
Chi phi lien quan de'n giao hang (chi phi giao hang).
4.
Chi phi xua't khi san ph§rn (hang h6a) dt! trii' bj thie'u
hl;lt.
5.
Chi phi lien quan de'n thu va

ht<;1ng
hang
h6a
(san phffrn) tie'p
va
rn9t
lo(;li
khong
phl;l
thu9c
vao
khO'i
lu'<;1ng
hang
h6a tie'p Nhung chi phi
ph1;1
thu9c
vao
khO'i
lu'<;1ng
hang
h6a
tiSp thu'ong
du'QC
tinh
gQp
VaO
gia hang h6a.
Ta
ky chi phi tiSp

y
de"n
tru'ong
h<;1p
gia
tie"p
trung blnh cua rn9t
san
phfirn khong d6i va ky C. Trong tru'ong
h<;1p
d6 C(Q) = C.Q. Khong rna'y
khi xay ra tru'ong
h<;1p
tren, nhu'ng trong
t€
thong thu'ong ta c6 xa'p xi
Nay
ta
xet
chi phi khong
phl;l
thUQC
vao
khO'i
lu'<;1ng
tie"p
D6
Ia
nhung chi phi cho gia'y
tO,

khong d6i.
Gia
hang
choN
l'an hang Ia NA.
21
Chi phi hiu kho:
Bao
g'Orn
nhung chi phi thue kho, thue
cac
thie"t
bi
bao
quan
trong rn9t
sO'
tru'ong
h<;1p
n6
g'Orn
ca nhung chi phi lien quan
de"n
hao
h1;1t
rna khong phai
lUc
nao
cling tren gia'y to. Nhung rna't
mat

ta't ca nhii'ng chi phi d6
rn9t each chinh xac.
Ta
ddn gian
h6a
tinh xa'p xi.
Ta
se
coi chi phi
lu'u
kho ty voi gia
thanh
san
phffrn
lu'u
kho
t<;1i
thoi d6.
sO'
ty
se
ky la
Iva
ta coi n6 khong thay d6i
theo
thoi gian va
gQi
la
sO'
chi phi

Chi phi giao Khi thlfc giao hang cho khach ta phai thlfc
m{)t
nhung
d{)ng
tac
nhu':
la'y
hang
tu
kho ra, xe'p hang len phu'ong
chuyen chd. Doi khi con phai chd hang de'n cho ngu'oi mua. Ngoai ra con
phai lam
h6a don thanh to an, gia'y bao hanh Nhung chi phi d6 ra't khac
nhau, nhu'ng n6i chung chung khong
phl;l
thu{)c
vao each
chc.m
cac phap
quan ly dlf tru.
Do d6 ta se khong xet de'n.
4/ Chi phi xua't khi
san
phfim dtf trt1
hi
thie'u
Ta xet chi phi lien quan
de'n
khi xua't rna ta khong c6 dlf tru,
th6ng he't hang.

cung
ca'p
cho khach. Trong tru'ong
h<Jp
th6ng
tv
tieu
thl;l
san phfim dlf
tru
thl ta se tinh de'n gia
tri
rna y m6c, cong nhan phai ngung
lam
vl thie'u
nguyen N6i chung gia chi phi khi thie'u viing cua 1 don vi hang h6a va
khach hang phai cho
c6 thS mieu ta
du'<)c
m{)t
ham II(t) khong giam
theo thoi gian cho
t.
Ham II(t) ra't khac nhau cho nhung th6ng quan ly
khac
nhau. Tren thljc
t€
ra't kh6 xac dinh
m{)t
each chinh xac cua

c'au
c6 kh6i lu'ong
IOn
hon 1 don vi thl chi phi d6
phlJ
thu{)c
vao
kh6i
lu<Jng
cua yeu
c'au
va slf
phlJ
thu{)c
d6 kha phuc Nhung dS don gian
ta se gia thie't
dng
chi phi cho 1 don vi hang h6a hi thie'u
hl;lt
luon luon
khong d6i.
Trang 6
5/ Chi
phi
lien
quan
de'n
thu
va
xll'

nhung chi phi cho may
m6c dS
xi't
ly thong tin,
b()
thu thong tin dS thu'ong xuyen thong
bao
gia ca san phfim va
dv
doan nhii'ng
yeu
c'au trong thoi gian toi. Nhu'ng
trong
m()t
sO'
tru'ong
hcJp
ta coi chi phi nay khong
ph\1
thu()c vao phu'ong phap
hanh
thO'ng.
Tie'p theo chung ta se
ban
de'n phu'ong phap
chQn
chie'n
lu'cjc
hanh
thO'ng.

lcji
chi phi la
hii'u
h<;1n.
Theo
tieu chufin nay ta
chQn
chie'n
lu'cjc
lam
eve
d<;1i
h6a
lcJi
blnh quan hang
nam
eve tiSu h6a chi phi blnh quan hang
nam.
Ne'u nhu'
lcji
trong khoang thoi gian t la B(t) va chi phi trong
khoang
thoi
giant
Ia
Z(t) thllcJi blnh quan hang
nam
B va chi phi blnh
quan hang
nam

lcji
chi phi trong
khoang
thoi gian
sa:p
toi. Nhu'ng ra't may
sv
l<;1i
xay ra khong hoan toan
nhu'
y.
Trong ling
dl;lng
thvc te' ca hai tieu chufin ta de'n hoac la
cung m()t phuong an
hay
1a
2 phuong an khac nhau khong dang
kS.
Ph'an con
l<;1i
ta se
lam
r6 xac dinh cac ye'u
tO'
nhien. DS xac
dinh
lcji
blnh quan hang
nam

toan
hQC
cua chung.
*****
Trang 8
II
MiJ
L
Ul)
TVU
11£5V
CAC
f)A.I
XAC
. . . .
*****
Ta
d'au
xet
quan
ly th6ng
dv
tnT
nghien cuu m()t
va1
mo
hlnh don gian, trong d6 cu'ang
d()
yeu
c'au hofm

du'QC
sll'
dt;mg
trong nhung
mo
hlnh phuc
t(;lp
hon.
Hon
nua
nhung ke't qua thu
du'QC
tu
nhung mo hlnh tren cho
phep
ta suy
Xet
tinh chfft cua cac
th6ng phuc
t(;lp
ca khi
yeu
c'au la
d(;li
lu'<Jng
ngiiu nhien.
A.
MO HINH DON GIAN XAC DINH MUC DO
BO
SUNG VOl

d'e
ra cho ta la di xac djnh thai
b6
sung va kh6i
lu'<Jng
b6
sung ciia m6i
d<Jt.
Ta
gia thie't
them
la thai
gian tie'p
't
(tuc
Ia
khoang thai gian
tu
luc hang de'n luc hang
du'<Jc
vao
kho) khong d6i
va
khong
ph1;1
thu()c
vao
A
va
kh6i

cac thai
to=
o < t
1
<

<
tn
<

voi kh6i
lu'<jng
hang
h6a
b6 sung la
Qo, Q1,
, Qn,···
va
thai b6
sung
tj,
hang
t'On
trong kho la
Sj,
i = 0, 1' 2, Ta't
nhien
So
= 0 va
si

g<)p
vao
gia thanh
san
phfim, voi chi phi
xU'
ly thong
tin ta gia thie't khong
phl,l
thu<)c
vao
each
hanh
th6ng.
Nhu'
tl;li
thoi di€m
tn
::;
t::;
tn+J.
lu'<Jng
hang
h6a
htu kho
se
la:
x(t) =
Qi
+

" IC
=
A(n
+
1)
+
2
(Qj_
1
+
Si_
1
+
SJTi
+ IC f
(Qi_
1
+
Si-
'A(t-
tJ)dt
I
IC " IC "
z(tn)
=
A(q
+ 1) + 2 Q
iti
+ 2 (Si_, + Si
)Ti

phu'ong an
(to,
tt.

,
tn,
Qo,
Qt.···,
Qn)
thoa
man
Si
=
Qi-1
+
Ti
-'ATi
:2::
0
Vi=
1,
2,

, n c6 1 phu'ong
an
sao cho
(to,

,
tn,

'ATi=
0
Vi=
1,
2,

, n
Trang 10
Va
t6ng chi phi z(t
0
)
ung
voi phu'dng
an
sau
luon luon
nho
hon
hoi;ic
chi phi z(
tn)
ung
voi phu'dng
an
tru'oc.
2) Khi ta
c6
dinh
tn

=
ti-I)
Vt =
1,
2,

, n
Va
chi phi z(t
0
)
ung
voi
phu'ong
an
sau
nho
hon
hoi;ic
chi
phi
z(tn)
ung
voi phu'dng
an
tru'oc.
Chang minh:
11
U'ng voi
phuong

+
1)
+
-L
Q
;_
1
t;
+
-:L
(S;_
1
+
S;)T;
2
i=l
2
i=l
Khi d6
hien
nhien:
si
=
'Qi-1
-
Ti
= o
Chi phi z(t
0
)

Gia
sti' (to. t,

' t;
Qo,
Q I'

'
Qn)
Ia 1 phu'dng
an
voi:
Vi =
1,
2,

,
n.
n n n
Thl: Q = L Q
i-1
=
LA.
T i =A. L
Ti
i=l
n=l
i=l
Trang
11

(n
+
1)
+
2IC'
L Q
;_,
2
II.
n
II.
dday:
n Q
Q
=
\fi, i =1, , n
va
ta
T"
=
tn-
to
n
n
0 =
t"
<
t"
= 1
.T

cho
chi phi
blnh
quan
hang
nam
nho
nhat
ta
chi
c'an
xet
nhfi'ng phu'dng
an
c6
cac
thai
di€m
b6
sung
hang
dl)'
trfi'
each
nhau,
va
khong
thai
gian
gifi'a

kho
Ia khong.
Chu
ky
ta
se
ky
laT.
Lu'\fng
hang
b6
sung
m6i
l'an
ta
ky la Q thl
hi€n
nhien
Q
='AT.
S6
chu ky
blnh
quan
cua
1
nam
se
la: 1/T =
'A/Q.

Ta
c6:
IC
l
z(l) =
A(n
+
1)+-nQT
+ IC
Q-'A(t
-t
)]dt
2
T n
r
IC
n(t)
= IC
(Q-
A.(t-
t )]dt <
Q.T
T n 2
Trang 12
1
.
z(t)
A
1
.

+co
lim
t-+
+oo
t-
nT
t
n
=
t
1
T
= 0
(Vl 0
::;;
t -
nT
<
T)
z = lim
z (
t)
A
IC . Q
(
AQA
+
.Q
J
=

mot
chu
ky.
m<$nh
d'e
tren
du'Qc
chung minh.
Menh
i!e 2: Chi phi blnh
quan
hang
nam
dt;tt
gi£1
tii
nho nha't.
Khi:
Q*
v oi gia
tri
d6:
Z op =
.J
2
AIC
A
(Cong thuc Wilson)
Chung minh:
Z =

nhau
cfing T = Q*l/
Ta
gia
sli'
thoi
diem
t:
tn:::;;
t
:::;;
tn+I•
ta hang
va
ta't
nhien
ta
se
du'QC
lu'<;jng
hang h6a d6
tl;li
thoi
diem
b6
sung
tn+l
+ m = (n + 1 + m)T voi m
0 nao d6.
Hien

nT
= t
0
•
Do
d6
t(;li
nhii'ng
diem
b6 sung ta
ding
hang.
b) Truong
h<;ip
-r/T khong nguyen:
't
= (n +
l)T-
t +
mT.
't
(n+l)T-t
-=
+m
T T
Vi
O<(n+I)T-t<I
T
Nen
m

't]
=
A't-
mAT
=
A't-
mQ
't
la 1
d(;li
ht<;5ng
khong d6i.
chung ta se hang r6i thl diSm
hang
trong kho con
1lu'<;5ng
la:
r = mQ trong d6:
't;
m = ['t/T].
Ta
se
xet
1 tieu chu§'n khac.
T£:li
thoi diSm hang
t,
ta con c6 nhfi'ng
hang da
du<;5c

hang con htu kho la =
A.
't.
B. TRUONG
HOP
YEU CAU XUAT HIEN
KHI
TRIEU HANG
Du' TRU THI CHO:
Trong ph'an A m9i
yeu
c'au xufft
du<_jc
thoa
man
tuc la khong
khi
nao
thie'u hang dlf
trfi'.
Bay gid ta
xet
tru'ong
h<_jp
t6ng quat hon: Cu6i
cung
ffiQi
yeu
c'fiu
xufft

dQi
cua
nhung
yeu
c'au khong
du'<_jc
dap ung ngay,
khhong gay
chota
them
chi phi
them
nao
ca. Ta se cho cho nhung
yeu
c'au
xufft
du Ion luc d6 ta b6 sung
s6
hang dung
s6
nhu c'au dang cho
d6. khac ne'u chi phi
cho
qua
IOn
thl ta
se
khong
bao

cho la
TI
+
f'It,
trong d6 t
Ia
thoi gian
yeu
c'au phai cho. Nhu'
chi phi
g'Om
hai
ph'an:
Ph'an
1:
TI
Ia
chi phi nhu'
nhau
cho
mQi
yeu
c'au voi
khO'i
lu'<Jng
1 don vi
hang
h6a
phai cho.
Ph'an

hang h6a
yeu
c'au chua
du'<Jc
dap ung
c6
cling
m<)t
1u'<Jng
la E 0. Nhu' sau khi
dap
ung
mQi
yeu
c'au cho thl
khO'i
lu'<Jng
hang
dl;l'
trii' con
1a
Q-
E.
Lu'<Jng
hang
h6a
d6
ph1;1c
v1;1
ngay tuc cho nhung

IC(Q-E).T
1
=
IC(Q-E)
2
1 2
2A
Chi phi cho trong m6i chu ky la:
n
fT,
1 1 E
2
I1
E +
I1
.b
A tdt =
I1
E + -
I1
=
I1
E + -
I1
-
2 2 A
T6ng chi phi trong m6i chu ky la:
IC 1 n
A+
-(Q-

Trang 16
Bie'n d6i cong thuc tren ta du'qc:
z(&,Q)
=
TI+
IC
(&
_
1cg-
I1A-J
2
2
Q I1+
IC
+
, ,
1
[JCITQ+21CIU+
2AA.(IT+IC)-ITzA.z]
2(IT+IC) Q
Nhin vao cong thuc
tren
ta thffy ne'u voi E
c6
dinh: 0
::;;
E <
+OO
thi
z(E,Q) =

= xay ra 1 c =
=, ,'
n + IC
Khi
fi
> 0 thi nhien f(Q) = +
oo.
Khi Q = +
oo
z(E,Q) nho nhfft khi E =
+oo,
Q =
+oo
thi
fi
= 0.
Va
ham
s6
f(Q) la
ham
s6khong
tang, tuc la:
2AA.IC-
II
2
A-
2
0 <=>
rr

cua
he$
th6ng) ta moi
b6
sung m()t
lu'<;Jng
hang dung kh6i lu'qng cua nhii'ng
yeu
c'au d6. Trong nhii'ng tru'ong
h<;Jp
COn
Z chi gia tri nho nhfft
CllC
(E*,
Q*)
0::;;
E*
<
+OO,
0 <
Q*
<
+OO
oz
=
Il+
IC
(£
_
ICQ-

]2
= 0
2(IC + TI) Q
(I') {
IC
£ _
ICQ
-
I1
A-
= O
('>
2
(TI-
IC)
" 2 A A ( n +
IC
) -
TI
2
A
2
.
n-
= o
Q2
(1')
(2')
g > 0
Ne'u

(
I1
+
JC
)
(2b)
Khi d6:
1 [
('>
]
z(E,Q);:::z(E*,Q*)=f(Q*)=
('>
ICTIQ*+ *
+2Im'A
2(I1+Iq
Q
=
('>
1
(2
1ciT[
2M(Ic
+IT)-
TI
2
2
2
J +
21au]
2(I1+

va
Zmin
=
TIA.
- Ne'u
E*'
Q*
xac
dinh bdi cong thuc
(1
b) (2b) c6 nghia va c6 gia
tq
du'dng thl z(E,Q)
d<;tt
gia
tri
nho nha't
t<;ti
(E*,
Q*).
-
Ne'u cong thuc
(lb),
(2b) khong c6 nghia gia
tri
khong
du'dng va ll
-:F
0 thl
Z(E,Q)

t6n kho la:
S(t) = Q* -
E*
- A(t-
tn)·
Ne'u S(t) < 0
thll
S(t) I chinh la lu'qng hang
yeu
diu
de'n thoi di6m d6
chua du'qc dap ung.
Tu'dng tlf nhu' d ph'an A,
t<;ti
thoi di6m hang lu'qng dlf
tru
t6n kho
t6ng
quat
se
la:
r* =
! l
- mQ* -
E*.
Trong d6
! l
=A
't.
m

nam
200 '
[
't
] [ 9 ]
m
-6
T *
12
.0,12
11
="A
't
= 200 x 9/12 = 200 x 0,75 = 150 don vi.
r* =
11-
mQ* - s* =
150- 144-
5 = 1 don vi.
ta hang thai
diem
trong khi dlf
tru
con 1 don vi.
Va
m6i l'an
voi
khO"i
lu'<;Jng
la 24 don vi.

se
cha.
Bay
gia
ta
xet
tru'ang
h<;Jp
khi
yeu
c'au xua't
hit%n
rna
hang
dlf
tru
khong con thl
yeu
c'au d6 bi ma't. Chung ta
se
chi ra ding trong tru'ang
h<;Jp
nay
lam
t6i thieu chi phi blnh quan hang
nam
va
vit%c
lam
eve

con C
Ia
gia mua m()t don vi hang h6a.
Khi d6
n€u f
0
ky
hit%u
khoang thai gian trong 1 niim, trong thai gian d6
th6ng thi€u dlf
tru
thll<;Ji
blnh
quan
hang
niim
se
Ia:
B =
"A(P-
C)(1 - fo)-
Tio"Af
0
-
(chi phi
hang
va chi phi
lu'u
kho).
=

chi phi
h;;ti)
c1;1
the blnh quan do thie'u
h1;1t
hang h6a
dv
trii'.
•
I1oAf
0
la
tq
s6
chi phi
h;;ti)
uy tin blnh quan hang narn.
• (P
+ IIo - C)Af
0
la trj
s6
chi phi t6ng
quat
blnh quan do thie'u
h1;1t
hang
d\1'
tru.
TI

la
luqng hang b6 sung cho rn6i rn9t l'an
b6
sung. d9
IOn
cua rn9t
chu
ky
la: T = (Q/A) +
T.
T6ng chi phi trong rn9t chu ky la:
IC Q
2
A+ +TIAT
2 A
s6 chu
ky
blnh quan hang narn la:
1 A
= , ,-
T
Q+AT
chi phi blnh quan hang narn
se
Ia:
AA
IC Q
2
TIA.AT
Z=

oo)
=
TIA
Trang
21
V
, •
d""
kh"
a xay ra
au
= 1 Q * =

IC
)N
K I
a
eu
ITA::;;
-v2AIC
A
<=>
IT
<
-A-
Ttic Ia chi phi do ma't
mot
yeu
c'au nho hon chi phi
hang

quan
to'i
thi€u hang
nam
tren 1 don
vi hang
h6a thi z
d(!.t
gia
tq
nho nha't khi T = o tuc Ia ta khong
bao
giO
d€
tho'ng thie'u hang
dl,l'
trii'.
Do
d6 ta
l(!.i
c6 cong thuc Wilson.
Trang 22