G6c giira ducrng thiing SB va m?t phiing ABC hling A... Khi quay tam giac xung quanh cua hinh n6n d6 b&ng A... Bi~t vectCY phap tuy€n ~ cua m~t phing cht'ra m~ch hqp vcri vectCY cam ung
Trang 1KY THI TOT NGHitP TRUNG HQC PHO THONG NAM 2020
Thiri gian lam bai : 90 phut , kh6ng ki thiri gian phat ai
Cau 1: C6 bao nhieu each chc;m hai h9c sinh tu m(',t nh6m g6m 10 h9c sinh?
Cau 2: Cho cfrp s6 c(',ng (Un) v&i ul = 3 va u2 = 9 Cong sai cua c~p s6 c(',ng da cho bftng
Cau 3: Nghi~m cua phuong trinh 3x - l = 27 la
Cau 4: Th€ tich cua kh6i l~p phuong c~nh 2 bi'tng
Cau 5: T~p xac dinh cua ham s6 y = log2 X la
A [O; +oo ) B ( OJ;+oo ) C (O;+oo ) D [2;+oo)
Cau 6: Ham s6 F ( X) la m(',t nguyen ham cua ham s6 f ( X) tren khoang K n€u
Cau 7: Cho kh6i ch6p c6 di~n tich day B = 3 va chi€u cao h = 4 Th€ tfch cua kh6i ch6p da cho bftng
Cau 8: Cho kh6i n6n c6 chi€u cao h = 3 va ban kfnh day r = 4 Th€ tich cua kh6i n6n da cho bftng
Cau 9: Cho m~t'du c6 ban kfnh R = 2 Di~n tich cua m~t du da cho bi'tng
A 32;r B 8JZ" C 167Z' D 47Z'
3
Cau 10: Cho ham s6 f ( x) c6 bang bi€n thien nhu sau :
f( x) / - _ ~
Ham s6 da cho nghich bi€n tren khoang nao du&i day ?
A ( -oo; -1) B ( O; 1) C ( -1; 0) D ( OJ;O)
Cau 11: V &i a la s6 thµc ducmg tuy y, log 2 ( a 3 ) bftng
A - log2 a B - log2 a C 3 + log2 a D 3 log2 a
Cau 12: Di~n tich xung quanh cua hlnh tn,1 c6 d9 dai duong sinh l va ban kfnh day r bftng
1
A 41rrl B 1rrl C -JZ"r! D 2JZ"r!
3
Cau 13: Cho ham s6 f ( x) c6 bang bi€n thien nhu sau :
Ham s6 da cho d~t cµc d~i t~i
Trang 2Cau 14: 06 thi cua ham s6 nao du6i day c6 d~ng nhu ducrng cong
trong hinh ben ?
A y=x 3 -3x B y=-x 3 +3x
4 2 2
C.y=x-x D y=-x 4 +2x 2 •
A • A A , ~ • , ~ x-2 ,
A y = -2 B y = 1 C x = -1
A (I0;+oo ) B ( 0;+oo ) C [10; +oo)
S6 nghi?m cua phuang trinh f ( x) = -1 la
D (-oo;l0)
y
D 8
D z=2+i
Cau 20: Cho hai s6 ph(rc Z1 = 2 + i va Z2 = 1 + 3i Phin th\fC cua s6 phuc Z1 + Z2 hiing
A Q(1;2) B P(-1;2) C N(l;-2) D M(-l;-2)
X
X
c6 t9a d9 la
A (0;l;O) B (2;1;0) C (0;1;-1) D (2;0;-1)
t9a d9 la
A (-2;4;-1) B (2;-4;1) C (2;4;1) D (-2;-4;-1)
vecta phap tuy~n cua ( P) ?
A n3 = ( 2; 3; 2) B n1 = ( 2; 3; o) c ii2 = ( 2; 3; 1) n n4 = ( 2; o; 3)
Cau A 25 : T rong kh" ong gian 0 xyz, c o h d ' uang t ang h' d : x-] y- 2 z+l o• A ' d , d" h " d?
2 = - 3- = ~ - 1em nao ua1 ay t u9c
A P(1;2;-1) B M(-1;-2;1) C N(2;3;-l) D Q(-2;-3;1)
SA= ✓2a, tam giac ABC vuong can t~i B va AC= 2a (minh h9a nhu hinh
hen) G6c giira ducrng thiing SB va m?t phiing ( ABC) hling
A 30° B 45°
C 60° D 90°
B
Trang 2/5
Trang 3Cau 27: Cho ham s6 f ( X) c6 bang xet dfru cua f' ( X) nhtr sau :
S6 di€m C\fC tri cua ham s6 da cho la
Cau 28: Gia tri nh6 nhfrt cua ham s6 f ( x) = x4 -1 0x2 + 2 tren do?n [-1; 2] b&ng
Cau 29: Xet cac s6 th1,rc a va b thcia man log3 ( 3a_6 ) = log9 3 M~nh d~ nao du6'i day dung?
Cau 30: S6 giao di€m cua d6 thi ham s6 y = x 3 -3x + 1 va tf\}c hoanh la
Cau 31: T~p nghi~m cua bfrt phmmg trinh 9x + 2.3x -3 > 0 la
Cau 32: Trong khong gian, cho tam giac ABC vuong t?i A, AB= a va AC= 2a Khi quay tam giac
xung quanh cua hinh n6n d6 b&ng
A 5tra2• B ✓51ra2• C 2✓51ra2• D 101ra2•
Cau 33: Xet f xe x 2 , dx, neu d~t u = x 2 thi f xe x 2dx bang ,
4
0
Cau 34: Di~n tich S cua hinh ph~ng gi6'i h?n bai cac duong y = 2x2 , y = -1, x = 0 va x = l duqc tinh
I
A S = tr f( 2x2 + 1) dx
0
C S = f( 2x2 + 1) dx
0
I
0
I
D S = f( 2x2 + 1) dx
0
Cau 35: Cho hai s6 ph(rc z, = 3 - i va Z2 = -1 + i Ph.ln ao cua s6 phuc z, Z2 b&ng
Cau 36: G9i z 0 la nghi~m phuc c6 ph.ln ao am cua phuang trinh z2 - 2z + 5 = 0 Modun cua s6 phuc
z 0 +i b&ng
Cau 38: Trong khong gian Oxyz, cho hai di€m M(l;0;l) va N(3;2;-l) Duong th~ng MN c6
phuang trinh tham s6 la
{
A y = 2t
z= l+t
{
x = l+t
B y=t
z =I+t
{
X = } - !
C y = t
z = l +t
{
D y= t
•
Trang 4-Cau 39: C6 6 chiec ghe duqc ke thanh m9t hang ngang Xep ng&u nhien 6 h9c sinh, g6m 3 h9c sinh lap A, 2 h9c sinh lap B va 1 h9c sinh lap C, ng6i vao hang ghe d6, sao cho m6i ghi c6 dung m9t h9c
sinh Xac suit d~ h9c sinh lap C chi ng6i qmh h9c sinh lap B b~ng
AB= 2a, AC= 4a, SA vuong g6c v&i m~t phting day va SA= a (minh
1
D -
5
C
bx+c
.,.+ oo
kh6i tn,i duqc gi&i h~n bai hinh tr1,1 da cho b~ng
"
0
225
225
225
225
J' (x) + 0 0 + 0
2~/2~
Trang 4/5
B
Trang 5Cau 47: Xet cac s6 thvc dmmg a,b,x,y thoa man a> I, b > 1 va a x = b y = ./;;E Gia tri nho nhit cua bieu thuc p = X + 2 y thu9c t~p hqp nao du6i day ?
Cau 48: Cho ham s6 f ( x) = x + m ( m la tham s6 th1,rc ) G9i S la t~p hqp tit ca cac gia trj cua m
x+l sao cho maxlf(x)l+minlf(x)I = 2 S6 ph~n tu cua S la
(O ; l) (O ; l)
l6i c6 cac dinh la cac diem A,B,C,D,M,N,P va Q bing
Cau 50: Co bao nhieu s6 nguyen x sao cho t6n t~i s6 thvc y thoa man log3 ( x + y) = log4 ( x2 + y2 ?
- HET
Trang 6-Ao
KY THI TOT NGHI:tP TRUNG HQC PHO THONG NAM 2020
Bai thi: KHOA HQC Tl/ NHIEN Mon thi thanh phin: V ~ T Li
~
Thai gian lam bai: 50 phut, khong kd thai gian phat iJJ
···
Can 1: D~t hi~u di~n th~ Uvao hai dftu mc)t do~n m~ch di~n thi cuong de) dong di~n khong d6i ch~y qua do~n m~ch la J Cong suftt tieu th\! di~n nang cua do~n m~ch la
Can 2: Mc)t m~ch kin phing co di~n tich S d~t trong tir tnrong d€u Bi~t vectCY phap tuy€n ~ cua m~t phing cht'ra m~ch hqp vcri vectCY cam ung tir B m<)t goc a Tu thong qua di~n tich S la
A <I>= BS cos a B <I> = B sin a C <I>= S cos a D <I> = BS sin a
Can 3: M6i lien M giua tftn s6 goc m va tftn s6 f cua mc)t dao dc)ng di€u hoa la
Cau 4: Mc)t con Hie lo XO dang dao dc)ng di6u boa CCY nang cua con Hie la
A t6ng dc)ng nang va th€ nang cua no B hi~u dc)ng nang va th€ nang cua no
C tich cua dc)ng nang va th€ nang cua no D thu<Yng cua d()ng nang va th€ nang cua no
Cau 5: Bien de) cua dao dc)ng CCY tilt dftn
A khong d6i theo thai gian B tang dftn theo thai gian
C giam dftn theo thai gian D bi~n thien di6u hoa theo thai gian
Cau 6: Cong thtrc lien h~ giua bucrc song A, t6c de) truy€n song V va chu ki T cua mc)t song CCY hinh sin la
A l = vT B A = - C A= vT 2 • D A = - 2 •
Can 7: Trong giao thoa song ca, hai ngu6n k€t hqp la hai ngu6n dao dc)ng
A cung bien de) nhung khac tftn s6 dao dc)ng
B cling tftn s6 nhung khac phu<Yng dao dc)ng
C cung phu<Yng, cung bien de) nhung co hi~u s6 pha thay d6i theo thai gian
D cung phu<Yng, cung tftn s6 va co hi~u s6 pha khong d6i theo thai gian
Can 8: T6c de) truy€n am co gia tri 16n nhftt trong moi tnrong nao sau day?
A Nham B Khi oxi C Nuac bi~n D Khi hidro
Cau 9: Cuang de) dong di~n i = 4cos1201Ct (A) co gia tri C\fC d~i biog
Cau 10: D~t di~n ap xoay chi€u co tftn s6 goc m vao hai dftu cuc)n cam thuftn co de) t\T cam L Cam khang cua cuc)n cam la
Cau 11: Khi ho~t d<)ng, may phat di~n xoay chi€u ba pha t~o ra ba suftt di~n d<)ng xoay chi6u hinh sin cung tftn s6, cung bien de) va l~ch pha nhau
1(
C -
2
D 31C
4
Cau 12: M<)t may tang ap li tuong co s6 vong day cua cu<)n SCY cftp va cu<)n th(r cftp 1§.n luqt la NI va Nz,
K€t lu~n nao sau day dung?
A N 2 <N1• B N 2 >N1•
Trang 1/3
Trang 7Cau 13: Ml;lch dao d(mg li tuang gbm t\l di~n c6 di~n dung C va cu()n cam thufrn cod◊ tµ cam L Trong ml;lch dang c6 dao d()ng di~n tir tµ do v6i chu ki T Gia tri cua T la
Cau 14: Trong chan khong, s6ng di~n tir c6 bu6c s6ng nao sau day la song nglin vo tuy€n?
Cau 15: Cfru v6ng bay slic xuftt hi~n sau con mua duqc giai thich dµa vao hi~n tuqng
A ph6ng Xl;l B quang di~n trong C quang di~n ngoai D tan slic anh sang
Cau 16: TiaXv6i tia nao sau day c6 cung ban chftt la s6ng di~n tir?
A Tia h6ng ngol;li B Tia p+ C Tia /T D Tia anpha
Cau 17: Theo thuy€t Iuqng tu anh sang, anh sang duqc tl;lo thanh boi cac hl;lt nao sau day?
Cau 18: Xet nguyen ru hidro theo miu nguyen ru Bo Bi€t ro la ban kinh Bo Ban kinh quy dl;lo dung K
c6 gia tri la
Cau 19: S6 nuclon c6 trong hl;lt nhan ~~K la
Cau 20: Tia/T la dong cac
A electron B proton C natron D pozitron
Cau 21: M()t di~n tich di~m q = 5 10 -6 C duqc d~t tl;li di~m M trong di~n trucmg thi chju tac d\lng cua h,rc di~n c6 d9 16n F = 4.10-3 N Cuang d9 di~n trucmg tl;li M c6 d9 Ian la
A 9000 V/m B 20000 V/m C 800 V/m D 1250 V/m
Cau 22: M()t con Ilic don c6 chiSu dai 0,5 m dao d()ng di Su hoa tl;li nai c6 g = 9, 8 m/s2 • Con Ilic dao d<)ng v6i tin s6 g6c la
A 4,4 rad/s B 28 rad/s C 0,7 rad/s D 9,8 rad/s
Cau 23: Tren m<)t sqi day dan h6i c6 hai dAu c6 djnh dang c6 song dung v6i 3 b\mg song Bi€t song truySn tren day co bu6c song 60 cm ChiSu dai cua sqi day la
Cau 24: D~t di~n ap xoay chiSu co gia tri hi~u d\lng U vao hai dAu cu<)n cam thuAn thi dong di~n Chl;ly
trong cu<)n cam co cucmg d<) hi~u d\lng la 3 A Bi€t cam khang cua cu<)n cam la 40 n Gia tri cua Ubing
Cau 25: D~t di~n ap xoay chiSu vao hai dfru di~n tro R thi dong di~n ch~y qua R co cucmg d<) hi~u d\lng
la 1 A Bi€t cong suftt toa nhi~t tren R la 40 W Gia tri cua R la
Cau 26: M<)t song di~n tir co tfin s6 15.106 Hz truySn trong m<)t moi trucmg v6i t6c d<) 2,25.108 mis
Trong moi trucmg do, song di~n tir nay co bu6c song la
Cau 27: Trong thi nghi~m Y-ang vS giao thoa anh sang, khoang van tren man quan sat la 0,5 mm Tren man, khoang each tir van sang b~c 4 d€n van trung tam c6 gia tri la
Cau 28: Trong chan khong, buc x~ c6 bu6c song nao sau day la buc x~ thu<)c miSn h6ng ngo~i?
Cau 29: Khi chi€u buc Xl;l don slic ma photon cua n6 co nang luqng s vao Si thi gay ra hi~n tuqng quang di~n trong Bi€t nang hrqng cfin thi€t d~ giai ph6ng m<)t electron lien k€t thanh electron dan (nang luqng kich hol;lt) cua Si la 1,12 eV Nang luqng sco th~ nh~n gia tri nao sau day?
A 1,23 eV B 0,70 eV C 0,23 eV D 0,34 eV
Cau 30: H~t nhan ~He c6 d9 h\lt kh6i la Mz = 0,03038 u Lfty I u = 931,5 MeV/c2• Nang luqng lien k~t cua ~He la
A.86,6MeV B 22,3 MeV C 30,8 MeV D 28,3 MeV
Trang 8Cao 31: Tac d\mg vao h~ dao d<)ng m<)t ngo~i l\fc cuang buc tuftn hoan co A
bien d9 khong d6i nhung tftn s6 f thay d6i duqc (fog v6i m6i gia tri cua f
thi h~ se dao d<)ng cuang buc v6i bien d<) A Hinh ben Ia d6 thi bi8u di~n sv
phv thu<)c cua A vao f Chu ki dao d<)ng rieng cua M gin nhit v6i gia tri
nao sau day?
··· 1··· -+ ·· -+···
~ -· ,) t ·
- -r···r-
Cau 32: M<)t nguai co mit khong bi t~t va co khoang C\fC c~n Ia 25 cm D8 quan sat m<)t v~t nho, nguai
nay SU d\lllg m<)t kinh lup co d<) tv 20 dp S6 b<)i giac cua kinh lup khi nguai nay ngim chimg (J VO C\fC la
Cau 33: Dao d<)ng cua m<)t v~t Ia t6ng hqp cua hai dao d<)ng di€u hoa cung phuong, cung chu ki 0,2 s vm
cac bien d<) la 3 cm va 4 cm Bi~t hai dao d<)ng thanh phftn vuong pha nhau Lfty rc 2 = 10 Gia t6c cua v~t
co do 16n CUC dai Ia
Cau 34: M<)t di8m M chuy8n d<)ng d€u tren m<)t duang tron v6i t6c d<) 10 emfs G9i P la hinh chi~u cua M
Ien m<)t duang kinh cua duang tron quy d~o T6c d<) trung binh cua P trong m<)t dao d<)ng toan phftn bfulg
Cau 35: M<)t sqi day dan h6i ding ngang v6i hai dAu c6 djnh Song truy€n tren day co t6c d9 khong d6i
nhung tAn s6fthay d6i duqc KhifnMn gia tri 1760 Hz thi tren day co song dimg v&i 4 bvng song Gia
tri nho nhftt cuafbing bao nhieu d8 tren day v~n co song dimg?
Cau 36: Tr~:mg iicr !h\l'C hanh do dQ 1\f cam cua m<)t CUQn day,
h9c sinh mac noi tiep cu<)n day do v&i m<)t di~n tra thanh m<)t
do~n m~ch D~t di~n ap xoay chi€u co tAn s6 goc (J) thay d6i duqc
vao hai dftu do~n m~ch r6i do t6ng tra z cua do~n m~ch Hinh
ben Ia d6 thi bi8u di~n S\f phv thUQC cua Z2 theo (1) 2 • DQ t\l' cam
cua cu(m day bing
D 800 Hz
z2 (n2)
- ,.' _ ·-' - - ~ ' · -· , ' ' - ' - · - -~ ' ·- ·-'
:: ···!···!··· 1 ··· 1 ·· ··· 1 ····'··· : ···r···t
H O> O • OO O O ~ • • - • • • • ••- : • • • • "" r •• • O H ' t ' • • O N O ~
Cau 37: M<)t con Hie Io XO g6m v~t nh6 kh6i luqng m va Io XO nhy co dQ cung 40 Nim, duqc treo vao m<)t
di8m c6 dinh Gifr v~t a vi tri lo xo dan 1 0 cm r6i tha nhy, v~t dao d<)ng di€u hoa theo phuong thing dung
Bi~t t6c dQ C\fC d~i cua v~t bing 70 emfs Lfty g = 9,8 mfs2 Gia tri cua m Ia
Cau 38: d m~t chftt long, t~i hai di8m S1 va S2 each nhau 28 cm co hai ngu6n dao d<)ng ding pha theo
phuang thing dung ph.at ra hai song k~t hqp G9i Ll1 ya ~2 I~ hai duang thing a m~t chftt long cung \
vuong goc v&i ~o~n thang S1S 2 va each nhau 9 cm ~iet so diem clJc di;ii giao thoa tren L'.l1 va L12 tuang r ~
Cao 39: D~t di~n ap u = 80 cos (wt+ rp) ( (J) khong d6i va : < rp < ; ) vao hai dAu doi;in mi;ich mic n6i ,( ~,
ti~p theo thu t\f: di~n tra R, CUQn cam thuAn L va tv di~n co di~n dung C thay d6i duqc Khi C = c l thi y
di~n ap gifra hai dAu tv di~n Ia u 1 = 100 cos wt (V) Khi C = C2 thi di~n ap giua hai dftu do~ m~ch chua
R va L Ia U z = 100 cos ( OJt + ; ) (V) Gia trj cua rp gin nhit v&i gia ttj nao sau day?
Cau 40: Di~n nang duqc truy€n tu m<)t nha may phat di~n ~6m 8 t? may d~IJ nai tieu thv bftng,duang day
tai ,di~n m<)t pha Coi di~n ap hi~u dvng a nha may khon~ doi, M so cong suat cua mi;ich di~n ban~ 1, cong
suat phat di~n cua cac to may khi hoi;it d<)ng Ia khong doi va nhu nhau Khi hoi;it d<)ng v&i ca 8 to may thi
hi~u su~t truy€n tai la 89% Khi hoi;it d<)ng v6i 7 t6 may thi hi~u su~t truy€n tai la
HET -Trang 3/3
Trang 9KY THI TOT NGHIEP TRUNG HOC PHO THONG NA.M 2020
1 "¥7"'~£~':fJ;~ -::;" Bai thi: KHOA Hoc Tlf NHIEN
, O Mon thi thanh ph§n: HOA HQC
Thai gian lam bai: 50 phut , khong kd thai gian phr:it cti
···
• Cac thS tich khi d€u do a di€u ki~n tieu chu§.n; gia thiSt cac khi sinh ra khong tan trong nu&c
Cau 41: Kim lo:;ii nao sau day khong tac d1;mg v&i dung dich CuSO4?
A Ag B Mg C Fe D.Al
Cau 42: Kim lo:;ii nao sau day la kim lo:;ii ki€m?
Cau 43: Khi X sinh ra trong qua trinh d6t nhien li~u h6a th:;ich, rit d(k va gay 6 nhiSm moi trm'mg Khi X la
Cau 44: Thuy phan este CH3CH2COOCH3, thu duqc ancol c6 cong thuc la
Cau 45: 0 nhi~t d9 thuc'mg, kim lo:;ii Fe khong phan ung v&i dung djch nao sau day?
Cau 46: Dung djch chit nao sau day lam xanh quy tim?
Cau 47: Chit nao sau day c6 tinh luong tinh?
Cau 48: Silt c6 s6 oxi h6a + 3 trong hqp chit nao sau day?
Cau 49: Chit nao sau day c6 phan ung trimg hqp?
Cau 50: Phan ung nao sau day la phan ung nhi~t nhom?
Cau 51: S6 nguyen tu cacbon trong phan tu glucoza la
Cau 52: 0 nhi~t d9 thuc'mg, kim lo:;ii nao sau day tan hSt trong nu&c du?
Cau 53: Chit nao sau day duqc dung dS lam m€m nu&c c6 tinh cung t:;im thcri?
Cau 54: Dung djch KOH tac dµng v&i chit nao sau day t:;io ra kSt tua Fe(OH)3?
Cau 55: Chit nao sau day la chit di~n Ii y~u?
Cau 56: Thuy phan triolein c6 c6ng thfrc (CnH33COO)3C3Hs trong dung djch NaOH, thu duqc glixerol
va mu6i X Cong thuc cua X la
Cau 57: Natri hidroxit (con g9i la xut an da) c6 c6ng thuc h6a h9c la
Cau 58: Chit nao sau day c6 m9t lien k~t ba trong phan tu?
Trang 10Cau 59: Chit X c6 c6ng thuc H2N-CH(CJ-!3)-COOH Ten g9i cua X la
Cau 60: Thanh ph~n chinh cua v6 cac loai 6c, so, hen la
Cau 61: Cho m gam b9t Zn tac d\mg hoan toan v&i dung djch CuSO4 du, thu duqc 9,6 gam kim lo?i Cu Gia tri cua m la
Cau 62: Hoa tan hoan toan 0,1 mol Al bing dung djch NaOH du, thu duqc V lit H2 Gia tri cua V la
Cau 63: Cho 2 ml ancol etylic vao 6ng nghi~m da c6 s~n vai vien da b9t Them tir tir 4 ml dung djch
nghi~m tren la
Cau 64: Phat biSu nao sau day sai?
Cau 65: Thuy phan 68,4 gam saccaroza v&i hi~u suit 75%, thu duqc m gam glucoza Gia trj cua m la
Cau 66: Cho m gam Gly-Ala tac dl,lng het v&i dung djch NaOH du, dun n6ng S6 mol NaOH da phan ung la 0,2 mol Gia tri cua m la
Cau 67: Chit X duqc t?o thanh trong cay xanh nha qua trinh quang hqp 6 di~u ki~n thuang, X la chit
Cau 68: Phat biSu nao sau day sai?
Cau 69: H6n hqp FeO va Fe2O3 tac d\lllg v&i luQ'Ilg du dung djch nao sau day khong thu duqc mu6i si\t(II)?
Cau 70: Cho cac ta sau: visco, capron, xenluloza axetat, olon S6 ta t6ng hqp la
Cau 71: Nung 6 gam h6n hqp Alva Fe trong kh6ng khi, thu duqc 8,4 gam h6n hqp X chi chua cac oxit Hoa tan hoan toan X dn vira du V ml dung djch HCl IM Gia trj cua V la
ung het v&i 0,25 mol X dn t6i da 0,35 mol NaOH trong dung dich, thu duqc m gam h6n hqp hai mu6i Gia tri cua m la
Cau 73: Cho cac phat biSu sau:
(b) Dun n6ng dung djch Ca(HCO3)z c6 xuit hi~n ket ma
(c) Phen chua duqc su d1,1ng dS lam trong nu&c d1,1c
S6 phat biSu dung la
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