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Bất đẳng thức toán học và những viên kim cương: Phần 1

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Phần 1 Tài liệu Những viên kim cương trong bất đẳng thức toán học giới thiệu tới người đọc các nội dung: Những viên kim cương trong bất đẳng thức cổ điển, những viên kim cương trong bất đẳng thức cận đại, những viên kim cương trong giải tích. Đây là một Tài liệu hữu ích dành cho các bạn sinh viên và những ai đam mê toán học dùng làm Tài liệu học tập và nghiên cứu.

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Nội dung Text: Bất đẳng thức toán học và những viên kim cương: Phần 1

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  2. TRAN PHU’O’NG C{)n_g téc vién: Trn Tuin Anh l\guyén Anh Cuimg; Bi1iVie_“:tAnh i NHU’NG VIEN KIM CU’O’NG TRONG BAT DANG THU’C TO/§\N HQC (Tdi bdn lcin thzi nhd’t) NHA XUi\T BAN TRI THU’C
  3. MUC ugc CHU’O’NG I: NHU’NG VlEN KIM CU’O’NG TRONG BAT DANG THLPC CO DIEN 11 §1. Bit ding thirc AM - GM vi cic R9 thuit chqn aiém ro’i 12 §1.1. Bit ding thirc AM — GM 17 §1.2. NhCrng sic miu diim rdi trong bit ding thirc AM GM —~ 20 §2. Bit ding thirc Cauchy - Bunhiakowski — Schwarz vi ky 123 thuit chgn dié'm rdi §2.1. Bit ding thfrc Cauchy — Bunhiakowski Schwarz -— 123 Ky thuit chqn diim rdi trong bit ding thfrc Cauchy - ' ' BunhiaC6pski —Schwarz 126 §3. Bit ding thlfrc Holder vi ky thuit chgn diim ro’i 173 §3.1. Bit ding mac Holder 173 §3.2. Ky thuit su’ dung bit ding thllrc Holder 176 §4. Bit ding mac Minkowski vi kv thuit sir dung 193 §4.1. Bit ding thirc Minkowski 193 §4.2. Ky thuit su’ dung bit ding thirc Minkowski 196 §5. Bit ding thirc Chebyshev vi ky thuit sir dung 201 §s.1. Bit ding thirc Chebyshev 201 §5.2. Ky thuit sir dung bit ding thirc Chebyshev Z03 CHUUNG "3 Nl-‘|l~)’NG VIEN KIM CU’O’NG TRONG BAT DANG THUC CAN DAI 223 §6. Bit ding thirc hoin vi vi K9 thuit su’ dung 225 §6.1. Gidi thiéu v'é bit ding thirc hoin vi Z25 §6.2. Ky thuit sir dung bit ding thirc hoin vi 229 §7. Bit ding thirc Schur vi ky thuit sir dung 249 §7.1. Gidi thiéu vé bit ding thu’c Schur 249 §7.2. Ky thuit sir dung bit ding thllrc Schur Z54 Ung dung bit ding thin: Schur trong chirng minh bit ding thirc §7.3. -.. . .1. 265 don xu’ng ba blen §s. Djnh ly Muirhead vi bit ding thirc d6i xu’ng 279 §s.1. Gié'i thiéu dlnh I9 Muirhead 279 §8.2. Ky thuit s\'r dgng dinh ly Muirhead" 288 CHU’O’NG Ill: NHCPNG VIEN KIM cuowe TRONG GIAI TlCH 307 §9. Dinh ly Fermat vi (mg dung trong bit ding thvirc 309 §9.1. Gidi thléu dinh 19 Fermat 1 ' 309 §9.2. U'ng dung dlnh ly Fermat 311 §10. Djnh ly Lagrange vi cic (rng dung trong bit ding thirc 339 §10.1. Dlnh ly Lagrange cho him mét bié'n vi cac u’ng dung 339 §10:2. Cu'c trl cua him nhi'éu biin vi phu’dng phip nhin tu’ Lagrange 347 §10.2.1. Cgrc trj khéng c6 dléu kién ring buéc 347 §10.2.2. Cu’c tri c6 dféu kién ring bu
  4. 4 §11.2. K? thuit chgn diim rdi trong bit ding thirc Bernoulli 374 §12. Bit ding thirc Jensen vi k7 thuit sir dung 393 §12.1. Him léi, him l6m vi bit ding thirc Jensen 393 §12.2. K? thuit sir dqng bit ding thirc Jensen 399 §13. Bit ding th1'rc Karamata vi k9 thuit sir dgng 411 §13.1. Gidi thiéu ve bit ding thfrc Karamata 411 §13.2. Ky thuit su' dgng bat dang thirc Karamata 418 §14. Bit ding thirc vé’i céc him s6 léi bén phii vi l6m bén tréi 425 §14.1. Céc djnh Iv v‘é him s6 l6i bén phii vi l6m bén trii 425 §14.2. KY thuit sir dgng bit ding thirc RCF, LCF, LCRCF 43O §15. Bit ding thirc Popoviciu 457 §16. Bit ding'thL'rc trong tlch phin Riman 465 CHU’O’NG IV: NHUNG VIEN KlM cuowe TRONG BAT DANG THl}‘C HIEN DAI 513 §17. Phu'dng phép phin tich ting binh phlfdI1g(SOS) 515 §18. Phlrdng phép d6n bié'n (MV) 549 §19. Phu’o’ng phép ABC 627 §20. Phtrdng phép hinh hqc héa dii s6 (GLA) 681 §21. Phu’dng phép EV 735 §22. Phu'dng phép chia dé trj (DAC) 771 CHLPO’NG v: MQT so SANG TAO vE BAT DANG THU’C 805 §23. NhCI'ng bii vié't chqn lqc vé bit ding thllrc 805 §23.1 vé mr diy bit ding thirc bic ba vi (mg dgng 805 §23.2 D6i bié'n s6 di sing tio vi chfrng minh bit ding thirc 809 §23.3 Phu’0’ng phép dinh gié him $6 tii bién 817 §23.4 Phnrdng phép tié'p tuyin chirng minh bit ding thirc 829 §23.s Phu'0‘ng phép hé $6 bit dinh 833 §23.6 Céc phép d6i bié'n thuin nghich theo cic dé dii trong tam giic 879 §23.7 Phu‘dng phép dinh gii céc hé s6' cda da thc bing djnh Iv Viéte 891 §23.2; Bit ding rm'r¢ kh6ng thuin nhit 905 §23.9 Phu’dng phip SS 915 §23.1O Céc ting (I61 x|.'1’ng vi bit ding thirc hoén vi 933 §24. NhG’ng bit ding thirc chgn Iqc 949 §24.1 ca¢ bii toin cé nhléu lei giii 949 §24.2 Vé mét bit ding thirc thi toin quic té, 977 §24.3 Ciu chuyén v‘é bit ding thc Nesbitt - Shapiro 987 §24.4 Bit ding thirc Jack Garfunkel vi mét s6' m6 ring 1015 §24.5 Cic bit ding thrc cé ldi giii hay 1027 CHU’O’NG VI: TONG KET 1055 §25.1 Tém tit nhfrng vién kim cnrdng vi cic bit ding thfrc co’ bin 1055 §25.2 Céc bit ding thdc chqn lgc dinh cho bin dgc 1089 §25.3 Nhin lii vi m6 ra 1099 PHU LUC: Th6ng ké bii viét, bii toin sir dung vi tii liéu tham khio 1114
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  8. 8 day toén céc cép. cho nhfmg nhii nghién c1'1'u Yé tozin l16c p116 1h6ng... Tzic gia hi \>6ng 11161 b6 szich nhu' thé sé mang dén cho d6c gizi tin khi $11‘ 111‘ (T60 szich. sé 06 khoi gqi 1116 ot11hf1'ng cm I160 sinh 1116i tiép xL'1c v6'i Tozin h6c 11161 czich nghiém u'6'c 1110116‘ 11’1c 111211111 I160 sinh gioi tofm Qu6c 16. thiinh 111121 toén h6C vii niém 1i11 V510 kha néng hién thtrc hozi u'O'c 1110' 51). 4. M_6t bgi szich khzing djnh tri tug? sdng tgm Néu nhu' viéc gidi ton lit (ii tim czii tinh trong czii d6ng thi st!‘ szing 1310 khi \'2_‘111 dung phtrcmg phzip gizii chfnh 151 phzit huy czii d6ng cftc trong ctii linh. Hui 111511 d6i 1z_'1p dft hoii \'Z10 IE1111 11161 trong b6 szich ny. A B51 ding thirc 151m6t iinh vtrc khé nhung czii khé kl16ng n§1111 6 génh néng vé lu"6ng kién th1'1'c mii Cr yéu ceiu v6 6c quan szit_ linh cam tinh 16 \"i1 s1'1‘c szing 1&0 d6i diio cua ngtréri giai. M61 b6 szich 161 V6 béit ding th1'1'c phéi din rz1 11111c tiéu tr(11l1£1nh 11161 n1i6n dzit nu6i du'
  9. c Btich khoa. 5. Lé Trung Kién Hz} N61. Sinh vién khoa Bién 111— V1511 1h6ng kh6;12()()7 ~ Z01]. Truimg Dqi 6. Phan hc Bdch khou. H€1N(>i. Thimh Viét Sinh vién khoa T0zin_ khéa 2007 — 2011. T1"11‘O‘11g D211 hc 11_1'nhi6n. 7. va Quéc DHQG TP. HCM. Bzi can Sinh \"i§n khozl Du'(_>‘c. khéa Z006 — Z01 I. T1"11*(>'11g D511 hQC Y — DLl'Q'C C511 Tho". 8. Duo'ng Dc Lzim HQC sinh khézl 2003 — 2006. 1ru'(‘mg THPT Nguyén Trung Thién. Thach 9. Lé H'u mén Khué H21. H21 Tfnh. Sinh vién hé K§' 5111211 nzing. kh6z12()07 — 201 I. T1"11'O'11g Dai hQc Blois. Céng 10. Hoéng Trgmg Hién h(‘)u Phzip. u Sinh vién kh0z1T0zin — Tin. khéa 2008 — Z012. T1*u'Ong D211 hQc Baich kh0z1TP. 11. Nguyén Quéc HCM. Hung Sinh vién khoa Toain. khézl 2005 ~ 2009. T1"11'O'11g D211 I190 Khou hQc 111' nhién. DHQG TP. HCM. 12. B:_1ch Nggc Thénh Céng Ldp 12 chuyén mm. 11m 2006-2009. T1'l1'O'11g P110 111011; 11:11 P1101111 nn khiéu T1511 P1161. Taicfgia’ chain thimh cam on Gizio s11. Tién xi Vusilc Ci1‘1ujc v21 cho phép djch mét s6 ngili M.Lz1scu (Rumzmi) chuyén dé lrong cu
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  14. 14 ll. DIEM R0’! TRONG BAT DANG THU’C 1. V1 d(l dzfn: Tru'O'c khi di V510 khzii niém "diém mi" 06 tfnh chit hc lhué1_ mO‘i lifir ding rm;-¢~ AM _ ml i hgm dagc lilm qucn v (I+l7+c'-‘-(/=3((1+/>+('+d)I>1=3Z\~'6l)7 (' = z/+(!+/2 (I = a+[>+c* Chfmg la c6 thé lhy sai 15m b€1tngL16nt[1'sLrcéu ma khfmg kié/m Ira kg} diéu kién xay ra diu bfmg. min cch hinh lu'Qng hon chimg ta sé gi 121 diém ro‘i trong bit ding thirc.
  15. (‘lzmmg I: .\'lu7'/lg vién kiln ("m/11g trnng I111! zI11I1g 1/1 11'1" 013 1111711 15 2. 1);?! W111 J6: Trong 11111‘ p1111'1Y11g 11111111 1"1111'11g 11111111 11111 115111;; 111111‘ .\ 2 B 111 1|111‘1~'11;_1 1‘111'1'11g 11111111 111c11 11161 111111;; 11111 \11"111‘» \;111: S11‘ (I11 I: T1311 1'11 1111)" czic 1151 115111;: 111111‘ 111111; gizm ~ A 2.~\,21»\; 2... 2 .-\,,_| 2.-\,, 213 S11‘ 1111 2: T1111 111 c111‘ 11111 111111;; 111111‘ 111} p11f111 ‘"123! 51211211 +1.11: 2 B: hm X} .1; 21;: 2 0 11!‘ 213/ 1,1, 211 211 :7 ,\ ZB I? 112/? Dé 1:111 1'11 1111‘ 11211 11511111 111111‘ lrung g11111 111151‘ 1'111'1151 115111; 111111" 111} 11112111 111112111 C1111 _\' 1'§111g: Néu 1151 11:'111g 111111‘ "'l‘ru11g u'0‘11g: A 2 B" X11} 111 111111; 111111 "A = B" 1;_11 11611 chuz'111 P 11510 116 1111 131 tiéu chun P nZ1y 1:11 01:1 czic 11:11 11:'111g 111111‘ 11'u11g g1:111 11"1>11g 511' G13 1 1111111“ cc 11:11 115111;: 111111‘ bi» phzin (12111 ilrig th11'c a’_iapl1u'0'ng) 11‘011g so" (I11) 2 11111; 111111151 1h11"1 xriy 111 116111 bng. 1\"1111‘>11 11111 1'111'Q'c tiéu chun P 111 Q1111 Q1111 )" 111111 1161 .\1'1'11g CLILI 1115111 >5 \‘£1 11111111 1\'1§*11 xay 1'11 112111 b§111g lrong c111“ 11511 ding 1h1'1'c 06 1115111 AM—G1W: Cauchy — Buniakowski — Schwar; (CBS), Ber/louli hoc 111mg 0111‘ phu‘11'11g ph11p 111111 1111'1'_1'1‘ 11$ c{1p 111111; 111111111 $11011 111111‘: SOS, A/IV, ABC, EV, GLA, DAC. D11 \"i§1' 1111" 11111111 diéu 1\'iQ11 111311; 111111 "A = B" xa) 1'11 111c1> 11161 11611 QI1115111 115111 1113 dé 1111111 hu'1'1‘11g 1111111 11131 11111 \1‘1 \Z1 11111111 g1;1 1111' 11:11 d5111g 1h1'1‘1‘ 11*u11g g11111 1111510 b1} p11:_111 11611 Q13 1115 g1)i 1111" §' 111'11‘11g 11£1)' 151: "K_§ thut kiém tra diéu kién xziy ra du béng" 1111511‘ 1113 1h1': gqi 111151 111111 [111 111'1_111g 111111 151 "Ki thuzt ch1_)n diém r01’ trong b§1td§ngth1'1-c". Trong 1:hu'O'11g 1. c1111ng 101 S5 gidi 11111311 1-51 11-; vé "1
  16. 16 m. TOM TAT NQI DUNG BIII (l'(Ing tluic All — GM § 1.1 Gic'>’i thiéu vé bét ding thtvc AM - GM l. Dans . _ l6n2 & q uzit 2. Czic tru'b’ng hqp déc biét 3. Chtrng minh § 1.2 NhCvng séc méu diém rcvi trong bét ding thu»c AM - GM I. Diém ro‘i lrong dzinh gi£1u‘1'A;\/I sung G.\/I II. Diém roi trong dzinh gizi tir GM sang AM III. Nguyén 1y aésng béc l1'Ong bél déng lhtrc can IV. D510 biét héa dual vé bit dflng lhfrc d5ng bfac V. Phéi hqp hai b§1déngthL'1"c déng béc nguqc chiéu nhau v1. Phu'o'ng philp Qhuém héa bét aging lhtrc ba bién $5 VII. Bit ding thfrc déng bgic dang céng mgm VIII. B5. dng lhfrc déng béc cht1"ucén1ht1"c IX. Be‘1td:'ing lhirc khéng déng bf1c_ X. D510 biél héa b§td§1ngthL'rc khéng déng béc XI. Diém 1"0'i khéng déi xrng I XII. Phu'0'ng phzip cim bémg hé XIII. Ky thuét tzich phn thirc aim vil dzinh gizi m§u $6 XIV. ve d¢p diém ro'i trong bi: aémg ma-¢ lu''ng gizic XV. M61 bi tozin chn lc_>c _L'1'ng dung diém ro'i XVI. Céc bili tgip dimh cho ban dQc tu giai
  17. Chlrovzg I: Nhng vién kinz cumzg trong bt ring thlir c6 ziié l7 §1.1.B/QT BANG THUC AM - GM cAc DANG BIEU DIEN BAT DANG THU’C AM - GM 1. Dgmg tozng qzuit: Giél sir a, ,a2,...a” IE1 n s6 thuc khéng ém, khi dé ta cé: Mi D2_1ng 1 I D:_mg 2 k D2_1ng 3 N +42 +---+51” >,,/a +a3 +...+u” 211.4’/(z,a3...cz” 1 (11 '—a cz] fl! +a, +...+a” H H — 1 3"‘ ~ 2ala3....aH ' II ‘ Déng thfrc xziy ra a, =a3 =...=a” 20 ¢ 2. H_é qud: l /I S \7| S ' Néu a, +512 +...+a” =5 const thi Mc1.\'(ala3...a”)= —’ xa'.y ra z1| 1:23 =...=c1” =— /1 , n 0 Néu ala2...a” = P const thi Min(ai + a2 +...a” ) =n.Q/F xay ra al =a3 =...=a” = ’\'/F 2. Cdc trzr&ng h_0‘p dgic biét n n=2 n=3 12:4 Biéu kién Va,b2O Va, b, (‘Z0 Va, 12, W120 Dang 1 Lg-b 2\/E Ma +2 +£ 23/ubc Mwrbic +d 2%‘/abcd Dang 2 a+b22.\/ab a+b+c'23.§/% a+b+c+d24.\*/abcd 3 2 ' 4 D2_1ng3 K-Lgbj Zab %Z+1;+Cj> Za/90 %1+bZC+dj Zabcd Déubéng a=b a=b=(" a=b=c=d Binh lu:§n: Khi chtrng minh ding thirc, néi chung ta rét it gép céc bit ding thL'rc c6 bait dang cén déi, déy dfl nhu caic dang duqc phzit biéu trong 1y thuyét mi thuivng gép czic bét ding thrc cé mét vé phtrc tap, mét vé rL'1t gqn. Cflng giéng nhu‘ khi chirng minh déng thL'rc ta pheii dnh gié ttr \/
  18. 1 8 Brit zizfng th12'c AM - GM Khi dé viéc phn tich hiéu gifra hai vé Lhiinh téng caic binh phu'o‘ng sé ggip nhiéu khé khé1n.Gz_?1p bili toén ny chfmg ta it nghi ngay dén Su dung AM— G1\/I vi théi qucn lilm 1)? hinh thtrc “chi sd" dqmg AM— GM klzi mét cluia cdn th1'rc".Tuy nhién nhbr C6 vé c6 dang gqi y cho chimg ta “c6 3 mél tlzé; s1? dgmg AM — GM ngay cc? khi ed hai vé déu khéng chzia cn thlic ” ‘ w 'v — '1 -7 emu 16a/9(d—b):=4(4ab)((l—b):S4 4"b+("_b)0 =4F”";b)” =(a+b)4' 3. Chmzg mmh al +a, +...+a” " 21'/a,a3...a,I . Vu],u3,...a” 20 (1) IZ cs khoéing 40 czich Chirng minh bér d§1ngthU‘c (1). sau déy 121 hai czich Chirng minh tiéu biéu: I: M I‘ Czich Phu'0'ng phép quy ngap théng thuimg: ' Vo'1 n = 2: A Ta can chung mmh: (I +61, 2 \/a|a2 . Y/a[.u: 20. That vay ta co: +03 Tm/alaz -5(,/al Cl] 1 —\/(12) ,~— 2 20 :> al +113 l T21/a,a3.{-Dangthuc xay 1a a] =a2. - Gia sL'1'b§tdz“ing thtrc S”+] ”*'+ ”*' n+1 /1+ =q”*‘ Vp_qg() 1 Cl n+1 /1+! 11+! _ Ta se chu'n@C mmh , . n 2 +( ,+ I +1 I 2 2”:I =’" ' a l a,...a a /1-»l (2) Ta co , _ 11 11+] /H-I II 1 ll I ~11 ¢1=*["11—¢1(/> I1 H n+1 n+1 —q =J[I1p p_ n+1 n —c](p 11- ‘+p n~Z .q+...+q n» ‘H : [(p!1_qpn—l)+(pn_qZpn—Z)+-“+(pn_([n—|p)+(pn_qn):’ H : [:p/1~I +pn—Z(p+q)+m+p(pn~Z +17/1—3_(]+m+qI1—Z)+(pn~I +p!1—Zq+-uq/2-1 12+ Nhu'v2_?1y(2)C1‘u'
  19. Ch lrmzg Chli dn: I: _ Nh17“ng vién Tén gcpi A AM kim cmmg tron g bfit ring th 121' cox dién Geometrzc mean neu len ban chat cua bat dang thuc Céc séch tozin hcpc d xuél bén Cési. Ceich gqi nay Xuéu phzit m viéc nhil ton - G ; Viét Nam thuimg 4 _; h¢ 19 GM 121 viét tit cua thuét ngfr tiéng Anh Arithmetic mean — eCI+(lw+...+tI, Phzip Cési ll gQi bait déng thtrc lrén (Cauchy) 2 1'/a,a2...u” Va, 2 121 1:1 bit ding nguivi aéu tién O. thfrc d chtrng minh béit ding thirc nay vil éng d chtrng minh né bng mcfn phu'o'ng phép quy nap (150 biét cé thé gqi 151 phu‘o'ng phép "Quy nglp Csi” (Quy nglp Tién Lzli) . Y tu‘('>‘ng cla phuofng phép quy nap ny 151: Bzrc I: Kiém Ira ménh dé dng véi 11 = 2. Bzréc 2.- cm sir ménh aé dng vc3‘i )1 = /'i thiéu céch chtrng minh AM - GM ciia C6si CdchH2: Phurrng phép "Quy ngzp Cési” ~ Vé'i n = 2; a +a %-e/a,a: =i5-;- (x/”1"\/Q") z0;»%1z./(Ila; a +a (dung) Giéx str bit ding thirc dng vdi n = k, ta sé chfrng minh bit ding thirc dng véi 11 = 2k . Thét véy xét 2k $5 thuc a],a3,...a‘.,ak+1,...a2k 20. SL'1'd1,1ng gié thiét quy nap ta cé al+a2+...+a3k Zl a]+a3+...+ak +ak+]+...+a3k 2k 2 k k . 2 EB/al...ak +§/ak+,...a3,\12,/Q/a,...ak Q/a,\_+,...aZk =3(/a]a3...aA,...a2k Gié si1'b§I d:§1ngth£1'c dflng véri n = p, ta sé chimg minh bit déing thirc dng vdi n : p -1. Thét vaiy xét (p — 1) 56: a,,a3,....ap_]2O.Su'dunggia1hiétquy nap vdi n = p ta Q6: a1+a3 +...+ap_| +1’ -| /a,a3...a_l 2"a,...ap_l./’ /a]a3...ap_[ =/’_/ala3...ap_, P a,+a2 +...+ap_,+ p—l a1a2...ap_12p. p—l a]a2...ap_, +...+ap_, al +a2 +...+aP_l 2 (p—1)./"‘/a[a3...aP_, i—1i—~2 a] +413 p_ P"/a]a3...ap_1 Theo nguyén 1)? quy nap ta cc’) b§td§1ngthi1‘c dng vc'>'i mQi 112 2, rze N.
  20. 20 Brit ling thzic A1’V[- GM §1.2.NH13NG sAc MAU DIEM R01 TRONG BAT DANG THU'C AM - GM 1. DIEM RO’l TRONG DANH GIA TU’ TRUNG aim-1 CQNG SANG THUNG BiNH NHAN Chng ta ctmg buéc véo "thé giéi diérn r0*i"\/G1 bfai tozin don giém v51 quen biél sau dy: Bdi toxin xu1"1tphzit.' Cho u. b > O. Tim gi a' . 1 t r1' n h 0 nhat cua b1eu thu'c S = . .1 , b }£+— I 7 (I 01111". Sird11ngb€1tdé1ngtht1‘cAM—GM: s=%+[lz2/%~§=2.v11111=/11111M111s=2 (I (I Nhzjn 111111 T11 11211 101111 11:1y111 06 111é thay 1161 1111é11 11¢ aé cé 1111111 @111: 11211 1111111 SHU day; Bal 1. ., . .1 S=a +- 1 1 1. Cho 112 3. T1m gla , tr; nho nhat cua b1eu thu"c , , 1 a ‘ Binh lugm vd l0’i giéi I Sailz"§mth1rd’ng ggip: S = a + L 2 2 /a a - i a = Z :> MinS = 2 -\ INguyén nluin sai lm: MinS =2 21 =i=l a méu thugm vé"i gizi thiét a 2 3 IPhzin tich vd tim téi ldi girii: Xét béng bién thién cua a.l v21 S dé du doain Min S a 113'456{7‘s}9’101112' ------- -130 L a 1 3 1 4 1 L 1 l 1 L L _1_ L 1_____u111 5 6 7 8 9 10 11 12 30 1 1 1 1 1 ....... 1.3@_‘ 1 1 1 S 33 44 55 66 77 88 99101011111212 30 Nhin being bién thién ta théy khi a céng téng thi l a cng nhO nhung dé téng @1111 a rét i - lén so vdi dc} giém @1111 nén khi a cémg ting lhi téng S cimg lén tir dé d§n dén (1 v51 dgr c11>1111 11111 11 =3 1111 s 111113111 gié 111 111111 111151. aé 115 111é11 1211110 @1111 1111; 111 Se 11151 1§111g Min S = L30 dzglt t2_1i "Die§m r0‘i: a = 3". Do 11111 ding 111111 - AM GM xéy 111 11511 being 1111 diéu 1
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