А.Н.Шерстнев - Математический анализ
..pdfsWOJSTWO P. 27 TAKVE DOSTATO^NO DOKAZATX DLQ FORM WIDA !(x) = b(x)dxi1 ^
: : : ^ dxik ; (x) = c(x)dxj1 ^ : : : ^ dxjs. iMEEM
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(b(x)c(x))dxm ^ dxi1 ^ : : :dxik ^ dxj1 ^ : : : dxjs |
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d(! ^ )(x) = |
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(x)dxm ^ dxi1 |
^ : : : ^ dxik ^ dxj1 |
^ : : : ^ dxjs |
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+ P c(x) |
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(x)dxm ^ dxi1 |
^ : : : ^ dxik ^ dxj1 |
^ : : : ^ dxjs |
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^ : : : ^ dx |
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(x)dx |
^ dx |
^ : : : ^ dx |
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= (,1) |
b(x)dx |
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+ ( |
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@xm (x)dx ^ dx ^ : : : ^ dx ) ^ (c(x)dx ^ : : : ^ dx ) |
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= (,1) ! ^ d + d! ^ : |
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29. p R I M E R. pUSTX U | OTKRYTOE MNOVESTWO W R3 |
I ! | 1-FORMA |
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KLASSA C1 NA U : |
!(x) = p(x)dx1 + q(x)dx2 + r(x)dx3; x = (x1; x2; x3) 2 U. |
wY^ISLIM d!. iMEEM
d! = (@x@p1 dx1 + @x@p2 dx2 + @x@p3 dx3) ^ dx1 + (@x@q1 dx1 + @x@q2 dx2 + @x@q3 dx3) ^ dx2 + ( @x@r1 dx1 + @x@r2 dx2 + @x@r3 dx3) ^ dx3
= (@x@q1 , @x@p2 )dx1 ^ dx2 + (@x@r1 , @x@p3 )dx1 ^ dx3 + (@x@r2 , @x@q3 )dx2 ^ dx3:
30. u P R A V N E N I E. pUSTX ! | 2-FORMA KLASSA C1 NA U R3 : ! = pdx1 ^ dx2 + qdx1 ^ dx3 + rdx2 ^ dx3. pOKAZATX, ^TO
d! = (@x@p3 + @x@q2 + @x@r1 )dx1 ^ dx2 ^ dx3.
zAMENA PEREMENNYH W DIFFERENCIALXNYH FORMAH
31. pUSTX U OTKRYTO W Rn; V OTKRYTO W Rm, OTOBRAVENIE ' : U ! V NEPRERYWNO DIFFERENCIRUEMO. tOGDA W KAVDOJ TO^KE x 2 U OPREDELENO KASA- TELXNOE OTOBRAVENIE '0(x) : Rnx ! Rm'(x). pO\TOMU KAVDOJ FORME ! 2 k(V )
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MOVNO SOPOSTAWITX FORMU ' ! 2 |
(U ): |
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!('(x)); |
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ESLI k = 0, |
(x 2 |
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'0(x) !('(x)); |
ESLI |
k 1 |
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481
oTMETIM, ^TO
! 2 |
0;p |
(V ); ' 2 C |
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(U ); |
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' ! 2 |
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k;p |
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p+1 |
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k;p |
(U ); k 1: |
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! 2 (V ); ' 2 C |
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' ! 2 |
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pERE^ISLIM OSNOWNYE SWOJSTWA WWED•ENNOJ OPERACII (PREDPOLAGAETSQ, ^TO WYPOLNQ@TSQ PODHODQ]IE OGRANI^ENIQ NA U^ASTWU@]IE W \TIH SWOJSTWAH OTO- BRAVENIQ).
32. |
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'(!1 |
+ !2) = ' !1 |
' !2, |
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33. |
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'(c !)(x) = c('(x)) ' !(x), |
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34. |
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'(! ^ ) = |
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! ^ ' , |
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35. |
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' dy |
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j (x)dx |
= d' |
(x), GDE ' , i-Q KOORDINATNAQ FUNKCIQ OTO- |
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; : : :; dy |
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BRAVENIQ ', A dy |
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| BAZIS W L(R'(x); R), DUALXNYJ K STANDARTNOMU |
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BAZISU W |
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'(x) |
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36.' d! = d('!).
p. 32 O^EWIDEN, P. 33 | SLEDSTWIE P. 34, P. 34 | SLEDSTWIE P. 17. uSTANOWIM P. 35. dLQ 2 Rnx IMEEM
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' dy ( ) = dy ('(x))('0(x) ) = ('0 |
(x)) = |
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= d' |
(x)( ): |
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dOKAVEM P. 36. pUSTX SNA^ALA ! | 0-FORMA. tOGDA ' ! = ! ' |
d(' !)(x) =
=
d(! ')(x) = d!('(x)) '0(x)
0
' (x) d!('(x)) = d(! ')(x) = ' d!(x):
dLQ DOKAZATELXSTWA OB]EGO SLU^AQ DOSTATO^NO RASSMOTRETX FORMU WIDA !(y) = c(y)dyi1 ^ : : : ^ dyik . dLQ NE•E (S U^•ETOM P. 33{35)
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^ : : : ^ dy |
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)(x) = c('(x))d' |
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^ : : : ^ d' |
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(x): |
' ! = c('(x)) '(dy |
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482
pO\TOMU (S U^•ETOM P. 28 I RAZOBRANNOGO SLU^AQ 0-FORMY)
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(x) ^ : : : ^ d' |
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d(' !)(x) = d(' c)(x) ^ (d' |
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(x)) |
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+ ' c(x) ^ d(d' |
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(x) ^ : : : ^ d' |
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(x) ^ : : : ^ d' |
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= ('dc)(x) ^ d' |
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(x)) |
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= ('dc)(x) ^ (' dy |
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^ : : : ^ ' dy |
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=' d(cdy 1 ^ : : : ^ dy k )(x) = (' d!)(x): >
37.u P R A V N E N I E. eSLI m = n, TO
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^ : : : ^ dx |
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) = c ' det '0 |
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^ : : : ^ dx |
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'(c ^ dx |
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38. p R I M E R. pUSTX U OTKRYTO W R2, GDE ZADANY POLQRNYE KOORDINATY ( ; ), PRI^•EM U \ f( ; ) j = 0g = ;; V | OTKRYTOE MNOVESTWO W DRUGOM \KZEMPLQRE R2, GDE ZADANY PRQMOUGOLXNYE KOORDINATY (y1; y2), I OTOBRAVENIE ' ZADANO FORMULAMI
y1 = '1( ; ) = cos ; y2 = '2( ; ) = sin :
pUSTX ! = dy1 ^ dy2. tOGDA
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= (cos d , sin d ) ^ (sin d + cos d ) = d ^ d : |
' ! = d' ^ d' |
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tEOREMA pUANKARE
39.fORMA ! 2 k;1(U ) NAZYWAETSQ ZAMKNUTOJ, ESLI d! = 0. dIFFEREN- CIALXNAQ FORMA ! NAZYWAETSQ TO^NOJ, ESLI SU]ESTWUET FORMA TAKAQ, ^TO
!= d . w SILU P. 28 KAVDAQ TO^NAQ FORMA ! 2 k;1 (U ) QWLQETSQ ZAMKNUTOJ. wOZNIKAET WOPROS, NE SLEDUET LI IZ ZAMKNUTOSTI FORMY E•E TO^NOSTX? oTWET POLOVITELEN LI[X PRI NEKOTORYH OGRANI^ENIQH NA OBLASTX U.
40.nAZOW•EM OBLASTX U 2 Rn ZW•EZDNOJ, ESLI 9a 2 U 8x 2 U ([a; x] U ), GDE [a; x] = fta + (1 , t)x j t 2 [0; 1]g | OTREZOK W Rn. o^EWIDNO, KAVDOE ZW•EZDNOE MNOVESTWO LINEJNO SWQZNO, A KAVDOE WYPUKLOE MNOVESTWO ZWEZDNO• .
41.t E O R E M A. pUSTX U Rn | OTKRYTOE ZW•EZDNOE MNOVESTWO. tOGDA WSQKAQ ZAMKNUTAQ FORMA ! 2 k (U) TO^NA.
483
bEZ OGRANI^ENIQ OB]NOSTI S^ITAEM, ^TO W OPREDELENII P. 40 a = . oPRE- DELIM LINEJNOE OTOBRAVENIE J : k(U) ! k,1(U), ZADAW EGO NA ODNO^LENNYH FORMAH RAWENSTWOM
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1tk,1c(tx) dt)xi !; |
(3) |
Jfc(x)dxi1 ^ : : : ^ dxikg |
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GDE OBOZNA^ENO ! = dxi1 ^ : : : ^ dxi ,1 ^ dxi +1 ^ : : : ^ dxik . pRI \TOM J(0) = 0.
uTWERVDENIE TEOREMY SLEDUET IZ TOVDESTWA
(4) |
! = J(d!) + d(J!); |
KOTOROE PROWERQETSQ NEPOSREDSTWENNYMI WY^ISLENIQMI. w SILU LINEJNOSTI OTOBRAVENIQ J DOSTATO^NO DOKAZATX (4) DLQ ODNO^LENNOJ FORMY !(x) = c(x)dxi1 ^ : : : ^ dxik . iMEEM (SM. (3))
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d(J!)(x) = |
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tk |
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(tx) dt |
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]dxj ^ ! : |
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oBOZNA^AQ 1 = |
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!, POLU^AEM |
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j (tx) dt x |
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d(J!)(x) = |
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1tk,1c(tx) dt |
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(,1) ,1 dxi ^ ! |
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s DRUGOJ STORONY, |
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P1 +kZ0 |
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tk,1c(tx) dt dxi1 ^ : : : ^ dxik : |
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(x) dxj ^ dxi1 : : : ^ dxik g |
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J(d!)(x) = |
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(tx) dt xj) dxi1 ^ : : : ^ dxik |
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(,1) ,1( |
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(tx) dt xi )dxj ^ ! |
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= ( |
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0 |
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@x |
j (tx) dt x ) dx |
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^ : : : ^ dx |
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j=1 |
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sKLADYWAQ POLU^ENNYE RAWENSTWA, IMEEM
J(d!)(x) + d(J!)(x) = |
Z01 |
d |
[tkc(tx)] dt dxi1 ^ : : : ^ dxik |
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dt |
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= |
c(x)dxi1 ^ : : : ^ dxik = !(x): |
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> |
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484
sINGULQRNYE KUBY
42. pUSTX Ik = [0; 1]k Rk; U | OTKRYTOE MNOVESTWO W Rk TAKOE, ^TO Ik U . pUSTX : U ! Rn (n k) | NEPRERYWNO DIFFERENCIRUEMOE OTOBRA- VENIE. oGRANI^ENIE \TOGO OTOBRAVENIQ NA Ik NAZYWAETSQ k-MERNYM SINGULQR- NYM KUBOM W Rn. dOPUSKAQ NEKOTORU@ WOLXNOSTX, BUDEM OBOZNA^ATX \TO OGRA- NI^ENIE PO-PREVNEMU BUKWOJ ( : Ik ! Rn). eSLI OTOBRAVENIE DEJSTWUET W OTKRYTU@ OBLASTX V Rn, TO GOWORQT O k-MERNOM SINGULQRNOM KUBE W OBLASTI V . nULXMERNYM SINGULQRNYM KUBOM NAZYWAETSQ OTOBRAVENIE : f0g ! Rn. w ^ASTNOSTI, SAM STANDARTNYJ KUB Ik RASSMATRIWAETSQ KAK k-MERNYJ SINGULQR- NYJ KUB, QWLQ@]IJSQ OGRANI^ENIEM NA Ik TOVDESTWENNOGO OTOBRAVENIQ Rk NA SEBQ.
43. pUSTX ; 0 : Ik ! Rn | DWA k-MERNYH SINGULQRNYH KUBA. bUDEM GO- WORITX, ^TO 0 POLU^EN IZ IZMENENIEM PARAMETRIZACII (PI[EM 0), ESLI SU]ESTWUET DIFFEOMORFIZM p : Ik ! Ik (TO ESTX p | BIEKCIQ, NEPRERYW- NO DIFFERENCIRUEMAQ WMESTE S p,1, PRI^•EM p0; (p,1)0 DOPUSKA@T NEPRERYWNYE PRODOLVENIQ NA GRANICU Ik ) TAKOJ, ^TO
(i)0 = p,
(ii)det p0 > 0.
bUDEM PISATX , 0, ESLI SU]ESTWUET DIFFEOMORFIZM p : Ik ! Ik TAKOJ, ^TO WYPOLNENO (i) I
(iii)det p0 < 0.
w ^ASTNOSTI, 1-MERNYJ SINGULQRNYJ KUB W Rn ESTX GLADKAQ KRIWAQ W Rn W SMYSLE 178.1, A 2-MERNYJ SINGULQRNYJ KUB W R3 ESTX GLADKAQ POWERHNOSTX W R3 W SMYSLE 185.1.
44. u P R A V N E N I E. pOKAVITE, ^TO | OTNO[ENIE \KWIWALENTNOSTI W MNOVESTWE k-MERNYH SINGULQRNYH KUBOW.
iNTEGRAL FORMY PO SINGULQRNOMU KUBU
45. pUSTX ! | 0-FORMA KLASSA C0 W OBLASTI U Rn (TO ESTX ! : U ! R| NEPRERYWNAQ FUNKCIQ) I : f0g ! U | 0-MERNYJ SINGULQRNYJ KUB. pOLOVIM
PO OPREDELENI@ Z ! !( (0)).
46. pUSTX TEPERX ! 2 k;0 (U ) | ODNO^LENNAQ k-FORMA, TO ESTX !(x) = c(x)dx1 ^ : : : ^ dxk; x = (x1; : : :; xk) 2 U , GDE U Rk | OTKRYTAQ OBLASTX,
485
SODERVA]AQ STANDARTNYJ KUB Ik. pO OPREDELENI@ |
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47. (oB]IJ SLU^AJ). pUSTX ! 2 k(V ); V |
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k-MERNYJ SINGULQRNYJ KUB W OBLASTI V . sOGLASNO P. 31 S KAVDOJ k-FORMOJ |
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48. zAPI[EM QWNOE WYRAVENIE INTEGRALA (5) OT ODNO^LENNOJ k-FORMY
!(x) = c(x)dxi1 ^ : : : ^ dxik (i1 < i2 < : : : < ik). pUSTX : Ik ! V , TO ESTX t = (t1; : : :; tk ) 2 Ik ! (t) = ( 1 (t); : : :; n(t)) 2 V . tOGDA (SM. PP. 33,34)
!(t)
i
(dx s)
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oTS@DA (SM. P. 37) |
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oTMETIM SWOJSTWA INTEGRALA.
49.eSLI 0, TO DLQ L@BOJ k-FORMY ! Z ! = Z !.
0
486
50.eSLI , 0, TO Z ! = ,Z !.
0
pUSTX, NAPRIMER, 0. rAWENSTWO P. 49 DOSTATO^NO USTANOWITX DLQ OD-
NO^LENNYH FORM. pUSTX p : Ik ! Ik |
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w OBOZNA^ENIQH P |
. 49 |
IMEEM ISPOLXZUEM TEOREMU O ZAMENE |
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PEREMENNYH W KRATNOM INTEGRALE) |
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pROSTRANSTWO CEPEJ
51. rASSMOTRIM WE]ESTWENNOE WEKTORNOE PROSTRANSTWO Sk , ALGEBRAI^ESKIM BAZISOM KOTOROGO QWLQETSQ MNOVESTWO WSEH k-MERNYH SINGULQRNYH KUBOW W Rn. tAKIM OBRAZOM, \LEMENTY Sk | \TO FORMALXNYE SUMMY WIDA
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GDE 1; : : :; p | k-MERNYE SINGULQRNYE KUBY W Rn. pOLOVIM PO OPREDELENI@ |
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DLQ L@BOJ k-FORMY ! |
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ZADAN E]E ODIN \LEMENT |
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PROSTRAN |
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STWA Sk . |LEMENTY s I t NAZYWA@TSQ \KWIWALENTNYMI (s t), ESLI Z ! = Z ! |
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DLQ L@BOJ k-FORMY !; | OTNO[ENIE \KWIWALENTNOSTI W Sk (!!). pUSTX Sk | FAKTOR-PROSTRANSTWO PROSTRANSTWA Sk PO UKAZANNOMU OTNO[ENI@ \KWIWALENT- NOSTI. |LEMENTY \TOGO FAKTOR-PROSTRANSTWA NAZYWA@TSQ k-MERNYMI CEPQMI W Rn. mY PO-PREVNEMU BUDEM OBOZNA^ATX k-MERNYE CEPI SIMWOLOM (7). w ^AST-
NOSTI, k-MERNAQ CEPX NAZYWAETSQ NULEWOJ, ESLI Z ! = 0 DLQ L@BOJ k-MERNOJ
FORMY !.
52. z A M E ^ A N I E. eSLI | NULEWAQ k-MERNAQ CEPX I 1; : : :; p | L@BYE k-MERNYE SINGULQRNYE KUBY, TO = 0 1 + : : : + 0 p.
487
53. u P R A V N E N I E. pOKAVITE, ^TO PROSTRANSTWO Sk BESKONE^NOMERNO. fuKAZANIE: PUSTX p 2 N PROIZWOLXNO I U1; : : :; Up | PROIZWOLXNYE POPARNO
NEPERESEKA@]IESQ OTKRYTYE MNOVESTWA W Rn . rASSMOTRETX k-MERNYE SINGU- LQRNYE KUBY 1; : : :; p TAKIE, ^TO i (Ik) Ui (1 i p); CEPI 1 i (1 i p) NENULEWYE. pOKAZATX, ^TO \TI CEPI LINEJNO NEZAWISIMY.g
54. rASSMOTRIM PROSTRANSTWO k;0 = k;0(Rn ). nA PROIZWEDENII k;0 Sk
OPREDELIM WE]ESTWENNU@ BILINEJNU@ FORMU |
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55. bILINEJNAQ FORMA (8) NEWYROVDENA, TO ESTX |
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(B) ESLI h!; si = 0 DLQ L@BOJ s 2 Sk, TO ! = 0. |
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(A) SLEDUET IZ OPREDELENIQ NULEWOJ CEPI (SM. P. 51). |
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wOZXM•EM k-MERNYJ SINGULQRNYJ KUB W Rn, ZADANNYJ RAWENSTWOM |
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t = (t1; : : :; tk) 2 Ik; |
GDE U WEKTORA W PRAWOJ ^ASTI RAWENSTWA n , k NULEJ. pRI DOSTATO^NO MALOM> 0 c1:::k( (t)) > 0; t 2 Ik. sLEDOWATELXNO, DLQ CEPI s = 1 IMEEM
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^TO PROTIWORE^IT PREDPOLOVENI@. >
gRANICA CEPI
56. oPREDELIM SNA^ALA GRANICU SINGULQRNOGO KUBA : Ik ! Rn, TO ESTX CEPI WIDA s = 1 . pUSTX
Rki;,0 1 ft = (t1; : : :; tk) 2 Rk j ti = 0g
| GIPERPLOSKOSTX W Rk. bUDEM RASSMATRIWATX \TU GIPERPLOSKOSTX KAK (k ,1)-
MERNOE EWKLIDOWO PROSTRANSTWO S KOORDINATNYM PREDSTAWLENIEM, INDUCIRO- WANNYM IZ Rk. tAK ^TO ^ISLA t1; : : :; ti,1; ti+1; : : :; tk SUTX KOORDINATY TO^-
KI (t1; : : :; ti,1; 0; ti+1; : : :; tk) 2 Rk,1. aNALOGI^NO OPREDELIM GIPERPLOSKOSTX
i;0
488
Rk,1 ft 2 Rk j ti = 1g. pUSTX Ik,1 | SOOTWETSTWU@]IE STANDARTNYE GIPER- |
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57. p R I M E R. pRI k = 2 RASSMOTRIM STANDARTNYJ KUB I2 KAK SINGULQR- NYJ 2-MERNYJ KUB (TO ESTX EDINI^NYJ KWADRAT W R2), OPREDEL•ENNYJ TOVDEST- WENNYM OTOBRAVENIEM R2 NA SEBQ. tOGDA (SM. rIS. 29)
@I2 = ,I11;0 + I11;1 + I21;0 , I21;3:
p
58. w OB]EM SLU^AE DLQ PROIZWOLXNOJ k-MERNOJ CEPI = P i i OPREDELIM
i=1
p
E•E GRANICU RAWENSTWOM @ = P i@ i. iTAK, OPREDELENO LINEJNOE OTOBRAVENIE
i=1
@ : Sk ! Sk,1.
tEOREMA sTOKSA DLQ CEPI
nARQDU S LINEJNYM OTOBRAVENIEM @ : Sk ! Sk,1 RASSMOTRIM OPERATOR DIFFERENCIROWANIQ d : k,1;1(Rn) ! k;0(Rn ). iMEET MESTO SLEDU@]AQ OSNOW- NAQ TEOREMA MNOGOMERNOGO ANALIZA.
59. t E O R E M A. dLQ L@BOJ CEPI s 2 Sk (k 1) I L@BOJ FORMY
! 2 k,1;1(Rn)
(9) |
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60. z A M E ^ A N I E. rAWENSTWO (9), ZAPISANNOE ^EREZ BILINEJNU@ FORMU, WWED•ENNU@ W P. 54, IMEET WID
(10) |
hd!; si = h!; @si: |
(tO ESTX OPERATORY d I @ QWLQ@TSQ WZAIMNO SOPRQV•ENNYMI.)
61. dOKAZATELXSTWO TEOREMY. dOSTATO^NO OGRANI^ITXSQ SLU^AEM, KOGDA s = 1 , GDE | k-MERNYJ SINGULQRNYJ KUB. bOLEE TOGO, MOVNO S^ITATX,
489
^TO KUB STANDARTEN ( = Ik ), TAK KAK OB]IJ SLU^AJ TOGDA SLEDUET IZ WY- KLADKI
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NULEJ SPRAWA. eSLI E]•E PRINQTX WO WNIMANIE LINEJNOSTX INTEGRALA (9) PO !, TO DOSTATO^NO RASSMOTRETX ODNO^LENNU@ FORMU WIDA
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u^ITYWAQ P. 49, POLU^IM |
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w PRAWOJ ^ASTI \TOGO RAWENSTWA OTLI^EN OT NULQ EDINSTWENNYJ ^LEN (PRI
490