3.2. rQDY mAKLORENA \LEMENTARNYH FUNKCIJ
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1: ex = 1 + x + |
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+ : : : + xn |
+ : : : |
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2! |
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n! |
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2: shx = x + |
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x5 |
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x2n;1 |
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3! |
5! |
(2n ; 1)! |
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3: chx = 1 + |
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x2n;2 |
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2! |
4! |
(2n ; 2)! |
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4: |
sin x |
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3! |
5! |
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cos x |
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1 |
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x2 |
+ |
x4 |
2! |
4! |
; : : : + (;1)n;1 |
x2n;1 |
+ : : : |
(2n ; 1)! |
; : : : + (;1)n;1 |
x2n;2 |
+ : : : |
(2n ; 2)! |
6: (1 + x)m = 1 + mx |
+ |
m(m |
; 1) |
x2 + |
m(m ; |
1)(m ; 2) |
x3 + : : : |
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1! |
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2! |
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3! |
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(BINOMINALXNYJ RQD) |
7: |
1 |
= 1 ; x + x2 ; x3 + : : : + (;1)n;1xn + : : : |
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1 + x |
8: ln (1 + x) = x ; |
x2 |
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n |
1 xn |
2 + |
3 ; : : : + (;1) |
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x3 |
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n |
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1 |
x2n;1 |
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arctg x = |
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(2n ; 1) |
+ : : : |
10: |
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arcsin x |
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x + |
1 x3 |
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3 |
x5 |
+ 1 |
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5 x7 + : : : |
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2 3 |
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22 |
2! 5 |
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23 3! 7 |
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rQDY S 1-GO PO 5-YJ SHODQTSQ NA WSEJ ^ISLOWOJ PRQMOJ x 2 (;1 +1), A RQDY 6,7,9 I 10-YJ SHODQTSQ W INTERWALE x 2 (;1 1): rQD DLQ ln(1+x) SHODITSQ DLQ x 2 [;1 1)
7: |
y = sin(x2) |
x0 = 0: |
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w STANDARTNOM RAZLOVENII ZAMENQEM x NA x2 |
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2 |
x6 |
x10 |
(n |
1) |
x4n;2 |
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sin x |
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= x |
; 3! + 5! + : : : + (;1) |
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(2n ; 1)! + : : : |
8: |
y = cos x |
x0 = =4: |
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zDESX WOSPOLXZOWATSQ [ABLONNYM RQDOM SRAZU NELXZQ, T.K. RAZLOVE- NIE NEOBHODIMO PROWESTI PO STEPENQM (x; =4): nEOBHODIMO PROWESTI PREDWARITELXNYE PREOBRAZOWONIQ:
cos x= cos[(x; =4)+ =4] = cos(x; =4) cos =4;sin(x; =4) sin =4 = :::
tEPERX MOVNO ISPOLXZOWATX [ABLONNYE RAZLOVENIQ DLQ sin x cos x
ZAMENIW x NA (x |
; =4), RASKRYTX SKOBKI, PRIWESTI PODOBNYE ^LENY |
I ZAPISATX POLU^ENNYJ RQD W PORQDKE WOZRASTANIQ STEPENEJ. nO OKA- |
ZYWAETSQ, ^TO W DANNOM SLU^AE PRO]E POLU^ITX RQD NEPOSREDSTWENNO, |
WY^ISLQQ EGO KO\FFICIENTY PO FORMULE |
cn = |
f(n)(x0) |
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n! |
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f(x) = cos x x0 = =4 |
f(x0) = cos( =4) = p2=2 |
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f0(x) = |
; sin x |
f0(x0) = |
; sin( =4) = ;p |
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=2 |
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2 |
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f00(x) = |
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cos x |
f00(x0) = |
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cos( =4) = |
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p2=2 |
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p |
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f000(x) = sin x |
f000(x0) = sin( =4) = |
2=2 ::: |
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oKON^ATELXNO POLU^AEM RQD PO STEPENQM (x ; =4) |
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cos x= p2 |
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01;(x; =4);(x;2!=4)2 |
+ (x;3!=4)3 |
+ (x;4!=4)4 |
;:::1 : |
2 |
@ |
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A |
zAMETIM, ^TO ISPOLXZOWATX GOTOWYE RAZLOVENIQ MOVNO I DLQ FUNK- |
CIJ sin2 kx |
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cos2 kx |
ISPOLXZUQ FORMULY PONIVENIQ STEPENI |
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sin2 x = |
1 ; cos 2x |
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cos2 x = 1 + cos 2x |
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2 |
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2 |
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9: y = ex cos x |
x0 = 0: |
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ex cos x = 01 + x |
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x2 |
x3 |
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: : :1 |
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x2 |
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x4 |
: : :1 : |
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2! + |
3! |
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01 ; 2! |
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4! ; |
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@ |
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A |
@ |
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A |
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pEREMNOVAEM \TI WYRAVENIQ I PRIWODIM PODOBNYE ^LENY |
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x2 |
x3 |
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x2 |
x3 |
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x4 |
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x5 |
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x3 |
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5x4 |
x5 |
1 + x+ 2! + |
3! ; |
2! ; 3! ; |
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+ = 1 + x; 3 ; 24 ; |
12 + : : : |
(2!)2 |
2!3! |
p1 + x2 = (1 + x2)1=2 = 1 + 12 x2 + 12 (122!; 1)x4 + ::: = = 1 + 12x2 ; 2212! x4 + 213 3!3 x6 + : : :
aNALOGI^NO SWODQTSQ K \TOMU VE RAZLOVENI@ FUNKCII TIPA
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15: y = p |
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8 |
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; x3 x0 = 0: |
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3 |
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=8 |
1=3 |
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q8(1 ; x3=8) = 2 1 ; x3 |
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m = 1=3 |
x ! (;x3=8): |
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16: y = |
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1 |
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x0 = 0: |
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4 |
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1 |
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p1 ; 2x |
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= (1 |
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2x);1=4, m = |
; |
1=4 x |
! |
( |
; |
2x): |
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4 |
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p1 ; 2x |
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17: y = p |
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x0 = 9 |
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x |
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p |
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= p |
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= v |
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1=2 |
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9 1 + x ; 9 |
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= 3 1 + x ; 9 |
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x |
9 + x |
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9 |
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u |
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9 |
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9 |
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m = 1=2 x |
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x ;t9: |
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9 |
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18: y = |
1 |
x0 = 4: |
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x3 |
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;3 |
1 |
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1 |
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1 |
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1 + |
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;4 |
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x3 |
(4 + x ; 4)3 |
43 |
1 + x ;4 4!3 |
64 |
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m = |
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! |
x ; 4: |
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4 |
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x2 |
iSPOLXZOWANIE RQDA |
ln (1 + x) = x ; 2 |
19: y = ln(1 ; 3x2) |
x0 = 0: |
w [ABLONNOM RQDE ZAMENQEM x NA (;3x2)
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x3 |
; : : : + (;1)n;1 |
xn |
+ |
3 |
n + ::: |
ln (1 ; |
3x2) = (;3x2) ; (;32x2)2 + (;33x2)3 |
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= ;3x2 ; |
32 x4 |
33 x6 |
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3 ; : : : |
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20: y = ln v |
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1 + 2x |
x0 = 0: |
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u |
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pREOBRAZUEM FUNKCI@: |
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y = ln v |
1 + 2x |
= 1 ln 1 + 2x |
= 1 ln(1 + 2x) |
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1 ln(1 |
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t |
1 |
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1 |
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; 2 |
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u |
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tEPERX DLQ RAZLOVENIQ W RQD PERWOJ FUNKCII W [ABLONNOM RQDE |
ZAMENQEM x NA (2x) A DLQ WTOROJ {ZAMENQEM x NA (;x) A ZATEM POLU- |
^ENNYE RQDY SUMMIRUEM |
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y = |
1 |
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1 |
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1 |
02x |
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4x2 |
8x3 |
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2 ln(1 + 2x) ; |
2 ln(1 ; x) = 2 |
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+ 3 |
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@ |
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A |
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1 |
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x) |
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4x |
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;: : :1 = x;x2 |
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x x |
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;2 0x |
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;2x+ |
4 + 6 |
+: : := |
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A |
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= |
2x ; |
4x2 |
+ |
2x3 + : : : : |
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21: y = ln x x0 = 3: |
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pREOBRAZUEM ISHODNU@ FUNKCI@ SLEDU@]IM OBRAZOM |
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ln x = ln(x ; 3 + 3) = ln " 3 |
1 + |
x ;3 |
3 |
! # = ln 3 + ln |
1 + |
x ;3 |
3 |
! |
tEPERX W RAZLOVENII FUNKCII |
ln(1+x) |
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ZAMENIM x NA x ; 3 I K RE- |
ZULXTATU PRIBAWIM ln 3: |
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ln x = ln 3+ x ; 3 |
; |
(x ; 3)2 |
+ |
(x3; 3)3 |
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: : : |
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z A M E ^ A N I E. ~TOBY POLU^ITX RAZLOVENIE W RQD mAKLORENA FUNKCIJ WIDA
x3 cos 2x |
x sin2 x |
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arctg x |
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ZAPISYWAEM RAZLOVENIQ W RQD FUNKCIJ, ISPOLXZUQ STANDARTNYE RAZ- LOVENIQ, A ZATEM UMNOVAEM ILI DELIM RQDY PO^LENNO NA xk:
22: y = p |
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zAPI[EM FUNKCI@ W WIDE |
y = x |
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sTROIM RQD DLQ FUNKCII |
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ZAMENIW W STANDARTNOM RAZ |
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LOVENII (1 + x)m : m = ;1=2 |
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POLU^ENNYJ RQD NA x3:
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x3 (1 ; x2);1=2 = x3 |
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+ : : : : |
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arctgx3 |
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iSPOLXZUEM STANDARTNOE RAZLOVENIE W RQD FUNKCII arctg x |
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0x3 |
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x15 |
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= 1 ; 3 + |
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5 |
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pOLU^IM RQD mAKLORENA DLQ INTEGRALXNOGO SINUSA |
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24: Si x = Z |
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iSPOLXZUEM STANDARTNOE RAZLOVENIE W RQD FUNKCII sin x |
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5 5! |
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3.3. iSPOLXZOWANIE RQDOW W PRIBLIVENNYH WY^ISLENIQH
oSOBENO \FFEKTIWNYM QWLQETSQ ISPOLXZOWANIE STEPENNYH RQDOW K PRIBLIVENNYM WY^ISLENIQM OPREDELENNYH INTEGRALOW S ZADANNOJ STEPENX@ TO^NOSTI. tAK POSTUPA@T W TEH SLU^AQH, KOGDA INTEGRAL NELXZQ WY^ISLITX PO FORMULE nX@TONA-lEJBNICA W SILU NEINTEGRI- RUEMOSTI PODYNTEGRALXNOJ FUNKCII, KOTORAQ LEGKO RASKLADYWAETSQ W STEPENNOJ RQD. pRI \TOM NEOBHODIMO TOLXKO IMETX W WIDU, ^TO WSE NA[I DEJSTWIQ BUDUT PRAWOMO^NY I IMETX REALXNYJ WYHOD, ESLI INTERWAL, W KOTOROM MY RABOTAEM, CELIKOM PRINADLEVIT INTERWALU SHODIMOSTI POSTROENNOGO RQDA.
pRI WY^ISLENII OPREDELENNYH INTEGRALOW NEOBHODIMO: 1. rAZLOVITX PODYNTEGRALXNU@ FUNKCI@ W RQD.
2.pROINTEGRIROWATX EGO PO^LENNO, ISPOLXZUQ FORMULU nX@TONA-lEJBNICA.
3.oPREDELITX, KAKOE KOLI^ESTWO ^LENOW RQDA NUVNO OSTAWITX DLQ POLU^ENIQ NUVNOJ TO^NOSTI WY^ISLENIQ. oCENITX POGRE[NOSTX WY- ^ISLENIJ NAIBOLEE PROSTO W SLU^AQH, ESLI POLU^IW[IJSQ RQD QWLQ- ETSQ SHODQ]IMSQ ZNAKO^EREDU@]IMSQ RQDOM. tOGDA, SOGLASNO PRI- ZNAKU lEJBNICA, SUMMA WSEH OTBRO[ENNYH ^LENOW RQDA, QWLQ@]AQSQ POGRE[NOSTX@ WY^ISLENIJ, NE PREWY[AET PO ABSOL@TNOJ WELI^INE
PERWOGO IZ OTBRO[ENNYH ^LENOW RQDA, T.E. j j = j Rn(x) j < un+1:
w SLU^AE ZNAKOPOLOVITELXNYH RQDOW POGRE[NOSTX OCENITX TRUD- NEE. dLQ \TOGO NEOBHODIMO OCENITX WELI^INU OSTATKA RQDA, ISPOLX- ZUQ ODNU IZ FORM OSTATO^NOGO ^LENA FORMULY tEJLORA.
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wY^ISLITX SLEDU@]IE INTEGRALY S TO^NOSTX@ DO |
0,001. |
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1=2 1 |
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cos x |
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iSPOLXZUEM RQD mAKLORENA FUNKCII |
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cos x |
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1=2 1 |
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dLQ WY^ISLENIQ INTEGRALA S ZADANNOJ |
TO^NOSTX@ |
OKAZALOSX DOSTA- |
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TO^NO WZQTX DWA PERWYH SLAGAEMYH, T.K. TRETXE SLAGAEMOE, OPREDELQ- |
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@]EE POGRE[NOSTX WY^ISLENIJ, ESTX UVE WELI^INA PORQDKA 10;5. |
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x = t2 |
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2: |
Z arctg |
p |
x dx = j |
j = 2 Z |
t arctg t dt = |
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3 |
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0 079: |
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dLQ WY^ISLENIQ HWATILO PERWYH DWUH SLAGAEMYH, T.K. |
TRETXE SLAGAE- |
MOE, OPREDELQ@]EE POGRE[NOSTX WY^ISLENIJ, ESTX WELI^INA PORQDKA
0 0004:
3: |
2:4 |
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;1=4 dx = |
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Z p81 + x4 |
Z |
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rASKLADYWAEM W RQD PODYNTEGRALXNU@ FUNKCI@, PROWEDQ NEOBHODI-
MYE PREOBRAZOWANIQ ( m = ;1=4 |
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2:4 |
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2:4 |
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42 |
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tRETIJ ^LEN RAZLOVENIQ |
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BOLX[E 0.001, PO\TOMU |
DLQ PODS^ETA BEREM |
TRI ^LENA RAZLOVENIQ, A POGRE[NOSTX OPREDELQETSQ ^ETWERTYM ^LE- |
NOM RQDA I SOSTAWLQET 5 10;5: |
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rASKLADYWAEM W RQD FUNKCI@ e;x, PROWEDQ NEOBHODIMYE ZAMENY, ZA- |
TEM UMNOVAEM ^LENY POLU^ENNOGO RQDA NA px I POLU^AEM FUNKCIO- |
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lEGKO POKAZATX, ^TO \TOT RQD RAWNOMERNO SHODITSQ, TAK KAK EGO ^LE- |
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a; NEKOTOROE POLOVITELXNOE ^ISLO. pO\TOMU FUNKCIONALXNYJ RQD |
MOVNO PO^LENNO INTEGRIROWATX |
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Z px e;x dx = Z |
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= " |
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x7=2 ; : : :# j0 |
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dLQ WY^ISLENIQ INTEGRALA S TO^NOSTX@ |
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DO 0.001 |
DOSTATO^NO WZQTX |
DWA ^LENA POLU^ENNOGO RQDA, A POGRE[NOSTX BUDET OPREDELQTXSQ TRETXIM ^LENOM RAZLOVENIQ I SOSTAWIT WELI^INU PORQDKA 2 10;4:
]IH ODNOSTORONNIH PREDELOW
4. rQDY fURXE
4.1. rQD fURXE DLQ PERIODI^ESKOJ S PERIODOM |
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T = 2 FUNKCII, |
ZADANNOJ NA INTERWALE |
[; |
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rQDOM fURXE DLQ PERIODI^ESKOJ S PERIODOM |
T = 2 FUNKCII |
y = f(x) OPREDELENNOJ NA INTERWALE [; |
] NAZYWAETSQ TRIGO- |
NOMETRI^ESKIJ RQD |
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a0 |
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1 |
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f(x) = |
2 |
+ |
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an |
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(1) |
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KO\FFICIENTY a0 |
an |
I bn |
NAHODQTSQ PO FORMULAM fURXE |
a0 = 1;Z f(x) dx an = 1;Z f(x) cos nx dx |
bn = 1;Z f(x) sin nx dx: |
uSLOWIQ PREDSTAWIMOSTI DANNOJ FUNKCII RQDOM fURXE I SLEDSTWIQ |
\TOGO RAZLOVENIQ OGOWARIWA@TSQ SLEDU@]EJ TEOREMOJ. |
tEOREMA dIRIHLE. |
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pUSTX FUNKCIQ y = f(x) NA INTERWALE [; |
] |
IMEET KONE^NOE ^IS- |
LO \KSTREMUMOW I QWLQETSQ NEPRERYWNOJ ZA ISKL@^ENIEM KONE^NOGO ^ISLA TO^EK RAZRYWA 1-GO RODA (TO^EK KONE^NOGO SKA^KA FUNKCII). tOGDA RQD fURXE \TOJ FUNKCII SHODITSQ W KAVDOJ TO^KE INTERWA- LA [; ] I EGO SUMMA S(x) UDOWLETWORQET USLOWIQM:
1) w KAVDOJ TO^KE NEPRERYWNOSTI FUNKCII RQD fURXE SHODITSQ K ZNA^ENI@ FUNKCII W \TOJ TO^KE S(x) = f(x):
2) w KAVDOJ TO^KE KONE^NOGO RAZRYWA FUNKCII SUMMA RQDA fU-
RXE RAWNA POLUSUMME ODNOSTORONNIH PREDELOW FUNKCII W \TIH TO^KAH
S(x) = 12[f(x0 ; 0) + f(x0 + 0)]:
3) w KONCEWYH TO^KAH INTERWALOW PERIODI^NOSTI FUNKCII SUMMA
RQDA fURXE TAKVE RAWNA SREDNEMU ARIFMETI^ESKOMU SOOTWETSTWU@-
S(x) = 12[f(; ; 0) + f( + 0)]: