Ряды. - 37 стр.

UptoLike

§5. òÑÄÙ ôÅÊÌÏÒÁ. òÁÚÌÏÖÅÎÉÅ ÆÕÎËÃÉÉ × ÓÔÅÐÅÎÎÏÊ ÒÑÄ 37
äÌÑ ÒÁÚÌÏÖÅÎÉÑ ËÏÎËÒÅÔÎÏÊ ÆÕÎËÃÉÉ f (x) × ÓÔÅÐÅÎÎÏÊ ÒÑÄ Ó ÃÅÎÔÒÏÍ ×
ÔÏÞËÅ x
0
= 0 ÐÏÌØÚÕÀÔÓÑ ÒÁÚÌÏÖÅÎÉÑÍÉ ÏÓÎÏ×ÎÙÈ ÆÕÎËÃÉÊ. ðÏÓÌÅ ËÁÖÄÏÊ
ÆÏÒÍÕÌÙ ÕËÁÚÁÎÏ ÍÎÏÖÅÓÔ×Ï ÓÈÏÄÉÍÏÓÔÉ ÒÑÄÁ.
e
x
=
P
n=0
x
n
n!
= 1 + x +
x
2
2!
+
x
3
3!
+ . . . +
x
n
n!
+ . . . , |x| < ,
sin x =
P
n=0
(1)
n
x
2n+1
(2n+1)!
= x
x
3
3!
+
x
5
5!
. . . + (1)
n
x
2n+1
(2n+1)!
+ . . . ,
|x| < ,
cos x =
P
n=0
(1)
n
x
2n
(2n)!
= 1
x
2
2!
+
x
4
4!
. . . + (1)
n
x
2n
(2n)!
+ . . . , |x| < ,
sh x =
P
n=0
x
2n+1
(2n+1)!
= x +
x
3
3!
+
x
5
5!
+ . . . +
x
2n+1
(2n+1)!
+ . . . , |x| < ,
ch x =
P
n=0
x
2n
(2n)!
= 1 +
x
2
2!
+
x
4
4!
+ . . . +
x
2n
(2n)!
+ . . . , |x| < ,
ln(1 + x) =
P
n=1
(1)
n1
x
n
n
= x
x
2
2
+
x
3
3
. . . + (1)
n1
x
n
n
+ . . . ,
1 < x 6 1,
ln(1 x) =
P
n=1
x
n
n
=
x +
x
2
2
+
x
3
3
+ . . . +
x
n
n
+ . . .
, 1 6 x < 1,
(1 + x)
m
= 1 +
P
n=1
m(m1)(m2)...(mn+1)
n!
x
n
= 1 + mx +
m(m1)
2!
x
2
+
+
m(m1)(m2)
3!
x
3
+ . . . +
m(m1)(m2)...(mn+1)
n!
x
n
+ . . . ,
m R, |x| < 1.
ðÒÉ×ÅÄÅÍ ÎÅËÏÔÏÒÙÅ ÞÁÓÔÎÙÅ ÓÌÕÞÁÉ ÐÏÓÌÅÄÎÅÊ ÆÏÒÍÕÌÙ.
1
1+x
= 1 x + x
2
x
3
+ . . . + (1)
n
x
n
+ . . . , |x| < 1,
1
1x
= 1 + x + x
2
+ x
3
+ . . . + x
n
+ . . . , |x| < 1,
1
1+x
= 1
1
2
x +
1·3
2·4
x
2
. . . + (1)
n
(2n1)!!
(2n)!!
x
n
+ . . . , |x| < 1,
1
1x
= 1 +
1
2
x +
1·3
2·4
x
2
+ . . . +
(2n1)!!
(2n)!!
x
n
+ . . . , |x| < 1,
1 + x = 1 +
1
2
x
1
2·4
x
2
+ . . . + (1)
n
(2n1)!!
(2n+2)!!
x
n+1
+ . . . , |x| < 1,
1 x = 1
1
2
x
1
2·4
x
2
. . .
(2n1)!!
(2n+2)!!
x
n+1
. . . , |x| < 1.
îÁÐÏÍÎÉÍ, ÞÔÏ ÆÁËÔÏÒÉÁÌ ÎÁÔÕÒÁÌØÎÏÇÏ ÞÉÓÌÁ n ÏÐÒÅÄÅÌÑÅÔÓÑ ÆÏÒÍÕÌÏÊ
n! = n · (n 1) · (n 2) · . . . ·3 · 2 · 1,
ÎÁÐÒÉÍÅÒ, 7! = 7 · 6 · 5 · 4 · 3 · 2 · 1.
ä×ÏÊÎÏÊ ÆÁËÔÏÒÉÁÌ ÞÉÓÌÁ n ÏÐÒÅÄÅÌÑÅÔÓÑ ÓÌÅÄÕÀÝÉÍ ÏÂÒÁÚÏÍ
n!! = n · (n 2) · (n 4) · . . . ,
ÎÁÐÒÉÍÅÒ, 7!! = 7 · 5 · 3 · 1, 10!! = 10 · 8 · 6 · 4 · 2.
§5. òÑÄÙ ôÅÊÌÏÒÁ. òÁÚÌÏÖÅÎÉÅ ÆÕÎËÃÉÉ × ÓÔÅÐÅÎÎÏÊ ÒÑÄ                                                                            37

   äÌÑ ÒÁÚÌÏÖÅÎÉÑ ËÏÎËÒÅÔÎÏÊ ÆÕÎËÃÉÉ f (x) × ÓÔÅÐÅÎÎÏÊ ÒÑÄ Ó ÃÅÎÔÒÏÍ ×
ÔÏÞËÅ x0 = 0 ÐÏÌØÚÕÀÔÓÑ ÒÁÚÌÏÖÅÎÉÑÍÉ ÏÓÎÏ×ÎÙÈ ÆÕÎËÃÉÊ. ðÏÓÌÅ ËÁÖÄÏÊ
ÆÏÒÍÕÌÙ ÕËÁÚÁÎÏ ÍÎÏÖÅÓÔ×Ï ÓÈÏÄÉÍÏÓÔÉ ÒÑÄÁ.
              ∞ n
      x          x            x2   x3           xn
              P
    e     =      n! = 1 + x + 2! + 3! + . . . + n! + . . . , |x| < ∞,
                  n=0
                   ∞               2n+1
                              x                                     x3            x5                    x     2n+1
                       (−1)n (2n+1)!                                                   − . . . + (−1)n (2n+1)!
                  P
   sin x      =                      =x−                            3!   +        5!                           + ...,
                  n=0
                                                                                                                         |x| < ∞,
                   ∞               2n                          2             4                           2n
                              x                            x              x                        x
                       (−1)n (2n)!                                                − . . . + (−1)n (2n)!
                   P
   cos x      =                    =1−                     2!
                                                                    +     4!
                                                                                                        + ...,           |x| < ∞,
                  n=0
                   ∞
                         x2n+1                       x3            x5                      x2n+1
                  P
    sh x      =         (2n+1)!    =x+               3!   +        5!    + ...+           (2n+1)!    + ...,       |x| < ∞,
                  n=0
                   ∞
                         x2n                    x2        x4                            x2n
                  P
    ch x      =         (2n)!   =1+             2!   +    4!       + ...+              (2n)!   + ...,    |x| < ∞,
                  n=0
                   ∞                    n
                                                               x2            x3                               n
                       (−1)n−1 xn = x −                                           − . . . + (−1)n−1 xn + . . . ,
                  P
 ln(1 + x) =                                                   2
                                                                    +        3
                  n=1
                                                                                                                     −1 < x 6 1,
                     ∞                                                                                  
                         xn                               x2            x3                     xn
                     P
 ln(1 − x) = −           n      =− x+                     2    +        3    + ...+            n    + ... ,       −1 6 x < 1,
                     n=1
                       ∞
                                m(m−1)(m−2)...(m−n+1) n                                                  m(m−1) 2
 (1 + x)m = 1 +
                       P
                                         n!          x                                 = 1 + mx +          2!  x+
                        n=1
                  + m(m−1)(m−2)
                        3!      x3 + . . . +                             m(m−1)(m−2)...(m−n+1) n
                                                                                  n!          x                   + ...,
                                                                                                                  m ∈ R, |x| < 1.
   ðÒÉ×ÅÄÅÍ ÎÅËÏÔÏÒÙÅ ÞÁÓÔÎÙÅ ÓÌÕÞÁÉ ÐÏÓÌÅÄÎÅÊ ÆÏÒÍÕÌÙ.
         1
       1+x        = 1 − x + x2 − x3 + . . . + (−1)nxn + . . . , |x| < 1,
         1
       1−x        = 1 + x + x2 + x3 + . . . + xn + . . . , |x| < 1,
       √1
        1+x
                  = 1 − 21 x + 1·3
                               2·4
                                   x2 − . . . + (−1)n (2n−1)!!
                                                        (2n)!!
                                                               xn + . . . , |x| < 1,
                                                               (2n−1)!! n
       √1         = 1 + 21 x +          1·3 2
                                                     + ...+
                                        2·4 x                    (2n)!! x + . . . ,     |x| < 1,
      √ 1−x                                                             (2n−1)!!
        1 + x = 1 + 21 x −               1 2
                                        2·4 x        + . . . + (−1)n (2n+2)!! xn+1 + . . . , |x|                         < 1,
      √
       1 − x = 1 − 21 x −                1 2
                                        2·4 x        − . . . − (2n−1)!!
                                                               (2n+2)!! x
                                                                          n+1
                                                                               − . . . , |x| < 1.
   îÁÐÏÍÎÉÍ, ÞÔÏ ÆÁËÔÏÒÉÁÌ ÎÁÔÕÒÁÌØÎÏÇÏ ÞÉÓÌÁ n ÏÐÒÅÄÅÌÑÅÔÓÑ ÆÏÒÍÕÌÏÊ
                          n! = n · (n − 1) · (n − 2) · . . . · 3 · 2 · 1,
ÎÁÐÒÉÍÅÒ, 7! = 7 · 6 · 5 · 4 · 3 · 2 · 1.
  ä×ÏÊÎÏÊ ÆÁËÔÏÒÉÁÌ ÞÉÓÌÁ n ÏÐÒÅÄÅÌÑÅÔÓÑ ÓÌÅÄÕÀÝÉÍ ÏÂÒÁÚÏÍ
                                  n!! = n · (n − 2) · (n − 4) · . . . ,
ÎÁÐÒÉÍÅÒ, 7!! = 7 · 5 · 3 · 1, 10!! = 10 · 8 · 6 · 4 · 2.