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11 лекция дифференциальные уравнения
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11 6.
.
11 12
21 22
dx a x a ydtdy a x a ydt
= + = + (1)
0x y= = . :
( ) ( )11 12
21 22
2 211 22 11 22 12 21
0
Tr det 0
a aa a
a a a a a a A A
= + + + =
.
1) . (1)
2
11 2
1 2 21 1 1
1, , lnt t x xx C e y C e t y CC C
= = = =
.
) 1 2 0 < < , 2 2
1 11 2
0, 1
1 2 21
0, 0,t tt t
xx C e y C e y CC
> >
+ + = = =
.
0x y= = .
) 1 20 < < , ( )2
11 2
0
1 2 21
0, ,t tt t
xx C e y C e y CC
, 0x y= = . ) 0 = , 0x y= = , .
(1) .
3) 1 2 = = . (1)
21 2
1
,t t Cx C e y C e y xC
= = = . ) 0 < , 0x y= = . ) 0 > , 0x y= = . 4) 1 2 = = . (1) :
( ) 11 2 1 21 1 1
1, , ln lnt t Cx x xx C e y C C t e t y CC C C
= = + = = +
) 0 < , 0x y= =
. ) 0 > , 0x y= = .
(1) .
..
5) 1 20, 0 = . (1)
11 2,
tx C e y C= = . 7. .
( )
( )x f x = , (1)
( )f x - 1( , )C a b .
( ) ( ) ( ), ,xc
U x f d c a b = (2) .
(1)
( ) ( )
x p
p f x U x
=
= = . (3)
( )f x , ,
(3). 0x x= (1) 0 , 0x x p= = (3). 0x x= (1) ( )U x . , 0x x= ,
0( ) 0f x = , (2), 0 0( ) ( ) 0U x f x = . , 0x ( )U x ,
. . ( )f x - 2 ( , )C a b . ,
1) 0x x= - ( )U x ,
0 , 0x x p= = (3) ; 2) 0x x= - ( )U x 0( ) 0f x > ,
0 , 0x x p= = (3) . . 0 0x = , 0y x x= .
0x = - , ( ) (0)U x U> 0x .
( ) ( ) ( ) 2, 02pV x p U x U= +
- .
( )( ) 0V Vp U xx p
+ = , , , 0 , 0x x p= = .
0x = - ( )U x (0) 0f > , (0) 0U = , (0) (0) 0U f = <
( ) ( )N ( ) ( )( )
( ) ( )( )
2 2
0
1 10 0 0 , 0 12 2
f xF x
U x U U x U x x U x f x x
=
= + + = <
( )= =
0
0
p
f x.
=( ) 0f x (3)
n = =0, 1,2,...,ix x i n . ( )0, 0ix ( ),x p (2). , (3) , .. ( ) =0 0, 1,2,...,x if x i n .
, . , . . (1) . , , (1) (1) ( (2)). 20. .
0ix x= ( )f x ( )N ( ) ( ) ( )
== + + 0 0 0 0
0
( ) i x i i if x f x f x x x x x .
(2)
( )( )0 0, x i ix p p f x x x = = - .
=0ix x x . ( ),x p ( ) ( )= 0, , 0ix p x ( ) ( )=, 0, 0x p
( ) = = 0, x ix p p f x x . .
( ) ( ) ( )
= = = 2 0 0
1,20
10x i x i
x i
f x f xf x
.
( ) >0 0x if x , , ( ) 0p (2), , , (1) ,
= ( )dp f xdx p
(4)
(4) = ( )pdp f x dx , = +2 ( )2p f x dx C = +2 ( )p f x dx C .
, < 0p , = +2 ( )p f x dx C .
, C , , x . (4), , . , , ( )0, 0x , , t + t .
, ( )0,0x ,
= 0
2 ( )x
x
p f s ds . (5)
, (1) , ( )0 0,x p , , (1) . , , , . t + t . , t , . 40. . 1. .
( ) ( )= 2
2
d x x a x f xdt
, 0a > . 1- :
( ),x p p x a x = = (6) 1 20,x x a= = ( ) 0f x = (6) ( ) ( )=, 0, 0x p ( ) ( )=, , 0x p a . , ( ) = >0 0xf a ; ( ) = < 0xf a a , ( )0,0 - - , ( ), 0a - - .
(6). . 3,
= + = +2 ( ) ( )2p x x a dx C U x C , =
3 2
( )3 2x xU x a .
= + = +2 ( ) 2 ( )p x x a dx C U x C . (7)
( )f x C ,
(6) 1- 3.
1 ( )f x .
2 ( )f x :
= + = +2 ( ) ( )2p f x dx C U x C . , .
( )f x , 1. ( )f x
( ) 0f x > ( ) 0f x < . x 2
2p
, ( ) 0f x > . x a= ( )f x , ..
2
2p .
32a
32a
32a
S2
p
x
x
a
f(x)
x
( )= +22p f x d x C
a
a
. 2
. 3
S1
. 1
1S 2S , ( ) = 2
2pU x
. = x x =
0
( ) ( )a x
a
x a x dx x a x dx , ( ) =
0
0x
x a x dx . = 32ax .
x , 2
2p
.
x = 20
( )2
xp f x ds
( ) < 0f x , , = 2
( )2pU x
x . 3 (0, 0) .
(.3) , , . t .
, : = > 0dxpdt
, x
, .. . C . C ( )
2 ( ). (7) , , x .
C 2 ( ). (7) , C ( ), 0a . . . 3 (7) . . 0x
( ) ( ) ( )= = =2
02 , 0 , 0
d x x a x x x xdt
.
. . 30, , ( )0,0 , t + , t .
0x , , , ( )0,0 .
( ) ( ) =0 0x z , ( )( )0, 0x p . , ( )( )0, 0x p t + , ( )0,0 t + .
) - .
( )= 2 2 22 ( )d x f x x x adt . : ( )= = = = 2 2( ) 0 0 0,f x x x a x x a .
.4 ( )= 2 2( )f x x x a .
2
1
a -a
p
x
S1
S1 S1
-a a
2
2p
x
x
f(x)
a -a
.4
.5
.6
S1
xf 0,x x a= = : ( ) 0xf a . , 5, ( )0,0 - , ( ), 0a ( ), 0a - . = = +2 4 22( )2 4 2
x
a
p x xf x dx a C (. 5). ,
( )f x - , - , .
( ) ( )
= x xa a
f s ds f s ds , ( ), 0a ( ), 0a
: = 2 ( )xa
p f x ds .
6 . 1 2 . , 1 2 .
C . C OY . (.6, ).
C ,
OY , ( ) = 2
2xU x
(.5, ). < x a - (.6, ).
C
= 2
( )2pU x x .
C , 6 . ) .
( ) ( )= + < >1 20 0, 0, 0x x xf f a f a . , ( )0,0 - ,
( )1, 0a ( )2, 0a - . 8 = +2 ( )2p f x dx C .
0C > OY ( ). C , .
= 2
2
( )2
x
a
p f s ds . OY
( )2, 0a . (.9) ( )2, 0a . 1( ,0)a ( )
=
1
2x
a
p f s ds
(.9) .
.
2 -1
S2
.9
.8 2
2p
p
x
x
x S1
S1
S2 -1 2
f(x) .7
3. . :
= 2
2 ( ) sind x f x xdt
.
1-
, sinx p p x = = .
x m= ( ) 0f x = ( ) ( )=, , 0mx p m . , ( ) = = = +
1, 2,
1, 2 1xm k
f m k Zm k
, ,
( ) ( )( )+ = +2 1, 2 1 ,0kx p k - , ( ) ( )=2 , 2 , 0kx p k - . :
= + = +2 sin cos2p xdx C x C . = ( ) cosU x x , ,
= + 2 cos , 2p x C C . 10.
. 10
2C = , . 2 2C < < , ( , ). 2C > , ( ), .
. (0,0) 1) ; 2) , = +2 2( , ) 4 sin
2xV x p p .