дифференциальные уравнения лекция 11

  • Upload
    lehvb

  • View
    239

  • Download
    0

Embed Size (px)

DESCRIPTION

11 лекция дифференциальные уравнения

Citation preview

  • 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 .