21. , 100 r . , x . ,
,
x = 0, 1, 2, 3,.... ( ),
,
x = 0, 1/2, 1, 3/2,.... , n x 0, 1/ n, 2/ n, 3/ n,...,
,
.
1/ n = h, :
.
n ( n ¥, h 0) :
,
x 1- . , , x , r . :
, , P eC.
, P: , , . :
.
. 1- , Y .
22. Y , :
,
, , Y ( q). D:
.
Y D t. Y = Y 0 D = D 0 t = 0. , , Y = Y 0 ek×t. Y , dD / dt = qY 0 ek t. D = (q / k)× Y 0e k × t + C, C = const, . , D 0 = (q / k) Y 0 + C. , ,
D = D 0 + (q / k) Y o(ek×t 1),
, k, .
n -
y (n) = f (x).
n .
2- , , , P . ,
D = a + aP, S = b + bP,
l , ( ), :
|
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+ l(b a) P = l(a b).
P =` P = (a b)/(b a),
. = P ` P
+ l(b a) = 0.
. , k, :
k 2 + l(b a) = 0.
(a <0, b >0, l>0) l(b a) . . k 1,2 = i w. , (9.10) :
= C cos(w t e),
C e , , . , ` P, :
P = ` P + C cos(w t e).
. Yx , , x. Y 0 100 r . x (x = 0, 1, 2,...). x Yx .
Yx = (1 + r) Yx 1.
Y 0, , Yx = Y 0 x = 0. Yx , .. Yx 1; x .
, Y = Y (x), x, , , . , x, x, x + 1, x + 2,..., : x, x 1, x 2,.... Yx, Yx +1, Yx +2,... Yx, Yx 1, Yx 2,.... Yx :
D Yx = Yx +1 Yx ,
D Yx +1 = Yx +2 Yx +1,
D Yx +2 = Yx +3 Yx +2,
...............
D2 Yx = D Yx +1 D Yx,
D2 Yx +1 = D Yx +2 D Yx +1,
D2 Yx +2 = D Yx +3 D Yx +2,
...............
D3 Yx = D2 Yx +1 D2 Yx,
D3 Yx +1 = D2 Yx +2 D2 Yx +1,
...............
, x, Yx D Yx, D2 Yx, D3 Yx,.... :
j(x, Yx, D Yx, D2 Yx,D3 Yx, D nYx ) = 0, (1)
.
, . (1) , , , D Yx, D2 Yx, D3 Yx,... Yx, Yx +1, Yx +2,.... (1) :
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y(x, Yx, Yx +1,..., Yx + n) = 0, (2)
x(x, Yx, Yx 1,..., Yx n) = 0. (3)
Yx n - x (x = 0, 1, 2,...), n :
Yx = Y (x, C 1, C 2,..., Cn).
. - :
D = D (P), S = S (P).
, ,
D (P) = S (P).
( ), -, , :
.
. :
Dt = D (Pt) St = S (Pt 1).
, , . : Pt 1 S (Pt 1), Pt , . , Pt - Xt :
Xt = D (Pt) = S (Pt 1).
, P 0, P 1 X 1. , P 1, P 2 X 2 .. , Pt ( ):
D (Pt) = S (Pt 1).
, . 1, D S , ( ) Q. P 0. Q 0 S 1. P 1, Q 1 D (X 1), Q 0. Q 1 S, X 2, Q 2 D. P 2. , . 5. (-) Q 1, Q 2, Q 3,... D. Q. Q. , Pt ` P, ` P. - (Xt).
X S
(D; S)
x 2 Q 2
Q
` x
x 3 Q 3
x 1 Q 0 Q 1
D
O P 0 P 2 ` P P 3 P 1 P
. 5.
: D = a + aP, S = b + bP. ` P ` X
` X = a + a ` P = b + b ` P,
`P = (a b)/(b a), `X = (ba ab)/(b - a). (4)
Xt = a +aPt = b +bPt1. (5)
, . Pt = `P, Xt = `X t:
` X = a +a`P = b +b`P. (6)
`P `X, (4). , - , , (5) .
(6) (5) t = Pt `P, xt = Xt `X.
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xt = at = bt-1. (7)
(7) (5), , ( , ). . c = b/a (7), t
t = ct-1. (8)
0 t = 0 (8) :
t = 0 ct,
Pt = `P + (P0 `P)ct.