5y-6yk+2 6y-8yk+3) (e) Yk+1

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter11: Topics From Analytic Geometry
Section11.3: Hyperbolas
Problem 29E
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Plot the following curves, locate any fixed points, and obtain asymp-
totic expansions to their solution as k
(a) Yk+1 = y% +a², a =
Yk (y%+3)
3y+1
(c) 2y%+1 - 5yk+1Yk + 2y% = 2,
real number,
(b) Ук+1 —
(d) ук+1
ayk+1
Ykta »
(е) Ук+1
5y -6yk+2
6y -8yk+3'
(f) 5yk+1
5y+6yk+19
Transcribed Image Text:Plot the following curves, locate any fixed points, and obtain asymp- totic expansions to their solution as k (a) Yk+1 = y% +a², a = Yk (y%+3) 3y+1 (c) 2y%+1 - 5yk+1Yk + 2y% = 2, real number, (b) Ук+1 — (d) ук+1 ayk+1 Ykta » (е) Ук+1 5y -6yk+2 6y -8yk+3' (f) 5yk+1 5y+6yk+19
Example D
The equation
Yk+1 =
1/2yk +2-3/2yk
(2.193)
76
Difference Equations
corresponds to a hyperbola in the (yk, Yk+1) plane having asymptotes Yk = 0
and yk+1 =
slopes at (1, 1) and (3, 3) are, respectively, 2 and 2/3. Therefore, Yk = 1 is an
unstable fixed point, while yk = 3 is a stable fixed point.
A geometric analysis indicates that arbitrary starting points lead finally
to the stable fixed point. See Figure 2.10.
The first approximation to the solution of equation (2.193), near yk = 3,
is given by the expression
1/2yk + 2. There are two fixed points, yk = 1 and yk = 3. The
Yk = 3+ A(2/3)*,
(2.194)
where A is an arbitrary constant. Therefore, if we let
t = A(2/3)*, 2(t) = Yk,
(2.195)
then equation (2.193) becomes
2t
2:(0): ()
2(t)? + 4z(t) – 3.
(2.196)
=
We assume a solution of the form
z(t) = 3+t+ A2t? + Azt +....
(2.197)
Substitution of this expression into equation (2.197) gives, respectively, for
the left- and right-hand sides
2z(t)z
2t
= 18 + 10t + 2/3(13A2 + 2)t
+ 2/%(35A3 + 10A2)t² + ...,
(2.198)
and
z(t)? + 4z(t) – 3 = 18 + 10t + (10A2 + 1)t?
+ (10A3 + 2A2)t³ + ....
(2.199)
Equating the coefficients of corresponding powers of t gives
2/3(13A2 + 2) = 10A2 + 1,
(2.200)
2/9(35A3 + 10A2) = 10A3 + 2A2,
and
A2 = 1/4, A3 =
140.
(2.201)
Therefore,
z(t) = 3+t+at2 + 1/40t + ... ,
and
Yk = 3+ A(2/3)* +14A? (2/3)2k + 1/40A° (2/3)3k + ....
(2.202)
Transcribed Image Text:Example D The equation Yk+1 = 1/2yk +2-3/2yk (2.193) 76 Difference Equations corresponds to a hyperbola in the (yk, Yk+1) plane having asymptotes Yk = 0 and yk+1 = slopes at (1, 1) and (3, 3) are, respectively, 2 and 2/3. Therefore, Yk = 1 is an unstable fixed point, while yk = 3 is a stable fixed point. A geometric analysis indicates that arbitrary starting points lead finally to the stable fixed point. See Figure 2.10. The first approximation to the solution of equation (2.193), near yk = 3, is given by the expression 1/2yk + 2. There are two fixed points, yk = 1 and yk = 3. The Yk = 3+ A(2/3)*, (2.194) where A is an arbitrary constant. Therefore, if we let t = A(2/3)*, 2(t) = Yk, (2.195) then equation (2.193) becomes 2t 2:(0): () 2(t)? + 4z(t) – 3. (2.196) = We assume a solution of the form z(t) = 3+t+ A2t? + Azt +.... (2.197) Substitution of this expression into equation (2.197) gives, respectively, for the left- and right-hand sides 2z(t)z 2t = 18 + 10t + 2/3(13A2 + 2)t + 2/%(35A3 + 10A2)t² + ..., (2.198) and z(t)? + 4z(t) – 3 = 18 + 10t + (10A2 + 1)t? + (10A3 + 2A2)t³ + .... (2.199) Equating the coefficients of corresponding powers of t gives 2/3(13A2 + 2) = 10A2 + 1, (2.200) 2/9(35A3 + 10A2) = 10A3 + 2A2, and A2 = 1/4, A3 = 140. (2.201) Therefore, z(t) = 3+t+at2 + 1/40t + ... , and Yk = 3+ A(2/3)* +14A? (2/3)2k + 1/40A° (2/3)3k + .... (2.202)
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