6.3.3 Example C The equation Yk+1Yk – 2yk = -2 (6.38) can be transformed into the linear equation Xk+2 2xk+1 + 2xk = 0 (6.39) by means of the substitution Yk = *k+1/xk. (6.40) The characteristic equation for equation (6.39) is p2 – 2r + 2 = 0, (6.41) and its two complex conjugate roots are r1,2 = 1+i = V2etin/4 (6.42) Therefore, the general solution of equation (6.39) is æk = 26/2[D1 cos(Tk/4)+ D2 sin(tk/4)], (6.43) and - 15D1 cos[T(k+1)/4] + D2 sin[T(k+1)/4] Dị cos(Tk/4) + D2 sin(rk/4) (6.44)

Algebra & Trigonometry with Analytic Geometry
13th Edition
ISBN:9781133382119
Author:Swokowski
Publisher:Swokowski
Chapter11: Topics From Analytic Geometry
Section11.4: Plane Curves And Parametric Equations
Problem 44E
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6.3.3 Ехample C
The equation
Yk+1Yk – 2yk = -2
(6.38)
can be transformed into the linear equation
Xk+2 – 2xk+1+2xk = 0
(6.39)
by means of the substitution
Yk =
Xk+1/xk.
(6.40)
The characteristic equation for equation (6.39) is
p2 – 2r + 2 = 0,
(6.41)
and its two complex conjugate roots are
r1,2 = 1+i = v2e±i™/4_
(6.42)
Therefore, the general solution of equation (6.39) is
X} = 2k/2[D1 cos(tk/4)+ D2 sin(Tk/4)],
(6.43)
and
D1 cos[T(k+ 1)/4] + D2 sin[r(k +1)/4]
Dị cos(Tk/4) + D2 sin(tk/4)
Yk =
V2-
(6.44)
200
Difference Equations
Now, define the constant a such that in the interval -T/2 < a < T/2,
tan a =
D2/D1.
(6.45)
With this result, equation (6.44) becomes
V2 cos[(T/4)(k + 1) – a]
Yk =
cos(Tk/4 – a)
(6.46)
or
Yk
1- tan(ak/4 – a).
(6.47)
This is the general solution to equation (6.38).
Note that since tan(0+ 7) = tan 0, the solution has period 4; i.e., for given
constant a, equation (6.47) takes on only four values; they are
Yo = ]
tan(-a),
- tan(7/4 – a),
1- tan(7/2 – a),
1– tan(37/4 – a).
Y1 =1-
(6.48)
Y2 =
Y3
An easy calculation shows that yo = Y4.
Transcribed Image Text:6.3.3 Ехample C The equation Yk+1Yk – 2yk = -2 (6.38) can be transformed into the linear equation Xk+2 – 2xk+1+2xk = 0 (6.39) by means of the substitution Yk = Xk+1/xk. (6.40) The characteristic equation for equation (6.39) is p2 – 2r + 2 = 0, (6.41) and its two complex conjugate roots are r1,2 = 1+i = v2e±i™/4_ (6.42) Therefore, the general solution of equation (6.39) is X} = 2k/2[D1 cos(tk/4)+ D2 sin(Tk/4)], (6.43) and D1 cos[T(k+ 1)/4] + D2 sin[r(k +1)/4] Dị cos(Tk/4) + D2 sin(tk/4) Yk = V2- (6.44) 200 Difference Equations Now, define the constant a such that in the interval -T/2 < a < T/2, tan a = D2/D1. (6.45) With this result, equation (6.44) becomes V2 cos[(T/4)(k + 1) – a] Yk = cos(Tk/4 – a) (6.46) or Yk 1- tan(ak/4 – a). (6.47) This is the general solution to equation (6.38). Note that since tan(0+ 7) = tan 0, the solution has period 4; i.e., for given constant a, equation (6.47) takes on only four values; they are Yo = ] tan(-a), - tan(7/4 – a), 1- tan(7/2 – a), 1– tan(37/4 – a). Y1 =1- (6.48) Y2 = Y3 An easy calculation shows that yo = Y4.
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