In each of Problems 7 through 12, find the solution of the given initial value problem. Sketch the graph of the solution and describe its behavior as t increases. G 7. y"+y'- 2y = 0, G 8. y" +4y' + 3y = 0, y" + 3y = 0, y(0) = -2, y'(0) = 3 (60) G G 9. 10 n y(0) = 1, y'(0) = 15 y(0) = 2, y'(0) = -1

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
Question

9

Returning to the equation ay" + by' + cy = 0 with arbitrary coefficients, recall
that when r₁ r2, its general solution (18) is the sum of two exponential functions.
Therefore, the solution has a relatively simple geometrical behavior: as t increases, the
magnitude of the solution either tends to zero (when both exponents are negative) or else
exhibits unbounded growth (when at least one exponent is positive). These two cases
are illustrated by the solutions of Examples 3 and 4, which are shown in Figures 3.1.1
and 3.1.2, respectively. Note that whether a growing solution approaches +∞or - as
1 → ∞ is determined by the sign of the coefficient of the exponential for the larger root
of the characteristic equation. (See Problem 21.) There is also a third case that occurs
negative.
less often: the solution approaches a constant when one exponent is zero and the other is
G
In Sections 3.3 and 3.4, respectively, we return to the problem of solving the equation
ay" +by' + cy=0 when the roots of the characteristic equation either are complex conjugates
or are real and equal. In the meantime, in Section 3.2, we provide a systematic discussion
equations.
of the mathematical structure of the solutions of all second-order linear homogeneous
Problems
In each of Problems 1 through 6, find the general solution of the given
differential equation.
1. y" + 2y' - 3y = 0
1)+ (1Enia)+(18
2.
y" + 3y' + 2y = 0
1)+18
3.
6y" - y'- y = 0
4.
y" + 5y' = 0
5.
4y" - 9y = 0
6. y" - 2y' - 2y = 0
In each of Problems 7 through 12, find the solution of the given 19.
initial value problem. Sketch the graph of the solution and describe
its behavior as t increases.
G 7.
8.
badria
10 mie 0-=
0q+³0=3p
y"+y' - 2y = 0,
y" +4y' + 3y = 0,
y" + 3y' = 0, y(0)
2y"+y'- 4y = 0,
y" +8y' - 9y = 0,
y(0) = 1, y'(0) = 1
y(0) = 2, y'(0) = -1
= -2, y'(0) = 3
y(0) = 0, y'(0) = 1
y(1) = 1, y'(1) = 0
y(-2) = 1, y'(-2) = -1
G 9.
G 10.
G 11.
G 12. 4y" - y = 0,
13. Find a differential equation whose general solution is
y=c₁e²¹ +c₂e-³1.
101 110
G 14. Find the solution of the initial value problem
5
y" - y = 0, y(0)=, y'(0) = -
3
4
y(0) = 2, y'(0)
=
SH
1
2
Plot the solution for 0 ≤ t ≤ 2 and determine its minimum value.
15. Find the solution of the initial value problem
2y" - 3y + y = 0,
Then determine the maximum value of the solution and also find the
point where the solution is zero.
3.1 Homogeneous Differential Equations with Constant Coefficients 109
Inpass
yllups
16. Solve the initial value problem y" - y' - 2y = 0, y(0) = a,
y'(0) = 2. Then find a so that the solution approaches zero as
t→∞.
-
17. y" - (2a - 1) y' + a(a − 1) y = 0
18. y" +(3-a) y' - 2(a - 1) y = 0
mojadi ma
In each of Problems 17 and 18, determine the values of a, if any, for
which all solutions tend to zero as to; also determine the values
of a, if any, for which all (nonzero) solutions become unbounded as
t →∞.
Consider the initial value problem (see Example 5)
y" + 5y' + 6y = 0, y(0) = 2, y'(0) = 3,
where 3 > 0. olsu
a. Solve the initial value problem.
b. Determine the coordinates tm and ym of the maximum point
of the solution as functions of 3.
c. Determine the smallest value of 3 for which ym ≥ 4.
d. Determine the behavior of tm and ym as 3 →∞0.
20. Consider the equation ay" +by' + cy=d, where a, b, c, and d
are constants.bs not odj
oda. Find all equilibrium, or constant, solutions of this differential
equation.
T
b. Let ye denote an equilibrium solution, and let y = y - ye.
Thus Y is the deviation of a solution y from an equilibrium
solution. Find the differential equation satisfied by Y.
21. Consider the equation ay" + by' + cy = 0, where a, b, and c
are constants with a > 0. Find conditions on a, b, and c such that the
roots of the characteristic equation are:
a. real, different, and negative.
b. real with opposite signs.
c. real, different, and positive.
In each case, determine the behavior of the solution as t→∞.
Transcribed Image Text:Returning to the equation ay" + by' + cy = 0 with arbitrary coefficients, recall that when r₁ r2, its general solution (18) is the sum of two exponential functions. Therefore, the solution has a relatively simple geometrical behavior: as t increases, the magnitude of the solution either tends to zero (when both exponents are negative) or else exhibits unbounded growth (when at least one exponent is positive). These two cases are illustrated by the solutions of Examples 3 and 4, which are shown in Figures 3.1.1 and 3.1.2, respectively. Note that whether a growing solution approaches +∞or - as 1 → ∞ is determined by the sign of the coefficient of the exponential for the larger root of the characteristic equation. (See Problem 21.) There is also a third case that occurs negative. less often: the solution approaches a constant when one exponent is zero and the other is G In Sections 3.3 and 3.4, respectively, we return to the problem of solving the equation ay" +by' + cy=0 when the roots of the characteristic equation either are complex conjugates or are real and equal. In the meantime, in Section 3.2, we provide a systematic discussion equations. of the mathematical structure of the solutions of all second-order linear homogeneous Problems In each of Problems 1 through 6, find the general solution of the given differential equation. 1. y" + 2y' - 3y = 0 1)+ (1Enia)+(18 2. y" + 3y' + 2y = 0 1)+18 3. 6y" - y'- y = 0 4. y" + 5y' = 0 5. 4y" - 9y = 0 6. y" - 2y' - 2y = 0 In each of Problems 7 through 12, find the solution of the given 19. initial value problem. Sketch the graph of the solution and describe its behavior as t increases. G 7. 8. badria 10 mie 0-= 0q+³0=3p y"+y' - 2y = 0, y" +4y' + 3y = 0, y" + 3y' = 0, y(0) 2y"+y'- 4y = 0, y" +8y' - 9y = 0, y(0) = 1, y'(0) = 1 y(0) = 2, y'(0) = -1 = -2, y'(0) = 3 y(0) = 0, y'(0) = 1 y(1) = 1, y'(1) = 0 y(-2) = 1, y'(-2) = -1 G 9. G 10. G 11. G 12. 4y" - y = 0, 13. Find a differential equation whose general solution is y=c₁e²¹ +c₂e-³1. 101 110 G 14. Find the solution of the initial value problem 5 y" - y = 0, y(0)=, y'(0) = - 3 4 y(0) = 2, y'(0) = SH 1 2 Plot the solution for 0 ≤ t ≤ 2 and determine its minimum value. 15. Find the solution of the initial value problem 2y" - 3y + y = 0, Then determine the maximum value of the solution and also find the point where the solution is zero. 3.1 Homogeneous Differential Equations with Constant Coefficients 109 Inpass yllups 16. Solve the initial value problem y" - y' - 2y = 0, y(0) = a, y'(0) = 2. Then find a so that the solution approaches zero as t→∞. - 17. y" - (2a - 1) y' + a(a − 1) y = 0 18. y" +(3-a) y' - 2(a - 1) y = 0 mojadi ma In each of Problems 17 and 18, determine the values of a, if any, for which all solutions tend to zero as to; also determine the values of a, if any, for which all (nonzero) solutions become unbounded as t →∞. Consider the initial value problem (see Example 5) y" + 5y' + 6y = 0, y(0) = 2, y'(0) = 3, where 3 > 0. olsu a. Solve the initial value problem. b. Determine the coordinates tm and ym of the maximum point of the solution as functions of 3. c. Determine the smallest value of 3 for which ym ≥ 4. d. Determine the behavior of tm and ym as 3 →∞0. 20. Consider the equation ay" +by' + cy=d, where a, b, c, and d are constants.bs not odj oda. Find all equilibrium, or constant, solutions of this differential equation. T b. Let ye denote an equilibrium solution, and let y = y - ye. Thus Y is the deviation of a solution y from an equilibrium solution. Find the differential equation satisfied by Y. 21. Consider the equation ay" + by' + cy = 0, where a, b, and c are constants with a > 0. Find conditions on a, b, and c such that the roots of the characteristic equation are: a. real, different, and negative. b. real with opposite signs. c. real, different, and positive. In each case, determine the behavior of the solution as t→∞.
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