Please answer a, b, and c! Information about theorem one is attached.

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Author:Erwin Kreyszig
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Chapter2: Second-order Linear Odes
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Please answer a, b, and c! Information about theorem one is attached.
3. Consider the initial-value problem
dy = y²/³, y(0) = 0.
dx
Use separation of variables to obtain the solution y(x) = x³ /27.
(b) Observe that another solution is y(x) 0.
(c) Since this initial-value problem has two distinct solutions, uniqueness does
not apply. What hypothesis in Theorem 1 in Section 1.2 does not hold?
Transcribed Image Text:3. Consider the initial-value problem dy = y²/³, y(0) = 0. dx Use separation of variables to obtain the solution y(x) = x³ /27. (b) Observe that another solution is y(x) 0. (c) Since this initial-value problem has two distinct solutions, uniqueness does not apply. What hypothesis in Theorem 1 in Section 1.2 does not hold?
Theorem 1. If f(x, y) is continuous in an open rectangle R = (a, b) (c,d) in the xy-
plane that contains the point (xo, yo), then there exists a solution y(x) to the initial-value
problem
dy
dx
(1.11)
that is defined in an open interval I = (a, b) containing xo. In addition, if the partial
derivative df/dy is continuous in R, then the solution y(x) of (1.11) is unique.
=
f(x, y),
Qualitative Analysis
y(xo):
= yo,
This theorem is proved using successive approximations, but we shall not give the
details; see, for example, [1]. However, let us make a couple of remarks that will help
clarify the need for the various hypotheses.
Remark 1. We might hope that existence holds with a = a and ß = b, and indeed this
is the case for linear equations f(x, y) = a(x)y+b(x). But for nonlinear equations, this
need not be the case. For example, if we plot the slope field and some solution curves for
Y
= y², we see that the solutions seem to approach vertical asymptotes; this suggests
that they are not defined on I = ( ) even though f y² continuous on the
whole xy-plane. (When we discuss separation of variables in Section 1.3, we will be able
to confirm the existence of these vertical asymptotes for many nonlinear equations.)
=
=
Remark 2. Regarding the condition for uniqueness, Exercise 3 in Section 1.3 shows that
the initial-value problem y = y²/³, y(0) = 0 has two different solutions; the uniqueness
claim in the theorem does not apply to this example since df/dy is not continuous in
any rectangle containing (0,0).
Transcribed Image Text:Theorem 1. If f(x, y) is continuous in an open rectangle R = (a, b) (c,d) in the xy- plane that contains the point (xo, yo), then there exists a solution y(x) to the initial-value problem dy dx (1.11) that is defined in an open interval I = (a, b) containing xo. In addition, if the partial derivative df/dy is continuous in R, then the solution y(x) of (1.11) is unique. = f(x, y), Qualitative Analysis y(xo): = yo, This theorem is proved using successive approximations, but we shall not give the details; see, for example, [1]. However, let us make a couple of remarks that will help clarify the need for the various hypotheses. Remark 1. We might hope that existence holds with a = a and ß = b, and indeed this is the case for linear equations f(x, y) = a(x)y+b(x). But for nonlinear equations, this need not be the case. For example, if we plot the slope field and some solution curves for Y = y², we see that the solutions seem to approach vertical asymptotes; this suggests that they are not defined on I = ( ) even though f y² continuous on the whole xy-plane. (When we discuss separation of variables in Section 1.3, we will be able to confirm the existence of these vertical asymptotes for many nonlinear equations.) = = Remark 2. Regarding the condition for uniqueness, Exercise 3 in Section 1.3 shows that the initial-value problem y = y²/³, y(0) = 0 has two different solutions; the uniqueness claim in the theorem does not apply to this example since df/dy is not continuous in any rectangle containing (0,0).
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