In applications, most initial value problems will have a unique solution. In fact, the existence of unique solutions is so important that there is a theorem about the existence and uniqueness of a solution. Consider the initial value problem =f(x,y). y(x) =yo. Iff and dx af dy are continuous functions in some rectangle R={(x,y):a

Linear Algebra: A Modern Introduction
4th Edition
ISBN:9781285463247
Author:David Poole
Publisher:David Poole
Chapter2: Systems Of Linear Equations
Section2.4: Applications
Problem 15EQ
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In applications, most initial value problems will have a unique solution. In fact, the existence of unique solutions is so important that there is a theorem about the existence and uniqueness of a solution. Consider the initial value problem
af
are continuous functions in some rectangle R = {(x,y):a<x<b, c<y<d} that contains the point (Xo Yo), then the initial value problem has a unique solution (x) in some interval xo -8<x<x+8, where is a positive number. The method for separable equations
ду
dy 3
can give a solution, but it may not give all the solutions. To illustrate this, consider the equation =y
dx
1
dy
3
(a) Use the method of separation of variables to find the solution to =y
Begin by separating the variables.
dx
dy=dx
Solve the differential equation, ignoring lost solutions, if any.
dy
nie by
(b) Show that the initial value problemy with y(0)=0 is satisfied for C =0 by y=
For y = 0, y(0)=
Now, determine
of
ду
Using the general solution, substituting for x and for y(x) implies that C=. So, the solution
x>0, satisfies the initial value problem =y with y(0) = 0.
dy
dx
(c) Now show that the constant function y = 0 also satisfies the initial value problem given in part (b). Hence, this initial value problem does not have a unique solution.
=
dy
dx
1
3
dy
dx
(d) Finally, show that the conditions for the theorem are not satisfied for the initial value problem in part (b). Begin by identifying f(x,y) in the initial value problem in (b).
f(x,y)=
af
ду
=
Answer parts (a) through (d).
for x ≥ 0.
, and y
C
1
1
3
dy
Thus, it holds that the constant function y = 0 satisfies the initial value problem -= y³ with y(0) = 0.
dx
=f(x,y). y (xo) yo. Iff and
dx
Transcribed Image Text:In applications, most initial value problems will have a unique solution. In fact, the existence of unique solutions is so important that there is a theorem about the existence and uniqueness of a solution. Consider the initial value problem af are continuous functions in some rectangle R = {(x,y):a<x<b, c<y<d} that contains the point (Xo Yo), then the initial value problem has a unique solution (x) in some interval xo -8<x<x+8, where is a positive number. The method for separable equations ду dy 3 can give a solution, but it may not give all the solutions. To illustrate this, consider the equation =y dx 1 dy 3 (a) Use the method of separation of variables to find the solution to =y Begin by separating the variables. dx dy=dx Solve the differential equation, ignoring lost solutions, if any. dy nie by (b) Show that the initial value problemy with y(0)=0 is satisfied for C =0 by y= For y = 0, y(0)= Now, determine of ду Using the general solution, substituting for x and for y(x) implies that C=. So, the solution x>0, satisfies the initial value problem =y with y(0) = 0. dy dx (c) Now show that the constant function y = 0 also satisfies the initial value problem given in part (b). Hence, this initial value problem does not have a unique solution. = dy dx 1 3 dy dx (d) Finally, show that the conditions for the theorem are not satisfied for the initial value problem in part (b). Begin by identifying f(x,y) in the initial value problem in (b). f(x,y)= af ду = Answer parts (a) through (d). for x ≥ 0. , and y C 1 1 3 dy Thus, it holds that the constant function y = 0 satisfies the initial value problem -= y³ with y(0) = 0. dx =f(x,y). y (xo) yo. Iff and dx
Expert Solution
Step 1: Part a)

Use space the space method space of space seperation space of space variables space to space find space the space solution space of space dy over dx equals straight y to the power of 1 third end exponent
straight a right parenthesis
We space can space write
dy equals straight y to the power of 1 third end exponent dx
box enclose bold y to the power of bold minus bold 1 over bold 3 end exponent end enclose bold dy bold equals box enclose bold 1 bold space bold dx
Using space the space integration space rules
fraction numerator straight y to the power of negative 1 third plus 1 end exponent over denominator negative 1 third plus 1 end fraction equals straight x plus straight C
fraction numerator straight y to the power of 2 over 3 end exponent over denominator 2 over 3 end fraction minus straight x equals straight C
box enclose fraction numerator bold 3 bold y to the power of bold 2 over bold 3 end exponent over denominator bold 2 end fraction bold minus bold x bold equals bold C end enclose

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