Find an explicit solution of the given initial-value problem

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In summary, the conversation discusses finding an explicit solution to a given initial-value problem involving a differential equation. The individual follows the standard steps of separation of variables and integration by partial fractions, but makes a small error in applying the exponential operator. They eventually reach a correct solution and discuss the next steps of solving for the constant C.
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fd25t6
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Hello all, hoping to get a bit of help with a diff eq problem that goes like this:

Find an explicit solution of the given initial-value problem,

x^2*(dy/dx)=y-xy ; y(-1) = -6

I separated my variables to get:

S (1-x)/x^2 dx = S 1/y dy

Integration of left via partial fractions:

S 1/x^2 dx - S 1/x dx = -1/x - ln|x|

Integration of right :

S 1/y dy = ln|y|

therefore :

-1/x - ln|x| = ln|y| + C

Now this is the first Calc class I have taken in a while so I am assuming more than one error here:

e^(-1/x) -x = y + e^C
y = e^(-1/x) -e^C - x
y = e^(1/x - C) -x

Did I solve for y correctly here? If not is my issue in the integration? Also at what point is it best to solve for C in this equation?

Thank you in advance for any assistance.
 
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  • #2
fd25t6 said:
Hello all, hoping to get a bit of help with a diff eq problem that goes like this:

Find an explicit solution of the given initial-value problem,

x^2*(dy/dx)=y-xy ; y(-1) = -6

I separated my variables to get:

S (1-x)/x^2 dx = S 1/y dy

Integration of left via partial fractions:

S 1/x^2 dx - S 1/x dx = -1/x - ln|x|

Integration of right :

S 1/y dy = ln|y|

therefore :

-1/x - ln|x| = ln|y| + C

You had it right up to here. That's definitely good.

Now this is the first Calc class I have taken in a while so I am assuming more than one error here:

e^(-1/x) -x = y + e^C
y = e^(-1/x) -e^C - x
y = e^(1/x - C) -x

Did I solve for y correctly here? If not is my issue in the integration? Also at what point is it best to solve for C in this equation?

Thank you in advance for any assistance.

You're kinda applying the exponential operator all wrong here. Your first step should look like

[tex]e^{-\frac{1}{x} - ln|x|} = e^{ln|y| + C}[/tex]

From there, you'll want to separate the terms on the left via the exponential rule:

[tex]e^{a+b} = e^a e^b[/tex]

You should get something akin to [itex]e^{-1/x} \times \frac{1}{x}[/itex] on the left side, and of course [itex]e^C y[/itex] on the right side. From there, it should be rather easy to simplify and plug in your initial condition to solve for e^C.
 

1. What is an explicit solution in the context of initial-value problems?

An explicit solution of an initial-value problem is a mathematical expression or formula that directly gives the value of the dependent variable at any given independent variable value. It does not involve any implicit or hidden relationships between the variables.

2. How is an explicit solution different from an implicit solution?

An implicit solution involves a relationship between the dependent and independent variables that cannot be directly solved for the dependent variable. It is usually represented as an equation or inequality. In contrast, an explicit solution directly gives the value of the dependent variable without any hidden relationships.

3. What is the process for finding an explicit solution of an initial-value problem?

The process involves using mathematical techniques such as separation of variables, substitution, or integration to manipulate the given differential equation and initial conditions in order to isolate the dependent variable and solve for it explicitly.

4. Are there any cases where an explicit solution cannot be found?

Yes, there are some initial-value problems that do not have an explicit solution. This can happen when the differential equation is too complex or when the initial conditions are not well-defined. In these cases, numerical methods or approximation techniques may be used to find an approximate solution.

5. Can an explicit solution be verified?

Yes, an explicit solution can be verified by substituting the solution into the original differential equation and checking that it satisfies the equation for all values of the independent variable within the given domain. Additionally, the initial conditions should also be satisfied by the solution.

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