Find an explicit solution of the given initial-value problem

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The discussion focuses on solving the initial-value problem defined by the differential equation x^2*(dy/dx)=y-xy with the condition y(-1) = -6. The user attempts to separate variables and integrate, reaching the equation -1/x - ln|x| = ln|y| + C, but expresses uncertainty about their solution for y. A response clarifies that the user misapplied the exponential operator and suggests correctly applying the exponential rule to separate terms. The response emphasizes the importance of simplifying the left side and using the initial condition to solve for the constant C effectively.
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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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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

e^{-\frac{1}{x} - ln|x|} = e^{ln|y| + C}

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

e^{a+b} = e^a e^b

You should get something akin to e^{-1/x} \times \frac{1}{x} on the left side, and of course e^C y on the right side. From there, it should be rather easy to simplify and plug in your initial condition to solve for e^C.
 
Question: A clock's minute hand has length 4 and its hour hand has length 3. What is the distance between the tips at the moment when it is increasing most rapidly?(Putnam Exam Question) Answer: Making assumption that both the hands moves at constant angular velocities, the answer is ## \sqrt{7} .## But don't you think this assumption is somewhat doubtful and wrong?

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