MHB Raqandre's question at Yahoo Answers regarding a Cauchy-Euler IVP

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The initial value problem x^2 y" + xy' - y = 0 with conditions y(1) = 0 and y'(1) = 2 can be solved by assuming a solution of the form y = x^r. Substituting this into the differential equation leads to the characteristic equation r^2 - 1 = 0, yielding the general solution y(x) = c_1 x + c_2 x^{-1}. Applying the initial conditions results in a system of equations that determines the constants c_1 and c_2 as 1 and -1, respectively. Therefore, the specific solution to the IVP is y(x) = x - 1/x.
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Here is the question:

Solve the initial value problem x^2 y" + xy' - y = 0?

solve the initial value problem x^2 y" + xy' - y = 0 with initial conditions: y(1)= 0 & y'(1) = 2

I have posted a link there to this topic so the OP can see my work.
 
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Re: raqandre's question at Yahoo! Answers regarding a Cauchy-euler IVP

Hello raqandre,

We are given the IVP:

$$x^2y"+xy'-y=0$$ where $$y'(1)=2,\,y(1)=0$$

One way to proceed is the guess a solution of the form:

$$y=x^r$$

and so:

$$y'=rx^{r-1}$$

$$y''=r(r-1)x^{r-2}$$

Now, substituting into the ODE gives us:

$$x^2\left(r(r-1)x^{r-2} \right)+x\left(rx^{r-1} \right)-\left(x^r \right)=0$$

$$x^r\left(r(r-1)+r-1 \right)=0$$

$$x^r\left(r^2-1 \right)=0$$

$$x^r(r+1)(r-1)=0$$

Thus, the general solution is:

$$y(x)=c_1x+c_2x^{-1}$$

Differentiating, we find:

$$y'(x)=c_1-c_2x^{-2}$$

Using the initial conditions, we get the linear system:

$$y'(1)=c_1-c_2=2$$

$$y(1)=c_1+c_2=0$$

From which we may determine:

$$c_1=1,\,c_2=-1$$

Thus, the solution satisfying the given IVP is:

$$y(x)=x-x^{-1}=x-\frac{1}{x}$$
 
Re: raqandre's question at Yahoo! Answers regarding a Cauchy-euler IVP

MarkFL said:
Hello raqandre,

We are given the IVP:

$$x^2y"+xy'-y=0$$ where $$y'(1)=2,\,y(1)=0$$

One way to proceed is the guess a solution of the form:

$$y=x^r$$

and so:

$$y'=rx^{r-1}$$

$$y''=r(r-1)x^{r-2}$$

Now, substituting into the ODE gives us:

$$x^2\left(r(r-1)x^{r-2} \right)+x\left(rx^{r-1} \right)-\left(x^r \right)=0$$

$$x^r\left(r(r-1)+r-1 \right)=0$$

$$x^r\left(r^2-1 \right)=0$$

$$x^r(r+1)(r-1)=0$$

Thus, the general solution is:

$$y(x)=c_1x+c_2x^{-1}$$

Differentiating, we find:

$$y'(x)=c_1-c_2x^{-2}$$

Using the initial conditions, we get the linear system:

$$y'(1)=c_1-c_2=2$$

$$y(1)=c_1+c_2=0$$

From which we may determine:

$$c_1=1,\,c_2=-1$$

Thus, the solution satisfying the given IVP is:

$$y(x)=x-x^{-1}=x-\frac{1}{x}$$

Thank you.
 
Glad to help and welcome to MHB! (Cool)
 
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