Solve the linear equations by considering y as a function of x, that is, y = y(x). displaystylefrac{{{left.{d}{y}right.}}}{{{left.{d}{x}right.}}}+{left(frac{1}{{x}}right)}{y}={x}

chillywilly12a

chillywilly12a

Answered question

2021-02-24

Solve the linear equations by considering y as a function of x, that is, y=y(x).
dydx+(1x)y=x

Answer & Explanation

lobeflepnoumni

lobeflepnoumni

Skilled2021-02-25Added 99 answers

Variation of parameters
First, solve the linear homogeneous equation by separating variables.
Rearranging terms in the equation gives
dydx=yxdyy=dxx
Now, the variables are separated, x appears only on the right side, and yonly on the left.
Integrate the left side in relation to y, and the right side in relation to x
dyy=dxx
Which is
ln|y|=ln|x|+c
By taking exponents, we obtain
|y|=eln|x|+c=1|x|ec
Hence,we obtain
y=1Cx
where C=±ecandyc=1x is the complementary solution .
Next, we need to find the particular solution yp.
Therefore, we consider uyc, and try to find u, a function of x, that will makethis work.
Let's assume that uyc is a solution of the given equation. Hence, it satisfiesthe given equation.
Substituting uyc, and its derivative in the equation gives
(uyc)+uycx=x
uyc+uyc+uycx=x
uyc+u(yc+ycx)=0  =x
since yc is a solution
Therefore,
uyc=xu=xyc
which gives
u=xycdx
Now, we can find the function u:
u=(x1x)dx
=x2dx
=x33+c
Since we need to find only one function that will male this work, we don’tneed to introduce the constant of integration c. Hence,
u=x33
Recall that yp=uyc
Therefore
yp=1xx33
=x23
The general solution is
y=Cyc+yp
=Cx+x23
Integrating Factor technique
This equation is linear with P(x)=1xandQ(x)=x
Hence, h=1x=ln|x|
So, an integrating factor is eh=e

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