Solve the linear equations by considering y as a function of x, that is, y = y(x). y'+2y=4

Brittney Lord

Brittney Lord

Answered question

2021-03-11

Solve the linear equations by considering y as a function of x, that is, y=y(x).
y+2y=4

Answer & Explanation

Szeteib

Szeteib

Skilled2021-03-12Added 102 answers

Variation of parameters
First, solve the linear homogeneous equation by separating variables.Rearranging terms in the equation gives
y=2ydydx=2ydyy=2dx
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=2dx
Which is
ln|y|=2x+c
By taking exponents, we obtain
|y|=e2x+c=e2xec
Hence,we obtain
y=Ce2x
where C=±ecandyc=e2x 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)+2uyc=4
uyc+uyc+2uyc=4
uyc+u(yc+2yc)=0  =4
since yc is a solution
Therefore,
uyc=4u=4yc
which gives
u=4ycdx
Now, we can find the function u:
u=(4e2x)dx
=4e2xdx
=412e2x+c1
=2e2x+c1
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=2e2x
Recall that yp=uyc
Therefore
yp=e2x2e2x
=2The general solution is
y=Cyc+yp
=Ce2x+2
Integration Factor technique
This equation is linear with P(x)=2andQ(x)=ex
Hence,
h=2dx=2x
So, an integrating factor is
eh=e2x
and the general solution is

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