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.}}}-{y}={4}{e}^{x},{y}{left({0}right)}={4}

shadsiei

shadsiei

Answered question

2021-02-25

Solve the linear equations by considering y as a function of x, that is, y = y(x).
dydxy=4ex,y(0)=4

Answer & Explanation

2abehn

2abehn

Skilled2021-02-26Added 88 answers

Variation of parameters
First, solve the linear homogeneous equation by separating variables. Rearranging terms in the equation gives
dydx=ydyy=dx
Now, the variables are separated, x appears only on the right side, and y only on the left.
Integrate the left side in relation to y, and the right side in relation to x
dyy=dx
which isln|y|=x+c
By taking exponents, we obtain
|y|=ex+c=exec
Hence,we obtain
y=Cex
where C=±ecandyc=ex is the compleentary 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 make this work.
Let's assume that uyc. is a solution of the given equation. Hence, it satisfies the given equation. Substituting uyc, and its derivative in the equation gives
(uyc)uyc=4ex
uyc+uycuyc=4ex
uyc+u(ycyc)=0  =4ex
since yc is a solution
Therefore
uyc=4exu=4exyc
which gives
u=exycdx
Now, we can find the function u :
u=4exexdx
=4dx
=4x+c
Since we need to find only one function that will male this work, we don’t need to introduce the constant of integration c. Hence,
u=4x
Recall that yp=uyc. Therefore,
yp=4xex
The general solution is
y=Cyc+yp
=ex(C+4x)
Integrating Factor technique
This equation is linear with P(x)=1andQ(x)=4ex
Hence,
h=Pdx=dx=x
So, an integrating factor is
eh=ex
and the general solution is
y(x)=eh(c+Qehdx)
=ex(c+4exex

Do you have a similar question?

Recalculate according to your conditions!

New Questions in Differential Equations

Ask your question.
Get an expert answer.

Let our experts help you. Answer in as fast as 15 minutes.

Didn't find what you were looking for?