Solve the correct answer linear equations by considering y as a function of x, that is, \displaystyle{y}={y}{\left({x}\right)}.\frac{{\left.{d}{y}\right.}}{{\left.{d}{x}\right.}}+{y}= \cos{{x}}

sibuzwaW

sibuzwaW

Answered question

2021-03-07

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

Answer & Explanation

svartmaleJ

svartmaleJ

Skilled2021-03-08Added 92 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 is
ln|y|=x+c
By taking exponents, we obtain
ln|y|=ex+c=exec
Hence,we obtain
y=Cex
where C=±ecandyc=ex 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 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=cosx
uyc+uyc+uyc=cosx
uyc+u(yc+ye)=cosx=0 since ycis a solution
Therefore, uyc=cosxxu=cosxyc
which gives
u=cosxycdx
Now, we can find the function u:
u=cosxexdx=excosxIntegration by partsudv=uvvdu
=|u=cosxdu=sinxdxdv=exv=dv=ex|
displaysty≤={e}xcos{{x}}{e}x{(sin{{x}}{ft.{d}{x}right.})}

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