Solve the linear equations by considering y as a function of x, that is, y = y(x).displaystyle{y}'+{y} tan{{x}}= sec{{x}},displaystyle{y}{left(piright)}={1}

Globokim8

Globokim8

Answered question

2021-01-13

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

Answer & Explanation

Fatema Sutton

Fatema Sutton

Skilled2021-01-14Added 88 answers

Variation of parameters
First, solve the linear homogeneous equation by separating variables.
Rearranging terms in the equation gives
dydx=ytanxdyy=tanxdx
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=tanxdx
Let's solve the integral on the right side.
tanxdx=sinxcosxdx
=|cosx=tsinxdx=dt|
=dtt
=ln|t|+c
=ln|cosx|+c
Therefore,
ln|y|=ln|cosx|+c
By taking exponents, we obtain
|y|=eln|cosx|+c=|cosx|ec
Hence,we obtain
y=Ccosx
where C=±ec and yc=cosx is the compleentary solution
Next, we need to find the particular solution yp
Therefore, we consider uyc, and try to find w, 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)tanx=secx
uyc+uyc+(uyc)tanx=secx
uyc+u(yc+(yc)tanx)=0  =secx
since yc is a solution
Therefore,
uyc=secxu=secxyc
which gives
u=secxycdx
Now, we can find the function u :
u=(secxcosx)dx
=secxsecxdx

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