Solve the given differential equation by undetermined coefficients.

Ashleigh Shaffer

Ashleigh Shaffer

Answered question

2022-03-22

Solve the given differential equation by undetermined coefficients.
y+4y=4sin(2x)

Answer & Explanation

Raiden Griffin

Raiden Griffin

Beginner2022-03-23Added 13 answers

y+4y=4sin(2x) is a second order linear, non-homogenous ODE with constant coefficient.
The general solution can be written as y=yc+yp
yc is the solution of the homogeneous ODE y+4y=0 and yp is the particular solution, is any function that satisfied the non-homogeneous equation.
Find yc by solving y+4y=0
First find the solution of the equation y+4y=0. Solve the characteristic equation m2+4=0.
m2+4=0
m±=2i
When the roots are complex and distinct then the general solution is of the form:
The complex roots γ1=α+iβ, γ2=αiβ
the solution is of tthe form y=eαx(c1cos(βx)+c2sin(βx))
for m=±2i
solution is yt=e(0)x(c1cos(2x)+c2sin(2x))=c1cos(2x)+c2sin(2x)
Now, find the particular solution use the formula
1D2+a2sinax=x2acosax
siliarly
41D2+22sin2x=4(x4cos2x)=xcos2x
Hence solution is :
y=c1cos(2x)+c2sin(2x)xcos2x

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