Consider the following second-order nonhomogeneous linear differential equation.

Dexter Odom

Dexter Odom

Answered question

2022-03-22

Consider the following second-order nonhomogeneous linear differential equation. Use the method of undetermined coefficients to find a particular solution for each equation. Then solve each equation for real general solution.
y+100y=36cos(8x)+72sin(8x)

Answer & Explanation

uqhekekocj8f

uqhekekocj8f

Beginner2022-03-23Added 8 answers

Consider the differential equation as y+100y=36cos(8x)+72sin(8x)
The auxiliary equation of the homogeneous differential equation
y+100y=0 is m2+100=0
Solve the auxiliary equation m2+100=0 as follows
m2+100=0
m2=100
m=±100
m=±10i
m1=10i or m2=10i
Thus, the solution of the homogeneous differential equation is
yh=[c1cos(10x)+c2sin(10x)]
Since the right hand side of the differential equation y+100y=36cos(8x)+72sin(8x) is 36cos(8x)+72sin(8x), the the guess for its particular solution will be of the form
yp(x)=Acos(8x)+Bsin(8x)
Substitute yp(x) in y+100y=36cos(8x)+72sin(8x), then the guess for its particular solution will be of the form yp(x)=Acos(8x)+Bsin(8x)
Substitute yp(x) in y+100y=36cos(8x)+72sin(8x) and obtain the value of A and B
y+100y=36cos(8x)+72sin(8x)
[(Acos(8x)+Bsin(8x))+100(Acos(8x)+Bsin(8x))]=36cos(8x)+72sin(8x)
[(64Acos(8x)64Bsin(8x))+100Acos(8x)+100Bsin(8x)]=36cos(8x)+72sin(8x)
[(64A+100A)cos(8x)+(64B+100B)sin(8x)]=36cos(8x)+72sin(8x)
64A+100B=36 and 64B+100b=72 (Compare the coefficient of cos(8x) and sin(8x))
Solve the equation 64A+100A=36 and 64B+100B=72 as follows.
64A+100A=36
36A=36A=1
64B+100B=72
36B=72B=2
Thus, the particular solution of the differential equation
y+100y=36cos(8x)+72sin(8x) is yp(x)=cos(8x)+2sin(8x)
The general solution of the given differential equation is obtained as follows.
y=yh+yp(x)
y=c1cos(10x)+c2sin(10x)+cos(8x)+2sin(8x)
Jeffrey Jordon

Jeffrey Jordon

Expert2022-03-31Added 2605 answers

Answer is given below (on video)

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