y^ prime prime -3y^ prime +2y=10 sin x+2

Answered question

2022-03-20

y^ prime prime -3y^ prime +2y=10 sin x+2 cos 2x . Find a general solution of the following

Answer & Explanation

Vasquez

Vasquez

Expert2023-04-24Added 669 answers

We are given the differential equation:
y''-3y'+2y=10sin(x)+2cos(2x)

To solve this equation, we will first find the characteristic equation by assuming that y is a solution of the form erx. Substituting this form into the differential equation, we get:
r2erx-3rerx+2erx=0

Dividing both sides by erx (which is nonzero), we get the characteristic equation:
r2-3r+2=0

This equation can be factored as (r-1)(r-2)=0, so the roots are r = 1 and r = 2. Therefore, the general solution to the homogeneous equation y''-3y'+2y=0 is:
yh=c1ex+c2e2x

where c1 and c2 are constants.

Now we will find a particular solution to the nonhomogeneous equation y''-3y'+2y=10sin(x)+2cos(2x). We can use the method of undetermined coefficients, since the right-hand side contains only sine and cosine functions. We will try a particular solution of the form:
yp=Asin(x)+Bcos(x)+Csin(2x)+Dcos(2x)

Taking the first and second derivatives of yp, we get:
y'p=Acos(x)-Bsin(x)+2Ccos(2x)-2Dsin(2x)
y''p=-Asin(x)-Bcos(x)-4Csin(2x)-4Dcos(2x)

Substituting these into the differential equation and simplifying, we get:
(-A-4C)sin(x)+(B-4D)cos(x)+(4C-3A)sin(2x)+(4D-3B)cos(2x)=10sin(x)+2cos(2x)

This equation is satisfied if:
-A-4C=10
B-4D=2
4C-3A=0
4D-3B=0

Solving these equations, we get A=-207,B=-87,C=-928, and D=-114. Therefore, a particular solution to the nonhomogeneous equation is:
yp=(-207)sin(x)-(87)cos(x)-(928)sin(2x)-(114)cos(2x)

The general solution to the nonhomogeneous equation is the sum of the homogeneous solution and the particular solution:
y=yh+yp
=c1ex+c2e2x-(207)sin(x)-(87)cos(x)-(928)sin(2x)-(114)cos(2x)

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