Consider the following second-order nonhomogeneous linear differential equation.

Kason Palmer

Kason Palmer

Answered question

2022-03-24

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.
y4y+3y=(212x)ex+(60+40x)(e3x)

Answer & Explanation

anghoelv1lw

anghoelv1lw

Beginner2022-03-25Added 19 answers

Given that, the differential equation is y4y+3y=(212x)ex+(60+40x)(e3x)
Here, the DE is ofthe form (aD2+bD+c)y=g1(x)+g2(x)
Here, g1(x)=(212x)ex and g2(x)=(60+40x)e3x
Particular solution 1:
Consider the differential equation is y4y+3y=g1(x). That is,
y4y+3y=(212x)ex
Consider the particular solution as, yp(x)=(Ax2+Bx+C)ex
Now differentiate the function yp(x)=(Ax2+Bx+C)ex with respect to x as follows.
yp(x)=(Ax2+Bx+C)ex
yp(x)=(Ax2+Bx+C)ex+(2Ax+b)ex
Now differentiate the function yp(x)=(Ax2+Bx+C)ex+(2Ax+B)ex with respect to x as follows.
yp(x)=(Ax2+Bx+C)ex+(2Ax+B)ex
yp(x)=(Ax2+Bx+C)ex+(2Ax+b)ex+(2Ax+B)ex+(2A)ex
=(Ax2+Bx+C)ex+(2Ax+b)ex+2Aex
Substitute respective values in y4y+3y=(212x)ex
y4y+3y=(212x)ex
[(Ax2+Bx+C)ex+(2Ax+b)ex+2Aex4(Ax2+Bx+C)ex4(2Ax+b)ex+3(Ax2+Bx+C)ex]=(2ex12xex)
[2(2Ax+B)ex+2Aex4(2Ax+B)ex]=(2ex12xex)
{xex(4A8A)+ex(2B+2A4B)}=(2ex12xex)
Equate the coefficient of xe^x and obtain A as follows.
4A8A=12
4A=12
A=3
Equate the coefficient of ex and obtain B as follows.
2B+2A4B=2
2A2B=2
62B=2
2B=4
B=2
The value of C is 0.
Thus, the particular solution is yp(x)=(3x2+2x)ex
Particular solution 2:
Consider the differential equation is y4y+3y=g2(x).That is,
y4y+3y=(6040x)e3x
Consider the particular solution as, yp(x)=(Ax2+Bx+C)e3x
Now differentiate the function yp(x)=(Ax2+Bx+C)e3x with respect to x as follows.
yp(x)=(Ax2+Bx+C)e3x
yp(x)=3(Ax2+Bx+C)e3x+(2Ax+B)e3x
Now differentiate the function yp(x)=3(Ax2+Bx+C)e3x+(2Ax+B)e3x with respect to x as follows.
yp(x)=3(Ax2+Bx+C)e3x+(2Ax+B)e3x
yp(x)=9(Ax2+Bx+C)e3x+3(2Ax+B)e3x+3(2Ax+B)e3x+(2A)e3x
=9(Ax2+Bx+C)e3x+6(2Ax+B)e3x+2Ae3x
Substitute respective values in y4y+3y=(212x)ex,
[9(Ax2+Bx+C)e3x+6(2Ax+B)e3x+2Ae3x12(Ax2+Bx+C)e3x4(2Ax+B)e3x+3(Ax2+Bx+C)e3x]=(60+40x)e3x
[6(2Ax+B)e3x+2ae3x4(2Ax+B)e3x]=(60e3x+40xe3x)
[xe3x(12A8A)+e3x(6B+2A4B)]=(60e3x+40xe3x)
Equate the coefficient of xe3x and obtain A as follows.
12A8A=40
4A=40
A=10
Equate the coefficient of e3x and obtain B as follows.
6B+2A4B=60
2A+2B=60
20+2B=60
2B=40
B=20
The value of C is 0.
Thus, the particular solution is yp(x)=(10x2+20x)e3x
Now find the complementary solution as follows.
Consder the DE as y4y+3y=0. The auxiliary equation is m24m+3=0
m24m+3=0
m23mm+3=0
m(m3)1(m3)=0
(m3)(m1)=0
m=3,1
Here the complementary solution is, yc(x)=c1ex+c2e3x
Thus, the general solution is y(x)=c1ex+c2e3x+(3x2+2x)ex+(10x2+20x)e3x
Jeffrey Jordon

Jeffrey Jordon

Expert2022-03-31Added 2605 answers

Answer is given below (on video)

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