Method of undetermined coefficients question

Click For Summary
SUMMARY

The discussion focuses on the method of undetermined coefficients applied to the differential equation y'' + y' = g(x), where g(x) = x^2. The fundamental set of solutions for the homogeneous part is identified as y1 = 1 and y2 = e^-x. A participant questions the inclusion of an 'x' factor in the particular solution yp1, which is given as x(Ax^2 + Bx + C). The rationale provided confirms that the 'x' is necessary to avoid duplication with the constant term in the fundamental set of solutions.

PREREQUISITES
  • Understanding of second-order linear differential equations
  • Familiarity with the method of undetermined coefficients
  • Knowledge of homogeneous and particular solutions
  • Basic algebraic manipulation skills
NEXT STEPS
  • Study the method of undetermined coefficients in detail
  • Review examples of finding particular solutions for different forms of g(x)
  • Explore the implications of linear independence in solution sets
  • Practice solving second-order linear differential equations with varying g(x)
USEFUL FOR

Students studying differential equations, particularly those preparing for exams or needing clarification on the method of undetermined coefficients.

illidari
Messages
46
Reaction score
0

Homework Statement


y''+y'=g(x)
fundamental set of solns. of the homog. DE is:
y1= 1 , y2= e^-x

If g(x) = x^2 , yp1 = ____


Homework Equations





The Attempt at a Solution



I actually am looking at a key to an old test my teacher gave as a review for a test. The key has the asnswer as x(Ax^2+Bx+C)

Is there any reason why the x was added? Shouldn't it only be (Ax^2+Bx+C). Much thanks if someone can clarify this for me.
 
Physics news on Phys.org
I'm pretty sure its because when you're finding your particular solution, you can't start with terms that duplicate terms in the fundamental set. Since you have a constant as a solution in the fundamental set, you need to multiply the particular solution by x (because of C).
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 15 ·
Replies
15
Views
3K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K
Replies
4
Views
3K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 4 ·
Replies
4
Views
6K