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Mangoes
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There isn't a specific problem that's making me stuck, but I was hoping if someone could point me in the right direction here. I've looked up the topic online, but most of what I could find was through another approach or very unclear. The book I'm using also does not use the method my professor uses.
In my ODE class I've been using the annihilator approach to solve homogenous DEs. We moved on to solving nonhomogenous ODEs a while ago and covered undetermined coefficients and variation of parameters, but I had to miss the lecture on undetermined coefficients and there's something I missed which is messing me up.
I understand that if I have a simple ODE such as
[tex] y'' + 16y = e^{3x} [/tex]
I can see why the particular solution would take the form
[tex] y_p = Ae^{3x} [/tex]
You'd then differentiate as needed, plug in, and solve for the coefficients. This way of thinking has been recurring throughout the course so it doesn't feel foreign. However, in the later exercises, I'm having problems.
Consider the ODE
[tex] y^{(3)} - y = e^x + 7 [/tex]
If I just look at the RHS and think of what'll annihilate it, let D be the differential operator, then D(D-1) looks like it'll do the job. This means that the particular solution would look like the form:
[tex] y_p = c_1 + c_2e^x [/tex]
But if I were to differentiate that three times and plug it into the ODE, it wouldn't give me a nice result.
I noticed that the problems I've been struggling with have something in common though.
The LHS of the ODE is annihilated by (D-1)(D2 + D + 1). So (D-1) is a common annihilator of both sides of the equation and I suspect this has to do with what's throwing me off.
Could someone please shed some light on what's the algorithm for these types of situations?
In my ODE class I've been using the annihilator approach to solve homogenous DEs. We moved on to solving nonhomogenous ODEs a while ago and covered undetermined coefficients and variation of parameters, but I had to miss the lecture on undetermined coefficients and there's something I missed which is messing me up.
I understand that if I have a simple ODE such as
[tex] y'' + 16y = e^{3x} [/tex]
I can see why the particular solution would take the form
[tex] y_p = Ae^{3x} [/tex]
You'd then differentiate as needed, plug in, and solve for the coefficients. This way of thinking has been recurring throughout the course so it doesn't feel foreign. However, in the later exercises, I'm having problems.
Consider the ODE
[tex] y^{(3)} - y = e^x + 7 [/tex]
If I just look at the RHS and think of what'll annihilate it, let D be the differential operator, then D(D-1) looks like it'll do the job. This means that the particular solution would look like the form:
[tex] y_p = c_1 + c_2e^x [/tex]
But if I were to differentiate that three times and plug it into the ODE, it wouldn't give me a nice result.
I noticed that the problems I've been struggling with have something in common though.
The LHS of the ODE is annihilated by (D-1)(D2 + D + 1). So (D-1) is a common annihilator of both sides of the equation and I suspect this has to do with what's throwing me off.
Could someone please shed some light on what's the algorithm for these types of situations?
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