Advanced Math Question

[teutonicman]

I am currently working on the particular solution for 2cos(2t) + 4sin(2t) using undetermined coefficients method. I know that for sin or cos the general yp(particular solution) form is (A)cos(2t) + (B)sin(2t). But what would happed when both are given? Would it be (A)cos(2t) + (B)sin(2t) + (C)cos(2t) + (D)sin(2t)?

 

[Lukeje]

What do you mean by `solution'? Do you mean 2cos(2t) + 4sin(2t) = 0 (i.e. the roots of the equation) or something else?

 

[Hashime]

This is on my exam in monday, I should know it but do not. I would model it using a linear system, but I think I am missing the point. My roommate is in more advanced math so I will ask him.

 

[The_root_of_all_evil]

Won't you need a homogeneous term in there somewhere?

Edit: Sorry, non-homogeneous.

 

[Hashime]

If it is under-determined there should be an infinite number of solutions according to my understanding.

 

[Fetzenfisch]

wow OP's avatar just depicts what happens to 90% of the people reading his post

 

[teutonicman]

What do you mean by `solution'? Do you mean 2cos(2t) + 4sin(2t) = 0 (i.e. the roots of the equation) or something else?

I solved for the roots already, thus giving me my general eqn. Now I need the particular solution.

 

[SenseOfTumour]

I was all ready to say 'Look, 0.999 recurring is as close to 1 as you can get so it just doesn't matter!'

Then you actually have a question that's not the usual math trolling

Sorry I can't be of any help, We never dealt with all the sine and cosine stuff at my school.

However, just to add some discussion, tho of course, please help the guy above out too, if you can...

Say you're still at school and you answer math problems correctly, but not using the systems they gave you, should you be corrected?

For instance, if I was given say, 24x49, with no calculator, in my head I'd halve 24 and double 49 first, 12x98, that's now close to a 100 and easy, so it's 1200 - (12x2) 1176.

Of course I was taught to do 24x9, then 24x40 then add them together and I can do that, but it seems like a hassle when you can just round up or down to simple sums then adjust a bit either way.

I always felt like I was being punished for having found a short cut.

I'm still used as a calculator when I'm out with friends, if they want to know if something's a good offer when its 20% extra free and on 3 for the price of 2 and they want to know if that's better than the buy one get one free packs, or when we're splitting bills at the restaurant. (Tho gawd, I hate it when people start pissing about with coins after a meal, stop being tight and put a note in, tho tipping is of course for another thread).

 

[teutonicman]

wow OP's avatar just depicts what happens to 90% of the people reading his post

That.... yeah... I was a little disappointed. Luckily I have buddies to call for help.

 

[Aphobis]

Are you solving a differential equation, or is this this just a trigonometry problem? If it's a D.E. then I think your problem is having a general solution of similar form to your particular solution (N.B. if you have a D.E. of the form f(y'', y', y)=f(x), the general solution is when you set your f(x) equal to zero and solve the D.E., particular solution is when you incorporate f(x) and solve it, this only work if you you have a linear D.E. though), try A*t*cos(2t) as your particular solution.

 

[teutonicman]

Are you solving a differential equation, or is this this just a trigonometry problem? If it's a D.E. then I think your problem is having a general solution of similar form to your particular solution (N.B. if you have a D.E. of the form f(y'', y', y)=f(x), the general solution is when you set your f(x) equal to zero and solve the D.E., particular solution is when you incorporate f(x) and solve it, this only work if you you have a linear D.E. though), try A*t*cos(2t) as your particular solution.

That is exactly what I'm supposed to do(just talked to a buddy). Anyway thanks for posting a helpful answer.

Edit: No it's not a trig problem, it's part of a driven motion spring question.

 

[Aphobis]

No problem dude, maths can be a pain, but it is awesomely useful

 

[teutonicman]

This is on my exam in monday, I should know it but do not. I would model it using a linear system, but I think I am missing the point. My roommate is in more advanced math so I will ask him.

I have the final for this class on the same day as well.... and I see you're from Canada. What school do you go to?

 

[rokkolpo]

*crying*
Error error error error error.

Yeah i hate math.

 

[Hashime]

This is on my exam in monday, I should know it but do not. I would model it using a linear system, but I think I am missing the point. My roommate is in more advanced math so I will ask him.

I have the final for this class on the same day as well.... and I see you're from Canada. What school do you go to?

Waterloo.

 

[Ashcrexl]

well surely you must have solved it by now (or failed) so i leave you with my favorite advanced math equation.

 

[Nouw]

wow OP's avatar just depicts what happens to 90% of the people reading his post

I laughed.

Sorry but I'm nowhere near as advanced as your kind of math BUT! I asked my friend and he says to logically think about it as it doesn't seem that hard. He has no idea what you're on about also.

 

[smithy_2045]

DEs + Trig = fml.

Are you solving a differential equation, or is this this just a trigonometry problem? If it's a D.E. then I think your problem is having a general solution of similar form to your particular solution (N.B. if you have a D.E. of the form f(y'', y', y)=f(x), the general solution is when you set your f(x) equal to zero and solve the D.E., particular solution is when you incorporate f(x) and solve it, this only work if you you have a linear D.E. though), try A*t*cos(2t) as your particular solution.

But that sounds about right.

 

[SimuLord]

Ugh.

Sines, sines, everywhere sines, blockin' out the scenery, breakin' my mind.