Math Is Fun Forum

Are you sure k is supposed to be zero? Then the y' would be removed completely from the equation, how about 1? Then it wouldn't change anything in the equation.

I'm having some problems with understanding the problem, english is not my native language, but I guess the equation becomes (with k being zero):

Could we simply take F(t) = (1/2)cos(4t) above? If so, I could solve for y. I just want to make sure things gets right.

I'm also having major difficulties reading that. Nobody will take this seriously written this way, that's for sure.

Just a correction...

1) N = 7*(5^2 - 3^2) = 7*(25-9) = 7*16 = 112

Just search for pdf documents typically, they usually contains more serious and well documented topics for some reason, I've experienced.

Don't have time to read it all right now, but I downloaded so I can read later. Looks good

Hello Mads, nice to have you around

But if x=0 is a solution, the original question is invalid!

I'd be interested in hearing what you learnt

If you want to try solving your question with complex methods, use the fact that

If you have, for example, sin(7t), you simply put a 7 in the exponent of e^(ix).

Your question is the most simple example, cos(t), so I think you can follow it quite easily.

---

We know that

from above. Let

and

, so we get:

,

And so

Which means that

Thus, we must have that

since all derivatives disappear, which gives

So

Which becomes

Since

, this must mean that

I hope I didn't miss anything out.

Yeah, you can add them all together, you use the superposition principle (I think that's what it's called anyways). DE's are easy if you're being methodic, you rarely encounter higher grade DE's practically, I've been told.

For cosx and sinx I prefer using complex e-functions. Like cosx = Re[e^(ix)]. Try that method, it's really good imho, also if you have cos(7x) or similiar it works great.
I can give you a full solution to it later if you want, I got math exams tomorrow

I get the same homogenous answer, so lets see about the rest.

Let (z is a function, z(t))

, so

,

So we get

So

Let z=Ct+D, so z'=C and z''=0; then C must be 1, which gives z=t.

Whohoo, first time using these codes

Sony cybershot w50. It's small enough for my pocket, yet with an 2.5" LCD... until I learn all this code you guys use

^^ trying out my new camera