[Xarren]

Hey guys, bit stuck here. EDIT: And girls. Lets not be sexist here. Although we all know girls doing maths is like the cake.

d2y/dx2+4(dy/dx)+5y=65sin(2x)

This leads to

y=(A+Bx)e^(-2x) + sin2x - 8cos2x

"Show that for large values of x this general solution may be approximated by a sine function and find this sine function"

Now as x -> infinity e^(-2x) -> 0, hence the first part drops out.

We now have y=sin2x - 8cos2x

How do we go from there to sqrt(65)sin(2x-c) where tan(c) = 8 ?? (This is teh answer given in the back of the book)

I haven't a clue what they've done there.

Any ideas?

[TenOfThem]

What cake?

[Xarren]

(Original post by TenOfThem)
What cake?

Portal style cake.

The type of cake that's always a lie.

[Hopple]

Since you're dealing with 2x, see if you can match R*sin(2x+a) to sin2x - 8cos2x. Sometimes you might be asked for something in the form of R*cos(bx+a) but that's similar, just expand out and match.

[TenOfThem]

You use Rsin(2x+a)

[TenOfThem]

(Original post by Xarren)
Portal style cake.

The type of cake that's always a lie.

I will try to avoid answering any more questions from you then

[Xarren]

(Original post by TenOfThem)
I will try to avoid answering any more questions from you then

I'm only kidding, don't get your nuts in a twist. Oh, wait.. :P

And yeah - I completely forgot about that. C3 feels like another life ago.

I honestly don't know a single girl that does FM. Like in real life that is

[TenOfThem]

(Original post by Xarren)
I'm only kidding, don't get your nuts in a twist. Oh, wait.. :P

And yeah - I completely forgot about that. C3 feels like another life ago.

I honestly don't know a single girl that does FM. Like in real life that is

I teach it