can you help with my math homework?

[skisteven1]

I could use some serious help with this. Anybody want to step up? O

 

[bonkers325]

a problem statement would help

 

[chuckywang]

So what's the problem?

 

[QED]

Post the problem, and we'll do our best to help.

 

[JS80]

you better hope Loke doesn't see this thread. especially with your name and .edu email public

 

[JohnCU]

Originally posted by: MathMan
Post the problem, and we'll do our best to help.

 

[blueshoe]

Loke can help you

 

[zanieladie]

We'll all give it a shot...

The worst we can be is WRONG...lol.

 

[skisteven1]

I tried taking a picture of the problem -- but can't get it to come out clear with my phone, so i'll do my best:

"suppose that f is a function of period 2 such that f(t)=0 for -1<t<0 and f(t)=t for 0<t<1.

Show that: f(t) = 1/4 -2/(pi squared) SIGMA(of n odd)[cos(n pi t)/n^2] + 1/pi SIGMA(n=1 ->inf) [(-1)^(n+1)sin (n pi t)/ n]

.....which, believe it or not, is why I didn't type it the first time.

so the problem is, show that and sketch the graph of f. (The sketching i've got already)

b) Deduce the series summation in eq18 from the fourier series in part A

eq18 ===> SIGMA (n odd) 1/n^2=1+1/3^2+1/5^2....=pi^2/8

 

[skisteven1]

Originally posted by: JS80
you better hope Loke doesn't see this thread. especially with your name and .edu email public

I don't know who loke is, but i'm now kind of glad that I don't use that I didn't post my primary email.

 

[QED]

Originally posted by: JS80
you better hope Loke doesn't see this thread. especially with your name and .edu email public

I know you're probably trying to be funny... but in case you're not there is a world of difference between asking for help and offering to pay somebody $5 to do it for you.

 

[chuckywang]

Originally posted by: JS80
you better hope Loke doesn't see this thread. especially with your name and .edu email public

And is Loke good at math?

 

[QED]

Originally posted by: skisteven1

Originally posted by: JS80
you better hope Loke doesn't see this thread. especially with your name and .edu email public

I don't know who loke is, but i'm now kind of glad that I don't use that I didn't post my primary email.

No worries... Loke was a member here who ratted out a high school senior who made a post offering $5 for someone to actually do his math homework.

He got flamed to pieces for it, but some people here have a hard time dealing with academic intregity and distinguishing between asking for help and actually offering to pay someone else to do it.

 

[JohnCU]

so you're finding the fourier series of a sawtooth wave? do you know how to compute the coefficients and how to use them? aka do you have a book?

 

[skisteven1]

I have a book, and somewhat understand finding the coefficients of the series, but I'm not really sure where to start.

 

[JohnCU]

the fourier series representation of FS f = a0 + sigma(n=1->inf) an*cos(n*pi*x/L) + bn*sin(n*pi*x/L)

where a0 = 1/2L * int(f(x)dx) from -L to L
where an = 1/L* int(f(x)*cos(n*pi*x/L)dx) from - L to L
where bn = 1/L* int(f(x)*sin(n*pi*x/L)dx) from -L to L

i assume you can do these integrations, they just need integration by parts.

basically, what you're doing is taking a function, and making it repeat by adding up cosine and sines that have certain coefficients that make them look like a repeated version of the function you're trying to make periodic.. if you could add up an infinite number of them, you'd have a perfect representation. unfortunately, you cannot, so you may experience the Gibb's phenomenom at discontinuities.

 

[skisteven1]

Where does the Sigma of N for odd-n come from? Does that have to do with the even/odd'ness of the function? ...I don't think it should, but I'm not sure where it comes from.

 

[JohnCU]

i'm not sure, i think the oddness/eveness of a function only comes into play when talking about half-range or quarter-range expansions.

 

[QED]

Originally posted by: skisteven1
Where does the Sigma of N for odd-n come from? Does that have to do with the even/odd'ness of the function? ...I don't think it should, but I'm not sure where it comes from.

I think you will find when you do the Fourier Series expansion that the even terms will cancel out....

 

[skisteven1]

OK, i think i see that. I'm having a little trouble with the down and dirty algebra/basic calc though. I actually have this class in about 10 minutes, so I'll ask the prof and see if I can get any further.

thanks for the help!