Need Help @ Math

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27. December 2010 - 1:06
[MR.]KAKTUS
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Hey guys. im preparing to pre-exam atm, and need your fast help with math (differential equations). Have kind of theory task.

y'=sin(x)-tg(y). I need to prove that it has only 1 periodical solution in 'line' y in (-pi/2 ; pi/2).

If any1 can anyhow help me - contact me : or post here Big grin

Help is actual nearest 6 hours Big grin

2 beer or not 2 beer

ASSCARI * DSS wrote:
Kaktus has beer instead of brain, so better dont wait for him Tongue

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27. December 2010 - 1:20
#1
CSM> >HOLLOW
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Re: Need Help @ Math

LoL confused as hell... good luck with your exams Happy

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27. December 2010 - 4:31
#2
Matt
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Re: Need Help @ Math

matt + much beer = matt drunk²

good luck with ur math thing i am to drunk to answer u right..... ehhhmmm i mean i cant solve that question... ffs.... i cant do anything xD

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27. December 2010 - 10:45
#3
oldskool'shox
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Re: Need Help @ Math

where is abarth when you need him? he is a math-genius, try to contact him Winking

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27. December 2010 - 14:13
#4
|AbarTh|
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Re: Need Help @ Math

I'm not a math-genius, I even dont remember how do you know I love math Tongue But I just love, that doesnt matter I know it perfectly. But dont worry, 6 hours is long, I will try to solve it. Happy

EDIT: Ehh, didnt know I forgot almost everything from math. Sorry, can't do it. I would have to dig whole math from the start to do that task. Math is my hobby but I have not learned it from like 2 years. One day I'm gonna start learning just for myself. Happy
So for now... I'm sorry.

Nothing is impossible

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27. December 2010 - 14:35
#5
epsiplayer
THE ONE AND ONLY
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Re: Need Help @ Math

i'm sorry i failed too.. and i forgot many stuffs since 4 years ago..

i hope you asked this question on yahoo answers also .. cause there are some math freaks and might help ya.

answers.yahoo.com

cheers

Edit: what i saw lately was that:
the same equation can be writen as this:

y'=sin(x)-tg(y)

dy
__ = sin(x)-tg(y)
dx

dy
__ = sin(x)- (sin(y) / cos(y))
dx

i made the notation f(k) = sin(k)
=>

dy
__ = f(x) - ( f(y) / f(pi/2-y) )
dx

because cos(y) = sin(pi/2 - y)

this is the only way i can think of for having pi/2 in your equation .. i don't see other ways , yet xD

and after this you should try to use Fourier series with even and odds .. cause sin(x) is a odd function while cos(x) is an even function ...

even function means f(-t) = f(t)

hope this might help Happy
_________
epsislow


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27. December 2010 - 15:50
#6
APOLLO
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Re: Need Help @ Math

This can help, maybe!?!?

Trigonometric identities:

sin 2x + cos 2x = 1

1 + tg 2x = sec 2x

1 + cotang 2x = csc 2x

tan x = sin x - csc x = 1
cos x sin x

sec x = 1 - cotang x = 1 = cos x
cos x tan x sin x

sin (x ± y) = sin x · cos y ± cos x · sin y

cos (x ± y) = cos x · cos y + sin y sin x ·

tg (x + (-) y) = tan x + (-) tan and
1 - (+) x · tg and tg

sin (2x) = 2sin x · cos x

cos (2x) = cos ² x - sin ² x tan (2x) = 2TG x / 1 - tan ² x

sin (x) = ± (root) 1 - cos x
2 2
cos (x) = ± 1 + cos x
2 2
tg (x) = ± (root) 1 - cos x
2 1 + cos x
sin x + sin y = 2sin (x + y / 2) · cos (x - y / 2)

sin x - sin y = 2 cos (x + y / 2) · sin (x - y / 2)

cos x + cos y = 2cos (x + y / 2) · cos (x - y / 2)

c os x - cos y =-2sin (x + y / 2) · sin (x - y / 2)

Grade

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we grow old because we stop playing.
Never Be The First To Get Old!! Happy

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I have my own opinion & I insist.
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27. December 2010 - 16:34
#7
[MR.]KAKTUS
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Re: Need Help @ Math

Thx for trying to help Tongue With tips of teacher I passed this Tongue

Topic can be locked)

Gratz kakatus

2 beer or not 2 beer

ASSCARI * DSS wrote:
Kaktus has beer instead of brain, so better dont wait for him Tongue

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27. December 2010 - 17:53
#8
[MR.]MIRCWAR
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Re: Need Help @ Math

http://www.excessiveplus.net/forums/thread/math-help-needed

Your russian tovarich OMS seems to be online, just for future reference. GL.

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