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if you can help me i'll love you forever .. i'm so stuck
i think that all you do is find x=x(t) and y=y(t) for each but i dont know how!
do you think you can help me :(
It's simple without the last term xy, so I'm thinking!
ok thank you .. i'm thinking that you solve and just keep one as a constant? i'm not sure.
like the variable that your not solving for of course
this assignemnt is due tm morning and if i dont do it i'm soo screwed but I'm seriously so confused!
Is it familiar, as your lecture?
not relaly to be honest
Do you have any link for similar problem?
one sec... http://www.mast.queensu.ca/~math232/2012slides/slides2012-16/page02.jpg http://www.mast.queensu.ca/~math232/2012slides/slides2012-16/page03.jpg http://www.mast.queensu.ca/~math232/2012slides/slides2012-16/page04.jpg http://www.mast.queensu.ca/~math232/2012slides/slides2012-16/page05.jpg
i'm trying to figure it out using those .. did you get those links? it said i lost connection
I did, my PC fluctuate all the time. I'm reading!
ok, its like a combination of both it seems .. i'm not sure if i know what i'm doing..
do you understand it at all?
Nope! I'm getting help from other, see if it works (sighs)
i just dont understand becuase its mixing the 2 ideas .. so i dont know if i'm supposed to try and combine it or, .. i suck
2x(1 − x/3) − xy = 0 −2y + 3xy = 0 -> y ( -2 + 3x) = 0 => y = 0, x = 2/3
Look like we solving system of equation by substitution:
Replace y = 0 and x = 2/3 into (1)
is that what were supposed to do? or are we only supposed to sub y=0 into the other one since in that equation were not solving for x at all?
we have y = 0 and x = 2/3 to plug into: 2x(1 − x/3) − xy = 0 (1)
You figure it out?
yes i did! thank you!
y = 0 --> x = 0, x = 3
2 intersection points ( 0, 0 ) and ( 3, 0)
With x = 2/3 --> y = 14/9
point ( 2/3, 14/9)
So we have 3 solutions !
Do you think we're fine here?
how did you get (3,0) ? ok .. but since in each case your solving for one variable, you cant sub in both an x and a y into the first equation can you? like doesn't that not make sense?
Of course :P One at the time x = 2/3 or y = 0
So the whole concept is find intersection points
but if its a dx/dt and then a dy/dt can we do that? ahhh ok ok!
factor x, y out, then set = 0 --> x, y value from one equation.
use it value to substitude into the other equation.
ah ok ok!
ahah yes1 thank you!!!
Finally ( relieve sighs)
ahah sorry i was such a pain in the retrice
You need to organize your notes
Good thing is you have it to show me, so I figure out the whole idea is find intersection points
Otherwise I don't even know what you want me to do !
ahah i know i know .. i'm slacking a bit i'll admit, but totally appreciate you helping me .. want to help me with one more thing :) ? LAST thing i promise!
I'm really exhausted today!
Just post up to see if others better!
PLEASE :) its just a little one From the differential equations determine (for x > 0, y > 0) where x and y are decreasing and where they are increasing.
or if you even tell me how ..
Then I need some sample as you did show me!
its just for the DE above, the first ones we were working with!
dx/dt= 2x(1 − x/3) − xy
Now what to do?
i'm not sure how to find where its increasing and decreasing
Let me search internet, look like need second direvative
hhah awe, no dont worry about it! i'lll just leave it blank! go to sleep!
It says, all we'll do is plug it the other value around (0,0) and (3,0) to get the signs
suppose (1,0) or ( 0,1)
wish i understood this stuff, ok i'm just going to make something up.
It's not difficult, just plug value around max,min.
so its increasing if dy/dt<0 ? and decreasing if dx/dt<0?
really! wow, i just guessed.
You got it, At (1,0) , equation = 4/3 >0 => decreasing!
awesome! thanks so much for all your help! i really appreciate it! would have died without ya! :)
I did hear it from a guy today, I'm proud that I save couple of lives daily :P
What time from your area now?
its 12:33 am
Oh same here!
ahah then get some rest :) night!!
What grade are you?