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gosh i feel dumb...


not feeling too much like myself today, got some math homework covering things that we worked on last year and have just totally blanked on all of it.

it looks like a foreign language to me.

its not just math homework either. its every subject. i am looking at my homework as if it might as well be written in chinese.

i don't know what is up today, but i literally can not think at all.

i think im done with this homework, i'll just take the F and move on...

176 Comments


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inferiority

Posted

i don't really know, but i just can't concentrate on anything right now.

for the moment i have sort of stopped caring about getting my assignments done :P

Musicman

Posted

There's nothing bothering you more than usual? Nothing you want to talk about? Maybe through PM if not here? Or not at all? :P

Ehren

Posted

The same thing happens to me every once in a while. In my experience the best way to fix it is to get out of the house for a while and clear your head. Even just going to the store usually helps.

Although using pseud as a calculator works too :P

inferiority

Posted

sorry pseud, i don't think that that'll do me much good at the moment, i just can't figure out anything from any of my subjects, i must be preoccupied with something, but i just can't figure out what is gnawing at me right now.

im just feeling really down today, nothing bad has happened, but all my thoughts are like clouded over and concentrating is something of a wonder.

pseudome

Posted

well, sorry you are feeling so down. The offer still stands. I won't just do the homework for you either--I'll provide detailed explanations. I'm that bored...

inferiority

Posted

i would type out some of these math problems here, but i literally can not type out the symbols in the problems, but its good old limits with some funny greek letters or something in it.

pseudome

Posted

You can always substitute different letters.... you can just describe what the symbols look like. I'll figure it out...

inferiority

Posted

ok its given as lim x->2 (3x+2)

and another problem of lim x->2 (x^2 - 3)

directions:

find limit L. then find "upside down g symbol" > 0 such that |f(x) - L| < 0.01 whenever 0 < |x-c| < "upside down g symbol"

i can find the limit, but that's all i can do :o

pseudome

Posted

upside down g = delta...

working on it. (might get interrupted soon--still at work...:o)

pseudome

Posted

what's going on with the "c"?

Looks like you're basically finding how small a range you have to confine x to so that f(x) stays within .01 of the limit.

is c supposed to be 2?

pseudome

Posted

Yeah, yeah--c is 2, the thing x was approaching.

Ok, so the first one goes something like this:

You know already that lim x->2 of f(x) = 3x+2 = 8

so |f(x) - L| = |3x + 2 - 8| = |3x - 6|

So you need to find out what x has to be to satisfy:

|3x - 6| < 0.01

the absolute value is less than 0.01 as long as what's inside the absolute value bars lies between -0.01 and 0.01:

-0.01<3x-6<0.01

add 6 all the way through, then divide by 3 all the way through:

5.99/3 < x <6.01/3

x-c = x-2 so 5.99/3 - 2 < x - 2 < 6.01/3 -2

hence 0< |x -c| < delta-------> the delta is in this case .00333333333333..... (because that's what 6.01/3 - 2 is and what |5.99/3 - 2| is. Note that if those two yeilded different numbers, you'd take the smaller one.)

Does that make sense?

Musicman

Posted

Sorry I was gone for a while. Inf, why are you feeling so down today? Is it just the stress of everything adding up?

(Hey pseud)

pseudome

Posted

lim x->2 of f(x) = x^2 - 3 = 1

so |f(x) - L| = |x^2 - 3 - 1| = |x^2 - 4|

|x^2 - 4|<0.01 => -0.01< x^2 - 4 < 0.01

you need to solve for x. Add 4 all the way through:

3.99

sqrt all the way through, but note that x could be negative:

sqrt(3.99)< x < sqrt(4.01) or -sqrt(3.99)>x>-sqrt(4.01). I don't think the negative solutions actually matter.

now for |x-2| < delta, we need sqrt(3.99) - 2 < x - 2 < sqrt(4.01) - 2

which is something like -.00250.... < x-2 < .002498......

so you want to pick delta to be the smaller (in absolute value) of these. And you probably want an exact number, so leave it as delta = sqrt(4.01) - 2. Though any delta smaller than this also works...

Again, basically these questions are asking you how small you have to squish the x range down so that the f(x) stays within .01 of the limit as x approaches 2.

pseudome

Posted

hold on--I'll break it down in smaller steps for you. I realize that looks like a mess (I was trying to figure out what I was doing...).

give me a few minutes...

Musicman

Posted

hey mm i don't really know, could be i suppose

Would talking help, or do you just want to leave it alone and let it pass?

inferiority

Posted

i don't know mm, right now i really just feel like curling up in a ball and laying down, but that is not going to happen anytime soon


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