Rick Dalliessi 1:16 am
Harrison
If you have time tonight, can you please give me a bit of help.
It's the last undone question on my derivatives assignment.
Harrison Wang 1:16 am
if it's not something stupid
Rick Dalliessi 1:17 am
1(b)(iv)
Harrison Wang 1:17 am
the hell are you referring to
the same assignment?
Rick Dalliessi 1:17 am
Yes.
Harrison Wang 1:17 am
jesus how did you not finish that yet
Rick Dalliessi 1:17 am
I haven't been working on it.
Everything else has been done since before the weekend.
Harrison Wang 1:18 am
you're still on number 1?
Rick Dalliessi 1:18 am
No...
I've done EVERY question but 1(b)(iv)
Rick Dalliessi 1:18 am
I haven't done them in order, clearly.
Harrison Wang 1:18 am
using technology, draw an accurate graph of f(x)=x^(1/3)
find the derivative
f'(x)=(1/3)*x^(-2/3)=1/(3x^(2/3))
from your graph, given an explanation of why the derivative is not defined at x=0
f'(0) is a singularity
you end up with 1/0
Rick Dalliessi 1:20 am
Yes
I know all that.
Harrison Wang 1:20 am
so the slope is infinite there.
aka vertical slope
Rick Dalliessi 1:20 am
I'm just not able to prove it with the formal definition of the derivative setting x to 0
Harrison Wang 1:20 am
therefore it is an inflection point
well
i just told you the reason
>_>"
Rick Dalliessi 1:21 am
No no not that.
They want me to go through the whole f(x+h) - f(x) / h
Harrison Wang 1:21 am
no they don't.
Rick Dalliessi 1:21 am
With x as 0
Harrison Wang 1:21 am
where the hell did you get that
Rick Dalliessi 1:21 am
From question 1(a)
Harrison Wang 1:22 am
......
oh my god.
Rick Dalliessi 1:22 am
That's what he said he wanted.
Harrison Wang 1:22 am
okay well
if you have to do that
Harrison Wang 1:22 am
lim [f(x+h)-f(x)]/h as h->0
[(x+h)^(1/3)-x^(1/3)]/h
Rick Dalliessi 1:23 am
And that's where I got stuck.
Harrison Wang 1:23 am
hold on
Rick Dalliessi 1:23 am
He's only every given us ones where we can expand.
Harrison Wang 1:23 am
well...
lemme think of a trick.
Rick Dalliessi 1:24 am
Ok
Harrison Wang 1:25 am
okay
we're going to cube the whole thing.
[ [(x+h)^(1/3)-x^(1/3)]/h ]^3
[(x+h)^(1/3)-x^(1/3)]^3
[(x+h) - 3(x+h)^(2/3) *x^(1/3) + 3(x+h)^(1/3) *x^(2/3) -x] /h
Harrison Wang 1:27 am
ugh
i'm going to do this on a paper
this is stupid
Rick Dalliessi 1:27 am
Can it even be done...
Harrison Wang 1:27 am
yes
obviously it can be done
Rick Dalliessi 1:27 am
I don't even see the usefulness in this.
Rick Dalliessi 1:29 am
I wish there was a programme that you can easily write math on.
That way I wouldn't have to slowly copy this all out by hand.
Harrison Wang 1:29 am
use latex editor
Rick Dalliessi 1:29 am
I will look this up.
By the way, Wolfram Alpha can't even graph x^(1/3) properly.
Harrison Wang 1:35 am
yes it can...
Rick Dalliessi 1:35 am
It's plotting it all funny.
Harrison Wang 1:35 am
oh
Rick Dalliessi 1:39 am
None of the online graphers seem to recognise the negative sides of the functions.
Harrison Wang 1:42 am
okay looks like expanding it failed.
Rick Dalliessi 1:43 am
Yeah...
And the question is only worth 2 marks.
The other was worth 5.
Harrison Wang 1:43 am
there's another trick though
we could multiply top and bottom by (x+h)^(3)+x^(3)
Rick Dalliessi 1:44 am
Remember it says to do it setting x to 0.
Harrison Wang 1:44 am
OH
let's multiply top and bottom by (x+h)^(2/3)+x^(2/3)
Rick Dalliessi 1:45 am
While that would work, why would a question requiring this effort only be worth two marks...
But I don't see what else he wants done here.
Harrison Wang 1:46 am
(a+b)(a-b)=a^2-b^2
Rick Dalliessi 1:46 am
I know?
Rick Dalliessi 1:50 am
I think I'll draw the graphs instead of using technology.
It seems like it'll be easier.
Harrison Wang 1:57 am
i think i solved it
Rick Dalliessi 1:58 am
Cool
Rick Dalliessi (RickDalliessi) is idle 2:08 am
Harrison Wang 2:14 am
oh pineappleing peach
Rick Dalliessi (RickDalliessi) is available 2:14 am
Rick Dalliessi 2:14 am
?
Harrison Wang 2:14 am
i tried multiplying by something else and it worked.
>_>
Rick Dalliessi 2:14 am
=S
Harrison Wang 2:19 am
i'm never doing that pomegranate again.
Rick Dalliessi 2:20 am
If it took that much work, it can't be what he wants us to do. So what the hell DOES he want >.>
Harrison Wang 2:20 am
it wasn't "a lot of work"
it was just tricky
really tricky
Rick Dalliessi 2:21 am
Thank you, Harry.
Transfer complete: Problem 1b4.jpg 2:22 am
Rick Dalliessi 2:23 am
Wow
The hell...
Harrison Wang 2:24 am
look at the "identity" up top
(a-b)(a^2+ab+b^2) = a^3 - b^3
Harrison Wang 2:24 am
that's one of the things i learned a long time ago but never used...
i learned it with (a+b)(a-b)=a^2-b^2
Rick Dalliessi 2:24 am
He wanted us to do it with x = 0, remember.
Harrison Wang 2:24 am
doesn't matter
once you reach the end
you'll get h/(that whole garbage)
h/h cancels out
so you're left with 1/(that whole garbage)
it simplifies to 1/(3x^(2/3))
then you can say if you plug in 0 you get a singularity
implying an infinite slope.
you can do the rest without my aid.
Rick Dalliessi 2:26 am
Maybe...
I'll copy out the rest for now.
Harrison Wang 2:27 am
well
i obviously didn't simplify it to the end
you can do that yourself
Rick Dalliessi (RickDalliessi) is available 5:29 pm
Rick Dalliessi 1:17 am
Hi Harry.
By the way, today my lecturer showed how that question should be done.
And it's different to what you did.
Harrison Wang 1:18 am
what did he do?
just talk it out and i'll try to see if i understand you
if not then type it out
Rick Dalliessi 1:18 am
Setting x to 0 it went like this
((0+h)^1/3 - 0)/h
h^1/3 / h
1/h^(2/3)
Take the limit
Harrison Wang 1:19 am
as?
h approaches 0?
Rick Dalliessi 1:19 am
h -> 0
Harrison Wang 1:20 am
the limit is infinite.
Rick Dalliessi 1:20 am
Yeah.
That was the point.
Harrison Wang 1:20 am
doesn't matter though
my way was more general
Rick Dalliessi 1:20 am
Yes.
Harrison Wang 1:20 am
after finding the derivative
you can plug in any point and find the limit
why restrict yourself to x=0?
Rick Dalliessi 1:21 am
'Cause that's where the asymptote was.
Well, the singularity, as you say.
Harrison Wang 1:22 am
it's not an asymptote
-_-
an asymptote is a second function that a first function approaches as the the first function approaches infinity
not 0
...
f(x)=x+1/x approaches x as x approaches infinity
therefore, x is an asymptote
f(x) approaches infinity as x approaches 0
however, 0 is not an asymptote
it's a singularity
you might call it the vertical line x=0
Harrison Wang 1:24 am
but it's still not an asymptote
and that's because f(x) doesn't truly exist
you only spanned it out on a coordinate axis to view the behavior of the function
but it's fictitious
Rick Dalliessi 1:25 am
Either way, that's how he wanted it done.
It does seem much simpler.
But less general.
Harrison Wang 1:25 am
not by much and you can't use it whenever the hell you want to
did he mark you wrong?
Rick Dalliessi 1:26 am
No I asked him before the assignment was due.
Then handed in the assignment with that in it.
Harrison Wang 1:26 am
and then you discarded my answer, therefore wasting an hour of my time
Rick Dalliessi 1:26 am
What else was I supposed to do? Lose the marks?
Harrison Wang 1:26 am
you dumbass
if the answer is correct, it is correct
i thought i pineappleing told you that there was no single "correct answer"
= =
i'm never helping you again
pineappleing never again
i don't give a damn how much you need it
Rick Dalliessi 1:27 am
I don't quite think you understand the concept of you write what he wants.
Harrison Wang 1:27 am
you're an pimento
you don't need to "write what he wants"
you write what IS CORRECT
Rick Dalliessi 1:27 am
Yes you do...
Harrison Wang 1:27 am
ugh
ughhh
why are you pineappleing stupid
Rick Dalliessi 1:28 am
The two answers are different.
Harrison Wang 1:29 am
so?
does that make my answer wrong?
do you think your teacher is honestly so stupid that he can't think for himself?
Rick Dalliessi 1:29 am
He doesn't mark them.
The tutors do.
Harrison Wang 1:29 am
-_-
if asked you what 1+3+4 is
you can simplify it as 4+4=8
or you can do 1+7=8
does that make either one any more wrong?
Rick Dalliessi 1:30 am
The tutors are marking over 100 assignments. They have an answer key.
If it differs that much, what do you think they're going to do?
Harrison Wang 1:31 am
dude
tutors don't even use answer keys half the time
do you honestly think that 100 students are going to turn in identical assignments?
Rick Dalliessi 1:31 am
These tutors that I have
They're level 2 students.
They're not the highest quality >.>
Harrison Wang 1:31 am
just because they're level 2 students
doesn't mean they don't know what they're doing
and
if you have a problem you can bring it to your teacher
cuz your teacher ultimately determines your grade
not your tutor
Rick Dalliessi 1:31 am
By the way
Remember the person who told me about the discriminant in a cubic having a cube root
and you hated it
That was one of the tutors.
Harrison Wang 1:32 am
so?
your teacher decides your grade, not your tutor
Rick Dalliessi 1:32 am
They're not the biggest help, really.
Harrison Wang 1:32 am
obviously by ending up with the derivative of x^(1/3)
my solution was correct
your tutor can't mark you wrong for a correct solution
Rick Dalliessi 1:33 am
It's a big hassle to go through the appeal.
Harrison Wang 1:33 am
it's a big hassle talking to someone as stupid as you
you know what
you piss me off
go pineapple yourself
Rick Dalliessi 1:34 am
...
Harrison Wang 1:34 am
all you know how to do is copy
you're worthless
you should go back to music
at least you have pieces that good composers already written out to play
you obviously lack the ability to think for yourself
so why are you even in economics?
why are you even taking mathematics
it clearly requires too much ability
that a simpleton like you just can't grasp
Rick Dalliessi 1:35 am
Can you stop being so God damned unrealistic.
Harrison Wang 1:36 am
i don't even know why i wasted 45 bucks mailing you my calc book
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