#help-17
1 messages · Page 107 of 1
Thanks. May I ask how long you’ve been in Uni? I’m kinda curious, cause you know a lot for an undergraduate
Interesting okay
but before the university i didn t do maths in the free time
Do you stick out among your peers or are most at your level?
That’s wild lol
they are almost like me ...but we are 20 or less... in the previous years we were 100 or more
Okay yeah, I would imagine most that are not as smart don’t continue for as long
yes i didnt have that hobby before the university ... in fact when i have time i try to do some contest math
How long have you been doing that for?
i would not talk about smartness ... i think its all about the passion that you feel when you do maths ...somebody doesn't feel that passion as i feel it
I do think those two strongly correlate though. Someone who has a hard time with math probably doesn’t feel as passionate about it
Where are you from btw?
i think i see some contest math 4 hours a month
because i have no time for that
Understandable
italy
yes but i promised to me that i ll be a math olympiad tutor for high school ..maybe after the phd
Your students would be very lucky
no
i didn't
are you doing math in uni ?
No I’m still in high school
I’m trying to learn the Uni stuff on the side though cause it’s a lot more interesting
what will you study in uni?
I don't want to sound annoying but this is still @old niche 's help channel 
Pssssst
I’m not sure yet. I think I’ll decide once I’ve seen some more stuff
ok ...if you study math i'll help you to learn some complex argument if you want (like ring theory, differential geometry, algebraic geometry ec ec)
Thank you
Do you like set theory? It’s the topic I’m most interested in at the moment
thanks but it is also an opportunity for me to explain that complex thing to you and "to me"
Ahhh got it yeah
so i think this could be a good project for both
Possibly, though I will admit that geometry is the one thing about math that I don’t like 😅
no sorry xD .... i think its very fundamental math (like logic) ... I want to study some complex construction
I think our interests are quite different then
you ll see what type of geometry it is ..is not about euclidian or cartesian geometry
when i start to studing math (4 years ago) i try to interst me to everything ...so at the start i studied set theory by my own ...and my interst changed with time
and more skilled you are more you can jump through different fields
Yeah, I probably like set theory cause it’s so new to me. Different stages different interests
What do you want to do with your phd in the future?
i want to remain in the academia
So teach the things you learned to others?
do research
yes absolutely
That sounds very cool
this is very exiting for me
Yeah it’s a lot of fun
But you need to be very good at it if you want to make a living with it
But I think that shouldn’t be any problem for you
because years ago it seems imposible that a guy could prove thing...now it is possible every time more
i hope so ... i will do my best
Yeah it’s interesting to see how we learn to get better at proving things
The connections we form in our brain every time we see or create a proof
That allow us to see patterns in problems that let us prove them so much faster
now its late for me ... i enjoy chat with you ..goodnight
Good night!
🙂
@old niche are there still any open questions?
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ok
need more info
ok
best you could do here is isolate a
which will give you an expression for it in terms of b
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does dividing by 2 continous functions
Please don't occupy multiple help channels.
yea
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Can someone help with this question?
<@&286206848099549185>
@hollow prairie Has your question been resolved?
<@&286206848099549185>
Whats your base case
@hollow prairie Has your question been resolved?
I’ll send a pic of what I did
I’m confused. Wdym?
N=28 to n=32 are the base cases
Induction step comes after the base case
Which your induction step is the paragraph you wrote
I decided to follow her since she would be the expert, and most examples were done in the lecture
I mean, it doesnt change the argument, so it makes no difference
What exactly do you need help with here?
Oh I was stuck at the beginning, but now I wanted to verify if I did it correctly
It looks good
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,calc 5sqrt(14) 4sqrt(21)
Result:
342.92856398964
,calc 5sqrt(14) 4sqrt(21)/sqrt(3)
Result:
197.98989873223
Wat
The 2 disappeared somewhere in the third line
You made a mistake
Oh
That’s the only mistake you made
,calc 5sqrt(14) 4sqrt(21)/sqrt(6)
Result:
140
Yes
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✅
You can still simplify sqrt(28) even more
But it’s right
Wat
the assumption is that a is positive, if it’s the same as the other questions they’ve been posting
This should be the answer
ahhh ok sorry didn't have that context 
then yes all squared away captain 
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part b)
im not sure how i would approach this
for my equation of dy/dx i have (y-x^2)/(y^2-x)
in desmos the graph will look like this
how to find the points
yes
so first
how to find the point where tangent lines are horizontal
do you know implicit differentiation
Incidentally this is the name of the shape https://en.wikipedia.org/wiki/Folium_of_Descartes
i did implicit differentiation to get the equation i wrote out
dy/dx = (y-x^2)/(y^2-x)
yes
now if the tangent lines are horizontal it means the slope is zero at that point
the slope is just dy/dx right
correct
how would you justify getting to y=x^2
because for the tangent line to be horizontal, dy/dx is zero
since the slope can't be undefined we can ignore the denominator?
we can ignore it as long as x is not equal to y^2
since the denominator doesnt become zero for all other cases except that
the slope can be undefined, better to say infinity which gives a vertical tangent line but that is not what we want right
correct
but what we need is the slope to be zero
for a horizontal one
solving for dy/dx= 0 we get the relation y=x^2
hmm ok
see the graph intersects y=x^2 at a point
if you can imagine a tangent there, it will be horizontal
see in the origin
if we zoom in
theres a vertical and horizontal line
in terms of y=x^2 would it be correct to say that the horizontal tanget when x=2 y=4
so the horizontal tangent would be at (2,4)
how did you get x=2 y = 4
we need to solve x^3+y^3-3xy=0 and y=x^2
so we get a point right
that is the point of intersection of the blue graph and red graph
y=x^2 has many points and x^3+y^3-3xy has many but we need a point which satisfies both the equations
which means it lies on both of them
yes
I SUB IN X^2 FOR Y IN THE ORIGINAL EQUATION
yeah
YOU'RE A PSYCHO
will you be able to solve it?
i dont think they asked you for the point right?
okay
also for the second part
at (0,0)
theres two lines right
so we get two slopes
one 0 and one infinity
but we cannot define ONE and only one slope there
so since dy/dx gives one slope at a point
we cannot say dy/dx is zero or infinity
because theres two slopes the idea of dy/dx is wrong
so it does not exist
if you want a mathematical proof you can put x = 0 and y = 0 in the expression for dy/dx and you will get zero divided by zero
which is indeterminate or not defined
@north hamlet
i have 0=-4x^3 + x^6
after subbing in y=x^2
but now i dont know what to do
yes
so we get
x^3(-4+x^3)
wait you did a mistake
the original equation is x^3 +y^3-3xy=0
we put y=x^2
x^3 + (x^2)^3 -3x(x^2)=0
yes
yes
ouhh
x^3 - 3x^3 is -2x^3
mb i wrote -4
yeah
so now
x^3 ( x^3- 2) = 0
we get x=0 and x= cube root of 2
now
it is partially right since at (0,0) there is a horizontal line so at x=0 we have a horizontal tangent line
and also the other point is x = cube root 2
the green line is tangent at x = cube root 2
and since we know y = x^2 we can find y as we know x
yes
so y = (3rdroot(2))^2
would i have to smplify that
if you want to then we gotta use a calculator
ewwww
im pretty sure i dont need the equation of the tangent right
sure
its easy
so we need the equation of a horizontal line
that means the y coordinate is same right? at all points on the line
visualise it
yes
yes so
we got the point
the general equation of a horizontal line is y = k
as k varies the line shifts up and down but remains horizontal
here k is the y coordinate of any point on the line
here we got the y as (cube root 2)^2
which is about 1.59
so the equation will be y = 1.59
thank you so much
yeah no problem
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I think my brain just blew a fuse..
what?
This is my question. I think that the answer may be Θ(logϕ
n) ,but I'm not sure.
lemme read
Ok, Thank you
I think so
I've been using Chegg and Numerade to get some help with Algorithms.. Are there any other sites that you'd recommend for help.
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!15mins
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can you give a more clear picture?
how comfortable are you with elementary matrices
also can you take a proper pic of the elementary row operations
Hii
I think you did it?
Pretty comfortable
is that all? nothing else is missing?
This is what i got?
,rccw
yh but those are the operations, they want the elementary matrices that we will multiply to perfom those operations
for example if we wanted to R3 -> 3R1 + R2 subtract 3 times the first row you would have something like
$$\begin{pmatrix}
1 & 0 & 0\
-3 & 1 & 0\
0 & 0 & 1\
\end{pmatrix}$$
have you seen these before?
Owh
I don't think so 😬
best to look up a tutorial on them first
Wait what does an Elementary matrix mean
see the way you did R2-> R2-R1 up here, you can get multiply by an elementary matrix to get that
not a definition ik
@errant peak https://www.youtube.com/watch?v=QVKj3LADCnA&
MIT 18.06 Linear Algebra, Spring 2005
Instructor: Gilbert Strang
View the complete course: http://ocw.mit.edu/18-06S05
YouTube Playlist: https://www.youtube.com/playlist?list=PLE7DDD91010BC51F8
- Elimination with Matrices.
License: Creative Commons BY-NC-SA
More information at https://ocw.mit.edu/terms
More courses at https://ocw.mit.edu
this is how i got introduced
Oh so instead of the row operation we multiply by a matrix?
you can probably find a shorter vid idk but best to be comfortable with them first
Ok sure lemme go through this then
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how many integer values of x exist such that $\frac{(x^3 - 4x^2 + 3x + 16)}{(x-16) }$is an integer
AgentSpiely
i dont know if it is the most optimal method, but you can do polynomial division
Yeah I did exactly that
then write it in the form Q(x) + R(x)/(x-16)
Q(x) being your quotient
R(x) being your remainder
Q(x) obviously is always an integer for x integers
so you have to verify when R(x)/(x-16) is an integer
Indeed!
So I think my answer is partially right
i think for the R(x)/(x-16) you just have to check all the numbers taht divide R(x)?
,w factors of 3136
oh i guess thats it lol
i think you can work out the rest from this on your own
So there are ||21|| values of x right
i was thinking ||256|| lol
How you got there?
Or wait maybe its ||42 because you have negative values too||
Yes its ||42 || I think
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I'm not even sure of where to begin, please help!
@gloomy fulcrum Has your question been resolved?
#real-complex-analysis probably better
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surely someone can help
@forest maple Has your question been resolved?
No square number ends on 2.
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I'm converting series to sigma notation
I have the N already but I forgot how to get the constant
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I need help with this question

@graceful nimbus Has your question been resolved?
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!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
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May I plz have some help
I need to put the equations above into a a matrix
the matrix should follow Az=b
I understand what z should be but not A
so if i could have help constructing A that would be appreciated
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hmm
Could I get a hint on how to do this?
It is probably really obvious, but I can't quite understand. $$\frac{e^{iz}}{e^{z} + e^{-z}}$$
Konglekongen
thats the integral im supposed to calculate, from real x -infinity to infinity
then the real part of the e^iz will be our answer.
How did you get this, may I ask?
I would think so 
uh, if you use that identity then you need to somehow get rid of that isin(x)
$$\cos x = \dfrac {e^{i x} + e^{-i x} } 2$$
_Kookie
Anyways, assuming the way they'd want you to do it is through CRT
(for which it may be easier to remember that $\cosh(iz) = \cos(z)$)
@dull bear
Well you have that you're integrating $\frac{\cos(z)}{\cosh(z)}$ basically, if that reminds you of anything...
@dull bear
If they've given you anything for fractions of that form
Might be called that
it’s something like if f(z)/g(z) is such that g(z0)=0 and g’(z0) isn’t zero, then the residue of that at z0 is(…)
Yep yep 
So, then we can get the integral of the rectangle, using residue theorem, computing the residues where cosh(z) is zero, using the expression above.
Then, hmm.
Usually they show that the sides of the rectangle go to zero, or something like that.
And that the top and the bottom are equal.
I don't understand how to do that here.
hmmm
cosh(z) will be really big when the real part goes to infinity, right?
so maybe the sides do go to zero
And maybe e^z, the integral of the top of the rectangle will be -1 * the integral of the bottom, because e^i pi is -1
actually, that doesn't make any sense, then the entire integral would be zero
let me try it out, I'm thinking it's probably that the other three sides other than the real axis one will go to zero (that's usually how it goes!)
I do
for sure
At least for the side between $R$ and $R + i \pi$, you could parameterise out that line segment, and eventually you can bound the absolute value of that integral above by like $e^{-R} \int_{0}^{\pi} e^{t} + e^{-t} \dd t$, which goes to zero as $R\to\infty$
@dull bear
I think at least
In any case it's along the lines of this and that cos(z) is bounded on those sides
No worries
hope it goes well!
Also for the top side "exponentials beat polynomials" may turn out to be useful, just in case, to show it goes to zero too
Oh wait also I think I see why they suggested this one actually, my bad 
Think their idea was still CRT but then you'd compare the real and imaginary parts when you apply it on what they gave, noting that e^{iz} = cos(z) + i * sin(z)
Showing the "other sides" go to zero should be similar though at the very least
[edit: the top doesn't actually go to zero]
In fact I think showing those sides go to zero probably is much easier in that case!
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how do i get the particular and homogenous solutions out of this?
hmm
here's what it looks like when you plot it
anyway, have you found the homogeneous solution then ?
or, what methods do you know for solving DEs ?
no
its like dy/dx + y =0 right?
and then it becomes Ke^-at
well just Ke^-t
what have you done in your class then ?
that's literally the first DE you try to solve usually
@orchid pier
i skipped that lecture 😩
wait im going to try to solve it myself
@cyan talon so dv/dt =-v
yeah ?
so why is the v gone
yeah that's not at all what they're doing
a is -1
not v
so dv/dt = -v ok
then they divide by v
(dv/dt) / v = -1
they skipped one step lol
omg
it's not completely insane
but I get it
but what are they doing with B=-1
all the solutions of the equation look like A + Be^-t (with A and B being some numbers)
but if you give a value of the function at a certain point (here v(0) = 0)
you can find the corresponding A and B
and get just one solution
how is the particular solution 1? wth
idk how they got A=1 here tbf
is it the sol to the same problem you posted ? @orchid pier
yea
ah yeah it's the particular solution
v(t) = 1 solves the equation with u(t) on the right hand side
you get dv/dt + v = 0 + 1 = 1 = u(t)
but u(t) can be 0 too
they're talking about the t>0 case specifically here
they're covering the t<=0 case just after I guess
wtf is that book
fundementals of electrical circuits hahaha
?
wdym how is ?
there's no equation in what you wrote
@orchid pier
dv/dt = -v
divide both sides by v
(dv/dt)/v = -1
(dv/dt)/v yeah how does this equal 1/v
no when you intergrate it
integration becomes ln|v|(left side)
so left side will be 1/v
nope
you forgot one thing
chain rule
ln(v), v is a function of t inside
so $$\dv{\ln(v(t))}{t} = \mathbf{v'(t)}\cdot \ln'(v(t))$$
aPlatypus
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Complete each statement with a variable expression
You buy (m+5) bagels at 35 cents each. The cost is ________ dolars
The work I have done so far is that I thought of multiplying (m+5) by 35
I'm not sure if it's right but even if it is I wouldn't understand why can someone help
nevermind I figured it out
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how can I convert those permutations to 2 row notations? σ = (763)(245), τ = (16)(3427).
Please don't occupy multiple help channels.
what's a 2 row notation?
!1c
Please stick to your channel.
is this group theory?
close previous channel
like this
oh okay
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@proven garden Has your question been resolved?
so, 2 row notation tells us for each number where it goes after the permutation
what does the cycle (763) represent? where does each number go?
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How would I solve this
Have you learned similarity?
In similar triangles, the sides will have a constant ratio.
this is a good image that explains it without overcomplicating it
the ~ sign represents similarity
and the equal sign with ~ represents congruency (exactly the same)
Wait so how would I find the value of x?
because I dont understand how to put the x+5 and the 30 into a ratio
oh wait
just cross multiply
so would it be 75X+375=-750+300x?
U cna also compare the same sides
In the image i sent 4/5 = 8/10 right
U can apply the same logic in ur problem
so did I get it right then?
The left side is correct but the right side should be 120x-300
oh yeah I see where I messed up on that. Thank you lol
Np
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Please help with my geometryproofs.
pretty much did most of it just havr that little bit left
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how do i draw the graph?
how to find the y intercept
yes it is
what are you tlking abt
You said you wanted to find the y intercept
ok
I told you that you should plug in x=0
i mean how do i make the gfraph though
Because by definition, the y intercept happens when x=0
it says i did the graph worng
yesyes u r right
First identify the basic characteristics of a parabola. Begin by finding the vertex of the parabola. When the equation of the parabola is in the form f(x= )a(x-h) ^2k, the vertex is the point (h,k). Then determine whether the parabola opens up or down using the sign of the leading coefficient, a. Next, determine the axis of symmetry, x- and y- intercept(s). Finally, draw the graph of parabola using all the information.
it says this for what i did wrong
I mean there are TONS of parabolas that go through the (0,9), so you can't just make it go there and pray it'll be the good one.
Right so is the parabola upwards?
ya
They are the coordinates of the vertex.
it would be like f(x) = 1/3(x-h)^2 + k
Yes indeed
yea i know but i mean how do i find that from what they provide
i know i got -18 is correct
but i dont know how wide to make the graph
here look:
Once your vertex is placed, you can "open" the parabola up until it fits with the y-intercept you found
ax^2 + bx + c = a(x+h)^2 + k
The formula is usually h = b/(2a) and k = c-b^2/(4a).
oh
You can get those values by completing the square, but that's up to you
so h is -9
Yes.
uh k is getting weird r u sure that is the formula? c - b^2 / 4a?
k = -18
As you had before
Now if you place the vertex at (-9, -18) and open the parabola so that it intersects the y axis at 9
ohh
You will have it open enough
Yes
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Determine the speed at which water would flow through a point in the pipe that has a cross sectional area of 0.25 m^2 and a volume flow rate of 5.0 m^3/s
?
I need help
cool, read #❓how-to-get-help and ask in an unoccupied channel
!status
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2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
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5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
Hello Xenophan,
ive been working abit on it
i believe Q = A * v
where q is the volume flow rate
Yep
and A cross sectional area
and v = velocity
i divide the volume flow rate by the area
to solve for velocity
Yes
so my equation would look like V = (5.0 m^3/s) / (0.25m^2)
so i believe with those units im left with V= 20 m/s
I think you're entirely correct
so its just normal division with those units?
when i have m^3/s and i divide it by m^2 im just basically removing m^2
thank you xenophon sometimes i doubt my logic! thank you for making me less uneasy about this.
No worries. Good luck with fluids or whatever you are studying
yeah just physics in the fluid dynamic chapters haha @hasty lark
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what is the modulus and argument or z when |z| takes the least value and arg(z+3) = pi/3
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Is the idea of second order mixed partial derivative Fxy just evaluating the change of the slope in the x direction as y changes
So basically if I wanted to find my partial derivative when x=3 at some fixed y value
And I find it
And then if I were to basically
Find the slope at x=3 for several fixed y values
And see how that slope changes
Is that the meaning of my mixed partial derivative
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what is the trig identity of $\frac{cosx-1}{x^2}$
putridplanet
i need a trig identity
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
what’s the aim? You’re presumably finding the limit of that as x goes to zero?
yes
what are you allowed to use for that? Assuming the mention of trig identities implies you want to use one?
interesting they did it that way, I had another idea…
But basically one of the cos double angle but replacing x with x/2
the answer sheet says -1/2
Hmm, unless I’m missing something
Looks like it should be 1/2 to me
,w lim (tan(x) - sin(x))/x^3, x to 0
wait can you just keep using l'hopitals rule until it isnt undefined when you plug in zero
The workings here seem all valid
my one is sinx-tanx
Well if they gave you this one instead, then it’s -1/2 yeah
And in theory you should be able to I think, though I haven’t tried it to make sure the 0/0 conditions hold at each step
As for the comment about another way here, you can multiply top and bottom by (cos(x) + 1) as well and use identities and rearrange
what is the derivative of -sec^2x
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Can someone help me convert this two-parameter integral into a one-parameter integral?
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does anyone know how to do these questions
first i split the powers e.g. 2^n+2 = 2^n * 2^2
What's the objective?
I don't think this simplifies nicely
unless you mean as n is being tended to some limit?
The first does you just have to factor
this is what they got as answers (ignore 130)
This is good
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im stuck on part c, pls could i get assistance?
I have some definitions that will help
(i.e. such that x ∈ S◦).```
member of X (i.e. a set S ⊂ R such that X ⊂ S◦.)```
The interior of a set S is the set of all interior points of S. It is usually denoted S◦, but it can also be denoted Int S.
δ > 0 such that
(x − δ, x + δ) ⊂ S.```
not sure where to start though
How about
So you want to show that the set is infinite.
But infinity is hard to handle
Then, how about proof by contradiction?
I'm not sure we are meant to use that method for these questions
but maybe you're right
Did your prof disallow proof by contradiction?
Most topological problems heavily use contradiction method
So idk if that would be problematic
i think we are meant to be working from definitions to prove it
you cna do that with contradiction ofc, but you can do a direct proof with this one
Oh hmm. True
like if U is a neighborhood of l then (l-epsilon, l+epsilon) \subseteq U for some epsilon right? And then l is the infimum so something something l+epsilon....
Well technically
It is that U includes epsilon-nbhd of l.
yes this is the correct path i think
Yea I guess the key here is, you have two places with "is infinite" here.
Gotta match that puzzle
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How do i go about answering this
like in genreal
find the lim as x --> a+ and x-->a-
like for question one, you can try and plugin -3.99 ( for the negative) and -4.01 ( positive)
you mean negative 4.01?
-4.01 would be the left hand limit
and is that the only method?
only? no. efficient and a safe guess? sure
the modulus function is defined piecewise, so you'll need to split cases anyhow
what does that mean?
positive when x>=-4 and negative when x<-4
as in |x| has two separate parts in its definition depending on the sign of x, so you'll need to do the two cases separately
and so if -3.99 and -4.01 give me the same limit it means its two sided?
yep
think of it as getting closer and closer to the asymptope in the graph
since x =/= -4
hope that helps
try and graph thi
so much more easier to visualise whats happenings
heres the graph of the first equation
so you plugin values like -3.9999 and 4.0001
the value approaches +inf
alright thanks
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um in the last sentence isn't it supposed to be concave down?
i thought if it was > 0 it was up
and vise versa
am i mistaken
idk
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Can I do this
Yes
yes
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I can imagine
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how do i do 4?
what happens to f(x) when x approaches infinity
since the x's have the same power....
plus or minus infinity is infinity and -infinity
so i dont understand do i repeat it twice fo + and -
well just do one at a time
this is a hint
there is no double-sided limits here, if thats your question, only 2 one-sided
because you cant go above infinity
but how do i show that in math notation
just.... solve for positive infinity and negative infinity
what is x^2/x^2
idk if im explaining this right prob not
but i also have it solve it from the left and rigth
and i just dont understand how that works with infinity
it does not
1
yes
so would it be fair to say that f(x) = (x-4)^3/(x+4)^3 = 1
you can plug any value for x and it will approach 1
how so x+4 does not equal x-4
um idk how to explain this but really only the x^3 matters
when the function approaches infinity (an infinitely large number) a number as small as 4^3 doesnt really contribute anything
so its really just x^3/x^3
ah okay i understand the 4 is negligible relative to infinity so the two sided limit exists
well, you can expand (maybe do it with squares not cubes) and you can divide every term by x^3, so you end up with two 1s and a bunch of terms which approaches 0

