#help-33
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so for part a)
i got thiis
im not rly sure how to do part b tho
idk if this is the right idea but
i kinda grouped it so its like
(x^6+1/x^6) + 6(x^4+1/x^4)+(15(x^2+1/x^2)+20
im not sure wher to do from here tho
$(x^6+1/x^6) + 6(x^4+1/x^4)+(15(x^2+1/x^2)+20$
✯✡ρєввℓєѕ✡✯
seems correct
You just need equate the coefficients now
$U^6 + AU^4 + BU^2 + C$
✯✡ρєввℓєѕ✡✯
yep
yep i got that
$(x^6+1/x^6) + 6(x^4+1/x^4)+15(x^2+1/x^2)+20$
✯✡ρєввℓєѕ✡✯
but in this one
Oh the form is slightly different I miss that
✯✡ρєввℓєѕ✡✯
im but u see here its like slightly different
Why don't you move all the terms to the right of the equal sign? we need to make x^6 + 1/x^6 the subject
yes
i tried that
so then i ended up with
$x^6 +1/x^6 = (x+1/x)^6 - 6(x^4+1/x^4) - 15 (x^2+1/x^2) - 20$
✯✡ρєввℓєѕ✡✯
and $U = x + 1/x$
✯✡ρєввℓєѕ✡✯
So we have U^6 - some_terms = x^6 + 1/x^6. So the form seems correct
yes the only problem is
the powers r on the inside
its good for the first form
like
(x+1/x)^6
which is the same as U^6
So we now have two problems to solve expressing x^4 +1/x^4 in terms of U and x^2 + 1/x^2 in terms of U
but then im not sure what to do for the next ones
yeahhh exactly
Try to think about it. Maybe we could do something similar
!show
Show your work, and if possible, explain where you are stuck.
i couldnt figure out anything else
ive literally
gotten to this point
and now im lost
💀💀
I got idea but am not 100% sure
oh ok
idk ive been
doing this for ike
30 mins
still not getting past this point
could u please share what u know
Be creative. Maybe there is something you could do with U perhaps expansion
what is the problem type
Expand (x+1/x)^2
I see
Also consider (x+1/x)^4
part a was fine
yea a is ez
so
should i try it
and then
like
minus the excess?
yep
bruh
i dont think its orking
wait
nvm
i got it
holy
that toook a while
@low ruin thanks for suggesting the removing excess
got it now 🙏
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Where have they gotten 9x2^2k
@honest current Has your question been resolved?
I still don’t understand
there is a number which is greater than 10
tell me such a number
11
Yes it can
so yes if a number is greater than 10, it is also greater than 9
if u can write k > 10
u can also write k > 9
But it doesn’t mention greater than 10
k+1 > 10
k + 1 = apple
apple > 10
apple > 9
(k+1)×2^2k > 9 × 2^2k
(k+1) > 9
2^2k's goes
.
apple > 9
because it said that apple > 10
i said apple because it is just a number
i just used this as a variable
k+1 is a number after all
which is greater than 10
so k+1 also greater than 9
so you can write this: (k+1)×2^2k > 9×2^2k
because it says k+1 > 9
After 2^2k's are simplified
there is just k+1 > 9
which is not a wrong impression
because we knew that k+1 > 10
Ugh Idk why it’s not
Clicking
In my head
The whole thing has confused me
Like the steps they’ve done to prove it
Prove the statement
I mean the question
Like
I don’t understand why they’ve done what they’ve done
with that condition
ig they are trying for n ≥ 9
n ≥ 9,
prove that n! > 2^2n
is that all?
When going to some question requiring to prove something. Often we don't know what we are doing as result we just need to give it a go
I don’t understand why they’ve multiplied 9 by 2^2k
Why have they done it and how
Like the purpose
It just one part of steps as mention above ("why"). However we can examine how
So we have $(k+1)k! > (k+1)2^{2k} > 92^{2k}$
team132
from the assumption we get the first inequality
For the second inequality we assume the statement holds k = 9
If k = 9 then k+1>9
we find again what we assumed, it seems strange to me
like if you assume k! > 2^2k, k ≥ 9
(k+1)! ≥ 2^(2(k+1)) is expected to be
i don't know it seems strange to me
maybe i am wrong
For induction we assume statement is true for k (this comes from base case). We then prove that if the statement is true for n = k then it is true for n = k+1
k! > 2^2k
We then prove that if the statement is true for n = k then it is true for n = k+1
why do we need something ridiculous like n
we have k already which looks so cool
like n = k
like dude i did not change such a variable even when doing integrals
XD
this sounds ridiculous
n = k
what is n?
n is a variable
yes k is a variable too, why are we bothering with two of them
can't we use just k
if we prove that it is true for k, we already prove that it is true for n
because n = k
Initially our statement use n. Since dealing with k and k+1 we need two variables.
The symbol '=' is not really an equal sign in this context. It is more of an assignment operator
n represents a particular value for this which the theorem holds
okay let's continue
i still don't understand what to do with these two situations
how do we know that it provides for k+2 after seeing that it provides for k+1
because we need all integers greater than 9
Although after "k! > 2^2k, k ≥ 9" proving this the others are also proven
but i don't understand our purpose
i expected to understand something when i read this
but i couldn't
@low ruin can you continue the proof? if you are available
maybe i can understand from you
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how did the tan appear?
$\tan(\psi) = \frac{\sin(\psi)}{\cos(\psi)}$
lpieleanu
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Asked the same question yesterday, but not sure if the approach that was suggested then is the one I'm "supposed" to take in my math class
Find the orthonormal basis to the null space/room for the matrix A
So what I did was the following
x+y+z+w = 0
x+2y+2z = 0
y+z-w = 0
solving that i get
x+y+z+w = 0
y+z-w = 0
0*z+0*z= 0
which gives
x = -2s
y = s-t
z = t
w = s
If my understanding is correct, s and t gives the bases for the nullspace
so we have s(-2, 1, 0, 1) and t(0, -1, 1, 0)
and this is the part where I am so confused
The normating part is not my issue, there we get sqrt of -2^2+1^2+1^2
aka sqrt(6) for s
and t is sqrt(2)
but s scalar t isn't 0, which means they're not orthogonal
and the proposed solution (gram-schmidt) isn't in my course literature
and in fact, I am not able to find anything that would help me solve this..
my understanding is that A is a matrix with 4 vectors from r^3
But what does it then mean if we get a null space with 2 vectors with 4 numbers in them?
And if so, how could I make them orthogonal?
Checking the "solutions" (such a joke lmao) they get the same basis for the null space/room as I do, but they then get that an orthonormal base is 1/sqrt(2) (0,-1,1,0) and 1/sqrt(22) (-4, 1, 1, 2)..
What I do see is that you can get the second basis by doubling the s vector and then adding t to that, but I have no idea why that is happening :(
aka
first base is s(-2, 1, 0, 1)
second base is t(0, -1, 1, 0)
extending first base with 2
2*s(-2,1,0,1) = (-4, 2, 0, 2)
adding first base to that gives
(-4,2,0,2) + (0,-1,1,0) = (-4, 1, 1, 2)
@charred panther Has your question been resolved?
true
@charred panther Has your question been resolved?
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not on a specific question but how to in general solve questions like
given that length AC is [some number] OR given that points ABC form a triangle with [some number] area, determine the 2 possible locations of point C
sorry I mistyped my question its when AC is equal to some number find 2 possible locations of point C
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Yes
@still temple Has your question been resolved?
wht to do after first diff
@uncut oracle i'll go in your channel
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why is this not continuous?
not defined at x=1
but u can factorise top and cancel
it's still not defined at x=1
so for continuity u just sub in number
and if it doesnt exist its not cts?
the graph looks cts to me
surely the question is wrong and the graph is actually continuous
what is f(1)?
2
so the answer is yes then
u do just sub it in
limits dont matter
f(x) = (x^2 - 1) / (x - 1)
= ((x + 1) (x - 1)) / (x - 1)
= x + 1
how is that not correct
this shi dont make no sense to me man
the limit as x approaches 1 equals 2, yes
but f is not defined at x=1
so it is not continuous
x + 1 is defined at 1 tho, if the function can be simplified to x + 1 why is it wrong to write that
A function $f$ is continuous at a point $a$ if $\lim_{x \to a} f(x) = f(a)$
cwatson
for $a = 1$, $f(a)$ is not defined. it doesn't matter that $\lim_{x \to 1} f(x) = 2$. there is no $f(1)$.
cwatson
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I need help with limits at infinity
What problem are you dealing with exactly?
I need help with working with indeterminate forms
Ok, could you provide an example of a problem you've had issue with?
like I know I can use l'hopitals for any 0/0 or inf/inf, but what about when you plug something in and you have inf - inf? the example being lim x -> inf (10x+14+6x^2-x^4) = ?
like an integral, you can find limits by term
how so?
such as
trying to find the limit by term of 10x + 14 + 6x^2 - x^4 is what gets you ∞ - ∞ to begin with, so that wont always work
you can look to cancel things out, but you edited the question so that that doesnt happen
theres a rough tactic you can use in 0/0, ∞/∞, ∞ - ∞ where you "choose the bigger infinity"
How does that work?
have you heard of big O notation before
ive heard of it, but ive never formally learned it
you consider O(10x + 14 + 6x^2 - x^4)
that goes down to O(x^4)
therefore you consider the -x^4 term as the 'largest', and do lim -x^4 instead
this rough tactic is the easiest but the roughest
got it
if you want a less rough version,
begin with the ∞ - ∞ youre stuck with
consider ln(e^(∞ - ∞))
then thats ln(e^∞/e^∞)
in your case thats ln(e^(10x+14+6x^2)/e^(x^4))
youll notice that inside the ln is essentially a ∞/∞ that you can use l'hopital on
this is noticibly harder but that way you can convert a ∞ - ∞ into a ∞/∞
That is really clever
let me think about it for a second
wouldnt you end up with just getting e^-infinity/ e^infinity?
the top is e^∞ not e^-∞
I thought the derivative of ln was the reciprocal of its argument
oh youre doing l'hopital
also
thats not l'hopital
shouldnt l'hopital require a fraction?
it does
and whats inside the ln
got it
to be honest im still a little lost
what does your limit look like so far
it is looking like zero over zero, which I think is wrong
do you know what 0/0 means
the limit doesnt exist
no
what does it mean?
0/0 is an indeterminate form
right
an indeterminate form means that youre not done with the limit yet, you havent determined a number
also shouldnt you be getting ∞/∞?
let me go take a photo real quick
btw when you finish getting this limit, Ill show a polynomial-specific way to find this limit
thank you
bruh
I got -inf/inf, I dont know why I said zero sorry
listen
yes?
look at this
what do you think I meant when I typed that
Im a dumbass
let me retry it rq
theres so many things wrong with the work youve done
you look like youre going to make the same mistakes again
idk why I subbed it in so early
sorry
thats not the reason
see youre not thinking about why 0/0 and ∞/∞ are called indeterminate forms to begin with
where do you think youre heading from this
"subbing it in early" just sounds like "I made a mistake in a method I dont understand" instead of "Ive just done something that feels very wrong"
its both on my end, where can I find some good resources so I can adequately understand the method?
that would help
it would only help?
it would be a life saver actually
you need to put more thought into your words
we're going to work with ∞ here so words are important to get right
earlier I converted ∞ - ∞ into ln(e^∞/e^∞)
thats a shorthand, a figure of speech
that stands for "convert this - that into ln(e^this / e^that)"
or $\lim_{x\to\infty}(10x+14+6x^2-x^4)=\ln\qty(\lim_{x\to\infty}\frac{e^{10x+14+6x^2}}{e^{x^4}})$
mtt
that seems obvious now, I dont know why I didnt catch that
its only obvious now because you thought ∞/∞ was going to help
you didnt take the fundamental problem with ∞/∞ seriously
because we're doing this to get it out of that form in the first place
we're not discussing method right now
if its still in that form, its obviously wrong
you know the reason?
please give me a second to think
since an indeterminate form means that we havent determined a number for the limit, it (infinity/infinity) doesnt adequately describe what the function is approaching
thats pretty good
and what is it about dividing ∞ by ∞ that turns out vague?
if you do ∞/1, that = ∞
if you do 0/∞, that = 0
you can view this as shorthand for lim (a function that tends to ∞) / (a function that tends to 1) = ∞
its that there is no way inf/inf can be equal to one, since its infinitely dividing itself
thats not correct
right
,,1=\lim_{x\to\infty}\frac xx=\frac{\infty}{\infty}
mtt
,,2=\lim_{x\to\infty}\frac{2x}x=\frac{\infty}{\infty}
mtt
you were correct that an indeterminate form does not have enough to determine a number
here, you can see that ∞/∞ cannot equal just 1 or just 2, you need more information on where those ∞s come from
the fraction that you got those ∞/∞s from would be that information
thats what youre doing a limit for
right
however we know that ∞/∞ doesnt work but 0/∞ does
consider (function that tends to ∞) / (a different function that tends to ∞)
if the numerator "grows faster" than the denominator, it will dominate and you get ∞
if the denominator "grows faster" than the numerator, it will dominate and you get 0
between those, if the denominator and numerator grow equally, you get a finite number
the idea here is, like ∞ - ∞, both infinities are working against each other
and so which one wins requires more context
usually people think ∞ / ∞ = 1 because they'd think the same function is being placed for both ∞s since the same symbol ∞ is being used
let me think about that for a second
ok
what do you mean by growing faster? like the slope?
youll need to know more about big O notation
we now need to teach power
think of $\lim_{x\to\infty}\frac{x^2}x$
mtt
you would expect this to = ∞, right
right, since our numerator grows faster than our denominator
bruh
what did I miss?
look closer at this image and tell me if theres something off with you saying "grows faster"
growing faster has nothing to do with slope btw
it should be equal to zero since we have a vertical asymptote at x = 0
🤦♂️
the problem here is youre asking about "grows faster" as if you want a better sense of how to use that word
you then proceed to use "grows faster" regardless
you used it the very moment I mentioned an example btw
so you inadvertently lied here or there
lied how?
I didnt say you lied
I said you INADVERTENTLY lied
that means you didnt communicate what you were saying properly
you accidentally didnt say what you meant
surely I dont need to explain "inadvertently" to you man
screw this
okay, thank you for trying
we're skipping straight to that polynomial thing I mentioned earlier
wait
you wouldnt know how that works
because you dont know ∞ * 0
you see the issue here?
im missing alot of pre-req knowledge
yep so we're in fact sticking to this until you get this
as soon as that's built up, then we move on
got it
do you get this
oh btw Ive come up with a different way of saying what indeterminate forms are, it should work
I dont think I actually do
yep so lets stick to some examples
but before we do that, we need to address two things
first
the function is x^2 / x
and the limit is x -> ∞
so what do you mean by "it should be 0 because x^2 / x has a vertical asymptote at x = 0"
I dont think I thought that through as much as I should have, since the limit is dependent on the y-values not the x's
it should be infinity
does x^2 / x have a vertical asymptote?
it does, since 1/x at zero must have a vertical asymptote, because 1/0 is undefined
the value of x^2 doesnt affect where the vertical asymptote is
you dont think that the x^2,
which is x * x,
or denominator * denominator,
can affect anything in denominator * denominator / denominator?
it should be just the denominator
x^2 / x = x
here's a graph of y = x^2 / x
theres no asymptote
what you said about 1/x -> ∞ as x -> 0 is a rule for when theres a constant in the numerator
right, I think I was overthinking it and confusing it for when theres (x^2+c)/x
you can view a discontinuity as the case of "0/x when x -> 0"
its a "vertical asymptote with no width"
none of that's really true you-wise
for now you can consider the point here as a discontinuity that can be simplified
now here's the second thing
if youre still stuck on this, we can explain it afterwards, it means something weird
for now though you need the basics
what I know about vertical asymptotes, its where all y's are undefined
thats not what vertical asymptotes are often called
where x is in the denominator and equal to zero
I cant say yes or no to that without getting into the weird mentioned here
ok
first, you seem to have forgotten that keyboards often type different kinds of math because they only get to use keyboard symbols
do you think the ^ should be on your paper
No, I have no clue why I did that
you did it four times
in a row
youll need to address what caused that
(on your own)
theres also something else,
whats happening here
I cant make out what you wrote down
something stupid, its when I took your shorthand literally
to be more specific, you wrote an x in the denominator
is this $\ln\qty(\frac{e^{\infty}}{e^{\infty}})$
mtt
mtt
you can see there the b loses the - sign
I showed you this and I hoped you wouldve noticed (twice)
oh so its like the quotient property of logs
bit concerning that you went with that
surely theres an easier way to know this law
is this your first time seeing this law
No, we learned them in algebra two
youre correct that its very much like the log quotient property, but its not a good basis if you want to remember the law as making sense
usually its (sense) -> (exponent law) -> (log law)
the idea is if you have e^5 / e^3,
then thats (e * e * e * e * e) / (e * e * e), of which e * e is remaining
right
so in general e^(a - b) = e^a / e^b
which is the same as e^ 5-3
similar to how e^(a + b) = e^a * e^b
got it
while we're here, you can plug in a = 0 and b = 1 to get that
e^(0 - 1) = e^0 / e^1
or
e^-1 = 1 / e
so that would show that x^-1 = 1/x
right
not really relevant but its neat that it can come from e^(a - b) that quickly
alr brb
go explain what this means in the meantime
its bad notation for derivative with respect to x
it should be d/dx
yea and it should be before, not after
you only do it after for integration right?
sure
alr I gtg for now but Ill be back in maybe 30min
we've gone over all the errors in the picture now
thank you, ill rework it while you're out
alr
oh btw
for the polynomial-specific method, have the first step be forcibly factoring an x^4 out of the expression
alright
@kindred hinge Has your question been resolved?
ok so while trying to do it this way, I came across a problem, since e^(polynomial) derives into e^(polynomial) * (d/dx polynomial), how does it reduce to a determinate form?
you didnt write down this d/dx correctly
it should be two seperate ones, my bad
other than that yea I dont think this is getting anywhere
so the polynomial way would be the only way you oculd write down
try that instead:
,,\lim_{x\to\infty}(10x+14+6x^2-x^4)=\lim_{x\to\infty}(x^4)\qty(\frac{10}{x^3}+\frac{14}{x^4}+\frac6{x^2}-1)
ill start on it
mtt
ok maybe we need to continue with the basics
yep thats correct
awesome
thank you for putting up with me, im especially sorry for putting carets on paper lol
it couldnt hurt, I really want to be sure I actually understand this
right
so lets say you have ∞/∞, this represents dividing a numerator and denominator that are both approaching ∞
call these functions $\lim_{x\to a}\frac{n(x)}{d(x)}$
mtt
right
now you know from earlier that 0/∞ = 0, this represents that lim (function -> 0)/(function -> ∞) is always a limit that equals 0
right, since zero is a constant, and any constant divided by infinity must be zero
thats not what I said
instead 0/∞ = 0 represents that lim (function -> 0)/(function -> ∞) is always a limit that equals 0
let me make sure im interpreting this correctly, so the limit as the x of n(x) approaches zero divided by the limit as x of d(x) approaches infinity must always equal zero
or is there something im not getting
if $\lim_{x\to a}n(x)=0$ and $\lim_{x\to a}d(x)=\infty$, then $\lim_{x\to a}\frac{n(x)}{d(x)}=0$
mtt
you got the idea
now you can see there that "0/∞" is pretty well defined
I see
maybe to decrease confusion, any time I do "0" in quotes, its short for "a function that approaches 0" or "a function whose limit is 0"
so lim "0"/"∞" = 0
got it, so it will always refer to the limit of the corresponding function
yep
same with "∞" also
that way we're only ever see the bare ∞ in rare situations
got it
now we expect lim "0"/"∞" = 0
lets see if lim "∞"/"∞" has a specific value
we can check what happens for various examples of n(x) and d(x)
for now, we're doing that $\lim_{x\to a}n(x)=\infty$ and $\lim_{x\to a}d(x)=\infty$
mtt
so an example of this is when n(x) = 2x and d(x) = 2x (and a = ∞)
now $\lim_{x\to\infty}\frac{2x}{2x}=\lim_{x\to\infty}1=1$
mtt
that makes sense, since the terms share a common variable, so all its reduced to is a constant
now consider $\lim_{x\to\infty}\frac{cx}{x}=\lim_{x\to\infty}c=c$
mtt
this is an example of n(x) -> ∞, d(x) -> ∞ where you can get almost any real number c from "∞"/"∞"
this looks identical to the 2x/2x scenario but instead its just 2x/x, leaving just 2 or in this case c
never mind, its because the x cancels always leaving c
yea
now through this, you can see that "∞"/"∞" can equal any positive number
why can't c be negative?
because we had to assume to begin with that n(x) -> ∞ instead of n(x) -> -∞
so c must have a consistent signage with the limit the corresponding function is approaching?
not really sure if I should confirm that
the limit here shows a corerct calculation for this particular fraction
which indeterminate form the calculation is depends on the value of c
if c is positive, cx/x equals the indeterminate form ∞/∞
if c is 0, cx/x equals 0/∞ which is not indeterminate
if c is negative, cx/x equals the indeterminate form -∞/∞
however ∞/∞ and -∞/∞ are often considered the same indeterminate form
similar to how 2 * ∞/∞ and ∞/∞ are still considered as a general "infinity over infinity"
right
youre looking for the general form it takes on
can you give me just a second to write this down^
ok
I got it down
alr
now notice that "∞"/"∞" can equal any positive number
because we created an example of that for lim cx/x
right
now "∞"/"∞" can also equal ∞ or 0, it depends on choosing differing kinds of n(x) and d(x)
examples are:
,,\lim_{x\to\infty}x^2=\infty,\lim_{x\to\infty}x=\infty,\lim_{x\to\infty}\frac{x^2}{x}=\lim_{x\to\infty}x=\infty
\\lim_{x\to\infty}x=\infty,\lim_{x\to\infty}x^2=\infty,\lim_{x\to\infty}\frac{x}{x^2}=\lim_{x\to\infty}\frac1x=0
mtt
I understand, so as long as there exists at least one x without a denominator (assuming no different signed x's), the limit as x approaches infinity must be infinity, and that for any constant over x as it approaches infinity must be zero
sure but dont form that pattern too strongly
n(x) and d(x) are more general functions
the point is what "∞"/"∞" can evaluate to
instead of "how to simplify x^2/x"
got it
and just to reiterate, "inf" means the limit as x of the corresponding function approaches inf
got it
for this raeson, ∞/∞ is called an indeterminate form
since it can be any of those 3
yea
this can mean "if you get a limit that evaluates to ∞/∞, then youre not done figuring out the limit"
this can also mean "by itself, ∞/∞ doesnt tell you enough to equal a number, so its indeterminate"
that makes alot of sense now
now observe that ∞/∞ is happening depending on how "strongly" n(x) and d(x) approach ∞
how would you define strongly?
usually its dividing n(x)/d(x) to verify how comparatively strong n(x) and d(x) are
so you can see its a bit circular to get the sense of "strongly"
the definition is if $\lim_{x\to\infty}\frac{n(x)}{d(x)}=0$, then $d(x)$ is stronger or grows larger or grows faster than $n(x)$
mtt
does this imply that d(x) likely has a greater exponent on x compared to n(x)?
you can consider it that way
formally this is called "d(x) dominates n(x) asymptotically"
so all of our sense of bigger/stronger/larger/faster is better described as "asymptotically"
what do you mean by asymptotically? im assuming it just meants that d(x) is in the denominator, but im not sure if thats the case
put it in quotes even
this is just what its called
formally
^
my bad
I dont know how I missed that
brb
alright
so just to make sure I understand, if a function dominates another function asymptotically, it must mean that the first function has greater strength compared to the other, which we can consider the first function to have a leading term whose exponent is greater than the second function's leading term's exponent
@kindred hinge Has your question been resolved?
back
you here?
yes
great youre back
polynomials arent the only functions out there
if n(x) and d(x) are both polynomials, youd be right
how would you define strength for some of the non-polynomials?
let me repeat
if $\lim_{x\to\infty}\frac{n(x)}{d(x)}=0$, we say $d(x)$ "dominates $n(x)$ asymptotically"
mtt
for example $\lim_{x\to\infty}\frac{x}{e^x}=0$, so $e^x$ dominates $x$ asymptotically
mtt
"d(x) dominates n(x) asymptotically" is equivalent to saying that
"d(x) grows faster than n(x)"
"d(x) grows larger than n(x)"
"d(x) is stronger than n(x)"
I have a question
so if d(x) grows faster than n(x), doesnt that mean that the derivative of d(x) must be larger than n(x)'s?
to be more specific, are you asking that:
,,\lim_{x\to\infty}\frac{n(x)}{d(x)}=0\implies\lim_{x\to\infty}\frac{n'(x)}{d'(x)}=0?
mtt
let me think for a second
also again youre thinking of slope
that is incorrect
this has nothing to do with derivatives
asymptotic dominance has nothing to do with slope
so what do you mean by growth here?
I already told you
it specifically means the outcome of this calculation
THIS is your definition
this is the third time youve seen it
do you need me to tell you it a fourth?
no
I keep making a false equivalency, im sorry
lets address derivatives then
growth has two separate definitions
the first one is the derivative
the second one is this
got it
now we're talking on a more fundamental scale than just derivatives
you already have a sense that x^100 is in a sense stronger or fundamentally steeper than x^2
right
its not the case of what the slopes are
its a case of how the function behaves
and that x^100's shape is fundamentally different and will always surpass x^2
also like how x surpasses 1/x
I see
you could multiply 1/x by a constant
you could have it be 999999/x
but that doesnt change that its shape fundamentally goes down compared to x
that it has to shrink compared to x
im really trying to wrap my head around this
youre not looking for values
youre comparing shapes
youre considering that one of them is an x while the other is merely a 1/x with a constant
this is where o notation starts to appear, also
asymptotic dominance is like a <
so 1 = o(x)
what is n subscript o?
maybe you shouldnt be reading what you dont understand
if we didnt address it yet
thats a 0
not an o
do you want the formal definition now? I still havent told you how to do f(n) = o(g(n)) yet
not yet
when you get that lim x -> ∞ f(x)/g(x) = 0,
you say that f(x) = o(g(x))
for example, 1 = o(x) because lim x -> ∞ 1/x = 0
and x = o(e^x) because lim x -> ∞ x/e^x = 0
I see
you can see that using an = sign here is a bit off
o(g(x)) is only as precise as saying "a function that is asymptotically dominated by g(x)"
you can see it isnt very precise
for example, all you would know about a function f(x) = o(x^2) is that lim x -> ∞ f(x)/x^2 = 0
that can still allow a lot of functions, like f(x) = x^1.99 or f(x) = 1
right, since f(x) is unknown here
its like saying "even + odd = odd" for numbers
its not exact but it explains what its trying to explain
alr if you cant notice asymptotic dominance intuitively, we'll just leave it as this particular fact
you can see that using this acts as a < sign
theres a very similar version that acts as a > sign
alright
$\lim_{x\to\infty}\frac{f(x)}{g(x)}=\pm\infty$ means that "$f(x)$ dominates $g(x)$ asymptotically"
mtt
youll notice that all of the statements above can be flipped to use this version instead
$\lim_{x\to\infty}\frac{e^x}{x}=\infty$, so $e^x$ dominates $x$ asymptotically
mtt
$\lim_{x\to\infty}\frac{x}{1/x}=\infty$, so $x$ dominates $\frac1x$ asymptotically
mtt
$\lim_{x\to\infty}\frac{x}{1}=\infty$, so $x$ dominates $1$ asymptotically
mtt
heres an equivalent symbol for that
f(n) = omega(g(n))
so x = omega(1), e^x = omega(x)
1 = o(x) and x = omega(1) mean the same thing
like 1 < 3 and 3 > 1
or more specifically 1 = (number less than 3) and 3 = (number greater than 1)
too much math for me
let me think about this for a second
dont read into it too closely
alr
you didnt get enough of this
theres a list of which functions dominate which others
do you want to see that
sure
its better sooner than later
lim x -> ∞ weaker ones / stronger ones = 0
one more thing, if you get lim x -> ∞ n(x)/d(x) = (a nonzero finite number), n(x) and d(x) are "equal asymptotically"
here the image wants the limit to = 1, but its not that big of a deal
the idea here is that x ~ 2x because theyre both lines
you expect them to behave similarly and be "equally strong"
so now we have a <, an =, and a >
which is o, ~, and omega
alr heres the list
first theres constants, like f(x) = 1, f(x) = 2, or f(x) = -3
right
above that theres f(x) = x^(a power)
in a polynomial, you consider the highest power
same with x^1.5 + x^0.5 for example, you consider x^1.5
higher powers > lower powers
got it
so basically, the higher the degree, the higher the order, and the higher the strength
sure
I think "order" is the best normal word you can pick
higher and lower orders
this is just a more detailed way to use degrees on functions that arent just polynomials
now heres an interesting one
ln(x) is between constants and x^(a power)
so $\lim_{x\to\infty}\frac{\ln(x)}{x^{0.001}}=0$
mtt
??????????
do you want a proof?
sure
before we do that, we need to consider a more believable example
exponentials like e^x are more powerful than any polynomial
so $\lim_{x\to\infty}\frac{e^x}{x^{100}}=\infty$
mtt
this limit up here, you can prove if you consider doing l'hopital 100 times
the top is still e^x
the bottom becomes a constant because x^100 -> 100x^99 -> ... -> a constant
so is strength determined by the number of derivatives you can use on it??
Right
strength is determined by $\lim_{x\to\infty}\frac{f(x)}{g(x)}$
mtt
if this is 0, its like a <
if this is ±∞, its like a >
if this is any number in between, its like an =
right, so what exactly makes e^x more powerful than any polynomial?
exponentials like e^x are more powerful than any polynomial
so $\lim_{x\to\infty}\frac{e^x}{x^{100}}=\infty$
mtt
this limit up here, you can prove if you consider doing l'hopital 100 times
the top is still e^x
the bottom becomes a constant
each time you d/dx, you decrease the power by 1
so d/dxing 100 times would decrease the power from 100 all the way to 0
the 100th derivative of x^100 is just 100 * 99 * 98 * ... * 3 * 2 * 1, a constant
I understand that
is "powerful" and strength a false equivalence here then?
theyre both words that we're using to describe asymptotic dominance
they both mean the same thing
I dont know how youre missing the english here
surely itll occur to you that if something requires multiple close-by words to attempt to describe it, its only close to but none of them?
oh okay
im going to stare at the asymptotic dominance definition for a minute
going off of experience, youre not gaining anything from doing that
let me repeat the correct definitions
ok
,,\lim_{x\to\infty}\frac{f(x)}{g(x)}=\pm\infty\implies f(x)\text{ dominates }g(x)
\\lim_{x\to\infty}\frac{f(x)}{g(x)}=0\implies g(x)\text{ dominates }f(x)
\\lim_{x\to\infty}\frac{f(x)}{g(x)}=c\text{ where }c\ne0\implies f(x)\text{ and }g(x)\text{ are asymptotically equivalent}
mtt
,,\lim_{x\to\infty}\frac{f(x)}{g(x)}=\pm\infty\implies f(x)=\omega(g(x))
\\lim_{x\to\infty}\frac{f(x)}{g(x)}=0\implies g(x)=o(f(x))
\\lim_{x\to\infty}\frac{f(x)}{g(x)}=c\text{ where }c\ne0\implies f(x)\sim g(x)
I got it! (I think)
mtt
and I didnt get to keep going but the list youll usually need is:
1/x^3, 1/x^2, 1/x, 1/√x, 1, ln(x), √x, x, x^2, x^3, e^x, x!, x^x
it literally just the limit it produces. so if you find the limit using lhopitals, and it just so happens to be +/- inf, we know that f(x) must dominate g(x)
by using this definition, you ignore constants changing the order
2x ~ x
2e^x ~ e^x
x = o(2e^x)
99999999x = o(2e^x)
youll notice there that $\lim_{x\to\infty}\frac{99999x}{2e^x}=\frac{99999}{2}\lim_{x\to\infty}\frac{x}{e^x}=\frac{99999}{2}\cdot0=0$
mtt
Ok, you had me then you lost me
do you know that you can move constants out of limits
I did not know that
bro im in precalc
then what makes you think you can handle ∞ - ∞ if you cant handle that
you need to go one step at a time
We were never taught anything beyond limit substitution
and specifically how to handle that case, but I didnt quite understand why it worked so it was hard to remember
then what kind of excuse is this
thats a strong accusation
limits are pure calculus
you cant say "no I wasnt being taught any calculus" as a cop-out when I tell you to learn it
I will learn it then
I shouldnt be making excuses, though I genuinely did not know that you could do that until now
khan academy isnt the only place to learn calculus
but its a good place to start
once you learn the basics, then you can properly handle limits
alright, thank you for helping me mtt
np
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Is multiplicative commutativity by a scalar not a property of a vector space?
like $a \times \mathbf{v} =\mathbf{v} \times a$
CrazyCuber217
I don't think I've ever seen it written like that, but I think it's true
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I am trying to solve (b) but I am getting zero which is definitely not correct
@frosty bronze Has your question been resolved?
How are you getting 0 from that work
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oh nvm I got the third derivative wrong 🫠
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how do i do this question, it's Pythagoras in 3d. pls be nice and gentle im a sensitive stupid little scrawny 10th grader 
3-2



Use the slant height formula
wait so it'd be:
h^2 = 3^2 + 10^2
h^2 = 109
h = sqrt109
h = 10.44
???
i got the answer but idk how you get this
what's the hypotenuse?
careful with your values and the side of the hypot
i'd recommend first drawing a cross section
oh alralr
its 6-4 and then you divide that by 2
thats the width of your triangle
aka the base
and the height is not the hypotenuse
so watch out there as well
the correct answer is in fact sqrt(99)
c^2 = a^2 + b^2
so,
c^2 - a^2 = b^2
ohhhhh i see i see
wait sorry i'm a bit confused on what numbers c, a and b are i've kinda been staring at the question and can't figure it out myself i'm a bit slow minded 
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e
hello
can somebody help me with this one
Im not sure what the question is looking for
for b
<@&286206848099549185>
Make a diagram for it and you will see that a right triangle is formed with hypotenuse CT and base L root 2 /2 which is half the length of diagonal of the base square and third side being height of pyramid which is given
L is also given
Yes it seems so
how is the diagonal equal to ST tho
for a the answer says its 356
nvm it isnt
fucck me
The diagonal is not ST
yup
let me try again
holdup
@sick tinsel so with the diagonal length
how do I determine CT
T is the top T' is point directly below T so T'T is height of the pyramid (given)
length of diagonal is 522
so half of that is t1 no?
wait
no
cuz its 440 root 2
How is it coming 522
It should be somewhere around 620
And half of that will be CT'
mistake mb
Pretty much multiply 440 by 0.707 to get length of CT'
yup
And now pythagoras