#help-17
1 messages · Page 186 of 1
But what would be the definition that to find the sup I can also increase it with a quantity that no longer depends on x, so that this quantity is valid for all x
That is, the quantity depends only on k after
well i am not sure exactly what you mean. do you just want to look at a particular x value? that just gets you a sequence of real numbers. it would be helpful if you clarified what you meant by “increase it”
The first is the sequence of functions, the second is the limit function, I decreased this quantity with 1/k, so the sup tends to 0 as all the x's vary
wait this is a uniformly bounded thing. what you’re describing is uniform convergence.
like this is an example of a sequence of functions that is uniformly bounded
by “mean” do you want an interpretation or like how it fits into the big picture?
Where it is written that if I decrease with something that no longer depends on x then the sup is that for every x
Wdym
“the sup is that for every x” doesn’t make sense to say
sup here didn’t depend on x, it’s defined for functions and intervals
not a particular x value
Example pls
yeah, take the function f(x) = x and i wanted to find the sup of the function. What input would i give the sup? not a specific x-value, but an interval like (0,1)
Sup is a real number right?
yes, it takes in a function and an interval and outputs a real number
I don't remember exactly if it could also be +∞
or infinity yeah
But in the first case isn't it infinite? (f(x)=x)
well, it depends on what the domain of f was. but if you let the domain be all of the reals then yes the sup would be infinity
but if i say “f was defined on the interval (0,1)” then the sup of f on that interval would just be 1
but in any case, notice that the sup depended only on the function and its domain, and NOT on any particular x value
There is the sup is the largest element when all the x's vary
yes, it’s the largest possible output (sort of)
sometimes you can’t quite get there, but it’s the least upper bound of that set
it still only depends on the function and its domain
Example $x^k in I=[0,1]$ the sup is $x^{k}-0$ so it would be 0?
sofficino
yeah, so the sup is the max output, which is 1
If x is 1 the limit function is 1 so sup=1^k-1=0
i see what is happening here i think
But it doesn't converge uniformly, so my reasoning is wrong but I don't know why
so the supremum takes in only one function. so for EACH k you need to get a supremum for |x^k-1|
also remember absolute value bars when you do this btw
so you are correct that the pointwise limit is f(x)=1
Isn't it always 0??
oh yeah sorry, the pointwise limit is 0
it’s late and i’m tired mb
but okay the supremum of x^k for a fixed k is 1 though
No wait maybe you're right
But don't you subtract the limit function?
i skipped a step in subtracting the pointwise limit function because it didn’t affect us. here is the thing that we are computing in a series of steps:
first we subtract the x^k function and the limit function (and take the absolute value if necessary
THEN take the supremum of that, and let k go to infinity.
if we get 0 then the sequence converges uniformly, and if we don’t then it doesn’t
so let’s do the x^k example. we know that the pointwise limit is 0
May I know the steps for this example pls
But it is 0 if x≠1
what is
The limit function is 0 if x lies between [0,1) and is 1 if x=1
yes
well, we can say it’s this function if you want
Ok
i was just gonna do x^k with domain (0,1) instead
so that the limit function is nicer
Okay
it won’t change the final result i promise
Okay
but in this case then you agree that the limit function is actually 0
okay, so now we’ll take x^k and subtract 0, with abs bars if necessary
for an arbitrary fixed k
what i mean is take the function f_k(x) = x^k and subtract the 0 function (which was the limit function), just like usual function subtraction
Ok
we get back x^k again
Yes
okay now we take the supremum of that function on the interval (0.1)
Isn't it 0?
In (0,1)?
yeah
6
There is no maximum
yeah, but what is the least upper bound
1
okay, so that’s the supremum of x^6 on (0,1)
that is what i mean and that’s the standard terminology
For every k it is always 1
yep
To get to this result, I had to necessarily see it as [0,1) otherwise I could never find it
Otherwise I would have found 1-1=0
why? how are you getting 1-1?
there was no subtraction anywhere except for subtracting 0
okay, i’ll make a remark about it at the end. let’s keep going for now.
we note that sup x^k over (0,1) = 1 for any k
Yes
okay now we let k go to infty
so lim_k to infty of 1 is 1
Yes
which is not 0, so the x^k are not uniformly convergent
Yes
No
okay, a metric space is just a set equipped with a distance function
what were doing when we take the uniform convergence is we’re equipping the set of functions with a distance function (namely “how far apart CAN THEY POSSIBLY get”) and then determining if that sequence converges with respect to that distance function
I just saw something
so in this example, it was possible to get far apart even as k went to infinity, so the distance between x^k and 0 didn’t go to 0
now, the second remark: even if you consider x^k on the closed interval [0,1], you still get that sup|f_k-f| = 1, where f is now the more complicated pointwise limit function
Wdym
but even still sup|f_k-f| was 1, so the distance between those functions was 1
This i mean
eh maybe it’s not that much more complicated
the point of this uniform convergence stuff is to say either “yes the functions actually look like they’re approaching the limit” or “sure they’re doing it pointwise but it doesn’t really seem like the functions themselves are taking the shape of the limit function as k goes to infinity”
same with the equicontinuity, equilimited, etc stuff as well, but with different statements like that
Function sequences tend to become the limit function
only sort of. if the convergence is uniform it is even better
the shape approaches the other shape quicker in a sense
Is it uniform?
really think about how the shapes are changing. the stuff near 1 really didn’t want to change in the x^k example. i think some sleep will help this concept now. i am too tired to say more about it because i stayed up way too late.
And yes, because for every x the distance is less than epsilon, with a fixed epsilon
?
Anyway, thank you very much for this great help
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seems like they combined ln|x| + c into a single ln, then took the exponential of both sides
$\ln \left| \frac{y-1}{y} \right| = \ln|x| + \ln(e^c) = \ln(e^c|x|)$
lgkoo
then taking exponentials on both sides
as long as c is real yh
then he just called it lncx
and that canceled the ln
yh
and it became cx
the one thing I'm not sure though
where c is actually c
is that you can just drop the modulus on both sides without more info/context
does the e here cancel the ln
wym
but
because $e^{\ln(t)} = t$
lgkoo
how'd he do ln e^c in the first place then
you can re-write any constant c as $c = ln(e^c)$
lgkoo
or $c = e^{\ln c}$
lgkoo
exponential and logarithm are inverse of each other
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I am a bit confuse about this type of exercise
Should It be like the first or the second
Do you mean to solve it?
OK give me 1 min
I suggest you sketch the region R, then it will be obvious which of these is correct
well, the top line is y=2x not x=2y
There are two ways of integrating over this region. Either scanning a horizontal line vertically, or scanning a vertical line horizontally
Notice that scanning a horizontal line means you would need to split the region, since the bottom side is made up of 2 equations. So it is better to scan a vertical line across
This means dy first then dx
ok, think I get it
Can you tell which of these is right now then?
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Guys help me with it
,rotate
ƒ(Why am. I here)=I don't Know
What sub means
Substitute
you'll then get 1$6y^3-68y+16=0$
ƒ(Why am. I here)=I don't Know
Wait
now find the product of the roots
yes
@split cradle Has your question been resolved?
@heplers
<@&286206848099549185>
Still not getting
Help me out
Here is the question again
,rotate
take log_5 of both sides
which will give
$$(\log_5{x})(16(\log_5{x})^3-68\log_5{x}) = -16$$
Pro_Hecker
substitute y = log_5{x} for y
@astral pilot i will be lucky if u will check ur dm btw sorry for bothering u
Guys I did logging but I don't know where to proceed
<@&286206848099549185>
<@&286206848099549185>
Guyzz?
Help me
dont ping multiple times
@split cradle Has your question been resolved?
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Inside a circle of radius 1, n circles of radius rn are drawn so that these circles are tangent to each other and are also all tangent to the large circle. In the figure below, this situation is drawn for some values of n as an illustration. Which of the following relationships holds between radius rn and n? You may assume here that n ≥ 3.
Please don't occupy multiple help channels.
:/
It’s a diff question
Why would this be wrong?
Answer is D but is there a way to get there w my thing
is this an olympiad question ?
kinda
might want to ask in the olympiad server
Where do I find the link?
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Follow up question to #help-29 message, it is not needed as context though.
Does "(...) T> (...)" mean the same thing as " '(...) -> (...)' is a tautology"?
Let T> denote tautological implication and (...) just be some arbitrary formula
@fresh cave Has your question been resolved?
@fresh cave Has your question been resolved?
Do ping me if you reply btw
@fresh cave Has your question been resolved?
@fresh cave Has your question been resolved?
@fresh cave Has your question been resolved?
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how would we go about finding interval of convergence for $\sum_{n=2}^\infty\frac x{1-n}$
Vѳrtєx-
Is the x supposed to be to the power of n?
no
just x
its harmonic series-esque but the 1-n is throwing me off
You might as well put it in front of the sum for the case when it's nonzero
Vѳrtєx-
You can flip the sign and then compare to the harmonic series
oh i guess $\sum_{n=2}^\infty\frac 1{1-n}=1+x+x^2+\cdots$
oh it starts at n=2 but yeah
No, that's not what I meant
This is just wrong
oh no it definitely doesnt
sorry lmao
so you compare $-\sum_{n=2}^\infty\frac 1{1-n}$?
Vѳrtєx-
1/(1 - n) = -1/(n-1)
So you should have 1/(n-1) in the sum
And then compare that series to the harmonic series
Reindexing the sum to start from n=1 would directly give you the harmonic series
oh i see
i suppose you can also write $x\sum_{n=2}^\infty\frac 1{1-n}$ as $x\sum_{n=1}^\infty\frac {-1}{n}$ now that i think about it
Vѳrtєx-
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HELP
ok so uh
yea
not rlly a problem specifically
k
but is there any trick to
factoring any quadratic equation
that is more efficient
than doing it manually?
no, i don't think
than the A/C method or other traditional methods
google!!!!!!!!!!!!!!
well the only method that works 100% of the time is the quadratic formula, but that can be a fair bit more calculation than just guessing (at least, if the factors are integers)
well u can practice to recognise patterns
tell me more
ik but what type of patterns lol
i can solve most that are a=1
lol
it will be better with time
slove more factorising problems it will help alot
welcome
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Question two
Is that absolute value of t
Or is it outer measure
T is a scaler? So it's absolute value
t is scalar so it would be absolute value yes
Oh okay so in the no trival case
Where both t and a are non zero and finite
I'd take the infinitim of the sum of open sets that cover a
Because I can move abs of t out of the summation it become
|tA| <= |t||A|
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Hello. I would like to get the expression on top ( $5\sqrt{4x}$ ) to be written without the squareroot. However I'm not sure how to go about with this, I know what I've done is wrong
Reuben
you can split the square root: $\sqrt{4x} = \sqrt{4} \cdot \sqrt{x}$
cloud
Oh right, I forgot 🤦♂️. Thanks, I have no idea why I've been getting exponents messed up these days
5x2x x^1/2
It's always the easy simplifications asw, I just correctly simplified this and now I did this
u forgot to sqre the 4
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Second one
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u solving for x?
yes
first multiply both sides by x-5, since we'd like to remove the dominator
I don't understand how to multiply it like that
as in change the equation to x²+x+x-150 ÷ x+x-25 =1 ?
ohhh thank you
u get x=-5 as x=\5
wait so when multiplying the numerator by x-5 do you just subtract it??
yes thats what i meant
wdym subtract it
are u talking about after you get
x^2 + x - 30 = x - 5
ya
and then it becomes x^2 -25
yeah just cancel out the x's and solve for x^2
yessir
so that's x^2 - 25 = 0
you'll get two values of x, but you need to plugboth of them into the original equation to see if they work
ohh ok give me a second to try and work it out
go ahead
yeah
you'll get
x^2 + x - 30 = x - 5
you already simplified
the right side becomes 0
subtract both sides with x
x^2 - 30 = -5
add 5 to both sides
x^2 - 25 = 0
let me write that down
yeah go ahead
because 20 - 25 = -5 so I assumed then x must be the square root of 20
wait show me all of your steps from the beginning
to be honest i didn’t really understand what was going on so my working out might not make sense
then -5 + 25 + 20
on the top you wrote
x^2 + x - 30 = x - 5
and ten u subtracted x
so it should be
x^2 - 30 = -5
Who know trigonometry
open a help channel #❓how-to-get-help
ohh i got confused because before the person was saying that when u multiply by x-5 it becomes x^2 - 25 =1(x-5)
but i got messed up
sorry im not that good at this
issok
okay so how do i multiply both sides by x-5?
i genuinely don’t understand
ok wait i got it nvm
is it x^2 + x - 30 = 1 (x - 5) ?
ohh and then subtract x-5 from both sides?
so x^2 - 25 = 1?
wait nvm
subtract x?
so x^2 - 30 = -5
<@&286206848099549185>
yes?
i think the person hhelping me is offline
this step is right
np
ok so do i add -5?
we all start at diff points
so x^2 -25 ?
yes
now see from this eq we can kknow x^2 is less than 30 as in rhs is negative
now we add +30 in both sides
we get x^2=25
oh!
now sqrt on both sides
so it’s either 5 or -5?
hhow do we know that
do you remember that u multiplied x-5 on both sides?
ya
we do that assuming that x is not equal to 5
or else it will break math
in this case
thank you soooooooooo much
welcome 🙂
lol if u practice then u got a shot
good practice improves
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how did the "yellow highlighted" part get cancelled out, I don't get it
The objective here is to simplify
What is x^2 - x^2?
0
Nothing but where did you get x^2 - x^2
1 + x^2 - x^2
oh wait so the yellow part, 1 remains
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anyone can help me w this function if the results is gonna be higher than 21 000 at some point ?
well, they want to find if f(t) exceeds 21, right?
and since e^3 is smaller than 21, then in order to exceed 21 f(t) has to exceed e^3
the equations are them showing that f(t) doesn't do that
yeah but i don t get how they do it w e^3
like why even
the sign changes as well > why
they're examining different parts of the function
so they've taken the fact that $e^{-0,5t^2 + t + 2} > 0$ bc $e^x > 0$ for all x
Out Of Nosh
and then using that to say that if that expression is subtracted from any other, it will necessarily be smaller
it might help to think of $f(t)$ as $e^{3} + (-e^{-0,5t^2 + t + 2})$
Out Of Nosh
how do ı know that e^3 is smaller / bigger than the other part
ı m so confused
I'm not sure i understand
sorry my brain ain t working
you're not trying to find whether e^3 is bigger/smaller than the other part
you only need to find (for affirmation 2) whether the whole expression is bigger than 21
well, f(t) works in units of 000s anyway
ohhhhhh
okay that s already smth
and so how do ı prove that
ık the language and i still can t figure it out LMAO
i think so? I don't understand perefectly what you're asking
sorry for not speaking french
no worries lmao
and so just why do we only start by one part of the function here
and put smaller than 0
well, it's the only part that changes
e^3 is fixed, after all
think of it like 8 - sin(x)
if you wanted to know if that could go over 8,8, you'd start by saying that -1< -sin(x)<1 and then using that to show that 7 < 8-sin(x) < 9
we're doing similar, but we don't care about the lower bound
and it's exponential rather than sinusoidal
do you see @inner cove
and i can do that w whatever thing that is fixed?
i don't understand
like whatever thing that has a fixed value
hold on, let me start over
no no ı got it from here
so you know how e^x can't go lower than 0 for any real x, right?
which means that if you subtract e^x from something it can only get smaller
here the "something" is e^3
so e^3 - e^x is always less than e^3
which, in turn, is less than 21
yeah
-0,5t^2 + t + 2 is always real if t is, and t is always real
so all this stuff holds, and f(t) = e^3 - e^{-0,5t^2 + t + 2} is less than 21 for all t
mm?
the sign > changed to < because ?
knowing that e^x can t be <0
ohhhh
multiplied by -1 ?
yes
it s very slay but way too compliclated
or subtraction of the whole expression, if you prefer
💜
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how would i do this question? i rearanged x=6sin(t) so its t = arcSin(x/6) but if i sub that into y i dont get it in the form they ask for
See the parametric integration comment I made the other day, $\int y \dd x = \int y \dv{x}{t} \dd t$
@dull bear
oh right, i forgot about that formula
Of course, limits and stuff and all 
(It’s basically an application of the integration by substitution thing, so there’s that
)
so i got 30sin(2t)cos(t), but its still not in that form
Much better, can you change anything in there?
Yea there you go 
are the bounds in terms of t already?
wait they are right
You’d need to think about the bounds a little bit in general though
The bounds of the original, in terms of x, are 0 and 6; you want the lower t bound to correspond to x = 0 and the upper t bound to correspond to x = 6 (but of course, as 6sin(t) is increasing between 0 and pi/2, it’s easy here)
In other examples it may be more subtle, but, cross that bridge when we get to it, tl;dr “treat it like any other integration by substitution problem”
i just thought about y=0 so arcSin(0)=2t=0 and then (pi-0)/2 = pi/2
Yeaaa that works in this case at least 
charttttttttttttttttttttttttttttttttttttt
Water beeeeeaaaaammmmmmmm 
sorry to interupt guys but now im trying to intergrate it and im doing it by parts. i got $$u=sin(t) , \frac{du}{dt} = cos(t)$$ $$\frac{dv}{dt}=cos^2(t) , v=(0.25sin(2t)+0.5t)$$ and now i have $$60[(0.25sin(2t)+0.5t)(sin(t)-0.25 \int (sin(2t) +0.5t)(cos(t)) dt]$$ how would i intergrate the 2nd time?
morphine_addiction
Why did you choose u = sin(t) though 
whats the difference?
(see the reverse chain rule section)
i try my best to avoid that at all costs
Oh wait are you doing it by parts-
Ouch 
With that second integral it’s not very “nice” without e.g. cancelling out the work you’ve done or doing more than you need to
what would be the best way to intergrate it?
Though the reason they give it to you in the form they do is because it should be immediately apparent that if you e.g. do it by substitution, setting u = cos(t) or by recognition
(Incidentally, there are product-to-sum identities, noting yesterday’s conversation, but unfortunately they’re not given in the formula book
)
so the best way to do it would be $60 \int sin(t)u^2 dt$?
morphine_addiction
Yep, though remember what happens when you change variable too!
i think im overcomplicating it again but i got -cosec(t) du = dt, arcCos(u) = t, so should it be \int sin(arcCos(u)) * u^2 * -cosec(t) du? this def dosnt seem correct
Yeeeeaaa overcomplicating it a tiny bit
remember when you do integration by substitution you want to find du/dx (or dx/du) and rearrange so you can replace dx with [something] du
In this case, u = cos(t), and t plays the role of x, so you can find du/dt and then rearrange that to get a nicer integral
(You should ideally also change the integral limits, though not super essential tbf, provided you change everything back if you don’t)
ohh du is - sin(t) dt ao i can just sub in -du into sin(t)
so i got 20 as my final answer
Nice 
ty again for the help
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x=cos(u) probably
What's the thought process?
x= cos2t should be better i think
I've only seen trig sub be used when there is a square under a sqrt
But ill try doing it this way
(1-cos(2x)=2sin^2(x)
I c
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help
with implicit diffrentiation
No need to ask “Can I ask…?” or “Does anyone know about…?”—it’s faster for everyone if you just ask your question! See https://dontasktoask.com/
find dy/dx
lny^2 + cos^2x=1-y
i derived it and got an answer of
(1/x)y^2*2ydy/dx -2sinx=-dy/dx
$\ln y^2 + \cos^2 x= 1 - y$
Pro_Hecker
Is this correct?
How did you get 1/x?
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I need some help with permutations, powerindex and a few other things
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consider a 3 by 3 matrix A satisfying $A^2-5A+7I=0$
if $A^5=aA+bI$
ƒ(Why am. I here)=I don't Know
ƒ(Why am. I here)=I don't Know
ƒ(Why am. I here)=I don't Know
ƒ(Why am. I here)=I don't Know
Yes
now this can further be simplified to give
you must escape the matrix🐺 🔥
$A^5=(25A^2+49I-70A)A$
ƒ(Why am. I here)=I don't Know
which is again
matrix algebra suksssss
Crazy
It does, this is simple but I made some calculation mistakes twice
so I'm posting it here
Nvm got it
as I work better blah blah
gather all your 17 uncles and form a tower to escape the matrix🐺
or $A^5=(25(5A-7I)+49I-70A)A$
ƒ(Why am. I here)=I don't Know
ok, this is getting out of hand
I'm having to sub in A^2 multiple times
anyway around this?
Why are u doing that
doing what?
Unlikely
Also this is easy to simplify
,w divide x^5 by x^2 - 5x + 7
yeah
Bot dying
U can do this too
Divide x^5 by the quadratic
That will give u x^5 in terms of the quadratic (hopefully)
Then u just sub in
WHAT THE HECK BOTS CAN DO THIS
the remainder is the answer
bots big w right here
wait, what
Huh?
you're trying to find A^5 mod A^2 - 5A + 7
What no
the answer is 149A - 385
how do i do this cool stuff with the bot i didnt know that u couldndo that
how so?
It is?
That makes sense
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this is just an application of the factor therom ?
no i would rather say its an application of division
just as how if 5 = 0, then 37 = 2 mod 5
well yes
✅
I still don't follow
how can you set 5=0
Its congruence
She's using = to denote equivalent
hmm
And also I think they forgot to add mod 5
Polynomial long division will allow us to write: A^5=(A^2-5A+7)(Q(A))+P(A) (P must be linear, or constant). Since A^2-5A+7=0,
A^5=P(A)=Linear in A, which us what you want
wait, how does this conclude A^5 is linear in A
I edited it. I hope its more clear now
👍 this is just equiv. To looking at A^5 mod A^2-5A+7, which is what snoseeph had said
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Can someone explain to me coneptually what a triple integral even mean
like I know that a double integral calculates the volume of the surface
under the surface
but what is a triple integral? does it calculate a 4th dimension object under a volume??
Maybe this might help https://byjus.com/question-answer/what-does-triple-integral-represent/
integrate one thing then integrate again
This doesnt rly help me understand 😭
what
what are u saying
..
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Can algebra and indices co-incide with each other?
for example, perfect squares and stuff
yes
Ahh all good then thanks
Don't need to add unnecessary stuff to my study guide
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first off do your boundaries
Whats the correct variant.
neither, try to imagine the regions they trace out
I am not sure I understand
I am quite new to the subject
And I have a lack of knowledge
aight
so the x ranges from -2 to 2
that’s correct
but if you sketch it out
the y goes from x^2 to 4
So I mistake the region?
I think yes
aight
Can you draw the region?
What should the boundaries be ?
x is between -2 and 2
y is betwen x^2 and 4
That s make sense
Yes is because the y is on to of the x^2
Thanks a lot
Can I show you another one?
Just to be safe
@potent gorge is this good?
The region is between y=0, x=pi/2,y=rad x
yup!
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Hello, good afternoon, I need help with this combinatorics exercise please. I don't know how to approach the exercises.
Ex.20) The elevator of a building carries 10 passengers and can stop at any of the 12 floors of the building.
a) Distinguishing between people:
- in how many ways can the 10 passengers descend?
- In how many ways if on the 10th floor exactly 3 people descend?
- In how many ways if at most one passenger descends on each floor?
b) If no distinction were made between people, what would be the answers to the questions posed in a?
a)i think 12^10
Each of the 10 passengers can choose any of the 12 floors to descend. Since the choices are independent, we can use the multiplication principle
b)binomil coef thing
(10)
( 3) ,The remaining 7 passengers can descend on any of the remaining 11 floors, which can be done in 11^7
@south ember Has your question been resolved?
yes, is correct
I have another answer from this
@south ember Has your question been resolved?
@south ember Has your question been resolved?
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<@&286206848099549185>
I think we have the solutions to the question, we may have added some restrictions/assumptions on your question though
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im kinda confused with using implicit diff
i got the equation but im not sure what that really means tbh
i got x(dx/dt) + y(dy/dt) = 0
dx/dt is rate of slipping of bottom
dy/dt is rate of slipping of the top
u basically got the whole formula
u gotta substitute values
@warm horizon
alr
so for part a do i make dx/dt the subject?
sorry no dy/dt is the subject right
and dx/dt = 2cm/s? and x = 200?
yep
wait
yea dy/dt
if he gave one of them is 2 u can find the other one
cuz u know the equation
dx/dt is given
so ull get dy/dt
@warm horizon
ok
i got dy/dt = 2/15 * (sqrt15)
and for the second one i think its 14/15 * (sqrt15)?
also why dont u change the units ?
cos for part a the rate of change is in cm/s but the distance is 2m
i would assume you would have to convert rate of change to m/s or distance to 200cm
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How to find p?
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hey guys how do you show that any 3 non-zero vectors which are orthogonal one to each other are linearly independant? I pretty sure it includes constructing a matrix and proving it for one case then using the 'without loss of generality' but im not too sure from there, i tried and can send the actual question if anyone needs
,rccw
thanks!
