#help-28
1 messages · Page 303 of 1
Azyrashacorki
It's often easier than checking paths and such
@bitter tree Has your question been resolved?
ohh oke thx so much
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\begin{document}
\textbf{Problem 6.}
In the accompanying figure is represented the cube ( ABCDA'B'C'D' ), with ( AB = 8 ) cm. The diagonals ( AC ) and ( BD ) intersect at point ( O ), and the lines ( A'B ) and ( AB' ) intersect at point ( E ). Point ( F ) is the midpoint of segment ( CC' ).
\begin{enumerate}
\item[(2p)] \textbf{a)} Show that the volume of the cube ( ABCDA'B'C'D' ) is equal to $512$ cm( ^3 ).
\begin{center}
\( V = l^3 = \dots = 512 \) cm\( ^3 \)
\end{center}
\item[(3p)] \textbf{b)} Prove that the lines \( FO \) and \( DE \) are perpendicular.
\end{enumerate}
\vspace{1cm}
(Note: The figure shows a cube in perspective with points ( O ), ( E ), ( F ) marked, together with the space diagonals and some face diagonals.)
\end{document}
Allstars
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What do you need help with
I can only do this with pure geometry
I need help with B
Soooo?
No
@upbeat tiger
Pure geometry only
hi
seems pretty elementary with vectors
whats the doubt?
dk about geo tho
wait is geometry?
b part
what geometry are you allowed to use
Like all the things before vectors
Like pure geoemetry
🥀
Im in 8th grade
hm..
!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
1
for question A since its a cube so base line height and width equal
set those equal l, then volume = l^3 = 8^3
he only has doubt in B supposedly
o let me see
Yes
It is the middle line so it is parallel
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which kind of functions have empty image
Empty function
Function f: empty symbol -> B
You know a function is when given any x only return exactly one y value for each x right
Alo, care to respond? -.-
you mean a function with a empty domain
Yep
that is a empty function
If no domain then no codomain to image
yeah, precisely
any x in domain
My bad for respond long i was typing translate and do code
what?
You nailed it
I. Was. Using. Google. Translate.
i see
yeah i think that is the only possibility right
If you have a domain that have no elements, then you cant have an output
that the domain is empty
Like putting no fruits in blender and expect to have smoothies
Yes
i see
Function (empty symbol)
.close
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I have a couple of PDE-related problems i should be able to solve but am too brainrotten to rn, and deadline is today. If someone could nudge me in the right direction, i'd be very grateful.
1
I have proven a result showing for $x\in\mathbb{R}^3$, $R>0$ [
\int\limits_{|y|=R}\frac{dy}{|x-y|}=\int\limits_{|y|=R}\frac{dy}{\max{(|x|,R)}}.
]Using this, i need to show the following: for $0 \leq f \in L^1(\mathbb{R}^3)$ a radial function, prove that there exists $M>0$ such that for $|x|$ large
enough, we have
[\int\limits_{\mathbb{R}^3}
\frac{f (y)}{
|x - y|} dy \leq \frac{M}{
|x|}.]
🇵🇸μ🔆
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i think the idea of this problem is to split the integral by $|x|>|y|$ and vice versa, so we integrate over a ball (or its complement) for fixed $|x|$, there the radiality of $f$ should prove useful
but just some step isn't clicking
🇵🇸μ🔆
it is also obvious the constant will be a multiple of the L1 norm of f
<@&286206848099549185>
Yeah?
here's an idea of what might work as a solution but i don't think it makes sense.
\begin{align*}
\int\limits_{\mathbb{R}^3}
\frac{f (y)}{|x-y|}
\leq \int_{|x|>|y|}f(y)/|x|dy+\int_{|x|<|y|}f(y)/|x|\leq 1/|x| (\int_{|x|>|y|}|f(y)|dy+\int_{|x|<|y|}|f(y)|dy)\leq ||f||_{L^1}/|x|
\end{align*}
🇵🇸μ🔆
:/
@subtle thorn Has your question been resolved?
I think there is shortage of helpers, dont worry 
<@&268886789983436800>
thx, i'll try to solve it in the meantime
inflicting sensitive topics?
Good for you, but don't spam in random help channels please
Why you invading a help channel if you don't have anything useful to say?
@subtle thorn Has your question been resolved?
@subtle thorn Has your question been resolved?
no it hasn't and i don't expect it will be.
@subtle thorn Has your question been resolved?
In the first equation the right part is supposed to be infinity, so there is a mistake, i think
what do you mean by that
you integrate over R^3 the constant, it is infinity.
oh you're right, the integral is supposed to be over |y|=R
sorry about that
<@&268886789983436800>
in the second equation also the same?
no, it's supposed to be over R^3 in the inequality.
what you mean by f- is a radial function, it depends only on radius?
yes, ie it's rotationally invariant
the conditions still seem strange to me because for equations shouldn't matter how big x is
i suppose you should rewrite equation in radial coordinates to better understand behavior of integral
$dx dy dz =r^2 \sin(\theta) dr d\theta d\phi$
mikhail_kolesnikov
if f is a radial function it will be actually $L^1(\mathbb{R})$ and and the analysis will be reduced to integration over one variable am not sure how to write |x-y| but i suppose y shoulduse formula |x|^2=(x,x) where (x,x) is a scalar product
mikhail_kolesnikov
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yeah yeah i was just hoping there would be an easier way while incorporating the previous result
like the computation is very much analogous
like i can WLoG rewrite f(y_1,y_2,y_3) =g(|y|)
the problem that f(r) can have pole in r=x
but it's a removable singularity so do we mind
that's why we split the integral right
and since f is L1 then the integral is finite
honestly idk
now i'm just not 100% sure what to do on the ball's complement
to elaborate, by previous result, i already know integral of 1/|x-y| is finite
(on the ball)
so multiple by L1 function is no problemm
its finite on sphere by previous result
exactly
It's not obvious to me
well, i'm just tryna find the upper bound, right?
so, [
\int_{|x-y|<R}f(y)/|x-y| \leq \int_{|x-y|<R}|f(y)|/|x-y|\leq ||f||{L_1}\int{|x-y|<R}\frac{1}{|x-y|}]
🇵🇸μ🔆
am i making a logical leap
f(y) is a vector function?
well $y\in\mathbb{R}^3$
🇵🇸μ🔆
the whole time $x,y\in\mathbb{R}^3$. Idk if that wasn't super obvious, sorry
🇵🇸μ🔆
no am asking if $ f:R^3\to R$ or $f:R^3\to R^3$
right dude im so fucking spent lol
mikhail_kolesnikov
I don't think the last inequality is correct, it needs to be integrated by parts and carefully
sr gotta go
ofc, thanks for your time anyways
you're the only one on here who actually gave big effort it's v appreciated :3
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What the fuck is this twin
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I need help with proving this problem
I tried doing some calculations but got stuck
What am I supposed to do in that problem?
s^2 + c^2 = 1
Okay, what am I supposed to do after that one?
what's your goal again?
To prove this problem
with all of these problems the correct thing to do is to immediately convert both sides into sin and cos
using s^2 + c^2 = 1 and t = s/c
Alright, I'll try right now
Oh alright i got it
Thank you
.close
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am I the only one who think this is worded a bit ambiguously ?
to me it sound like shes earning 300 per trip
that does appear to be what it says
I think it would be 300 + earnings for apples each trip?
so you are saying that a sentence "for each trip lennox earns 300 dollars" does not mean 300 dollars TOTAL ?
ye its so annoying
but it could be 5 trucks going on 15 trips per week getting $4500?
it COULD, but I would say that its a lot more reasonable to interpret it this way
this happens sometimes, not a big deal
Each truck goes on 3 trips per week, 1 trip is 300$ so 3 trips would be 900$ meaning 1 truck earns 900$ per week so there are 5 trucks then right
saying "for each trip lennox earns 300 dollars" would not be accurate then
why is this not correct then ?
Because you didnt consider the fact that there are multiple trucks going
Its not ONLY 3t/W its 3t/W x no.of trucks
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Can someone explain to me why velocity is going downwards
I’m confused
as the acceleration is pointing downwards, it forces the velocity to (eventually) also start pointing down
or were you looking for a more mathematical explanation?
But I don’t even understand why acceleration is pointing downwards
gravity
Acceleration is supposed to be the instantaneous rate of change of velocity right ?
So how is it that
yeah?
gravitational acceleration is just taken as a constant system condition
you are always going to have -9.81 m/s^2
Again this isn’t explaining how that’s acceleration comes about from what we understand the derivative is
That’s gravity but I don’t get why that’s acceleration which is the instantaneous rate of change of velocity
i am saying that you should be looking at it from the opposite direction
given the acceleration, what is the velocity at any time t?
Integrate it
yes
Since there is no horizontal acceleration, the horizontal component remains constant
ok i mean
Yeah Idk man
we can be proper about it too
Can you explain it in terms of how acceleration is the rate of change of velocity
well we know that the acceleration is the rate of change of the velocity, and we also know that the acceleration is -9.81 m/s^2 (because that's how gravity works), so we compute the velocity from that
more explicitly the thing we end up with is v = (initial velocity) - 9.81t
if you differentiate that then you get -9.81 m/s^2
(which is the same as how gravity should work because we specifically chose this formula to make it work out that way)
your position at any time $t$ is going to be [
\vv r(t) = \vc xx(t)+\vc yy(t)
]
if you launch the projectile from an initial height $h$ with an initial velocity $v_0$ at an angle $\theta$, the components are going to be
\begin{align*}
x(t) &= (v_0\6\cos\theta)t \
y(t) &= h + (v_0 \sin \theta)t - \412gt^2
\end{align*}
due to the standard kinematics equations. Differentiating those, you get:
\begin{align*}
v_x(t) &= v_0\6\cos\theta \q(\t{note it being constant}) \
v_y(t) &= v_0 \sin \theta - gt
\end{align*}
Take the derivative once more, you get:
\begin{align*}
a_x(t) &= 0 \
a_y(t) &= -g
\end{align*}
Although, truth be told, this is like circular reasoning as the kinematics equations are derived from the above procedure done in reverse, so...
@foggy prairie Has your question been resolved?
Sorry you lost me at “how velocity works”
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DAG: Directed Acyclic Graph
I don't understand the fourth bulletpoint of this proof. What was taken to be the inductive hyptohesis?
I guess all DAGs of order <n have a topological ordering
strong induction?
well it's weak induction since we only use the fact for n-1
but it doesn't really matter
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im so confused rn, i should be getting x+4-4 but im getting x-4-4
,rccw
and i’ve tried using ai to explain it to me but i lwk need human help
can you show your whole process
and the original question too
,rccw
i think you wrote your $x$ as $y$
1 divided by 0 equals Infinity
forget the <-4 that’s me bent a dumbass
i kinda notice that for a long time
like wdym i switched x and y to find the inverse
im stuck on trying to prove it’s an inverse
huh?
which one are you doing gang
im doing a
1 divided by 0 equals Infinity
1 divided by 0 equals Infinity
well yeah and?
im getting f inverse x =2x^2+16x+58 lowk ;-;
that’s js u
so what are you getting as answer?
i mean what is the answer supposed to be
well it’s supposed to be x+4-4 which is just x
ik im not crazy
and i asked ai and it says that too but it’s talking abt some absolute value and changing the sign to negative for some reason and idek
bruh
im asking the uh f inverse function
it’s like saying this but idek what the absolute value has to do with it
WOW
..??
there we go
mb forgot to divide by 2
i already know that part i just wanna know how to verify that it’s an inverse
if g(x) = f-1(x) then g(f(x)) = x
and im genuinely right there but like im stuck right here
there is a mathematical process rather than just guessing lowk
yeah but what im not getting is x im getting -x-4-4
its not its the f inverse function lol
it is tho
its better than swapping x,y
lwk man i give up idek
.close if ure done
@tame sundial Has your question been resolved?
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Hellooo
Does anyone understand why this is?
X² becomes 2x
& -2x becomes (2-1) since x is 1 & it basically is the same thing when you multiply it??
But how did they get -1×2x^0
Do you know power rule for derivatives
No 😅
,tex .diff rules
riemann
More or less you'll need to memorize those. Certain the second and third for this problem
Is this the same?
yes
What's the difference between () & []?
nothing
Oh! & Its an increasing function if x/y + & decreasing if the x/y is - rigjt?
no idea what you just said
Oh okay tysm
?
For a certain function f which has a derivative, if f ' is positive, then f is increasing (upwards slope), and viceversa for negative values.
if f ' = 0, then the original function f is constant.
Ah okay tysm
@timid shore Has your question been resolved?
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\textbf{Problem (English).} Let $f=f(x,y)$ satisfy the partial differential equation
[
\frac{\partial f}{\partial y}=\frac{\partial^2 f}{\partial x^2}-2\frac{\partial f}{\partial x}.
]
Show that one can choose real numbers $a,b\in\mathbb{R}$ such that the function
[
u(x,y)=e^{ax+by},f(x,y)
]
satisfies the simpler equation
[
\frac{\partial u}{\partial y}=\frac{\partial^2 u}{\partial x^2}.
]
Also determine the values of $a$ and $b$.
Quantie
so idk what im supposed to do
do i first solve the last equation du/dy = d^2u/dx^2
then show that that also solved the first equation
you plug u(x, y) into the last equation and show it's true
so the first equation is just a factiod
well it could be, the dudes that wrote my literature love to do that kind of stuff
i don't know what you mean by factiod
just fun thing to know
i could try to solve it too
ok but imma solve the last equation
after deriving and simplifying i get
bf + df/dy = a^2f + 2adf/dx + d^2f/dx^2
which i think is wrong
do you know how id go with starting to deriving
this is just deriving u(x,y)
the word is differentiating
oh right yeah, my prof talked about that
in swedish, differentiate and deriving are two different things lol
ohh ok i plug this into the first equation then i get an easier equation to solve
dope
.close
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I asked chatgpt and looked online but I cant understand how to integrate two unrelated trignometric functions. Can anyone explain how I'm supposed to do this?
integrate by parts 
could you elaborate?
I'm sorry but I dont understand this formula
v is generally the one which is easy to integrate and u is the one which gives simple things on differentiation
read the beginning of https://tutorial.math.lamar.edu/classes/calcII/IntegrationByParts.aspx
In this section we will be looking at Integration by Parts. Of all the techniques we’ll be looking at in this class this is the technique that students are most likely to run into down the road in other classes. We also give a derivation of the integration by parts formula.
in this case, better to take u=x and v=sinx
it follows from product rule for derivatives
I see so I have to integrate and differentiate at the same time
thank you I will
f' = derivative of f yes
yes but its very simple just try it
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theres alot of useless info here
number of bathrooms and time in the shower
well i mean, from what i sse in your writing, you used those informations? honestly im not even sure what im seeing right now as its incredibly messy. also making sure again, your only using divisions right as a challange?

honestly i reccomend trying to do it normally, then trying to fit the challange for division after you solved it regularly
cause honestly trying to do it directly is just an extra headache
basically i would try and just spam a×b=a/(1/b)
as doing it regularly should be much simpler
were you able to find a formula for the total money spent first?
@empty tangle Has your question been resolved?
@empty tangle Has your question been resolved?
the 3 bathrooms and 480 minutes information is practically not used at all
i mean not needed
72 litres per person, meaning 432 litres for 6 people from there u can calculate
i dont understand it either how did you get here?
how about you try this method to get to the answer tho ?
x6p
works i guess
people normally find multiplication more intuitive though
in case i had 8 boxes with 9 pencils in each i would do $8 box \times \frac{9 pencil}{box}$ rather than $\frac{8 box}{\frac{box}{9 pencil}}$ due to how we describe things in english
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this is a Magnetic flux density-time graph the figure related to it is on top.can some one explain me plz why E2 is reduced? why it is not being added ,as area increase?
Physics server might be slightly more helpful
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Can I get help at b? Im quite stuck. It says to bring the expression to its simplest form (for context tg is tan and ctg is cotangent)
Are you trying to prove both sides are equal to each other?
No, there's an expression and i need to bring it to the simplest form
do you know the identity $a^2 - b^2 = (a+b)(a-b)$
parthisjoking
is it cos(x^4) or cos^2(x)? if the latter, then you can use the identity the person gave above
remember that cos^4(x) = cos^2(x) * cos^2(x)
Hmm let me see
So uh at the part with (cos²x-sin²x)²/(sinx*cosx) do i apply that for (cos²x-sin²x)²? Or at the last thing i wrote
just apply the identity i told u in the question
doing cos and sin is a waste of time
solve it in tan and cotangent
Oh, indeed I see it now
My teacher usually told us to do sin cos at the beginning bruh
It's easier working with tan and cotan, thanks for the idea, ill see what I do
Is this alr?
looks perfectly fine to me
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What is this formula and how can I use it?
show the full context
It gives an example of how you can use it on 84
have you read that example
and also understand what alpha_i represents
Alpha I is basically the power of (in 2^7, 7 is alpha I
product, you multiply all the numbers from i = 1 to i=k
and yeah, it is a capital pi
ai+1 ways to choose how times it appears in the factor why?
did you understand this
Yeah
Result:
128
try listing all the factors of 128
I'd be here all day lol
i don't know why but i expected you to just have memorized all the powers of 2 upto like 32 ngl
1,2,4,8,64,128?
amazing
missed a few
jsut missed two
16
usually a good idea is to pair them up like d, and n/d, so they multiply to n
and
one more
18
... no
again
try it like this
shush okay
32
correct\
the reason why the formula works is just basic combinatorics. which nobody has explained for some reason
ngl, just following riemann's lead
to make divisors of n you can pick some number between 0 and alpha_1 to be the exponent on p_1. similar with all the other primes. there are 1 + alpha_1 choices for the exponent on p_1
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048
Hey 2048 taught me something
following multiplication principle, the number of ways to pick an exponent on each prime is the product in question
the question is whether they even understand what prime factorization has to do with sth being a divisor, thats where riemann was heading i think
1+alpha b/c of the zero?
yes
i just don't understand why this is even a part of this book
like anyways youd have to know the prime factorization of the nubmer
yea
why would we even select a number less than alpha?
because doing that makes more divisors
doing this makes all of them
So 0 | n always right, but if you have a choice between 0-alpha every single time, aren't you counting 0 multiple times?
for each prime
0 does not divide n
also when you pick 0 on all the exponents, the corresponding number is 1
not 0
when you don’t pick 0 on all the exponents, the corresponding number will not be 1
there is no double counting going on but maybe that takes a little bit of convincing
it’s basically just that prime factorization is unique and so each distinct choice of exponents gives a distinct product
Oh mb x | 0, irrelevant here though mb
but can't you multiply them in any order and that also produces a factor?
are you suggesting that like… picking (1,2,5) as exponents will give the same number as when we pick (2,1,5) for exponents
Like for the example 84, the prime factorization is 2^23 * 7. We can do 2^03*7 to produce 21 as a factor? Is that the purpose of the formula?
yes?
That typed out really weird mb
you can type \* to avoid that
every triple (a,b,c) with 0 <= a <= 2, and 0 <= b, c <= 1 corresponds to a unique (positive) divisor of 84
there are 3 * 2 * 2 such triples

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problem in probability
I dont understand why this isn't a "stars and bars" problem where we put the green tomatos first which is x_1+...+x_n=n then complete the rest with red tomatos. I might be making this too combinatoric..
what exactly are you going to count with stars and bars?
you can do it with stars and bars but kinda complicated for no reason
number of ways to distribute green tomatoes then complete the rest with reds
it appears to be wrong though..
the thing is that a constraint like 0 <= x_i <= 2 is maybe more difficult to deal with than you’re imagining
i forgot to bound them by 2
it can be done. just not as easy
honestly it’s pretty irrelevant
im pretty sure i was wrong by assuming the tomatos of same color are indistinguishable
the answer will be the same whether you treat them as distinguishable or not
but if you get into some messy combinatorics instead of taking a probabilistic approach, you do need to decide whether to make them distinguishable or not
got it
though just to be clear, if we treat them as indistinguishable then there's only 1 configuration for this event, and thus the probability is 1 over the size of the sample space right?
which is the answer to the stars and bars calculation
hmm i have an objection to this
the “total configurations” are not all equiprobable i think
when you look at it like that
can i give you a suggestion on how to do the problem
start with making 1 basket. what’s the probability there is one red and one green tomato?
you pick one tomato at random, then another from amongst the rest
n choose 1 times n choose 1?
it should be depend on n
we pick a tomato. then the probability we pick a different color tomato to go with it is n/(2n -1)
there are 2n-1 total tomatoes left after after we pick one, and n are the other color tomatoes
yes i understand
you set one then figure the probability of getting the other
so we start with 1 basket and then?
go on to the next basket
(n-1)/(2n-3)
then the probability of this event is (n!)/(2n-1)!!
alright i think i got enough to go on from here, thanks
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Question
2 circles of radii 2cm have their centres 2√2 cm apart. Find the perimeter and the area of the shaded region (as shown in diagram)
My solution, what went wrong and where and why?
parthisjoking
while calculating
Oh that
area of sector
i love people who use pythagorean theorem here
Yea, as both triangles are congruent, so x = 45, and theta is formed by 2x so 90
Can't tel if this is sarcasm or not-
it is
but u took theta as pi while calculating area of sector
Oh shi- yes it's supposed to be π/2
Lemme recalculate
ye
Yup, that fixed it. Thanks for the quick assist
What method would you consider using here?
Could you explain me a bit?
are you familiar with vectors
I am a bit
atleast the projection of a vector on another
Yea
So how does it play a role here?
Yea, A can be split into Acostheta and Asintheta right?
yes
similarly
in the question
try splitting the length of 2sqrt2
into two parts
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How do I find the vertex with a standard quadratic form?
You know how to convert from standard form to vertex form?
h=-b/2a
Using the vertex form: since the squared term has a minus next to it, then the maximum of f is when that term is 0. Meaning for x=0.5, f is max, which makes f(x)=6.25
The vertex form is simply a clear way to see the max/min of the function
Without the vertex form:
The vertex is
(-b/2a , f(-b/2a))
That is just always truee
because if vertex form is a(x-h)^2 + k, expand:
ax^2-2axh+ah^2+k,
ax^2 = ax^2, bx must equal -2axh, c = ah^2 + k,
bx = -2axh,
b=-2ah,
h=b/-2a
I thought it was -b/2a?
This is likely not an appropriate question to ask... but, is there a channel I can go for math at a lower level, or are all the channels similar to this?😅
I was able to find 2 points (0, 6) and (1/2, 0)
idk bruh i js joined this server 20 minutes ago
wrong guy to ask
Would I plug these points in
Or is that just for finding A
im even a bit intimidated
Yes, I would appreciate that.
Let’s take it slow
First what does x-intercept mean?
The point thats on the X axis
And the x-axis is where y=0
Do you agree?
No
Why not?
It’s the reverse
If a point lies entirely on the x-axis
The y value of said point is 0
You took linear equations before yeah?
Yeah
y=0 is the same as the x-axis entirely
Moreover, x=0 is the same as the y-axis entirely
Huh
When you plot the line y=0
this line lies entirely on the x-axis
Since you vary x, but y is just 0
Yea
same with the x=0
y varies but x is always 0
So the line lies on the y-axis
Is that clear?
Yes
So from this conclusion we can have two rules
x-intercept is where the y value is 0
y-intercept is where the x value is 0
clear?
Yes
I substituted those
But for some reason i could not find 6.25
Even though it says it on the vertex form
That is the last part
Are you familiar with completing the square ?
Yeah
Try completing the square on
-x^2-1x+6
See what will happen
Add on subtract to in the same side
+6-6 (is still 0 so the expression is equivalent)
- there was a mistake on my part
It was supposed to be -x^2+1x+6
When completing the square think of a scale where the weights are equivalent.
Suppose I took away or added extra weight.
The scale side won’t be equal anymore so we try to make up for the lost weight to preserve the equality by adding what we took away, or taking away what we added.
In completing the square the idea still occurs
We add the square of the middle term divided by 2 but we also subtract to keep both sides equivalent
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I don’t understand how this integral is divergent. Wouldn’t the limits make those terms go to 0?
Check again
You got zero inside your interval
Doesn’t breaking the integrals up allow you to avoid that.
Not necessarily
At x=0 the limits shoot up to infinity
lim x->0 1/x^p doesn’t even exist for odd powers and is infinity for even powers
So the first limit would go to - infinity which makes it div?
Yes
And also the second term
In anyway
If one of those separated integrals diverges the whole integral diverges
Ah, I see, ty!
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help me
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
3
Tính delta
bài 3.1 anh ơi đ phải 3.3
Đúng rồi
3.1 delta j hả a
tiền lãi 1 xe là bn
=giá bán - giá sản xuất
Tính ra rồi thì đó là lãi 1 xe, rồi lấy tổng tiền vốn chia tiền lãi 1 xe là ra số xe cần
@glossy tapir Has your question been resolved?
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Why isn’t tan2x equal to 2sinxcosx
tan^2 u + 1 is sec^2 u
Yes
not 1 - tan^2 u
lmao
💀
luckily not
Omg 😭😭😭
anyway .close if ur done
Yuh
lmao yeah
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alr
<@&268886789983436800>
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hi!!! just checking if my work is correct
,w integrate sqrt(y+1) from 0 to 3
Dang man good handwriting
,w integrate t^3(1+t^4)^3 from 0 to 1
do u guys know anything abt binomials and inverse and norm distributions and all
thank you i try!!!
both r correct
Cooked
!occupied
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Good thing i misspelled
fhank you sonmuch !
Ahem no one saw that
👍
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y do u guys use ! this sm
Cuz we're jerks
!redir
This channel is only for on-topic discussion. Please take casual conversation to #discussion or #chill.
oowww
Don't be that guy now yoda
either way, if you want to ask your question, please use an available channel
thats acc cool ngl
it was a joke bruh cz they were asking y we use it so much
Are you still upset at me about the pre uni remarks 😭
YES
Oh
im a valued member of the preuni community
You are
:)
I value pre uni community too cough
tuff members of pre uni gng
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I need help i have a division test tomorrow on math from 1st quarter to 4th quarter lessons, I'm grade 10
what kind of division
Well mostly i need help with circle, tangent and secant
It is like from the 1st quarter lesson to the 4th quarter lessons, we'll do a test on that
Wow looks hard
I'm a fast learner but I want to ace this lol
Dangg, i believe in u, keep going
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Hi
can someone view my proof?
i'm not sure if i'm doing transfinite induction correctly
@drifting summit Has your question been resolved?
This looks fine to me (although it's been a while since I've done set theory)
I assume "$V_\beta^$ is transitive by $()\beta$" is meant to be typeset more like "$V{\beta^}$ is transitive by $()_{\beta^*}$"?
Edward II
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Hi, given that a general quadratic polynomial around two variables to be f(x, y) = ax^2+bxy+cy^2+dx+ey+f. I know that cross sections of this polynomial form a parabola. How can I prove that the minimal point of all the cross sections also form a parabola?
kinda vague but you can parametrize the "minimal points" and show that the resulting eqn is a parabola
This is what I am working with
cross sections with x constant or y constant or something else
Sorry I am not sure what you mean by parameterize. The process goes like this: for all the cross section parabola, extract the vertex(or the minimum point) and put it in a set. May I know if this infinite set forms a parabola as well?
I think constant y is what I am looking for
i think hes saying that you pick the constant y, find the minimum point based on that y, thus parameterising them
Sorry, I still don’t understand. May I know how we pick the constant y? I thought we were using all cross sections in the form of y=#
maybe find two or three non overlapping parallel parabolas first and write them here along with the conic with actual constants
Sure, I can do that! Just making sure, do you want me to find the vertex of three cross sections parabolas to find the parabola containing all the vertices?
<@&286206848099549185>
say if i look at $f(x,y_0) = ...$, i take the derivative with respect to x $\frac{d}{dx} f(x,y_0)$ and i equate it to zero, ill find the x, which for that $y_0$ gives the minimum of that cross section, in this case $x=\frac{-by+d}{2a}$
CherryMan
If I let g be the minimum value of f(x,y) for a specific y, then $g(y) = a(\frac{-by+d}{2a})^2 + b(\frac{-by+d}{2a})y + cy^2 + d(\frac{-by+d}{2a}) + ey + f$
CherryMan
that means, the minimums do form a parabola
and the plane the parabola is formed in is defined by x = -by+d /2a
(consequently the same holds for cross sections with x constant)
idk i might have made a mistake
Ok, that makes sense to me! So you first took the partial derivative to find a general equation of a cross section vertex. Then you plugged it back to the original function and it was still a general quadratic right?
Got it, thank you so much! May I know if the same logic applies when determining if a general cubic equation around three variables have cross sections that satisfies the property of a general quadratic?
Oh ok, I think I got it for quadratics, but have not understood how to generalize it for high degree polynomial
<@&286206848099549185> can anyone help me prove or disprove the generalization of this problem? Greatly appreciated!
@misty garden Has your question been resolved?
for n = 3 it is not true the resulting curve neednt be a polynomial take $f(x) = \frac{1}{3}x^3 + xy^2 - x$, if you take set y constant and take the partial derivative wrt x, you get the minimum at $x = +- \sqrt{1-y^2}
k
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
so points (+-sqrt(1-y^2), y, some z)
I understand, thank you for showing a counter example! 🙏
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Matrix matrix multiplication?
X(n) = M^n V where M is your matrix, and V is your vector
Do you know how to find the nth power of a square matrix?
no
i just started this unit
Do I have the right setup?
ive been stuck on this question for an hour 😭
The numbers are a bit jumbled. Currently, you've got a 20% chance that a juvenile becomes a juvenile, where you want a 20% chance they become an adult
Knowing how to mutiply a vector by a matrix is needed for this problem, make sure you know how to do that
But, even further, you are going to multiply two matricies together too
Are you studying ahead? This is a bit far from the beginning of a course
im only one lesson ahead sadly
Jeez they're not taking it easy on you haha
ah okay I got it now, i thought I was doing matrix matrix multiplication
i guess thats what happens when the midterm was as light as it was lmaoo
easy probability and easy recurrence solving + bernoulli's equation
and now after the midterm they have us doing expectation, variance, std dev, and now this
in a week
😭
is a vextor just a single column matrix?
Yes! A vector-matrix multiplication is still just a matrix-matrix multiplication
Or, a matrix-matrix multiplication is where you take the right matrix, break it into column vectors, multiply each by the left matrix, then reassemble the result
ah perfect tysm
i’m done looking ahead for today
I also like this graphic for visualizing matrix multiplications
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How to solve x^{5}+10x^{4}-16x^{3}+7x^{2}-10x+1 = 0?
$x^5+10x^4-16x^3+7x^2-10x+1=0$
Minhh
Wolframalpha?
No machines allowed.
He need to understand how to get to that answer
You won't have rational roots here
Not to rely on AI or digital tools
Not AIs like WA.
Do you know galois stuff maybe
nope
And how have you solved quintics until now?
Because I'm not even sure this is possible
i have not
Where did you find this problem
self-question
This one doesnt have beautiful coefficients.
This involves complex solutions for sure.
Yeah i kinda expected it
At least 2 conjugate pairs
why
can't it have all roots real
reason?
Cuz it have real coefficients
You should plot it if you want to be sure
Maybe 1 pair minimum
isn't that just a guess?
You can use conjugate pair root theorem, but it must have complex sols
In any case you probably won't find any roots because they are very complicated (there is no rational solution here)
I just chucked random x values in my calc, i only approximate a real sols in the interval -11, -12, so i assume the rest of 4 are complex, then 2 pairs, could be wrong
shouldn't there be a procedure?
No
Especially for degree 5 and above
You could be in a special case but then you'd have to use galois and such
An entry to #SoME2. It is a famous theorem (called Abel-Ruffini theorem) that there is no quintic formula, or quintic equations are not solvable; but very likely you are not told the exact reason why. Here is how traditionally we knew that such a formula cannot exist, using Galois theory.
Correction: At 08:09, I forgot to put ellipsis in betwee...
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for part b, how do i calculate P(X = 10) if i am approximating as a normal distribution?
total probability theorem?
how is it applicable here?
i have an idea, that is i calculate P(X <= 10) - P(X <= 9), but i'm not sure if that's correct
is 5% the prob of a board being defective or is it the percentage of the total boards that are expected to be defective
i don't see the difference
well i mean that works
if it is the former, then you can just apply total prob theorem
if latter then, 5% is the expected value , i.e. the mean observation
Have you seen continuity correction
i briefly read about it when the formula when the formula for P(X <= x) to approximate bin dist is introduced
but i'm not sure how to apply it to calculate P(X = x)
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What formulaes do you know about vector addition?
what did i do wrong
...
what is not perpendicular?
Bro its not a right angle triangle u cant use pythagoras here
these two vectors must be in a right angle to use the pythagoren theorem
simple vector addition works
perhaps you meant that the triangle isn't right-angled? $\va$ is still the hypotenuse
حسیب ♥
They are not in the same direction