#help-42
1 messages · Page 57 of 1
i meant sequence*
im no good at math so dont take what i say too seriously
So the context of that problem it’s a sequence
I think
I just don’t ljke how it says it doubles every four hours
Cuz now getting the ratio is hard
is n in days or hours?
That’s what I’m wondering
I think I have to convert it to days
Because an is in the days measurement
But idk
if it's in days then do 6(n-1) for the exponent
cuz it doubles every 4 hours
so it doubles 6 times a day
So it’s 3 million(2)^6(n-1)?
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how do you find the equation of a cubic graph
is there a video
beacuse for me the equation is k(x - a)(x - b)(x - c)
but i see this function and i get confused f(x) = ax³ + bx² + cx + d
@verbal otter Has your question been resolved?
do you have a sample?
Lemme get the question rq
if you're given a graph and want to determine the function you can use k(x - a)(x - b)(x - c) as you mentioned
now you just need to multiply out the brackets
which gives you the function in form ex³+fx²+gx+h
sorry for the trash quality 💀
ok so we can see the x-intersections
-2 1 3 I presume
so your function would be k(x+2)(x-1)(x-3)
and you still need to find k
@verbal otter so far clear?
Yeah thanks for the help
can you find k?
not really sure how to do that
so far we used all intersections with the x axis
meaning where the function is equal to 0
so let's find another point on the graph whose value we have
the y-axis intersection
is at 6
meaning f(0) = 6
and we know f(x) = k(x+2)(x-1)(x-3)
so let's set these two equal to find k
f(0) = k(0+2)(0-1)(0-3) = k*6
and since f(0) = 6 ====> k = 1
Ill try to send a better photo
ye
nop since we want -2 to be a root
meaning that if our function has the factor (x+2)
then if we insert x = -2
that factor becomes 0
:)
ohhhh
that's why you flip the signs
k so we have g(x) = k(x+2)(x-1)(x-3)
now we need k
the graph g(x) intesects the y-axis at 6
so we know g(0) = 6
.-.
wait so is 6=k or just g(0)
obv we need to find that out first
g(0) = k(x+2)(x-1)(x-3) = k*6
and since we know g(0) = 6
==> k = 1
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I don't know where to start with a problem like this- I was always really bad at the 3D conceptual stuff.
This triangle they're talking about lies inside a plane. Now with three points, you should be able to get two vectors in that plane. Do you have a tool that, if given two vectors, will spit out a vector orthogonal to both?
Cross product?
Indeed.
So try and find two vectors using the coordinates you're given. Then use the cross product to find a vector orthogonal to the plane the triangle is in (and hence orthogonal to the triangle itself).
You'll have to normalize it, since they are asking for a unit vector.
This correct so far?
Careful, you have to take the cross product of vectors not points.
So for instance, a first one could be the vector given by the side with endpoints (4,2,2) and (1,0,-4), which you can get the vector for by subtracting those two, giving (3, 2, 6)
Oh, right, I forgot about that part!
So then I could get another possible vector by doing (4,2,2) and (0,2,1) right?
Yes, that would work.
This look good so far?
Yes, that should be right!
Oomf, forgot about that part too.
Admittedly I don’t understand normalizing it all that much, what does that mean again?
To make it orthogonal right?
I thought we had already done it in the form of the cross product here?
Now you have the vector that is orthogonal to the triangle.
YOu want it normalized, so you have to divide it by its own norm.
I’m sorry, I don’t believe I quite understand what you mean.
RIght now, the vector you have has some length that isn't 1.
You want it to have the same direction, but length 1.
If you divide the vector by the length it has, then it keeps the same direction, and the resulting vector has length 1.
So divide it by itself? I think I’m recalling unit vector definition now from what you’ve said, although it’s a bit fuzzy since I still don’t have the greatest handle on it.
Yes somewhat. You divide by the length of the vector.
For instance, the vector (1,1) has length sqrt(1^2 + 1^2) = sqrt(2). This isn't 1. So if we take the vector
1/sqrt(2) * (1, 1) = (1/sqrt(2), 1/sqrt(2)), this new vector has length 1 but it still has the same direction.
Oh, I remember that length calculation- so it’d be the coordinates I have currently divided by the length?
Which would be the square root of each coordinate squared and added together?
So that’d be 2, 21, and -8 divided by the square root of 509?
That should be it.
That’s very messy…
How does this look?
I think that's good if they want 2 digits of precision.
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Not sure where i went wrong here?
How do you find the area of a parallelogram that is bounded by two vectors? EASY!
- Find the cross-product
- Find the magnitude OF that cross-product.
DONE.
I followed this video's instructions.
do u have work
That last bit next to the k says (36-40)
Nevermind, I just solved it- it was a calculation issue. Thank you!
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what was your reasoning for setting up this equation? 15 = 3n + 2
15 is an
Oh
What
What’s an then
these are your a_n values, you listed them before, what you mena to do is find the last one i assume? that would be plugging in 15 for n to find the a_15
you dont need to know it
you have a, d and n
then just use the sum of arithmetic progression formula
a_n is the score available on the nth question
not the total number of questions
15 is your NUMBER of questions
a_n represents how many points the nth question is worth doesn't it? the test has 15 questions, 15 is not a particular amount of points a question is worth
two weeks is 14 days no?
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How many ways can you arrange the letters in the word ARRANGEMENT such that no two As are adjacent and all Rs are adjacent
neat question
Maybe if it was just one condition say, no two As together, I could have gone about it by doing 9! × 2C2. ah no there's reptitions. it's confusing
can you find the number of arrangements if no restrictions are set?
that's 11!/(2!×2!×2!×2!) right?
exactly!
now, let's look at the second restriction
two R's are adjacent
hm, we could see them as one element in that case
since they're always next to each other
so we only have 10! / (2! * 2! * 2!)
so far clear right
yes got it
yup makes sense
ok, now what we can do is:
we look at the negated first restriction
so we'll look at all cases where A's are together and R's are together.
and we subtract these cases from the cases where R's are together
because then we get the cases where R's are together and A's aren't together
alright yes
to express it in set theory: |notX and Y| = |Y| - |X and Y|
where X, Y are your restrictions here
Will this be 9!/2!×2!?
right!
therefore:
10! / (2! * 2! * 2!) - 9! / (2! * 2!)
[R's adjacent] - [R's & A's adjacent] = [R's adjacent and A's not adjacent]
and the result is 362880 🦇
yess
oh damn okay
as a general advice, it's often easier to consider the opposite case
don't get too hung up on specifically finding the combinations for the desired case
bc subtracing the opposite is sometimes easier
say just for this one restriction where we have to find out the number of arrangements with no two As adjacent.
And I know one approach now is to consider the opposite case and subtract it from 11/2!×2!×2!×2!
Although if I were to do it directly, how could I do it?
yup!
hm, would have to think a bit, makes the cases quite annoying
probably by tree splitting
but maybe there's a faster way
by directly I mean, I saw this one video where he did it by thinking of this as gaps between the letters.
so it was no vowels together in a word.
so he arranged all the consonants and now there's a number of spaces between them for the vowels
lunatic mind helping me out when u finish this?
sorry if I'm taking some timee
you can occupy your own channel here and passengers will eventually come by and guide :)
i did and ive been waiting for 30 minutes lol
nono you occupied the channel, you can keep it as long as you wish
the channels don't run out
others can simply open a new one
oh okay
oh k, will look in a sec
ty and good luck harry
hm I think tree splitting would be the best I guess?
but it's still somewhat horrible in contrast to doing the opposite case
@tawdry lodge sir can u help me
.-.
It was this
yes I understand
im in the 10th grade lol dont know logarithms
yea in this case it's easier to do this separate aspect
first placing down the consonants and then the vowels
would work for the initial as well true
why was it 6P3?
what do you use APB as notation for?
permutations
because you place three vowels onto 6 possible spots
ok
-D-G-H-T-R-
each - is a possible spot
for the vowels
and you distribute 3 of them onto the 6 spots
in our case, or in any case where say all the vowels were same we'd do 6C3 tho right?
that's by 6P3
yea since order is irrelevant
np 🐛
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I just do as I like (as everybody does)
essentially voluntary guidance for strangers :)
true. It's voluntary
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i forgot how to change my bounds....
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let's call the point at which the rectangle touches the circle "P"
we know that OP = CD, correct?
Yes
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So its 6
yes
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@final zephyr if ur just looking for answers in this server you wont learn anything im guessing this is a test for your math class or something
nah it's probably practice
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perchance
It helps if you know the indefinite integral of log
any tips on where to stop?
look for the line u know how to integrate
so i integrate until idk how to integrate anymore?
no
don't use tabular method for this if you're getting confused
it helps to understand what's actually going on when applying ibp
just do basic integration by parts
look at the integral you get
seee if you can solve that
👀
yeah essentially im just getting a bucnh of u v
tabular method is like a speed up trick for IBP, but you have to really know what is going on like Mqnic said
but usually it stops when i can lets say simplify it
but when it comes to ln idk wheres the line i should stop at
Try it without using the tabular method
Show what the result is
(if you get stuck)
here
mhm not on this problem in particular but
i wanna ask how i can translate
where to stop here on the tabular
If you don't know where to stop using the tabular method don't use it
Normal integration by parts is all you need
I've never used that tabular method in any of my classes
thing is my teahcer knda requires it
I doubt that
at least he said idk if hes gonnna grade it differently
That would be very dumb, as the tabular method is just integration by parts
written less cleanly as to make you go faster
true
alos im redoing it cuz i did it worng apparently
wait
just curious
cuz i think i figured it out
on tabular do we stop when we can find a product on the row that can be integrated
anyway ty!
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did I utilise the properties of the binomial series correctly?
@thick sinew Has your question been resolved?
@thick sinew Has your question been resolved?
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I dont know what I did wrong
u = 3x+9
(u-9)/3 = x
So sub it in to get
((u-9)/3)(u)^9
Remember, dx = du/3
No wrong steps so far, just reminding you that dx has to be changed into du/3
I still dont follow sry
OK, when you substitute, you have to substitute for the dx part as well
The dx part in the integral
Why does it become du/3
Ahhhh yes
I think I remember this rule now
That was what I did wrong 😇
Thank you! I think I can finish it now
❤️
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.reopen
i need help to solve it
try to convert that (i^2)/(4^i)
that is what i have now
teacher explained how to do it, but havent finished
i also know that sum of i/4^i = 4/9
and sum of 1/4^i = 4/3
but it's from i =0 to oo
here we have k = 1 not 0 in the last line and i don't know why
someone please help
gpt saing that the answear is 5\9
but when i am splitting the last equation i have:
sum of (2k-1) / 4^k
sum of 2k / 4^k - sum of 1 / 4^k
second sum is 4/3 from what i know
so we have
sum of 2k / 4^k + 4/3
sum of 2k / 4^k is my question i have no idea what to do with it. I tried the next:
sum of 2k/4^k is two sums of k/4^k which is from what i know 4/9. so:
2 * 4/9 which is 8/9
then we have
8/9 - 4/3 = - 4/9
which is not correct as i suspect
and i don't know where is my mistake
here is my messi notes if it will help
I have explained my problem as detailed as possible for me. Please help me to solve it and if you need something else - ask
sry for my bad english 😢
no worries
not really helpful honestly
@leaden bluff Has your question been resolved?
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Questions: (1) what is an algebraic subvariety? it does not seem to match the definition on wikipedia where it is the set of zeros while here it is a polynomial system, (2) what is the set sigma in the example supposed to be? a set of polynomials? (3) how is sigma calculated in the example?
R is the vector space representing systems of n polynomials in n variables with complex coefficients
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Working on a lab, could someone confirm that I'm doing my math when substituting values of k into the chi-square distribution equation?
@noble notch Has your question been resolved?
<@&286206848099549185>
Please help 
Oh wait I just realized sumn
The gamma function is in terms of k/2, not x, silly me
new k=4
new k=2
oops- factorial should be on the outside of the parentheses
I finally got it I think, lemme draw them graphs
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after I put 3x on the same side with 8 do I divide by -2?
depends on what the question is asking for
The slope and y-intercept
show your attempt
If I divide by -2 I get: Y=3/2x+4
you didn't divide properly
i meant 4
wrong sign
looks ok now
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✅
I dont know how to simplify
are you aware of this identity? :
Reaper
Yes
do you see something similar in the question?
the numerator
Idk
Yea because the first and second are the same
the numerator and one term in denominator is same
so it would just be x+7
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i have this
i need help on setting the integrals up lol
functions are
2x=1-2y-y^2
y=-x
y=-3
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do you know the form of a line when it passes through a particular point (x1,y1) and has slope m?
$(y-y1)=m(x-x1)$
Reaper
so do i find the gradient
yes and you can do that by using the 2 points given to you
and use this specific equation ^^
is it the same as y-b=m(x-a)
yes
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@onyx quiver Has your question been resolved?
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how would someone solve this using grade 12 advanced function, i dont quite know how to check if something is a possible solution
<@&286206848099549185>
@hallow mountain Has your question been resolved?
you need to know something about csc. and you need to know some spacial values for such functions. can you express csc in terms of cos or sin?
@hallow mountain
csc is just 1/sin i think
right
i would like to know how do i plug in 5pi/3 to get possible solutions
just a moment.
write 1/sin instead of csc. what do you get?
1/(sin(x))
now modify this equation to get sin(x)= ...
i dont see how i can do that without multiplying a sinx to the 2/root(3) than i dont know how i would remove it from the 2/root(3)
is 1/sin x = -2/root(3) a possible step?
yes but how i would remove the 1/ from sinx
Just plug in 5pi/3 into the equation
That should be easier than solving the equation
since it doesnt equal 0 doesnt it mean its not a solution
but the question says it is
,w 1/sin(5pi/3) + 2/sqrt3
?
Your calculator is set to degrees my friend
yep
yea
k thx i was super confused
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[tan(x)csc(x)]/cos(x)
I cant tell if its 1 or sec^2
You want to take its derivative or just want to evaluate it
$\frac{\tan(x)\csc(x)}{\cos(x)} =
\frac{\tan(x)}{\sin(x)\cos(x)} =\frac{\sin(x)}{\sin(x)\cos^2(x)}$
Sherif Player
Then you can see what value you should get
So its sec^2 (x)
Yeah
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Not sure where to begin
I have never dealt with a function where they specify "on the entire real axis" or one thats a piece-wise or whatever its called
"Differentiable on the entire real axis" = "differentiable everywhere"
right, okay
It should be pretty easy to imply that most points are differentiable. Any giving you any trouble?
Well its just the general setup
Im not sure how to word or write it
In fact, I don't even know what happens when we square a two-piece like this
It's not really important that it's a piecewise function
What definition of ReLU are you using here?
So f(x) = x² for any x > 0, clearly differentiable
f(x) = 0 for any x < 0, clearly differentiable
But the point x = 0 is weird
As that's a join between y = 0, and y = x²
We can refer to the definition of the derivative, to see how this should be differentiated
why is this point weird?
To the left, we've got y = 0.
To the right, we've got y = x².
Is this even differentiable?
mhm
Let me get the definition
But
from the definition we see that it's x^2 for x >= 0
and not just for x > 0
@civic dirge
mhm
Like you're saying, the right-hand limit obviously exists, because that's all just x²
https://en.wikipedia.org/wiki/One-sided_limit limit not derivative
oh, okay
Rigth, we have a right-handed limit
Which is x^2
Are you here?:)
<@&286206848099549185>
No I meant left-handed derivative
That is, the limit for the definition of the derivative, but only taken as the left handed limit
We can "better expose" this, by subbing -h in for h:
lim [f(x - h) - f(x)] / -h
Does that exist for x = 0?
@latent zinc Has your question been resolved?
kheryhvargen zunichan therthurkiler
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Does anyone know how they came up with this? I couldn't find any other resources online aboout it
@foggy plume Has your question been resolved?
@foggy plume Has your question been resolved?
<@&286206848099549185>
Perhaps something related to this?
Probably better to ask in #real-complex-analysis
Also $\tan(ix)=i\tanh(x)$
Max
It's not really complex analysis though...
that's why I was scared to ask there...
$\frac{1+\frac{b}{a}i}{1-\frac{b}{a}i}=\frac{a+bi}{a-bi}$
Max
They might have just got the identity wrong?
Someone is more likely to recognize it there
I verified it though, it works
Engineers induction?
how would you go about starting that then?
Oh that was a joke lol
Engineers induction as in subbing in values
$a+bi=re^{i\theta}\Rightarrow \frac{a+bi}{((a+bi)(a-bi))^{1/2}}=e^{i\theta}$
Max
I think this is how they did it
So I've divided both sides by the magnitude of $a+bi$ (which is $\sqrt{(a+bi)(a-bi)}$)
Max
but it's not....
It should be
the magnitude is $\sqrt{a^2-b^2}$
OmegaAplha
Split complex numbers?
Huh okay lmao
In algebra, a split complex number (or hyperbolic number, also perplex number, double number) is based on a hyperbolic unit j satisfying
j
2
=
1.
{\displaystyle j^{2}=1.}
A split-complex number has two real number components x and y, ...
I like some of your ideas though, some of these formulas could be good starting points for finding the solution
I got no idea tho, I guess alot follows from CA tho like how Trig identities follow to Hyperbolic
Good luck
thank you 🙏
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Can someone help me understand tensor products?
for v.s. U,V : U⊗V has elements z=x⊗y ; with x and y from U and V respectively
The problem is that absolutely every source refuses to define x⊗y in any concrete manner.
All I know is that there is some kind of bilinear property between x and y
My textbooks says "x⊗y should define a bilinear (vector-valued) function of x and y."
The dot product is a bilinear function of x and y, right? x•y
So is the dot product in U⊗V?????
On the other hand, it seems that these elements z exist for each pair of x and y as opposed to being
And I have had physics friends define x⊗y as being a "tensor" that could take the form of
[x1y1, x1y2, x2y1, x2y2],
or
[x1y1, x1y2,
x2y1, x2y2]
depending on who you ask.
The more I look into it, the less consistent and more confusing it gets.
You might get some more help in #old-network, there is a physics specific discord there.
I'm not in physics at all. I am taking the second course in a linear algebra series. It is more abstract and mathematical.
tensor product is a very general object
in the same way that a "product" is a general object
it is a famously tricky concept when you first encounter it
@orchid tendon find your own help channel, read #❓how-to-get-help
Someone else said 5
I don’t see a available channel
Oh okay thx
I really don't get the 'generality' of it. Is there any kind of explanation?
well the vector/matrix example from your physics friends is correct
in fact the tensor product of two vectors is both of these things
ok, so how is that object related to or representative of a bilinear function as my textbook states?
neither is the "correct" one
@peak lava don't GPT post, come back in a couple hours
Previously on the blog, we've discussed a recurring theme throughout mathematics: making new things from old things. Today, I'd like to focus on a particular way to build a new vector space from old vector spaces: the tensor product. This construction often come across as scary and mysterious, but I hope to shine a little light and dispel a litt...
i would stick about to explain further but i gotta run
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how do i solve a depressed cubic say x^3+x+1=0
real solutions only btw
are you aware of cardano's formula
no
well it's a direct result for solving cubics of that form
you can avoid having to memorize it by following the same substitutions used in its derivation
okay ill check that out
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So for this question you should apply rule of product axiom and rule of addition axiom
is this for part i and ii respectively?
<@&286206848099549185>
<@&286206848099549185>
for part i), the only way that the player would have no chance of winning is if both dice show the same number, so just show the probability of rolling 2 of the same numbers
@prime topaz Has your question been resolved?
oh i see so is it 1/6
wait so how do u do part ii)
you just work out the probability that the player rolls a winning roll on the third die. its a bit more involved than the first part but its not too much more complicated
but how..
on the third die, a 1 and a 6 can never be winning rolls, if they roll a 2, with a 1/6 probability, the first two dice rolls must be 1&3 or 1&4 or 1&5 or 1&6, and you work out those probabilities. there might be a more elegant way but if i was doing the question in an exam i would just brute force it.
and you do that for each roll of the third die
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What to do next? I can't seem to do anything with (x^2+2) to remove (x-1)
what happens if you substitute x = 1 in there?
Can you make it more clear? It’s blurry
Yes
wait
the top becomes 0
OK
which is why i need to get rid of (x-1)
Can you make it more clear? It’s blurry
what's wrong with that
I cant see it clearly
Isn't that against the rules in limit
Wait
......
No, why?
would you have a problem with $\lim_{x\to2}\f{x-2}{7}$?
0/3 would be 0
hayley!
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sorry for the hassle
LOL
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Discrete mathematics problem
Especially the b one
what did you try
you already know how to represent a even number E(x)
for any could be said as \forall
yeah
wait I know about these symbols and logical thing
cool
do you mean how to write out in TeX?
what is tex?
can you explain to me please
I mean I have to represent it into symbols and formulla
hey
whats O(x)
@alpine cedar
$$(E(x) \forall x \in \mathbb{Z}) \rightarrow (E(x) + 1 = O(x))$$
ℕaive
I assume O(x) is any odd.
@alpine cedar Has your question been resolved?
@alpine cedar did you solve it? :)
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can someone help with this?
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i need to define DF using a and b, i know that ∆AFD is similar to ∆CEF
Please help, also why are vectors so hard.
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@leaden tinsel Has your question been resolved?
is the a vector AB or BA?
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help
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I have a true/false question. This is the statement:
Let V be a set that contains the 0-vector, and such that whenever u and v are in then u+v is in V. Then V is a vector space.
I know that I need to check the axioms to verify that it is a vector space, but I'm not sure what to say about the scalar ones.
@tired gyro Has your question been resolved?
<@&286206848099549185>
True?
That is what I assumed, but I'm not sure if the addition was defined to be standard addition.
The only thing I can really say for sure is that it fulfills additive closure and additive identity.
BotToes
I see, so since the statement jumps to the assumption only based on the additive axioms and not the scalar axioms, I can say it's false since it doesn't mention V being closed under scalar multiplication.
Ok, I understand now. Thanks!
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This doesn't seem right
I'm not sure how I can proceed with the -4sec(theta)^3 * sec(theta) * dtheta
Ok I figured out it's right
I just need help with one thing
Since its x^2-16, does that mean x is -4sec(theta), or is it +4sec(theta)
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hello!
i think i'm misunderstanding this question on self-dual connectives in predicate logic
phi is just some sentence and f its truth function
try asking in #foundations
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i have to show that it exists 2 constants A ans B such as there's this equality
P is a polynom of degree 1
I have no idea how to do it, developing P doesn't seem that much helpful at first glance
@random stratus Has your question been resolved?
i found the integral is equal to a + b
so a + b = A(a*alpha + b) + B(a*beta + b)
Idk if this could be true
<@&286206848099549185>
yes that is correct
assuming that it is required for any or all P(x) = ax + b
as in a and b are arbitrary
well A and B doesn't depend on a and b so that's fine
gl :)
i solve the system and i found B = 1/alpha - beta and A = -B
i think that's correct
thx for the help
ye i'm dum
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A lot of the time, people use f'_n uniformly convergence to f' to prove f_n uniformly convergence to f. Does the reverse implies? Does f_n -> f uniformly implies f'_n -> f' uniformly?
if f_n -> f uniformly, sometimes f' doesn't even exist even though f_n' does
hmmm, what about if f', and f'_n exist?
still you can find counterexamples
take fn(x) = x^2sin(1/(x+(1/n))) on [0,1]
this converges uniformly to f(x) = x^2sin(1/x)) when x non 0 and f(0) = 0
fn and f are both derivable
yet fn' cannot converge uniformly to f' because f' is not continuous whereas fn' is
small update, i had to change to [0,1] to have uniform convergence
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i changed the function again sorry
now it should be good
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Pete’s Sno-Cone Stand sells three different size sno-cones. Pete will earn $6 for each large sno-cone,
$3 for each medium, and $2 for each small that he sells. Suppose Pete sells twice as many small snocones as he sells large sno-cones. If Pete sells 55 total sno-cones and earns $175, how many of each size
sno-cone did Pete sell can you help me put it in augmented matrix
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how can I approach this
@teal hull Has your question been resolved?
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Having trouble again with this indexing
My question is only about the sentence beginning "Argue that there is a strictly increasing..." and before.
I don't really understand how what is stated is equivalent to x being cauchy here
dont we need to put some restriction on k?
I understand that we could equivalently state whatever like
so it could be more restrictive
i still don't believe it
i guess i dont mean equivalent in that way
i mean, how do we know this will be true given (x_n) is cauchy
use cauchy definition with a well chosen epsilon
also actually it is equivalent to being cauchy I just noticed
i may need help 
ive been playing with it
i get that you could just let m,n > N in whatever cauchy defn you have
then just take n_k to start at the m such that m>N
and fix n>m>N to fix that problem
then we may as well just select epsilon = 1/k^2 for all it matters
but this doesnt resolve the issues does it
that's precisely it
oh 
select epsilon = 1/k^2
right and there doesnt need to be any care put into that
this gives us N such that for m,n > N, ...
hmmm
is that necessary
i guess yea you want to describe n_k
or, its possible
anyways
i think i can struggle forward 
thanks
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can someone help me find a counterexample to show this statement is false? (or tell me why its true but i think its false)
I was thinking like what if you just made a set out of the terms of the infinite series $\sum_{n=1}^{\infty} \frac{\sqrt{2}}{n^2}$ ?
goobybalooby
or does that not do it? are the irrationals closed under addition?
well im thinking $\sum_{n=1}^{\infty} \frac{1}{n^2}$ is bounded because it converges to $\frac{\pi^2}{6}$, but all the terms would be rationals
goobybalooby
so then just multiply everything by an irrational number
o sure if you can use that then you're good
oh fosho?
yea
i mean i think i can use it lol we havent proved it but its come up in other hw problems so i hope i can use that
and the irrationals are closed under addition? is that true?
you also need that sqrt(2)*pi^2/6 is irrational
no
e.g. sqrt(2) + -sqrt(2) is rational
i think we can take this as a given
hmmmm okay so maybe its not a good one to use then
well it's not hard to prove all the partial sums of this series are irrational?
this one rather
how can you do it if the irrationals arent closed under addition?
for nonzero rational p and irrational q, p*q is irrational
just factor our sqrt(2) for every term?
yea
right
okay that makes sense. thank you!

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