#help-39

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graceful garden
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Oh so 2 seperate functions

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What

glass meadow
pearl pondBOT
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@graceful garden Has your question been resolved?

graceful garden
pearl pondBOT
#
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pearl pondBOT
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crimson nebula
pearl pondBOT
crimson nebula
#

The velocity is expressed in polar coordinates. But I didn't understood the last line .

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How can we express the basis vectors r hat and θ hat as a function of time ?

unborn abyss
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well, they rotate around the origin along with the wheel, right?

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rhat is the direction the spoke is pointing, and thetahat is 90º ccw from that

crimson nebula
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My question is

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See the fourth last line

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They have expressed velocity in terms of r hat and θ hat

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And they are saying , we need to know how r hat and θ hat are changing

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My question is .... How can I do it

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How can I write r hat and θ hat as function of time

unborn abyss
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coming up with an equation might be kind of annoying but you need:
rhat(0) = (1, 0) [pointing to the right]
rhat(w / (π/2) ) = (0, 1) [pointing up]
rhat(w / π) = (-1, 0) [pointing left]
and rhat(w / 2π) = (1, 0) [pointing to the right again]
like it needs to be a unit vector rotating in a circle

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there's probably a clean way to do it

crimson nebula
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I respect your effort , but I think u r not getting my question

chilly trellis
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Do you know about polar unit vectors and how to express them as Cartesian unit vectors? This could make explaining the translation easier but if not I don’t want to add confusion

crimson nebula
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Yes i know

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Basis transformation

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But ....

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I want answer in purely polar coordinates

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Expressing unit vectors as a function of time

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But Not in terms of î and j

sharp ravine
unborn abyss
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oh yeah that's a good idea

crimson nebula
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.close

pearl pondBOT
#
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royal galleon
#

He defines delta k / delta t as F * delta x/ delta t. But then we he multiples be delta t he has dx and dy. How did he just miswrite ?

prime stream
royal galleon
# prime stream again, better add the link to the video and the timestamp

https://youtu.be/R74EhX8O0Nw he gets the last line at around 23 30

For more information about Professor Shankar's book based on the lectures from this course, Fundamentals of Physics: Mechanics, Relativity, and Thermodynamics, visit http://bit.ly/1jFIqNu.

Fundamentals of Physics (PHYS 200)

The discussion on the Law of Conservation of Energy continues but is applied in higher dimensions. The notion of a fun...

▶ Play video
prime stream
royal galleon
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Yes I see that delta x is just for one dimension. But he can have delta x and delta y represent the x and y components in 2 dimensions. What I don't understand how we get dx and dy since those are instanaous

prime stream
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when they are not the part of the $\dfrac{df}{dx}$ symbol, then they are different things

jolly parrotBOT
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Dedekind

royal galleon
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Ok I see. Thanks for clarifying

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left anchor
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How do I get the eigenvectors of a 3x3

pearl pondBOT
left anchor
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I only found methods for 2x2 so far if I’m not mistaken
They were talking about characteristic polynomials and means and other stuff

I’m not really familiar with any computations around this topic but I have a matrix and I’m supposed to find both the eigenvalues and -vectors

toxic lichen
left anchor
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I think I understand the meaning of
Matrixvector = scalarvector

Which I wrote as
M x = lambda x

If you rewrite it you get to
(M-lambda*identity matrix) x = 0

Right?

left anchor
toxic lichen
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the roadblock is whether you know how to calculate 3x3 dets

left anchor
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All i managed so far was writing down rje same matrix but with -lambda on the diagonals which isn’t really helping

toxic lichen
left anchor
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111
011
001

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Sorry for the format

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Is this right or did I fuck something up

toxic lichen
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1 1 1
0 1 1
0 0 1
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this is your original matrix?

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the third -λ is on the wrong entry.

left anchor
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Yes

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Sorry I’m distracted

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So it’s (1-lambda)^3

toxic lichen
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what you should have is $$\det \bmqty{1-\lambda &1&1 \ 0&1-\lambda&1 \ 0&0&1-\lambda} = 0$$

jolly parrotBOT
toxic lichen
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should be fairly easy to tell the eigenvalues here.

left anchor
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Doesn’t change my result does it

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Should apply to any Matrix diagonalized like this

toxic lichen
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anyway yeah the only eigenvalue you got is λ=1. with algebraic multiplicity 3.

left anchor
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Im looking for the eigenvalues/vectors only
Does the degree have any effect on those?

left anchor
toxic lichen
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multiplicity as a root of the charpoly.

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the degree is a sanity check: for any n by n matrix its charpoly has degree n.

left anchor
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I see

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So I get degree n

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See that I didn’t make a mistake

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Get lambda=1

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And have the only eigenvalue?

toxic lichen
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yes. λ=1 is your one and only eigenvalue here.

left anchor
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Can I already decide whether I could diagonalize this matrix?

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My guess would’ve been no because there’s one eigenvalue and 3 columns

toxic lichen
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so like

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generally when you have less eigenvalues than the size of the matrix, you're right to SUSPECT that the matrix could fail to diagonalize.

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and in fact this matrix is non-diagonalizable,
but it is not always so in general.

left anchor
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Is
100
010
001
A possibility?

toxic lichen
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also if you're going to type out matrices the dumb way then please at least put spaces between the entries.

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there's no rule of matrix algebra that says a matrix entry can only be one single digit.

left anchor
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I don’t have the time to learn latex notation

toxic lichen
toxic lichen
left anchor
toxic lichen
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the problem is that it looks like ass

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anyway we can keep arguing about typography and defense of bad habits, or we could go back to the math

left anchor
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1 0 0
0 1 0
0 0 1

Happy?

toxic lichen
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yes that's better.

toxic lichen
left anchor
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Is this approach right for that matter?

toxic lichen
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no

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first, put lambda=1.

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second, just write it as an ordinary algebraic linear system.

left anchor
toxic lichen
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there's a third equation that boils down to 0=0 but yes.

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x is left free.

left anchor
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I added a third row with all zeros
I just forgot it on the picture

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Checks out with my visual solution for the question
I assumed it was only the x axes that was holding the eigenvectors

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Since we have a specific line of eigenvectors
Can we conclude there’s only one such line and say it can’t be diagonalized?

toxic lichen
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we have only one eigenvector up to scaling: [1; 0; 0]

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so yes, that's not enough

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therefore not diagonalizable

left anchor
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I was supposed to find all eigenvalues, -vectors and decide whether it’s diagonalizable
Ig I’m done then

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.close

pearl pondBOT
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frozen lynx
#

<@&268886789983436800>

pearl pondBOT
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vestal thistle
#

Hello, could someone check if this proof looks good please?

\begin{Definition}[Subset of a set]
    Suppose $A$ and $B$ are sets. If every element in $A$ is also an element of $B$, then $A$ is a \emph{subset} of $B$, which is denoted $A \subseteq B$.
\end{Definition}

\begin{Definition}[Substraction of sets]
    The \emph{substraction} of $B$ from $A$ is the set $A \setminus B = \{ x : x \in A \text{ and } x \notin B\}$.
\end{Definition}

% --------------------------------------------------------------------------------

\begin{Theorem}
Assume $A$, $B$ and $C$ are sets.
If $A \subseteq B$, then $A \setminus C \subseteq B \setminus C$.
\end{Theorem}

\begin{proof}
Let $A$, $B$ and $C$ be sets.
Either $A$ is empty or non-empty.
First, suppose $A$ is empty.
Then, $A \setminus C = \emptyset \subseteq B \setminus C$. 
Now suppose $A$ is non-empty.
Then, either $C$ is empty or non-empty. 
Suppose $C$ is empty.
Then $A \setminus C = A \subseteq B = B \setminus C$, which is what we wanted to prove.
Now suppose $C$ is non-empty.
Let $x \in A$.
There are two cases for this: either $x \in C$ or not.
\begin{case}
Suppose $x \in C$.
Then, by the definition of the substraction, $x \notin A \setminus C$.
Since $x$ was chose arbitrarily, it holds for any $x$ in $A$. 
Thus, $A \setminus C = \emptyset \subseteq B \setminus C$.
\end{case}
\begin{case}
Suppose $x \notin C$.
Then $x \in A \setminus C$.
Because $A \subseteq B$, we have that $x \in B$, so $x \in B \setminus C$.
Since $x \in A \setminus C$ implies $x \in B \setminus C$, by the definition of the subset,
we have that $A \setminus C \subseteq B \setminus C$.
\end{case}

Therefore, in any case, if $A \subseteq B$, then $A \setminus C \subseteq B \setminus C$.

\end{proof}
glass meadow
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x in C does not mean A \ C = emptyset

vestal thistle
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Allow me to elaborate

jolly parrotBOT
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Mor Bras

vestal thistle
glass meadow
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Did you only change "Case 1"? I'm not reading all that again

vestal thistle
glass meadow
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Ok, it's still wrong

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I know what you're trying to do but that just doesn't work

vestal thistle
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<@&268886789983436800>

vestal thistle
glass meadow
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That premise is only a special case though

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You seem to only consider the cases where all elements of A are in C or none of the elements of A are in C

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In general, A can contain some elements that are also in C and some that aren't

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Just take A = {1, 2} and C = {2}

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Your case 1 would only apply to the element 2, since it's the only element in both A and C

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Yet, A \ C is not empty

vestal thistle
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I see

glass meadow
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Then your case 2 would apply to the element 1, and there it actually works but without case 1 working, your proof is wrong

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I'd say you're just going about it wrong

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You want to show that A \ C included in B \ C

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So pick any element of A \ C, and show that it is also in B \ C

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(it's actually just what your case 2 does, so in reality your case 1 is useless, but you need to tidy that up)

vestal thistle
#
\begin{proof}
Let $A$, $B$ and $C$ be sets.
Either $A$ is empty or non-empty.
First, suppose $A$ is empty.
Then, $A \setminus C = \emptyset \subseteq B \setminus C$. 
Now suppose $A$ is non-empty.
Then, either $C$ is empty or non-empty. 

\begin{case}
Suppose $C$ is empty.
Then $A \setminus C = A \subseteq B = B \setminus C$, which is what we wanted to prove.
\end{case}
\begin{case}
Now suppose $C$ is non-empty.
Let $x \in A \setminus C$.
Then, by the definition of substraction, $x \in A$ and $x \notin C$.
Because $A \subseteq B$, we have that $x \in B$, so $x \in B \setminus C$.
Since $x \in A \setminus C$ implies $x \in B \setminus C$, by the definition of the subset,
we have that $A \setminus C \subseteq B \setminus C$.
\end{case}

Therefore, in any case, if $A \subseteq B$, then $A \setminus C \subseteq B \setminus C$.

\end{proof}
jolly parrotBOT
#

Mor Bras

glass meadow
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Maybe make it clearer that you have x in B and x not in C, so x in B\C

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I know you said x not in C in the previous sentence but it reads like you're deducing x in B\C from just A included in B

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Also, since you care to special case the case of an empty A, you need to care about the case of an empty A\C

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(example, A = C = {1, 2}, then neither A nor C are empty yet A\C is)

pearl pondBOT
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@vestal thistle Has your question been resolved?

vestal thistle
#

Here is version 1.2:

\begin{proof}
Let $A$, $B$ and $C$ be sets.
Either $A$ is empty or non-empty.
First, suppose $A$ is empty.
Then, $A \setminus C = \emptyset \subseteq B \setminus C$. 
Now suppose $A$ is non-empty.
Then, either $C$ is empty or non-empty. 
Suppose $C$ is empty.
Then $A \setminus C = A \subseteq B = B \setminus C$, which is what we wanted to prove.
Now suppose $C$ is non-empty. Either $A = C$ or not.

\begin{case}
If $A = C$, then $A \setminus C = \emptyset \subseteq B \setminus C$.
\end{case}

\begin{case}
Otherwise, suppose $A \neq C$.
Then, there exist $x \in A$ that is not in $C$.
Let $x \in A \setminus C$.
Then, by the definition of substraction, $x \in A$ and $x \notin C$.
Because $A \subseteq B$, we have that $x \in B$.
Since $x \notin C$, by the definition of substraction, we have that $x \in B \setminus C$.
Since $x \in A \setminus C$ implies $x \in B \setminus C$, by the definition of the subset,
we have that $A \setminus C \subseteq B \setminus C$.
\end{case}

Therefore, in any case, if $A \subseteq B$, then $A \setminus C \subseteq B \setminus C$.
\end{proof}
jolly parrotBOT
#

Mor Bras

vestal thistle
#

<@&286206848099549185> Hello, could someone check if this proof looks good please?

shut elm
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Looks good

#

You can skip the C empty/nonempty part though

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i.e.

#
\begin{proof}
Let $A$, $B$ and $C$ be sets.
Either $A$ is empty or non-empty.
First, suppose $A$ is empty.
Then, $A \setminus C = \emptyset \subseteq B \setminus C$. 
Now suppose $A$ is non-empty.
Either $A = C$ or not.

\begin{case}
If $A = C$, then $A \setminus C = \emptyset \subseteq B \setminus C$.
\end{case}

\begin{case}
Otherwise, suppose $A \neq C$.
Then, there exist $x \in A$ that is not in $C$.
Let $x \in A \setminus C$.
Then, by the definition of substraction, $x \in A$ and $x \notin C$.
Because $A \subseteq B$, we have that $x \in B$.
Since $x \notin C$, by the definition of substraction, we have that $x \in B \setminus C$.
Since $x \in A \setminus C$ implies $x \in B \setminus C$, by the definition of the subset,
we have that $A \setminus C \subseteq B \setminus C$.
\end{case}

Therefore, in any case, if $A \subseteq B$, then $A \setminus C \subseteq B \setminus C$.
\end{proof}
jolly parrotBOT
#

Coolempire93

shut elm
#

The A =/= C case covers C empty because we never assume there exists an element in C

shut elm
# shut elm Looks good

Actually, A =/= C could mean there is x in C not in A, which is a case you haven't considered it appears

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i.e. if C is a subset of A

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Is a case not included in your original

vestal thistle
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Does it matter for this proof?

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I believe all cases are covered

shut elm
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Let me reread and make sure

vestal thistle
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if x in C not in A, then x not in A \ C

glass meadow
shut elm
#

Consider A = {1}, B = {1,2,3}, C = {1,2}

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It's down to Case 2 since A is nonempty, C is nonempty and A =/= C

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But we go by supposing there exists x in A not in C

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This is not true here

vestal thistle
#

I see, I'll recheck this later

#

Thank you very much for your comments!

#

.close

pearl pondBOT
#
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plucky wagon
#

.

pearl pondBOT
shut elm
#

<@&268886789983436800>

#

.close

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eager jewel
#

what did bro do

slow oak
#

spam bot

unborn abyss
slow oak
#

the mark of the mr beast

eager jewel
#

o lol

pearl pondBOT
#
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crimson nebula
#

In the proof , why do we require |xn|< 1+ |x|
Can't we just write , M to be Supremum of {|x1|,....,|xn| }
Since if, M is the Supremum of absolute value
All |xn| ≤ M

worldly jewel
#

What do you mean by "M to be Supremum of {|x1|,....,|xn| }"

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what is n here

crimson nebula
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xn represent the nth term of sequence X

worldly jewel
#

yes...

crimson nebula
#

Well after all this is a sequence

worldly jewel
#

but what do you mean when you say "M to be Supremum of {|x1|,....,|xn| }"

crimson nebula
#

A set

worldly jewel
#

How do you know the supremum exists?

crimson nebula
#

Okay ....

#

I understood

#

We had to take some number that's greater than all of the terms of sequence...?

worldly jewel
#

The proof strategy is essentially this. You want to pick some M so that |x_n| < M for all n, right?

crimson nebula
#

Yes

worldly jewel
#

Now you know a finite set of points {x1, x2, ..., xk} is always bounded because you can simply take the maximum

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It is the infinite tail that needs to be taken care of

crimson nebula
#

One question....

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We have shown that |xn| <1+|x|

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Can't we just write M= 1+|x|

worldly jewel
#

Well ok, so by the convergence property you can pick a number K so that x-1 < x_k < x+1 for all k >= K, right?

crimson nebula
#

Yeaa

worldly jewel
#

This takes care of the tail, but you still have the finitely many terms in front, ie. x1, x2, ..., x_(k-1)

#

To take care of the front, you can take the maximum of x1, x2, ..., x_(k-1)

#

and to take care of the tail you can use |x|+1

crimson nebula
#

I m not familiar with this infinite tail concept

worldly jewel
#

By tail I just means the terms that come after x_K

crimson nebula
#

Okay

crimson nebula
worldly jewel
#

If you write M = 1+|x| you only bound the terms that come after x_K

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the terms x1, x2, ..., x_(K-1) can fall outside this bound

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that's why you need to take the maximum {|x1|, |x2|, ..., |x_(K-1)|, 1+|x|}

crimson nebula
#

Okhayyy I understood

#

Because in convergence, we consider a k, above which they are within a certain limit

worldly jewel
#

Yes

crimson nebula
#

And we have shown that this 1+|x| using that convergence idea

worldly jewel
#

Mhm

crimson nebula
#

These proofs seems so easy

#

But little am I aware of the in depth idea hidden

#

.close

pearl pondBOT
#
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cerulean ledge
#

hmm how do you see if the function is strictly monotone ascending?

cerulean ledge
#

like where does he see the y value

#

is it like this y = 2x ?

weary ledge
#

the y mentioned in the above context is chosen from the domain of f

#

it is not the same y = f(x) that we normally take

cerulean ledge
#

ohhh

#

i still don't see where the y comes from

weary ledge
#

y is just another value like x

cerulean ledge
#

but how do they see if y > x here?

weary ledge
compact ridge
#

yeah they're trying to show that if $s < t, f(s) < f(t)$ for monotone increasing

jolly parrotBOT
compact ridge
#

and $s < t, f(s) > f(t)$ for monotone decreasing

jolly parrotBOT
weary ledge
#

they say one thing for y>x and another for y<x

compact ridge
#

for all s, t in the domain

cerulean ledge
#

second case if x < y and -x^2 > -y^2

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yeah i don't even see a number where this is possible?

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must be a negative number

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-5 < -1 and -(-5)^2 > -(-1)^2

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so this is true for negative numbers?

weary ledge
weary ledge
#

sorry for being afk for a while btw

compact ridge
#

the domain is when x, y are now nonnegative

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so from x < y you can directly conclude x^2 < y^2

#

then -x^2 > -y^2

pearl pondBOT
#

@cerulean ledge Has your question been resolved?

cerulean ledge
#

yeah i feel like some parts of math are confusing because of definitions like this

#

like most of the concepts are very easy to understand anyway they usually just present it in a complex way

compact ridge
#

that's one of the field axioms

compact ridge
#

it's so easy to take mental shortcuts which will hurt later in mathematics

cerulean ledge
#

thx for the help

#

.close

pearl pondBOT
#
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junior anchor
#

Do variables in LP always have to be non negative

junior anchor
#

LP = Linear Programming

bitter herald
toxic lichen
#

technically no. but if you do have one that is allowed all real values, and has a nonzero coeff in the cost function, then p sure you'll end up with unbounded optimum.

bitter herald
#

No they dont

junior anchor
#

Is it just a "pretty sure"

#

Or a guarantee of any soet

#

Sort

toxic lichen
#

can probably cook up some proof there

#

i am reasonably certain of my assertion in the case of linear programs

bitter herald
#

most algorithms like the simplex method require the problem to be converted into a 'standard form' anyways where all variables are nonnegative

junior anchor
#

Yeah , so does it work to cut up a variable x which can be any real value into
x- and x+ of sort

#

x+ being (-1) times x-

#

And both forced to be non negative

#

Idk I'm like very new to lp

#

Just started learning about it like 10 minutes ago

toxic lichen
#

you can write $x = x_+ - x_-$ with $x_+ = \max(x,0)$ and $x_- = \max(-x,0)$ and then $x_+, x_- \geq 0$

jolly parrotBOT
toxic lichen
#

in this way you can reduce an LP with an unconstrained variable into one with ≥0 constraints but +1 variable count

#

note btw that even if some x is not itself constrained, other constraints may imply it can't actually vary over R

junior anchor
#

Ah makes sense

#

Thanks

#

.close

pearl pondBOT
#
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pearl pondBOT
#
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unborn charm
pearl pondBOT
unborn charm
#

idk how to start, I can just say if x = 0 then I must have a_n = 0

worldly jewel
#

Hint: base-p expansion

unborn charm
#

oh lol

#

is there anything that I even have to prove then?

autumn fossil
#

is it really that obvious that we can express every number in base-p expansion?

#

there is definitely something to prove

unborn charm
#

no but if I am using that to begin with, I already have a sequence

#

or are you implying I prove that

#

i guess yeah that would make sense

#

my bad lol

autumn fossil
#

yep, im implying exactly that. The statement is equivalent to "every number in 0,1 can be represented in base p expansion"

#

but its still something not entirely obvious and it does deserve a proof

keen star
#

can u construct a sequence like that works for all p

worldly jewel
#

You can give an algorithm which outputs a1, a2, ... given an x, and then prove that the corresponding sum converges to x

unborn charm
#

hmm yeah

#

I guess we are to use the division algorithm since a_n is strictly less than p

cursive wraith
#

I'm pretty sure you'll have to do a separate case for x = 1, but apart from that the "algorithm" should work

unborn charm
#

yeah I would need a starting point

unborn charm
pearl pondBOT
#

@unborn charm Has your question been resolved?

worldly jewel
#

if they always pick .999... then I guess it should work for 1

pearl pondBOT
#
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#
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junior anchor
#

Given two random non equivalent Boolean functions, what is the chance that they agree for >p% inputs

pearl pondBOT
#

@junior anchor Has your question been resolved?

azure kite
#

can you give us some of your inputs on the problem

junior anchor
#

Inputs as in?

#

What I have worked out?

#

It started with this

#

He seems to have said "B1 B2 may disagree rarely"

#

As a way to discard that algorithm

#

But if the B1 B2 disagreeing rarely case itself is rare

#

Then I would reconsider discarding it

#

That's why I was wondering how to start working out the chances

#

I have no idea of how to begin tackling this

#

<@&268886789983436800>

pearl pondBOT
#

@junior anchor Has your question been resolved?

pearl pondBOT
#

@junior anchor Has your question been resolved?

pearl pondBOT
#
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empty oriole
#

Show that the set of differentiable real-valued functions 𝑓 on the interval
(−4, 4) such that 𝑓′(−1) = 3 𝑓 (2) is a subspace of 𝐑^(−4, 4)

empty oriole
#

I don't know how a set* of functions works as vector spaces

rough stream
#

Vector spaces are anything that can be added or scalar multiplied

#

(Where adding/scalar multiplication are defined by the 10 axioms for a vector space)

#

f(x) + g(x) is a new function
a(f(x)) is a new function

So functions can be added and scalar multiplied

toxic lichen
#

that's (kinda) all you need for a vector space

empty oriole
#

Yeah

#

But, for proving the existence of a zero vector, I need to prove the existence of the zero function

#

I still don't get how there exists a zero function for any x on the differentiable real set of numbers (-4, 4)

rough stream
#

f(x) = 0 is the zero function

toxic lichen
#

quite badly

empty oriole
#

How do I know that f(x) = 0 holds true for any x over (-4, 4)?

toxic lichen
#

"differentiable" is a property of functions, not numbers, not sets of numbers.

rough stream
toxic lichen
empty oriole
rough stream
#

f(x) = 0

#

That's what it is

toxic lichen
#

what you're examining is the space of all possible differentiable functions from (-4,4) to R,

rough stream
#

f(2) = 0

toxic lichen
#

in particular kaynex is directing your attention right now to the zero function in that space

#

and the zero function's whole thing is that, viewed as a function, it maps all x's to 0

#

R^(-4,4) is a huge space. one single function is just one point in that space.

empty oriole
toxic lichen
#

not sure what else there is to say though like... hm

#

have you seen other vector spaces before this

empty oriole
#

Sure

toxic lichen
#

R^3 for example

empty oriole
#

Yeah

toxic lichen
#

or maybe polynomial vector spaces

#

P_5(R) or something

empty oriole
toxic lichen
#

mmm

#

right

#

yeah this sounds like a case of abstraction related motion sickness

#

but im not sure how to treat it

tiny nexus
#

Yo guys

#

Checkout ts question

#

Funner than whatever was here before

#

Quit this derivative stuff

empty oriole
toxic lichen
#

this you rn?

rough stream
#

Like, I think you're maybe asking how to prove f(x) = 0 is indeed the zero vector? This kind of thing is usually taken as "known" and isn't in every proof

toxic lichen
pearl pondBOT
tiny nexus
#

Wrong grammar

empty oriole
#

And I understand it as a prototype of R^{1,2,3}

tiny nexus
#

Occupied!*

#

This making me mad

toxic lichen
tiny nexus
#

Ann ur buns at English

empty oriole
#

?

rough stream
#

<@&268886789983436800>

tiny nexus
#

What to do jext

#

Next

toxic lichen
#

gtfo of this channel that's what

mortal seal
tiny nexus
#

What does gtfo mean

toxic lichen
tiny nexus
#

Yoo

#

Mods u seeing ts

toxic lichen
#

don't tell me you don't know this old internet slang

dim linden
zinc pewter
empty oriole
toxic lichen
toxic lichen
mortal seal
#

Let’s not get mad at each other and go back to helping andre, you shouldn’t give attention to trollers, that only encourages them

empty oriole
toxic lichen
#

got it off a blog

empty oriole
#

lol

toxic lichen
#

... from 9 yrs ago

#

i gtg though

empty oriole
#

cya

plain wing
#

whio can hielp me wioth 1plius 1 i need heolp

#

plis anuyone

toxic lichen
plain wing
#

pliease i need help

radiant terrace
#

Don't troll here

plain wing
#

yiou doniunbt beliuve me

empty oriole
#

Does this happen often? lol

plain wing
#

sioryuy i need help

radiant terrace
#

I muted them and they left

rough stream
#

Clearly an alt?

empty oriole
#

So, how do we define a function to map to the same result?

#

That is what's confusing me

#

Because I had the intuition that the elements of a set don't repeat

#

is f(2) a different element than f(-1)?

rough stream
#

These functions are in R^(-4,4).

That is, they take elements from the real interval (-4,4) and return back real numbers.

The only other rule we have is that this function must be differentiable.

And that's it. f(2) can be the same real number as f(1) if they want. Can even be the same as f(1.2).

empty oriole
#

Certainly, every real number is differentiable, right? (off-topic real analysis question)

#

Eh

#

doesn't matter

#

Thank you for your help!

#

How do I give points?

#

.close

pearl pondBOT
#
Channel closed

Closed by @empty oriole

Use .reopen if this was a mistake.

rough stream
#

Functions are differentiable, not sets. Maybe I misunderstood you?

empty oriole
#

Forget it. It's a silly question (I can just google it.)

#

Thanks

#

.close

pearl pondBOT
#
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pearl pondBOT
#
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royal galleon
#

For 24 how could you pour water in if the vertex is up?

sharp vigil
#

assume the cone has a base

royal galleon
# sharp vigil assume the cone has a base

Yes I did. I can understand if the vertex is down and we are pouring water through the base but if the vertex is up and we pour through the base wouldn't our rate change since gravity is opposing it and if not wouldn't it just be an identical problem?

sharp vigil
#

where exactly you pour water in from doesn't affect things really

#

what does matter is that the shape of the tank is different

royal galleon
#

I don't see how. It is just upside

sharp vigil
#

yes

royal galleon
#

It is still a right circular cone though

grave mirage
sharp vigil
royal galleon
#

Oh ok so it is filling up a different shape which will affect how the height is changing.

#

Thanks. .close

#

.close

pearl pondBOT
#
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pearl pondBOT
#
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amber pagoda
#

hi

pearl pondBOT
amber pagoda
#

i asked lot of ai like chat gpt gemini copilot and grok all are giving me different anwers

sly jacinth
#

ok so y and z have to be equal right?

amber pagoda
sly jacinth
#

do you knowwhat the sum of all the interior angles of a triangle should be

amber pagoda
#

180

sly jacinth
#

so if you were to have all the angles equal to 50

#

does that equal 180

amber pagoda
#

oh wow ur right

amber pagoda
sly jacinth
#

it helps you determine the angle measures of y and z

#

since this is an isosceles triangle y = z

#

50 + z + y = 180

amber pagoda
#

ah

sly jacinth
#

you can set y and z to the same variable

amber pagoda
sly jacinth
#

so, 2w = 130

#

solve for w

pearl pondBOT
sly jacinth
warped violet
#

rather, come here 🙂

amber pagoda
#

i thought the 50 is the vertex

sly jacinth
#

they're all vertexs

#

if i understand what vertex means

amber pagoda
sly jacinth
#

i cant just tell you it

amber pagoda
#

true

warped violet
#

This is all you need

sly jacinth
#

yeah ig so

amber pagoda
#

what if i check a yt video rq about this

#

and come back is that possible

warped violet
sly jacinth
#

what he said

#

its not a very complicated concept to grasp

#

just try to understand what i said

amber pagoda
#

cause if all angles should be equal to 180

#

all the answers are more than 180 cobined

warped violet
#

I didn't mean it that way. We all start from somewhere. I just want to understand where to begin explaining

warped violet
#

Okay

#

First of all

warped violet
amber pagoda
#

the blue sticks u drew?

sly jacinth
warped violet
#

Yes

amber pagoda
#

affirmative

sly jacinth
#

well my wifi is dying so ill lleave it to him

warped violet
#

And we see 2 triangles

amber pagoda
#

yeah

warped violet
#

What do we know about them

amber pagoda
#

oh

#

so there are 2 traingles

#

so both of the triangless sum shoudl add up to 180

#

not both

#

but each

warped violet
#

"triangles sum" doesn't really make sense

amber pagoda
#

interior angles sum

warped violet
#

yes.

#

Let's take a look at the right triangle first

#

We have 3 angles

amber pagoda
warped violet
#

z, y and one that measures 50°

amber pagoda
#

yeah

#

so z and y should be 50 too

warped violet
#

And their sum must equal to 180°

warped violet
amber pagoda
#

erm cause the angles arent equal no?

warped violet
amber pagoda
#

forget it cause it doesnr make sense

warped violet
#

You understand this right

amber pagoda
#

exactly

warped violet
#

Okay, so we can write

#

$50^{\circ} + z + y = 180^{\circ}$

jolly parrotBOT
#

USS-Enterprise

warped violet
#

Subtract 50° on both sides

#

$z + y = 130^{\circ}$

jolly parrotBOT
#

USS-Enterprise

warped violet
#

So the sum of z and y must be 130°

#

But this yet doesn't tell us enough to figure out what z and y are

amber pagoda
#

yeah

warped violet
#

z could be 1 and y 129. z could be 80 and y 50

#

So we need another piece of information

#

Look at the triangle

amber pagoda
warped violet
#

What can you tell me about it

amber pagoda
#

that y and z should be equal

warped violet
#

Yes, why?

amber pagoda
#

cause they look the same

warped violet
#

😂

#

2 of the sides are equal

sly jacinth
#

he aint wrong

warped violet
#

they are both the radius

#

so that makes this triangle a(n) __________ triangle

amber pagoda
#

vro why u making it hard

warped violet
#

what

amber pagoda
#

the angles side by side are equal

warped violet
#

Yes

#

but you can't just say that

amber pagoda
#

ture

warped violet
#

okay

#

so

#

again

#

what kind of triangle is this

amber pagoda
#

equirtaeral traingle

warped violet
#

What's an equilateral triangle?

amber pagoda
warped violet
#

Yes

amber pagoda
#

i see ur tiny sticks here

warped violet
#

All 3 sides are equal

amber pagoda
#

exaclty

warped violet
#

Are there 3 sticks here

#

or 2

amber pagoda
#

2

warped violet
#

yes

#

we don't know anything about the length of the segment from angle y to angle z

amber pagoda
#

we just know that they are same value

warped violet
#

But we do know the two segments going to the center are the same length

#

So this is not an equilateral triangle

#

But it is a different type of triangle

amber pagoda
#

wat

warped violet
#

3rd times the charm

warped violet
warped violet
#

I just said the segment from angle y to z is not the same length

#

Therefore this is not an equilateral triangle

amber pagoda
#

ok

warped violet
#

Plus, if it were

#

all 3 interior angles would be 60°

#

and we clearly see one is 50°

#

Okay

amber pagoda
#

true

warped violet
#

so

#

again

#

what kind of triangle is this

amber pagoda
#

no clue

#

its not a right traingle

warped violet
#

ever heard of an isosceles triangle?

amber pagoda
#

isolces

#

UES

warped violet
#

Yes

warped violet
amber pagoda
#

TRUE

warped violet
#

And notice how the angles at the base are the same

#

?

amber pagoda
#

YES

warped violet
#

The base is the one segment which doesn't have a "little stick"

#

Okay, so

#

$z + y = 130^{\circ}$

jolly parrotBOT
#

USS-Enterprise

warped violet
#

Now we have that another piece of information

#

Which is?

amber pagoda
#

where did 130 came from

warped violet
amber pagoda
#

ok so

#

$130/2

warped violet
#

yes

amber pagoda
#

why didnt the command work

warped violet
#

need dollar sign at the end

#

plus, fractions are \frac{numerator}{denominator}

amber pagoda
#

$180/2$

jolly parrotBOT
#

!ᐯᗩᒪIᑌᗰ

amber pagoda
#

ah i see

#

so

warped violet
#

130, not 180

amber pagoda
#

i forgor

warped violet
#

okay

#

so z and y are

amber pagoda
#

65

warped violet
#

yes

amber pagoda
#

and x

warped violet
#

Ever heard of vertical angles?

amber pagoda
warped violet
#

yes

#

This means $\alpha = 50^{\circ}$

jolly parrotBOT
#

USS-Enterprise

warped violet
#

And you have the same situation as before

#

So x is?

amber pagoda
#

same

warped violet
#

yes

#

They are all 65

amber pagoda
#

65

#

SO 65 65 65

warped violet
#

yes

amber pagoda
#

BRO I THOUGHT IT WAS 50 50 50

#

cause i saw there is 50 so other should be 50 too

warped violet
#

If it were, the right triangle's sum of interior angles would be 150°

#

That can't be

#

not because of that

#

but because the sum of interior angles of a triangle is always 180°

#

so it can't be 150°

amber pagoda
#

casue here ost of them are equal so ithought this one would be too

warped violet
#

$180 \neq 150$

jolly parrotBOT
#

USS-Enterprise

amber pagoda
#

true

warped violet
#

Anyway, hope I've been of help

#

I gotta go sleep

#

midterm tomorrow

amber pagoda
#

thanks man

#

+rep

warped violet
#

today actually

#

👋

amber pagoda
#

i got a equa tmrow

#

cya

#

.close

pearl pondBOT
#
Channel closed

Closed by @amber pagoda

Use .reopen if this was a mistake.

pearl pondBOT
#
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pearl pondBOT
#
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empty oriole
#

Show that the set of differentiable real-valued functions 𝑓 on the interval
(−4, 4) such that 𝑓′ (−1) = 3 𝑓 (2) is a subspace of 𝐑^(−4, 4)

west sapphire
#

unfortunately the channel auto-closed because you deleted the first message

#

you'll have to open a new one

pearl pondBOT
#
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pearl pondBOT
#

Please don't occupy multiple help channels.

dense jasper
#

.close

pearl pondBOT
#
Channel closed

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Use .reopen if this was a mistake.

eager jewel
#

bruh i want to close one

#

nvr closed someone elses channel

pearl pondBOT
#
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crimson hawk
#

Let P be a point outside circle (O). PA and PB are two tangents to the circle at A and B. A secant line PDC is drawn such that D lies between P and C. A line KL passes through A and is parallel to PB, where K and L lie on BD and BC respectively. Prove that A is the midpoint of KL

crimson hawk
#

I have tried to form AK/X = AL/X or AK/AL = X/Y × Y/X but ive failed

#

:<

dapper kraken
#

smells symmedian

pearl pondBOT
#

@crimson hawk Has your question been resolved?

crimson hawk
dapper kraken
#

idk i havent got it either lmao

#

but its construction is like a symmedian construction

#

CD is the symmedian to ABC

naive sandal
#

this makes my head hurt bro im working on it tho

crimson hawk
#

i asked my classmate construct auxiliary lines and try to find similar triangles but i have not found the solution 🙁

crimson hawk
dapper kraken
#

err

#

ok i kinda reversed the problem, with a given triangle ABC first

#

should be identical tho

#

KDLC is concyclic but dunno how that helps

crimson hawk
dapper kraken
#

u sure?

crimson hawk
dapper kraken
crimson hawk
subtle oak
#

KL and BP are parallel so trying to use equal angles?

crimson hawk
subtle oak
crimson hawk
subtle oak
#

Wait could be mistaken, gimme a minute

crimson hawk
subtle oak
#

‘‘‘ok, AK/AL = AD/AC; AB^2 = AD * AC; then you have AK = APAD/AB and AL = AP * AC/AB; multiply these to get AKAL = AP^2 * (AD*AC)/AB^2 now substitute AD * AC = AB^2 and you‘ll end up with AK * AL = AP^2; you know AP = PB; and AKL and APB are similar so AK/AL = AP/PB = 1‘‘‘

subtle oak
#

KL || PB So AKD and APB should be similar and ALC and APB should be, so AK/AP = AD/AB and AL/AP = AC/AB, I think

crimson hawk
#

ABP isnt equal to AKD or APB?

dapper kraken
#

AKD and APB isnt simmilar

#

ALC and APB isnt even close to simmilar??

#

yeah lowk idk

#

maybe you meant diffrent triangles?

crimson hawk
dapper kraken
#

nah i was talking to the guy that said that the triangkes were simmilar

#

yeah im out of ideas

#

maybe menelaus might work? but i couldnt get it

#

my last idea is trig bashing but id rather not

subtle oak
#

You‘re right, made the drawing wrong, then I don‘t know

crimson hawk
subtle oak
#

Sorry

subtle oak
#

Maybe with coordinates? That would be my last guess how to do it tbh

crimson hawk
subtle oak
naive sandal
pearl pondBOT
#

@crimson hawk Has your question been resolved?

crimson hawk
naive sandal
#

i just realized after i sent it ts has me crying 🫩 ill try again

subtle oak
#

You haven‘t learned vectors?

#

maybe try projecting the line BD and BC onto line KL from center A. AC/ADD = BC/BD. I think that could help coming to a result?

crimson hawk
crimson hawk
subtle oak
#

Bye

pearl pondBOT
#

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vast berry
#

can someone please explain the hihglighted part to me

tropic saddle
#

you should have seen that same construction previously

#

G/H

#

x~y iff x^-1 y in H

#

the same here with H=stab(s)

vast berry
tropic saddle
#

the set of the left cosets of H

#

G/H = {aH: a in G}

#

sry, gtg

vast berry
#

oh ok

pearl pondBOT
#

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twin portal
pearl pondBOT
twin portal
#

If D is the midpoint of the side BC of a trianlge ABC and E is the midpoint of AD, find the value of AF/FC.

pearl pondBOT
twin portal
toxic lichen
#

are vectors allowed or not

twin portal
#

noup

proper nova
#

-# knew it

#

-# no vectors allowed, it's just a geo problem

toxic lichen
twin portal
proper nova
jolly parrotBOT
#

1 divided by 0 equals Infinity

proper nova
#

it's just a diagram assumption

toxic lichen
#

assuming the answer equals 1/2 is just a bozo tier move

proper nova
#

and knowing that, i can try to let $G$ be the midpoint of $FC$

jolly parrotBOT
#

1 divided by 0 equals Infinity

proper nova
#

and prove $AF = FG = GC$

jolly parrotBOT
#

1 divided by 0 equals Infinity

proper nova
toxic lichen
#

guessing the what

thorn agate
#

ew geo

proper nova
twin portal
#

Let area(BED) = area(DEC) = x.
Let area(GEA) = y and area(AEF) = z.
We have area(GEB) = x - y and area(EFC) = x - z

Now area(CEF)/area(AEF) = area(BFC)/area(BAF)
So, (x-z)/z = (3x - z)/(x + z)
x^2 - z^2 = 3xz - z^2
x = 3z
x - z = 2z
(x-z)/z = 2:1
area(FEC)/area(AEF) = 2:1
FC/AF = 2:1
AF/FC = 1/2

#

Is this correct and good?

thorn agate
#

type shit

proper nova
jolly parrotBOT
#

1 divided by 0 equals Infinity

twin portal
#

ABC is any triangle.

proper nova
#

can you explain why?

twin portal
#

AE = ED, and hence area(ABE) = area(DEB) = x. Now subtract from this area(GEA) = y.

proper nova
proper nova
#

since when did you let $S_{ABE} = x$?

jolly parrotBOT
#

1 divided by 0 equals Infinity

toxic lichen
twin portal
#

I let area(DEB) = x, which is equal to area(DEC). Then I concluded that area(BEA) = x. I realize that I missed a few steps.

twin portal
#

D is the midpoint of BC. Again, I could have written in the first line that x = area(BED) = area(DEC) = area(BEA).

proper nova
#

as in prove why the areas are equal

twin portal
#

Oh.

twin portal
#

Both have bases of equal magnitude and the corresponding heights are the same as seen by dropping the altitudes.

thorn agate
#

ED still remains median dividing the triangle into two equal parts

twin portal
#

I guess it's correct. I have another question.

#

.close

pearl pondBOT
#
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twin portal
#

Thanks btw.

thorn agate
twin portal
pearl pondBOT
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wary vault
#

Suppose there are 100 students, and we wanna make a 5-member committee out of them, which will consist of 5 different roles: president, vice president, secretary, cashier, and a prospective member. Suppose, now, that we have 2 students, George and Catherine, both of which are part of the 100 students eligible for a place in the commitee. We wanna calculate the number of ways that { George is elected president or Catherine is elected cashier }.
This is an exercise our prof gave us, and upon solving it, i found the number of ways to be equal to:
2C(99,4) -C(98,3) . The reason for that is because i took the ways George can be president, which equals the ways Catherine can be cashier, and then i subtracted the ways both of them can be in their respective roles. It comes out to 7.376.656 .
The solved exercise says it is equal to 179.777.472 . Like wtf? did i do smth wrong?

wary vault
#

heres the proof provided in the notes

#

honestly the solution provided does look correct too. i just dont get what i did wrong

unborn abyss
#

the 5 roles are all different

#

so P(99, 4) is the correct thing to use, not C(99, 4)

wary vault
#

oh shit, using C it chooses them for any position

#

yeah i forgot abt that

#

thanks

#

.close

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sly jacinth
pearl pondBOT
thorn agate
sly jacinth
#

mb was js abt to send

thorn agate
#

instanttaneous

sly jacinth
#

LOL

thorn agate
#

the curves would flip after intersection point

sly jacinth
#

uhm

#

what does that mean

#

like 5 would be first then -10sin

thorn agate
#

add these for each

sly jacinth
#

ok so i integrate each individually

#

then add them

thorn agate
#

yeah

sly jacinth
#

from the same range i assume?

thorn agate
#

yes

sly jacinth
#

ok

#

hold on

#

could you explain y

thorn agate
#

wait i have a doubt

thorn agate
sly jacinth
#

yeah

thorn agate
#

i'm sorry unable to help ping helpers

sly jacinth
#

alright

#

<@&286206848099549185>

#

thanks in any case

#

.close

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eager jewel
pearl pondBOT
eager jewel
#

ive got the answer in a form but im not able to convert it to the questions form

#

let me send my working

#

my t = sqrt(1+x^2) + x

#

.close

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thorn agate
#

then simplify

eager jewel
#

t/180 ah

#

ts fine i got it

thorn agate
#

alr

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wary vault
#

Hi. So, a pizza restaurant advertises that they sell over 500 kinds of pizza. It is given that they have 9 different ingredients that they can put in a pizza. To calculate the amount of different pizzas they can make, the given solution does it with whether one ingredient is used or not every time, and thus the amount of pizzas is 2^9 = 512. That seems correct, but doesnt that assume that we dont concern ourselves with which order each ingredient is put in the pizza? If we did care for that, would the amount of pizzas equal 9!+1 or am I far off?

fast briar
#

The calculation of (2^{9}=512) is correct for the scenario described, and if order mattered, the calculation would involve a summation of permutations of subsets, not (9!+1).

jolly parrotBOT
#

uraverageindian

fast briar
#

thats what i think

wary vault
#

oh i think i get you

fast briar
#

(\sum _{k=0}^{9}P(9,k)=\sum _{k=0}^{9}\frac{9!}{(9-k)!})

jolly parrotBOT
#

uraverageindian

toxic lichen
fast briar
#

To calculate all possible unique ordered pizzas (assuming you can choose any number of ingredients from 0 to 9), you would need to sum the permutations of every possible subset of ingredients. The general formula for this would be the sum of permutations for all subset sizes (k) from 0 to 9:

wary vault
#

yeah 9!+1 would be if we used 9 ingredients for sure

jolly parrotBOT
#

uraverageindian

fast briar
# wary vault sheldon would

"according to the bubble and the fact that my left buttcheek is itchy, then that means that the pepporoni was put on first"

wary vault
#

facts

#

lol

#

thanks for the help

#

.close

pearl pondBOT
#
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fast briar
#

np

pearl pondBOT
#
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wary vault
#

Hi. Suppose we have a roundtable, and 5 people who wanna sit around it. How many ways are there, if 2 specific persons out of the 5, have to sit together? the solution says it is 3!,
. But the way i see it, it equals 2×3! because the two people can exchange seats, no?

wary vault
#

nvm im stupii i didnt see the entire solution lmao

#

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wary vault
#

i scroll down a bit each time to not spoil myself lol

pearl pondBOT
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toxic lichen
#

the columns for the edges in a cycle add up to 0

#

with a linearly independent set of columns this never happens

#

the columns for the edges in a cycle add up to 0
this is already a nontrivial linear combination

pearl pondBOT
#

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warped violet
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celest turret
#

can someone tell me if this is correct and if not what am i doing wrong

celest turret
#

.close

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fading ledge
pearl pondBOT
fading ledge
#

i applied ratio test for checking convergence

dusty jungle
#

x is any positive number? or are they asking you to determine all x for which it converges?

fading ledge
#

only when x>0

#

how do i check convergence

#

ration test

pearl pondBOT
#

@fading ledge Has your question been resolved?

still hamlet
fading ledge
#

R is r

still hamlet
#

💔

#

what's lim n-> inf n²/(n+1)²

pearl pondBOT
#

@fading ledge Has your question been resolved?

midnight haven
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crimson nebula
#

I have learnt about *m-tail of a sequence".
But what do we mean when we we say "tail of a sequence".
ie "m" is not mentioned

autumn fossil
#

usually it'd just mean some m-tail of a sequence

crimson nebula
#

Some of the people wrote in their replies

#

So i thought there might be some concept

autumn fossil
#

I think it's just m-tail, where you dont want to specify the m

#

so like "all tails do x" would mean "for all m, m-tail does x"

crimson nebula
#

So for every m, that holds

#

Just use "tail"

autumn fossil
#

"some tail does x" would mean "for some m, m-tail does x"

autumn fossil
crimson nebula
#

If it holds for every m , then we can use simply tail ..

#

Depending on situation

autumn fossil
#

yeah, sure

crimson nebula
#

Okay , thanks

#

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green aurora
#

Why is the probability of the empty set 0 if it is in A then P(A)=1/n???

crystal dew
#

need context

green aurora
#

Like A={1,2}

#

A*={empty set,A,1,2}

#

So the probability of empty set is 1/4?

tardy reef
#

there are 2^n elements in P(A)