#help-39
1 messages · Page 25 of 1
X_ij tells you to add 1 to the total tally
so we need to sum up all these to get the expected value
wait
oh
right
wait i didnt even realise were throwing 2 coins
wait no
were throwing one

we're throwing a coin multiple times
it doesn't really matter if it's the same coin or multiple coins
there are just many coin tosses happening
ordered from 1 to n
oh so like
lets say
throw 1: heads
throw 2: tail
throw 3: tail
throw 4: heads
we wanna find out if throw 1 = throw 3 for example
so X_13 = 0
cuz theyre different
yes
OH
it's just a true/false value
well X_ij is a random variable
because of the probability tree
whats tyat
and there are many potential worlds
like
imagine many different parallel universes
one for each possible outcome of the coin tosses
then X_ij will take on different values in each universe
depending on what the outcome is
that's a random variable
but like
we can still do math on X_ij
cuz ultimately it'll just be a concrete value
once you realise which world you're in
but it's "random"
so like
P(X_ij = 1) = 1/2
the number of worlds in which X_ij is 1 (i, j match) is exactly half of them
okay good
so
to get the total number of matching pairs
we sum all the X_ijs
just like a tally
yes
good good
v nic
okay
so now
the most powerful trick in probability
use linearity of expectation to bring the sum outside
E[sum X_ij] = sum E[X_ij]
hmm
because every E[X_ij] will be the same
ill just guess
it's just 1/2
idk nc2 or smth lmao
hm but its the same right
i call that sus
next qn yes
yes
can't stay sorry

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i need help with this
use the point you are given (the y-intercept) to solve for c
Pretty sure it is
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✅
For this enter the x value for when Y is 0
so the answer in the first one is gonna be
x=0
x=1?
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hi guys i have quick question, how do i transform this to cosine π/something
do you know arccos or inverse cos?
i know arccos, but im not sure how i can use it here
cos(x) = y implies x = arccos(y)
if this number is in the domain of arccos, then you can just take the arccos of it to find x
@left zephyr Has your question been resolved?
still no idea what to do with arccos -(sqr2 /4 + sqr3 /4)
,calc acos(-(sqrt(2) /4 + sqrt(3) /4))
Result:
2.476024530295
that's your x
your 6 changed to a 3 magically
oh yea so soryy
x is your pi/something
so solve for something
type the correct version using this as a template
,calc acos(-(sqrt(2) /4 + sqrt(6) /4))
Result:
2.8797932657906
thank you for your help, but i dont think im able to understand this right now
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how does he go from 2^n+ 4 * 2^n to 5*2^n?
https://www.youtube.com/watch?v=KKjIRSnzKOM&feature=youtu.be
I explain question 24 from the 2020 UKMT intermediate maths challenge.
a(b+c) = ab + ac
a = 2^n, b = 1, c = 4
he just factored a 2^n on both terms
so 2^n * (4+1) = 5*2^n
but how did you go from 2^n + 4 * 2^n to 2^n*(4+1)
ohh wait I get it now
was just confused by the way its formatted
sorry for rearranging it weirdly

its ok now!
yea just didn't make the connection
that it was 2^n + 4*2^n = 2^n (1+4)
yh
fun questions tho
true
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!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'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
Might as well post that.
Huh?
I have a question about someone else's worked solution is what you opted for.
What is it?
So you just want an answer?
I dont mean to like
yk remove the importance of what u do fr
but yes I just want the answer because im not learning this shit either way
Wrong server.
How familiar are you with congruent triangles?
zero
Do you know what congruent means?
yes
Good.
Do you know there are some criteria for congruence.
There's not many.
SSS, AAS, ASA, SAS...
Does that seem familiar?
That's alright.
S stands for Side.
A for angle.
So strictly in order if your triangles have corresponding S or A as stated in the criteria equal, then your triangles are congruent.
mhm
Example.
corresponding
forgot what that meant in math
Corresponding is the key word.
I'll illustrate using an example.
Consider the third problem in what you posted.
UV = XY
Yes?
That's an "S" that's equal.
As you move.
To the other information they've provided about the triangle.
so its congruent?
Here.
ok
You need to show, which one of these you're using to get to conclusion the triangles are congruent.
so if its side thats congruent is prolly SAS
It's sas.
Good.
I think you roughly get the idea.
How about the second example?
Yeah that ones sas.
sense v and x are angles?
cool
Look congruent is not the way to go.
Try to think what criteria this matches if it matches any.
Yes.
What else could you say?
That's one thing you can say. But that doesn't make them congruent.
MO = QR?
then what does?
QR you mean.
yes my bad
As the criteria mentioned above states.
There's a few condition.
Either you want all sides to be equal. That makes them congruent. (SSS)
You can also have a side, an angle and a side to be equal such that the angle is included between those two sides. (SAS)
You can have two angles to be equal and one side to be equal. Like this, angle, angle and then the equal side. (AAS)
Or you could have angle side angle.(ASA)
In the second example, you'd say they are congruent because all their sides are equal.
SSS.
We didn't know if all three sides were equal.
Did we?
We knew, Side, angle and then side.
SAS
You need no numbers.
the check mark on side means they are equal.
Single check = single check.
Double check = double check.
That's convention.
So really, your just seeing what is equal? like if the sides are equal its SSS
Yes.
You don't need to measure them or anything. Just see what equals what.
Can you try 1?
This one's third.
Wdym
MN has double check
So does QP
They're equal.
That's how you show they're equal.
Same for the other two sides.
And it is SSS
Yes!
A thing to note
If two triangles are congruent, then all angles are equal too.
Then why did we not use angles to show congruence?
Because we didn't know if they were equal.
Only now we know after we've proved then congruent.
So however you prove them congruent, doesn't matter. After you've done that, you can claim corresponding sides are equal or angles.
Also, when you say two triangles are congruent. You need to kind of write the triangle in order so that you match the corresponding sides. What does that mean?
Well, in the third triangle
UV = YX
VW = XZ
So you'd say UVW is congruent to YXZ
Now here this is the only right way to write them.
ohh yah
it asks for that as well
I know
and number 1 is not congruent right?
Because
it has a marker on different sides of the triangle
meaning one side is equal on triangle but not equal on the other
meaning their no congruent?
Well, they are not congruent. They would have been if angle L was equal to angle G. Instead of J.
there in different spots
J isn't a side though, it's a vertex.
Not correct.

You've written MNO is congruent to QRP
When you say that, you mean MN is equal to QR, NO is equal to RP, and OM is equal to PQ
But is that really the case?
ohh no
That's what corresponding is for.
Sides are equal, but only the corresponding sides.
so
its
Lmk.
yes
That one's right.
Although it just might be that you tried so many times that it's a fluke.
So do the next one.
Wait that's wrong too?
Lol k
But the triangle order.
Final answer.
YXZ
Def
On an ending note, if you still want to master this. Totally a choice. You should watch a video on congruent triangles.
Oh 💀 thank you so much
Yah imma do that too
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why is e the answer not a
How did you get a?
4(t-3.25)
it says speed not velocity
,w plot abs(12t^2-78t+108) for 0 < t < 6
i see
riemann what have you figured out?
ed rightly pointed out speed is absolute value of velocity
the answer is a if you think the word it said was velocity but it says speed
so either do what riemann did and just use abs value or consider concavity
just continuing this. use the definition of absolute value to differentiate speed (not velocity) and find where the derivative is positive
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how tf do these vectors go to v?
Are you curious why w-u = v?
ok
when you connect the tail of w to the head of the red line this gives you w-u
but how would it be = to v
you have to imagine the vectors are being drawn from the origin
the only properties of a vector are direction and length
so you can forget about where you put the tail because you can put the tail anywhere and its still the same vector
i mean i guess that would make sense
i really meant moving the vector from where it is so that its tail starts from the origin
because as heavy said it doesnt matter where you start the vector all that matters is the length and the direction
also i think you've misinterpreted what w-u is
@vast dune Has your question been resolved?
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A kite string is let out 120 ft and is held 3.5 ft off the ground. If the string makes an angle of 42 degrees with the horizontal, how far above the ground is the kite?
Def not
Your answer implies that the kite didn't go really far up: only about 2.3 feet from your hands
What have you tried
I just tried again and got ~83.8 ft.
yeah
wth
120 is your hyp
epic
Welp
I have another problem
Could you help me with it?
You and a friend are standing on balconies of nearby builings. Your balcony is 40 ft above the ground andd your friends is 28 ft above the ground. When you loo kat your friend the angle of declination is 18.5 degrees. When you look at the top of your friend's building the angle of inclination is 44.2. Note: These angles are also called the angles of depression and elevation respectively. Use right triangles to determine the height of your friend's building.
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need help
turn it into simple shapess then sum the area of them
so turn it into a 2 rectangles and a triangle
I drew it
sso first rectangle has sides of 8 and 4
2nd hass sides of 6 and 3
and the triangle has base of 6 and a hieght of 8
8 x 4
sso solve for the areas of each then sum or add them all
base times height times .5
its essentially the rectangle formula but you cut it in half
for triangle?
48 x 0.5?
yup
74
yea
i got it wrong
how bruh
i have another one
you get the process or no ?
its alright ig
you have to solve for stuff
first rectangle is 6 * 4 2nd is 3 * 2 then the triangle is (6+3) * 5 * .5
i dont see a 3 on the 2nd rectangle
sorry 2
imma be honest ixl is like the most infuriating thing ever
52.5
yea
sure
i think i cut it incorrectly
no you can do it like that
just as long as you can solve for the area of each shape you make
kk
so 1st triangle has a base of 6 and height of 4
rectangle is 2 by 9
and 2nd rectangle is 3 by 5
yea
45
yup
sure
so you'd get rectangle 9 by 5 2nd rectangle 9 by 4 triangle 21 by 18
21 x 18 /2?
yup
yea
bruh im in shock right now
were doing dynamics in ap physics
and i got a question about the drag coeffcient of a parachute
this aint even a formula on the reference table
what grade you in
11th
wow thats how hard it is
the other stuff is a lot eaiser in this like review sheet
but i just got a question that we dindt even begin to go over
18 + 52 + 10.5
yea
80.5
yup
nice
thanku
i looked it up and i got it so im good
ap physics just angers me when they like ask you to only write in terms of other variables and put equation into equations
48 + 36 + 8*6/2
? already got it
Close?
yea make it solved
it stresses you?
not really
just really dumb questions they write like a whole essay for each question
heres one i have right now
An object is thrown with a fixed initial speed v0 at various angles α relative to the horizon. At some constant
height h above the launch point the speed v of the object is measured as a function of the initial angle α. Which
of the following best describes the dependence of v on α? (Assume that the height h is achieved, and assume
that there is no air resistance.)
im fairly good at it
but its one of the hardest courses but its also one with like the biggest curve
so getting a 70 is like a perfect sscore
for ap
5
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For #7, how do I know whether it’s 64/24 or 24/64? <@&286206848099549185>
Srry i meant 32 not 24
what part
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you just have to show its proportional
Wait no
because itss the same rectangle
How do i know what sides r corresponding
so RS/RU = ZY/ZW
But how do yk that
then you do 2nd divided by 1st for scale factor
id write how to go from 1st to 2nd times .5
bigger goes with bigger side so 64 goes with 32
This is so confusing
Ohh
its just rotated
Nvm
The sides r larger
I get it
Ty
And does the bigger number always belong in the numerator? @cosmic basin
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Hi! can i have some help with rotation of conics
do you have a specific question?
Prove that the unit hyperbola (x ^2-y^2)=1 is actually just a rotation of the function f(x)= 1/2x
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@versed needle do you still need help
@versed needle Has your question been resolved?
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Number of factors of p is
Result:
480
Number of factors of q is
Result:
300
Numbers that can divide p + Numbers that can divide q - Numbers that can divide both
$A \cup B = (A + B) - (A \cap B)$
NEONPerseus
🥳
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i have this pharse:
0 = cos(2x) - 2sinx
how do i solve this?
Do u know ur double angle identities
$\cos^2{x} - \sin^2{x} = \cos{2x}$
n!
Use this identity
^
(You can derive another one using this)
yes
Ok see which one would be most applicable for this situation
this one i think
Ok, but ultimately, u want everything in terms of sinx
How can we change that identity accordingly
maybe there's an identity to change cos^2x?
yes
So change this accordingly
Yes
great
Np
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Hi guys, I just want some clarification on ln vs logs. I have a formula here ill write it
Is there a reason why the log turns into an ln?
I've seen this with another formula or two aswell and I dont get why that happens
Or are they just used interchangeably?
monikanicity
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Just making sure here, v(t) would be s' and a(t) would be s'', correct?
Ye
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Hello, having problems here with this problem. I can't find where my error is
you used the derivative function for the y coord instead of the original function
Ah. So I plug the x values I find into the original?
yes
can someone help me understand why its that answer?
and not y-x^2/y^3?
bruh mb
sry
didn't know thsi was occupied
I forgot to close, no worries
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hi
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Sorry i had to go do something
But yes i have seen it
And i understand that ln is just log with a base e
But i don't understand if they're interchangeable here it seems like they might be but then i don't get why
$\log_b(x) =\f{\ln(x)}{\ln(b)}$
monikanicity
then derive it
Is this different than saying the same as what's written there except replacing the lns with logs?
Do you always have to evaluate the log with dividing the lns of the numbers? Or can you do it with normal log?
I don't understand
write out the log rules
the bases don't matter
or rather
the log rules apply to logs of any base
I understand the log rules but i don't get it where it uses ln and log
Why does it change
In the same formula
It's applying the log rule with c being e
This rule
Set c equal to e (2.718...)
ln is only log_e, its not interchangeable with log in general
If it isnt interchangeable why does it change in the formula?
But they give me the same answer
So doesnt that mean theyre interchangeable?
do you understand that ln is simply log_e?
Yes
then what's the issue
I dont get why it changes in the formula
there's no "change" here
what you've written is just simply a true statement
do you want to know why it's true or something?
But it changes
that's like asking why 1 changes to 2 because 1+1=2
makes no sense
what is written there is just a mathematical equation that turns out to be true
it's not derived from just "changing" some symbols on the left side to the right side
what base is the log in the second equation
so you mean to ask whether $\dv{}{x} \log_b x = \frac{1}{x \log_b b}$ is the same equation as the first?
Saccharine
I dont know
I just dont get why it changes
I know you said it doesnt change but i dont know how else to say it
is what I wrote what you meant by the second equation
In the one i wrote there isnt a b on the bottom right part
then what does "log b" mean?
How would I find these measurements with the info I have already written down?
you need to be specific about what you're writing
Claim a new channel
I dont know how else to say it im sorry
then how is anyone else supposed to know?
when you write something, the meaning has to be clear to everyone else
you're basically asking me the equivalent of "h afdskjhadskfjhaksjd fnfnma kfhdsajhkfjkhfjdhkaj" what does that mean?
I changed the letters
and then I ask you "what does h afdskjhadskfjhaksjd fnfnma kfhdsajhkfjkhfjdhkaj mean?" and you tell me "I don't know"
when people write mathematical symbols down, it is basically a language for communicating the underlying mathematics
you can't just change random letters and symbols around and then ask "why isn't the equation this" without actually saying what any of those symbols mean
it would be like "why didn't Lincoln write his Emancipation Proclamation like this: akdshfkdsafdsambtemnberbntertkjfdsahkj" and then when asked what "akdshfkdsafdsambtemnberbntertkjfdsahkj" means you say "I don't know"
How would I evaluate this derivitive, so it's like the same as the derivitive of ln 17 but we rewrite it as log base e
Is this how it would do
Yes
it's literally like saying "hi" in English or "hola" in Spanish
I understand
so what are you asking then
I just wanted to write it with log so that it can be clear that the base is e
Would that be the right way to evaluate the derivitive
huh????
$\dv{}{x} \log_e x \vert_{x=17} = \frac{1}{x} \vert_{x=17} = \frac{1}{17}$
it's literally just writing it in a slightly different way
do you not recognize
How is it just rewriting it
wtf now you're making me write wrong shit
this is absolutely not true
Saccharine
Whats that
Saccharine
I dont get why its ln on the right side and log on the left
Why not just keep it as log for everything
If we have like log base 5 of 12
Can we evaluate it as log base 9812 of 12 / log base 9812 of 5 and it'll still be the same thing as long as its the same base?
yes you can
So the point here is that it doesnt matter what the base is on the right side as long as its the same in the top and the bottom?
what, does $\log_b x = \frac{\log_e x}{\log_e b}$ make you happier?
Saccharine
a more accurate thing to say would be that $\log_b x = \frac{\log_2 x}{\log_2 b} = \frac{\log_3 x}{\log_3 b} = \frac{\log_4 x}{\log_4 b} = ... = \frac{\log_{3423} x}{\log_{3423} b} = ...$
Saccharine
i.e. $\log_b x = \frac{\log_c x}{\log_c b}, c > 1$
Saccharine
I think c can actually be less than 1 and it works
but it just can't be 1
and honestly couldn't be bothered
What happens if its 1? I dont see why 1 would cause a problem
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Is there an easy way to apply a arithmetic operation to every element in a list on a TI-84?
For example if I wanted to add 5 to every element of a list without manually adding 5 to each one, what would be a good way to do that?
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f is continous function on [a,b] and diffenrialble on (a,b)
show that for all x (a,b) f´(x)=0 that f(x ) is constant on [a,b]
Umbraleviathan
@mellow basin
@mellow basin Has your question been resolved?
0?
oh
i see
so your saying that f(x) is constant on (a,b) cause f´(x)=0 and integral of 0 is also constant
hmm but with constant it means like f(x)= c on [a,b] but if integral of a non diffentiable function is 0 it hasnt have to be c , no? @old geyser
Well it means that f = 0x + C
Well $\forall x \in (a, b), f(x) = C$ where $C \in \bR$
Umbraleviathan
C can be anything
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A={1,2,...,10}
B and C are subsets of A such that B and C has no common elements and B U C=A
find no. of ways to select B and C if ordering is ignored
Anagh
Is this answer correct?
yes
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does B simply equal to rhs?
or am i wrong?
Not necessarily. Is there more information?
no
Remember the question we did earlier, and the preimage stuff, it’s similar here 
Remember the preimage isn’t necessarily the same as the image under the inverse (and the function need not be invertible!)
in case of A [ ] f^-1(f(A)) it would be an inclusion though
And here too!
but there cannot be x1 = x2 such that f(x1) != f(x2), can it?
[remember how we took some function g : A -> {0,1}, g(a)=0 for all a in A, then g^{-1}({0,1}) is A but g(A)={0}]
Nope, that’s the definition of a function being well defined 
but it would mean that for x there might be few y
so it wouldn't be a function
in would be a relation instead
wouldn't it?
Consider that if f is not surjective, then it is possible for f^-1(B) to be empty, even if B is not.
For example f: R -> R where f(x) = x^2.
And let B = {-1}, a subset of the codomain.
Then f^-1(B) is the empty set
so f(f^-1(B)) is also the empty set
oh, okay, now I get it
ok, now it makes sense
i was thinking in the wrong direction
thanks for help
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Let (X, d) and (Y, p) be two metric spaces, and f be a mapping from X to Y.
prove f is continuous iff $f(cl(A)) \subset cl(f(A))$
rikusp2002
I posted this problem yesterday but I am still not sure on how to do the backward direction
it's easy to show if continuous then the result
But from the result I can't seem to get the continuity back
Even contrapositive doesn't work
Actually my bad.
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f:R-> R and f'(x) is continuous at some point x_0. Does f'(x_0) exist?
do you know definition of continuous
yeah
ok
oh sorry
then it should follow quite fast
i just assumed it was continuous
$\original$
active mental mutilation liker
ok one sec
Let $f$ be some function with $f:R\to R$ such that $\lim_{x\to x_0} f'(x_0) = L$. Is it necessarily true that $f'(x_0)$ exists?
please request a new nickname
is it differentiable at x_0?
That isnt given
idk this is the only thing that it says
the usage of f' seems to imply it is differentiable everywhere
like without any other context
Anyway
do you have a picture of the original question
because the usage of
i want to say they're implying it is differentiable about x_0
what would change if it were differentiable
if it is differentiable at x_0 f'(x_0) certainly exists by definition
oh well that seems obvious im gonna assume that it may or may not be differentiable at x_0
$\lim_{x\to x_0} f'(x_0) = L$




