#help-13
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@crisp flint Has your question been resolved?
@crisp flint Has your question been resolved?
!original
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
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I have a factor graph and am trying to calculate the probability P(x2=1) with the given probabilities
@raven sandal Has your question been resolved?
<@&286206848099549185>
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@raven sandal Has your question been resolved?
what should we find?
@raven sandal Has your question been resolved?
Is this the full question? It looks like you’re missing some information. What is f_a … f_f ? And how does x x’ relate to x y ?
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Ransik
that’s not a line thats just a point, or its two perpendicular lines
ah they’re probably referring to the actual lines x = 2 and y = -5, two separate lines
Oh woah
This is the vector form
(Position vector) + (direction vector)×(free variable)
Because z varies freely
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Cos=-0,8 need to find sin and tg
,tex .unit circle
Moosey
Sin^2=1-0,8^2?
Moosey
Sin^2 is 1,64??
-0,8
Moosey
$\sin(\theta)=\sqrt{1-(\cos(\theta))^2}$
Moosey
Will the - change to + ??
,calc (-.8)^2
Result:
0.64
,calc 1-.64
Result:
0.36
,calc sqrt(.36)
Result:
0.6
technically, sin(theta) will have two answers since we were squaring before.
and so tgnt will have two answers
ye :)
What about tg
we can verify that sin(theta)=-.6 with Pythagorean identity
for that, just use definition of tg
,calc (-.6)/(-.8)
Result:
0.75
Can you help me with a few more of these so i can get the hang of it
Ctg is. -sqrt3
Need to find sin cos tg
<@&286206848099549185>
use pythagorean identity involving ctg
alternatively draw out the triangle representing ctg. Also you need to specify which of sin and cos are negative
ctg =1/tg?
is this right?
ik tg and ctg now how do i find sin and cos
@subtle harbor
$(\cot(\theta))^{2}+1=(\csc(\theta))^{2}$
Moosey
yeah :)
soo sin is 1/2?
it comes from this identity when you divide both sides by sin(theta)^2
ye :), or -1/2
sin and cos have to have opposite sign tho
since ctg is negative
always?
only since ctg is negative
yea
if your question mentions something about quadrant that's important to include as well
i need help with one more and thats it
i need to find cos from
2tg^2a+3tga+1=0
@subtle harbor
let tga=u
ok so what now?
there is another pythagorean trig identity involving tan and sec
sec=1/cos
tan=tg
$(\tan(\theta))^{2}+1=(\sec(\theta))^{2}$
Moosey
i havent lernd sec and thoes stuffso is it posseble to do it other way
tg^2+1 eaquels 1/cos^2
???
you can also draw the right triangle that corresponds to tg=-1 and tg=-1/2
no i need to do it with thes formulas
alright, then yeah, use that formula
ok what do i do now with this formula
solve for cos^2
do i substitute tg?
ye
-1 or -2/4
both is good, since both are valid for tg
unless your teacher put any specification
so cos is 1 and 2 is this correct?
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how do I do this? I've used every standard convergence test I know
Joanna Angel
and then, when you show the convergence of this series, using the theorem on the differentiation of power series, you will calculate the sum of the appropriate power series
Ok I think I was able to prove convergence, but I have no idea how to use power series to find the sum, could you explain what you mean?
yes sure
look:
yoru series can be writtien in a scuh form:
$\sum_{n=0}^{\infty }\frac{\left( -1 \right)^{n}\cdot 3n}{4^{3n}}=3\sum_{n=1}^{\infty }n\left( -\frac{1}{64} \right)^{n}$
Joanna Angel
do you agree on it ?
yes
ok to evaluate its sum we have to replace
-1/64 with x
and we get power serries of the form:
$3\sum_{n=1}^{\infty }nx^{n}=S\left( x \right)\text{ }\text{ if}\text{ }\left| x \right|<1$
Joanna Angel
since center of the series is x = 0
and
Radius R = 1
that si easy to find
so to find oru sum we ned to find S(x)
we start form geometric series
$\sum_{n=1}^{\infty }x^{n}=\frac{x}{1-x}\text{ }\text{ if}\text{ }\left| x \right|<1$
Joanna Angel
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sorry need help with this again
does anyone here know how to map 3d points onto a plane
(theyre all coplanar)
i found the normal vector
and established 2 perpendicular vectors along the plane
to serve as x and y
idk what to do from here tho
@old ridge
sorry for ping
i rlly wanna get this over with tho
😭
Can you be more specific about what you mean by "map" in this case?
yea
so i have a bunch of points with x y and z
they all lie on the same plane
i want them to only have 2 coordinates
Oh, that's a fun thing to do. You've got a few things to do. You've already found the plane in the original coordinate system, but you need another coordinate system to map them into.
Does this plane intersect with the origin of the original space?
If it doesn't, does your use-case allow you to translate the plane and points such that it does?
use-case?
You're asking for a reason, right? (personal interest, a project, a class, ...etc)
math paper
my math paper is
finding the area when a cube is sliced by a plane
of the polygon formed
Oh, neat!
yea its alot of fun so far
i assigned the back right corner to be the origin
so now i have like
6 points in space
now i need to map them onto a single plane
so i can use gauss method
to find area
😄
You'll need to decide on an origin for the coordinate system of your plane in some concrete way - could be a point. You'll need to establish basis vectors for your coordinate system - could use two other points on the plane. You may want to correct that to be an orthonormal basis - not too bad hard from there. If you do all of these things, you can probably produce a linear transformation that encodes all of that work.
ok since all the points are coplanar i can justy make r_1 the origin right?
then from there i have my concrete point (r1) and i have 2 perpendicular vectors
Sure, just making any one of them the origin is a start.
i also have the nromal vector
so i have my plane fully established
but now how do i make it into x', y' ( ' = new plane)
rather than x, y, z
So think about that point you made the origin. Is there another point on the plane towards which you could draw a vector? If so, normalize that vector. You've got your x' basis. Then, take the cross product of that and your plane's normal. Now, you've got a y' basis.
i already have my x' and y'
i took a random vector between 2 points
then crossed that with normal
so i got x' and y'
Alright, fair enough. That'll do it. Now that those are real vectors and you have an origin, you need to set up a linear combination of those vectors that reach each other point.
Those linear combinations will be your coordinates in the plane's coordinate system.
Great question.
So
Take the vector from your origin (r1) to some other point (r2)
That's a perfectly valid vector, right?
ya
Now project it onto x'
There's the coefficient you get is the x' part of your coordinate.
Do the same again for y'
and you have the y' part of your coordinate
If your x' and y' are normal vectors in the original 3d coordinate system, then your area won't need to be scaled!
awesome
There's also another trick for getting that area, come to think of it...
a
cus thatll take so long 😭
i was hoping to make a general formula but i doubt thats possible
That depends on your target audience, honestly.
yea your right
IB is so unclear
when it comes to ia's
ok thanks for all the help!!
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is y=1/2(x+1)^2+5 a vertical compression by a factor of 1/2?
Please don't occupy multiple help channels.
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How do I find how many sequences of 100 consecutive numbers containing exactly 25 primes?
Not sure how to start
well, prime numbers are basically random, they don't have a pattern to them
are you allowed to write a computer program or smth
No you’re not.
I think it's useful to note that having 25 primes among 100 consecutive integers is very restricting
Key observation:||for n>11, there are at least 76 numbes in the seqeunce n,n+1,n+2,...,n+99 divisible by 2,3,5,7 or 11 and also note that the sum of 2,3,5,7,11=2310.||
You first eliminate all even numbers - there're 50 of them
Other numbers are of form 2k+1
They can be ±1, 0 mod 3
Okay lemme see
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how do i set this up?
i did $183=0.7x+0.3y$ and $93=0.1x+0.6y$
Joshii
and im currently at the matrix $\begin{bmatrix}
0 & 1 & 120\
1 & 6 & 930\
\end{bmatrix}$
Joshii
but i dont really understand what this would imply here
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So my approach in this problem is:
Let c be in R. We construct a sequence x_n of rational numbers in (c, ∞) that converges to c. Then limf(x_n) converge to c² + 1.
Now i construct a sequence y_n of irrational numbers in (c, ∞) that converges to c but then limf(y_n) converge to c. Therefore we get two different sequences in (c, ∞) that converges to different limits by sequential criterion. So right hand limit at c doesn't exist of f(x). Hence second kind discontinuity. Is this right ?
What does discontinuity of second kind mean
That left hand and/or right hand limit of the function doesn't exist at a point
Seems fine overall. Maybe you have to cite density of rational and irrational in R
Uhh yeh that's right i think even my prof mentioned it at a slightly similar problem before
Thanks for checking
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Anyone?
The problem not with the summation
It's the alpha and beta
Generalization for the roots
,rcw
To find some suitable n for that
The sum will be some function g(x)
g(x)=0 has a finite amount of solutions on the specified interval
Yeah g will depend on n
I used the sin AP series though
A pair of those solutions should satisfy the last relation
Hopefully it gives a strong condition on n
First I took alpha to be pi/n and 2pi/n as it's standard procedure
Then it didn't work
If you want to guess alpha then maybe you should search among alpha such that $e^{i \alpha}, ..., e^{n i \alpha}$ form a regular polygon on the complex plane
EQUENOS
2pi/n was a good try but there are also 4pi/n, 6pi/n, etc.
There would be many though
And n varies too
Brute forcing would extend it
I tried with n
One second
The relevant terms of sum are
Sin(nx/2) sin ((n+1)x/2)
The numerators
For alpha and beta should satisfy these
!occupied
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Hey I tried this
Alpha = a pi/n , beta. = bpi/n
Got me n = 37.5
Close in our range
If we do
Alpha = pi/n, beta = 4pi/n
We get n = 15
Can we manipulate it in some way to move n closer to our range?
@potent fractal
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Does anyone have any resources that can help me train for tests like this
Hi! For all?
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hi
@tawny drum Has your question been resolved?
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How to approach proving:
$\lim_{n\to\infty}\frac{f(n)}{g(n)}= 0$
kytsu1
...depends what f and g are
🧐
u can use big O definition
It is a task related to understanding the o expression, I am trying to figure out what the functions are. 
...ok wait can you just post the original task
...where does it say that that's the task
Sorry, this is the correct task:
What is this book called ? please
ok that makes a lot more sense
so probably the first step would be to look at the definitions of $\Theta$, $O$, and $\Omega$
bee [it/its]
Introduction to Algorithms by Cormen, T
ty
@thin galleon Has your question been resolved?
O(g(n)) = the output of f(n) is never greater than cg(n)
Θ(g(n)): ~∃ f(n) outside the bounds set by c1g(n), c2g(n)
Ω(g(n)) means f(n) cannot be under the curve of cg(n)
c is a positive constant, n0 is the smallest meaningful value - I don't know why n0 is the smallest value
ln x has negative y values when x<1, so perhaps n_0=1 for ln x
O(g(n))={f(n) | f(n)∈∫_n0^∞{cg(n)}}
I think an analogous problem is to prove that A ⊂ B <=> A ∩ B = A
This is fun! 🙂

@astral bay do you think this is a good solution?
...is what a good solution
as far as i can tell none of what you've said here is a proof of anything, just restatements of the thing you've been asked to prove
The Venn diagram shows the proof, that x is in A if and only if it is in B and C.
ok so here's a proof that every number between 0 and 100 is prime
is this proof correct?
@thin galleon
B and C should be prime numbers
why?
the venn diagram shows the proof, x is in A if and only if it is in B and C
i'm doing the exact same thing you did
your "proof" doesn't show that B and C are prime numbers
This is a good analogy, thank you

The O is for O(g(n)), not zero
so... is this proof correct?
the point i'm making here is
a "proof" of a statement isn't just a pile of symbols and various different obviously equivalent formulations of the statement
part of the point, the reason that proofs matter at all, is that you can only prove things that are true
so if you have a "proof" that works equally well at proving something false, it must not be valid
what a correct proof looks like is a series of steps where each step is necessarily true if the previous steps are true
producing out of nowhere the claim that $\Theta = O \cap \Omega$ is not a step that immediately and necessarily follows from nothing
bee [it/its]
if $\Theta$ is the set of primes, $O$ is the set of positive integers, $\Omega$ is the set of integers less than 100, then it's false, for example
bee [it/its]
and in fact nothing you can do by just symbol manipulation can ever prove that \Theta is the intersection of O and \Omega, because you'd always run into the fact that that's not always true
this is why i suggested looking at the definitions - you need to reference the definitions in the proof and deduce things from them
?
I am trying to translate this problem to the prime number example, I find it difficult, but it is interesting. Thank you for the explanations, they make sense.
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@formal pasture Has your question been resolved?
let the circle be a unit circle, which is $x^2+y^2=1$. then how can you express Q's coordinate, using $\theta$?
이재현
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how is acceleration m/s^2. I understand that it’s messaging the change is meters per second per second, so it would look like 5m/s/1s. However, wouldn’t 1s jump to the top, making it 5m•1s/s canceling out the seconds. Pretty sure the last part is where I’m making a mistake.
would just be m
its a sign convention, it means: change of velocity with respect to time
as velocity is written as m/s and time is written as s, change in velocity with respect to time will be m/s per second, which makes it m/s^2
So if a car can go from 0 m/s to 60 m/s west in 1 second then its acceleration would be 60m/s^2?
okay thank you
welcome
well, average acceleration over that second. probably not the same during the whole second
isn’t the average acceleration always different in between the start and end time
Also how can you find instantaneous velocity, position, and acceleration using algebra I thought that required calculus
@crimson delta
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@latent totem Has your question been resolved?
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How would you solve this?
first: there's a common factor in every term. what is it?
X
Ok, so that's factored out
We can pull x out
now we have x(x^3 + x^2 + 4x + 4)
Now: attempt to factor out something from x^3 + x^2 and 4x + 4 separately
From x^3 and x^2 we can factor out x^2
ok so we have x^2(x+1) and then for 4x+4?
4
But wait, what happens to the x we factored out beforehand too?
2
no, 4*x + 4 does not equal 4 times 2
(x^2 + 4) (x+1)?
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since it says linear you might want to put (x+2i)(x-2i) for the x^2 + 4
Really? Ok
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how is −4(1+k)(9) = -36-36k and not just 36k?
Multiply
my logic is that -4*(1+k) = -4k
That is false
and -4k*9=-36k
You need to distribute
okayy yeah i get it now
If you're ever unsure about that sort of stuff, try plugging in a concrete value of k
For instance k=-1
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11a
so sin4x
hey,, can i get some help w math?..
2 * sin2x * cos2x?
no
hm
we can so a substitution method at first to make it easier to understand
let’s say u = 2x
okay
you then have sin(2u)
then use the double angle formula
and you get 2 * sinu * cosu
yes
replace u with 2x
wdym again
4x?
?
yes
how did they get (2)(2sinxcosx)(cos2x)
sin2x = 2sinxcosx
i dont get where thr last came from
yes
so 2(sin2x)(cos2x) becomes 2(2sinxcosx)(cos2x)
they were probably focusing on sin2x first
become
that
like they just subbed in
the doublr angle
yes
oh well, now you know
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Goooodddd afternoon
I'm solving a question in logarithms that says i need to find the domain for f(x)=ln x^2-x-6. While solving, i ended up with the answer (-oo, -3)U(2, oo) as i used (x-3)(x+2) when factoring the problem. However, when using mathway to confirm my answer, it gives me (-oo, -2)U(3, oo)
I was wondering if the reversal of my answer actually matters or if there's something i'm doing wrong
When factoring x^2-x-6, -3 and 2 both multiply to -6 and add to -1, so i'd assume my answer was correct. But if the true answer is what math way gave me, what am i doing wrong?
here's the photo of the question
since the polynomial's domain is all real numbers, you just have to worry about the domain for the natural log function
what do you mean?
for what values is $ln(x)$ defined
Flappie
what do you mean defined?
i'm sorry if i'm a little slow, it's been hard trying to understand this
what is $ln(-1)$?
Flappie
ln(-1) actually is not defined
Ohhhhh i see my mistake there
yes, and for what other values for x is ln(x) not defined
0?
that's one value, yeah
0 is one of them yes, but which other ones
Any negative value im assuming?
yes
for any x<=0 ln(x) is not defined
Okay got that
what does this mean for the domain of ln(x)
I don't know
if i say the domain of some function f(x), what do i mean by that
All i know is that the domain is the x's
but if x<=0
we concluded a moment ago that ln(x) is not defined for those x's
so would those x's be in the domain?
No?
(0, oo)?
bingo
is 3 included?
this is correct
I don't know
I'm using parenthesis so i'm assuming not
Greater than 0?
if you have () brackets it means its not included, the [] means it is included
exactly
so now what if we look at the original question
what does that ask
it asks for the domain of f
and f(x)= ln x^2-x-6
*with an ln
Right sorry
I don't know
what did you say here
Oh right greater than 0
exactly
so then what about ln(x^2-x-6)
what needs to be greater than 0
for this function to be defined
x?
That's because 116 is a positive number
hint hint interval test
if the number is negative, it would be false, if it was positive, it'd be true
how would you check if its positive or negative
Well, i know that in the number line after i factor x^2-x-6, i pick any number in each section (in beween -oo and -3, -3 and 2, etc.) so i would replace x with that number and solve the problem
then the answer i get should be either negative or positive
that's how i learned it
x^2-x-6 = (x-3)(x+2), right?
Yes
so, ln(x^2-x-6)=ln((x-3)(x+2)), right?
Yes
and we need this function to be defined, so whatever is inside the brackets of the ln needs to be greater than 0
Are you saying that whatever is in the domain has to be greater than 0? Is that what you mean by inside the brackets?
ln(stuff inside the brackets)
OH okay
this is what i mean by 'stuff inside the brackets'
x^2-x-6 is a parabola and by factoring it, we can easily see what the intersections with the x-axis are
(x-3)(x+2) is that factorization, so what are the intersections?
-3 and 2?
close
Yup
so if we take the point x=3
if we go up, does it go positive or negative
if we go down, does it go positive or negative
same for x=-2
Well, for -2 if it were to go up it would become positive right?
so, if i fill in x=-1 it will be a higher value then when i put in x=-2?
Might be easier to graph it so you can visualise it
Oh wait. If i'm replacing the x's with -1, the answer would come out to be -4. But if i replaced with -2, the answer would be 6.
So if we go up, it will become negative
i think so
this is what you get
I still haven't come to understand how the answer would be (-oo,-2)U(3, oo) and not (-oo, -3)U(2, oo). But i think im getting somewhere
Ah okay
Okay
in this graph, for what intervals is this function positive
for what values of x, do we get a positive value for y
Oh 3 and anything above
Flappie
and what else?
and -2 and anything below
exactly
so we have the two intervals (-inf,-2) and (3,inf)
for which our function x^2-x-6 is positive
together with our knowledge of the domain of ln(g(x))
we know that ln(g(x)) is defined for g(x)>0
in our question, g(x)=x^2-x-6
with all of this combined
what is the domain of ln(x^2-x-6)
(-oo, -2)U(3, oo)
boom
Why what?
why this is the solution
😅
if i gave you ln(x^2-5x+6) would you be able to give the domain aswell?
Okay so i factored the first one you gave me. I factored it into (x-2)(x-3)>0
- =0, but yes
For the numbers in between and above/below, i chose -4, -2.5, and -1
since -2 and -3 are right next to each other, could either or just be used instead of a decimal?
like just use -2 instead of -2.5?
Oh okay
what you could do, is take the derivate and evaluate them at x=-2 and x=-3
After replacing x with -4 i got 42
Haha okay
solving that now
oh wait
?
well yeah, -2 + -3 = -5 and multiples it gives 6
okay wait now i'm confused
yes (x-2) and (x-3) to get the factors
but -2 and -3 are not the roots
(roots are where the fucntion is 0)
the roots are x=2 and x=3
because (2-2)(2-3)=0*-1=0 and (3-2)(3-3)=1*0=0
it'll be muscle memory once youre used to it
I hope so
Wait before i get the domain, do i need to change the sign of the numbers in the line? Cause i used -2 and -3 originally so i should change that to positive numbers?
(-oo, 2)?
Yeah
Would the factor for x^2+3 be (x-3)(x+3)?
Oh
you can see at a glance
Okay
when is this function positive
is x^2 ever negative?
No
so is x^2+3 ever negative?
No
so where is ln(x^2+3) defined?
we just concluded that x^2+3 is never negative
So it's never undefined?
exactly
So if it's never undefined
the whole domain is just R
Would the domain just be -oo, oo?
Oh okay
\mathbb{R}
$\mathbb{R}$
Flappie
here
thanks
Oh
idk if you've had those numbers
anyway
idk if i explained it properly
the whole thing
im new to this
It's a bit difficult to understand but it's not your fault. I'm a little bit tired and have been studying for a while trying to master logarithms
were the small steps useful or annoying
glad to hear
I was able to identify some mistakes i've made
I'll just need to practice more. Thank you though for the help i really appreciate it
Actually, if you don't mind, would it be okay if i can dm you if i need help with anything else? Despite my misunderstandings, you were really helpful and i'd like to learn a bit from you
yes sure, i dont mind
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how do i grpah this without a calculator
@modest shadow Has your question been resolved?
<@&286206848099549185>
It depends on how accurate the graph needs to be.
well then just think how the function behaves. eg. if x grows -> 0.2/x goes to 0 -> e^(0.2/x) goes to 1 and f(x) goes to 2. and so on. what happens if x goes to 0 from the left, then from the right, ...
what abt the asymptotes
i am not sure what you mean. what should be about asymptotes?
just as i said before: think how the function behaves. e.g. what happens to the graph if x grows?
what is with x = 1000, x = 10000, x = 100000, ...
@modest shadow Has your question been resolved?
didnt close it right 💀
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Hi
hi
How r u
Good and u?
Can anyone here teaches me grade 9 math
probably
Im tense about math
If you have a specific question you need help with, ask it
Otherwise the point of these channels are not to teach you entire subjects
Im not getting even a single thing
about what
Algebraic expression and Formulae
ask ur question
are you familiar with laws of power?
,,\expolaws
Yeah kind of
Pure
yeah I know thanks
Well if you know, these are all you need to solve that question
So where are you stuck?
ok
maybe in (ii) u can use the fact that:
(x-a)(x+a) = x^2 - a^2
I just dont know how to solve or go further like where to start
yeah
yes
aight u agree that y^3/y = y^2?
how
.
oh ok
can u try now to complete it?
ok
u can tag me if u need help with others
u sure x^-2?
oh it should be 1 / x^2
but how will it fit in equation
Ok its 2:24AM
Gn
see ya'll later
It would be nice @velvet hemlock if you finish answering me
@empty berry Has your question been resolved?
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Suppose Lisa has a collection of 20 necklaces. Twelve are made of pearls, 6 are made of gold, and 2 are made of both pearls and gold. If she randomly selects 5 necklaces to wear to a gala event, find each probability.
P(2 pearls and 3 gold or 1 pearl and 4 gold)
P(at least 1 necklace made of pearls or gold, but not both)
@graceful rose Has your question been resolved?
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
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For this question, I think I got a) and b), in the sense that a) is just P(AandB) = P(A)P(B), and b) is just when they are mutually exclusive P(AandB) = 0 so it's minimu, but what's the condition for the maximum?
Hint: if both A and B have happened, then A has to have happened, and B has to have happened...
@reef hare Has your question been resolved?
So it's... 1?
😭
Not quite 
You have to have A happen (which has probability 0.3) and you have to have B happen (which has probability 0.8) for A and B to happen both
So that's the same as a)? assuming that they're indepdent and just using the multiplication rule
Not quite either 
😭
It's not that they're independent that you want to look for, but rather, something else (not mutually exclusive either)
Ohhhhh
B is dependent on A?
or something like that
Actually A is dependent on B
like if B happens A is guaranteed to happen
or something like that
Those cat emojis are so cute
That's the idea 
I love the cat emotes 
So practically P(AnB) = P(B) because if B happens A is guaranteed to happen, as such P(AnB) = 0.8
But for example, it's more likely I'm typing this in bed than it is that I'm typing this in bed and drinking hot chocolate, that's the idea
Not quite P(B) either, almost though 
Given that P(B) has happened...

