#help-26
1 messages · Page 6 of 1
Notice it says y=**-**2, not y=2
Pro tip: Close the dollar signs before writing text
Guess it wasn't clear what was meant after all
The former
the first one
okk
In case of doubt, when replacing a variable with its value, put parentheses around the value
@half pike You can now .close this channel
hang on
real quick
8a is -3
8b is 9
8c is -2
Correct
Yes
how do u do the other ones
First of all do question a, it should be easy
Do you know what the "solution set" is?
not rlly
It's the set of all numbers that satisfy the equation/inequality
@half pike Does that make sense?
can u give an example
x^2=1, the set of all solutions for this equation are {1,-1}
Because x=1 and x=-1 are the only solutions to this equation
how does x = -1 if x = 1?
I'm not saying x=-1 and x=1
I'm saying that either x=-1 or x=1
ohh
are the only solutions to this equation
@half pike What do you think the solution set is for the inequality x > 0?
-1
-1,1?
yea
Because that was an earlier quesiton
oh
Read this again
-infinity?
Again, that's not a set
That's a number
Not only that, but it doesn't even satisfy the inequality
-infinity is not greater than 0
whats a set again
Just a collection of things
Although because we're talking about a solution set it must be a collection of numbers specifically
GG to the guy who just got automodded
oh ok
Wait
So do you know?
form?
It can be represented in multiple ways
Thus it's a form
(it's not actual terminology, I just think stuff like this)
Yeah sure but I think if they knew this they'd be able to answer
@half pike So should I take that to mean that you don't know the solution set for x > 0?
yes
Then you gotta teach them how to make a solution set
What do you think I was about to do 
Fair
Just testing their background knowledge first
What is it?
what si what
Oh 
Also sorry if u find my tone rude or anything, I'm bad at communicating
@half pike The set is (0,infinity)
Crying and shaking rn
oh
Nooooo
An interval is a set of numbers
Does it make sense that we're using an interval rather than {}?
Ok...?
@half pike What does the silence mean?
I have no idea where the set thing went
0 > infinity 📝
${ {x \in \mathbb{R}; 0 < x <\infty} }$
@half pike Last attempt, are you there?
yes
Kai The Doge
@half pike So does it make sense to you that for x > 0 we used an interval instead of the regular set notation with curly brackets?
i guess?
Both work*
Like for x^2=1 there are finite solutions
But if there are infinite, you cannot just give a few numbers or list them all, thus u have to use set notation
Hence we can write them all down like {1,-1}
But for x > 0 there's an infinite amount of solutions
So instead of spending an infinite amount of time writing them all down we just use an interval
@half pike Does that make sense?
yea
Great, do you think you can find the solution set for x+5<0?
uhhh
Great, now can you put it in interval notation?
Is -5 a solution to x+5<0?
it would be =
Is 0<0
no?
Right
Therefore -5 is not part of the solution set
So it should be (-5,-infinity), not [-5,-infinity)
Also (-infinity,-5)
Ohhh
Since smaller number...
I don't think it's a rule to do that but it's the convention
Also is both or one correct? @half pike (-6,infinity] and (-6,infinity)
Why
cuz infinity is suppose to end with ) always
Riemann spheres:
Not relevant until like prolly a lot more years


POV: You're a student and spent infinite time writing all the solutions until Cantor comes along and shows you you missed one
wait its (-infinity, -5)
nope
and idk how to
thr space is kinda small
Yeah, it is
Yes
It's a line
okk
Like a bad number line basically
Draw a number line, then draw it just like they did
and do i jsut write it on the line?
By the way because your interval goes all the way to -infinity you will only draw one parenthesis
Yes
Well do it on another piece of paper or in paint (the program not actual paint) first
So that I can check what you did
You really don't like different notation, do you 
Yes
okk
Nope, I really don't Xd
yes
yay
To remember this notation, you can think of a circle as an "open dot" and a point as a "closed dot"
open dot is excluded right?
oh yay
can we do the other one
Yes
How's it any different than the previous question?

Yes
wait rlly
oh what would it be
Is infinity less than -3
no
I don't really know how to make you realise this yourself
All I can say is wrong direction ⬅️ other way
-2?
not <
Why are we talking about -2?
Yes
That's the reason
Now I think you won't have any problem graphing it
@half pike Did you graph it?
can i ask one more quesiton
Or maybe I'm just not used to it because I'm lazy
the question is
Solve the linear inequality.
I can't believe neither of us is paid to do this
Anyways
Tell me the first one where you get stuck at
i dont get what its asking for
I assume it means isolate x
For example, something such as x <= 3 is considered solved
Because x is alone
@half pike Does that make sense?
idkk
hekp
You can just say "no"
okk
Basically in 2x <= 7, x is not alone
There's a 2 next to it
So you need to find a way to make it alone
Do you know how to do that?
= 
= 3.5
Yes
I think my teachers would accept this as an answer, not sure about yours
In theory both this and solution set form should work fine
Well same logic
Just do them all the same way and tell me if you get stuck at any of them
Yes
oo yay
hwo do i do 7 - x >= 5
If you rewrite it as -x+7 it becomes obvious
-x >= 5 -7
Oh there you go
No
If you're going to negate both sides the symbol flips
Like picture the number line in your head
Or even better, take a piece of string or a pen or pencil and think of it as the number line
Then flip it, which represents negating a number
Notice how everything that was on the left is now on the right and everything that was on the right is now on the left
That's why when you negative both signs of an inequality the symbol flips
ohh so its <=
Yes
Which one specifically?
@half pike The fractions don't make it hard at all
Typical numerophobia or whatever the frick its called honestly
Students do be like that
It's just the same as what you already did but you have to write more stuff down
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Does this series have a name?
I’m having a hard time finding the sum of this series but I can’t match it to any on Wikipedia
could you show the original question
Seems to be something special
There is a pattern though
$T_n = \frac{n}{n(n + 1)}$
Bot broken
The nth term is n/[n(n+1)]
Which is just 1/(n + 1)
Which is a harmonic progression
On shoot that’s right
I forgot about the term out side the series
If it’s harmonic doesn’t that mean there’s no sum.
So this series just goes to infinity
Yes it diverges
I probably did something wrong
this was the original question
for a I found it to be (1/k)(1/k+1)
Thanks for the help!
Really appreciate it
I don’t think you did something wrong, I got the same
so this is basically saying my expected value of getting a white is an infinite number of tries?
Yea this is weird let me see if I made a mistake
I guess it kind of makes sense for it to be infinite
cause the more black I choose the white basically just disappears
I guess
to the point where i keep drawing which just hurts my chances of getting the white
Yea that makes sense
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what would be a good hint for the anti deriv of tan x?
I'm trying to rewrite it but I got a product still in the end. Assume calc 1 knowledge
try substitution
yes
that's not how I'd do it
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for 8c
i dont get why u need the line after this one --> i thought u can find probability that B scores first from there
what do you mean?
i dont get why theyve done the last bit
to find that probability
so theyve done the first part to get enough information for the last part
this question always confuses me
yes
oh mb you can't say that the probability of A winning = 0.3 because that has the condition of B scoring first?
ohhh so u consider A winning if they do score first and if they dont
ohhhhhhhhhhhhhhhhh
thanks
they might be using the law of total probability in the denominator
whats dat lol
google it, there should be plenty of resources on it
Tl;dr this, those make up all the possibilities of A winning
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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
do you know what a log is
we know x is between 2 and 3
okay
2^2 = 4, 2^3 = 8, and 5 is between those
so how do we know exacly?
do we have to know what is it exactly or close?
the value of x
you just need to be able to estimate it is between 2 and 3
based on this
what about the rest of the q
how do we write x?
they gave you that x + 2y = 6
the smallest value to consider is x = 2
and the biggest is x = 3
plug them in and see the largest and smallest values for y
huh
huh
i will
@karmic monolith this is an estimation question
they want you to use the fact that x is between 2 and 3
I don care
?
Logarithms make it easier
i don't understand why you are being combative when the intended solution is clear
this is again more complicated than it needs to be
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Can someone give me the steps to solve this one please, my teacher only wants us manipulating one side.
It’s the one question I haven’t been able to figure out
if you expand out tan(X) as sin(x)/cos(x), then simplify, you'll see that becomes a trig identity
you were on the right track
here's a hint
$\frac{tan(x)}{sin(x)cos(x)} \\= \frac{\frac{sin(x)}{cos(x)}}{sin(x)cos(x)} \\ = \frac{sin(x)}{sin(x)cos^2(x)}$.
MellowDramaLlama
now simplify and bob's your uncle 🙂
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Tysm man I love you
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Are vector fields just the gradient of some level curves?
not all
ones that are are "conservative"
or are you not on about vector fields that are gradients of just some function?
By conservative, do you mean that whose partial derivatives of g and f with respect to x and y respectively?
Damn, I guess i'd have to go way back and read the textbook.
conservative vector fields are those whose line integrals over them only depend on the end points
Yeah, I've learned the same concept in Calc-based Physics as well.
yeah those are precisely the vector fields that are gradients of some function
Okay, so if those "some functions" are non conservative, then there can't be a gradient of any sort?
if the vector field is not conservative, it is not a gradient of a function
Got you
those arrows are some of the vectors in the vector field yes
and because this vector field comes from the gradient of phi, all the vectors are normal to some level curve
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I want to prove that the space of convergent sequences in $X$ is closed in $(X^\mathbb{N}, d_{\infty})$. $X$ is a metric space.
Casiel368
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✅
Please don't do that nor ping helpers. People are capable of doing both themselves
.close
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How do I do part a?
use newton's third law
I’d consider it as a system
What do you mean?
The topic is vectors
How would I relate that to vectors
draw a free body diagram showing the forces acting on each block as a vector
The outstanding forces are the gravitational forces
The tension is equal and opposite as cloud posited
Stephen
I’m still confused
This physics video tutorial explains how to calculate the acceleration of a pulley system with two masses with and without kinetic friction. It also discusses how determine the tension in the rope as well. The formulas and equations are all provided in the two practice problems & examples presented in this tutorial.
The full version of this v...
Does tension in the string equal downwards force+upwards force?
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Don't know how to find the non-trivial solution for this to get Kn and thus K3
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this seems too advanced for help channels try #odes-and-pdes
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Why didn't i need to flip the intergral to have the lowest value on the bottom.
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Uh I attempted but don't know how to get it to it's antiderivative
My attempt led me to 1/2 x (x-5)^-1
Now I'm gonna take a guess and say that's not it
Let u = 2x-5 and du = 2 dx
If you let u = that, then differentiating u gives du = 2 dx
So your integral becomes
1/(2x-5) dx
= 1/u * 1/2 du
Integral of 1/u is ln|u|
so
I let u equal the denominator
and then there's 1/u (from the x-5) and 1/2 from taking out half, multiplied by du
Then by antidiffing it, I get ln|x-5| x 1/2 x 2?
its 2x-5 not x-5
And where are you getting the 2 from?
we get the 1/2 because
du = 2 dx
dx = du/2
But we are integrating 1/(2x-5) dx
dx = du/2
Or 1/2 du
u = 2x-5
D(u) = D(2x-5)
D(u) = D(2x) - D(5)
du = 2 dx - 0
You can YouTube search "u substitution for integration"
To learn more about this technique
But essentially
We make a dummy variable by substituting the expression as something which we can easily integrate
Its all just algebraic manipulation of the expression
We know integral of 1/x is ln|x| but
1/(2x-5) is annoying to deal with
But if we could somehow mold this expression
Into something which does look like
1/x dx we would be able to easily integrate it
So we let u = 2x-5 and check if we are transforming from the x world to the u world
How will that affect dx and the integrand as a whole
Any integral has 2 parts
Integral of f(x) dx
The two parts are f(x) and dx
We know that 1/(2x-5) becomes 1/u
So replacing that we get
Integral of 1/u dx
Uh well we cannot really integrate this
variable in u but integrating in the x world
So we have to change dx into something du as well
u = 2x-5
means du = 2 dx
Or, dx = du/2
Now replacing that
We get
Integral of 1/u dx
Becomes
Integral of 1/u * 1/2 du
Or,
1/2 * Integral of 1/u du
Does that make sense?
If not, I highly encourage checking YouTube
U substitution
Uh just to check but this is just saying du is equal to whatever du is times dx right? which is why it's 2 times dx?
I follow everything before that though
and I get rearranging the equation to make dx the subject
If I understand you correctly, right
Try to solve similar problems like integrate sin(3x-9) to see if you have really understood it
Oh that'd be -1/3 Cos (3x-9) right
Right
I think I get the usual antidiff for ex, basic variables and circular, I just can't grasp the du changing thing
,w integrate sin(3x-9)
9-3x?
Oh ye, I thought that'd only give the -1/3
oh wait
Nevermind that comment I just realised what that meant
@magic night Has your question been resolved?
uh ye
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we have s = 60
i have PR, i dont have ps or pr
use sin 60 = PR/RS
If you do something like this, that is an equilateral triangle so all sides are the same
and you'll find this
?
i didnt quite understand
just started trigonometry this year
sin s = pr/rs
sin s = 60
sin 60 = root 3/2
understandable
then what?
8/2?
4?
ok so you have the equation
(root3)/2=8/RS
yes
And try pythagorean theorem here
Lemme explain 1 by 1
This picture shows an equilateral triangle, a triangle with the same three sides
this
so 16?
ah no
16/root 3
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16/3 * root 3?
nah
its 16 = x sqrt(2)/2
so it's 32/sqrt(2) = x
or 32 sqrt(2)/2 = x
or 16 x sqrt(2)
18.48
that aint even a option bruh
Ah bruh I made a mistake there
16/root 3 which makes it 16 by root root 3 * root 3 / root 3 which is 16/3 * roott 3?
AHHH
I know where the mistake is
It's here
Maybe I'm too tired
It's x^2 / 4
so 3x^2/4
or xsqrt(3)/2 = 16
so 16/sqrt(3)
yeah it's D
cause that's just the same but rationalized
so 16sqrt(3)/ sqrt(3)^2 or 16 sqrt(3)/3
Yah
I'm just too tired maybe I should play rest first
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Integrate x^(-a/b)*sin(x) dx from 0 to 1. Do it with partial integration (Done) and then by variable substitution with x=y^p for a well choosen p. Now whenever I try to select, 1, -1, 2, -2, +-5, +-10, +-9, +-10/9 I keep getting a thing I do not want when I get the dx/dy part. I think I'm missing something obvious. It's ok if we need to solve the integral with numerical methods after the substituion.
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What if you chose p=-b/a so the first part becomes simple 
Ok so I think I solved it but still get a wrong answer when I calculate it. So dx = py^(p-1) so $integral_0^1 p y^(2p-19/10)cos(y^p) dy, if I take p = 19/20 lots of the things cancel out and I can numericaly solve it in matlab with '''matlab integral(@(y) (19/20).*cos(y.^(19/20)),0,1)'''
so if I integrate, from 0 to 1 of (19/20) .* cos(y.^(19/20)) I get 0.7943
so if I integrate, from 0 to 1 of (x.^(1/10)) .* (sin(x)) I get 0.4369
But they should give me the same value
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I struggle with the following math exercise:
You can have friends from town A and Town B.
You can have at max 4 friends from A and unlimited friends (like N) from B
X is a random variable representing the number of friends you have from B
You can only have friends from B if you have 4 friends from A.
X is Zipf distributed.
Whats the probability that you have at least one friend from A
My approach was we introduce Y that represents the number of friends I have from A and calculate
P(Y=4 & X>0)
But now I struggle with calculating Y. I dont have any probability given for someone from A being my friend.
I just know that X is Zipf distributed with parameter 4.
Can someone maybe give me a hint or something like that ?
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Assume Calc 1 Knowledge.
For questions like these, aren't I just finding the first deriv and C, then I just plug in -1 into f'?
Do you know the FTC
idk what FTC is 🙂
i’m assuming it stands for fundamental theorem of calculus
The idea is that f(x)=F(x^2)-F(2) for some F that has the property that F'(t)=t/(t+1)
But if f(x)=F(x^2)-F(2), then certainly f'(x) = F'(x^2) - 0 = x^2 / (x^2 + 1)
this solution doesn't make sense to me
it looks like he subbed the upper and lower limit
like
when I do my u sub, I know I have to change the upper and lower limit
but he used those to sub his integrand??
idk why my Professor would include parts of a solution where he hasn't taught us how to do
Ok
Like, I did u sub on t + 1
$\frac{d}{dx}(\int_{a}^{f(x)} (g(x)) dx)$
=$g(f(x))(\frac{d}{dx} f(x))$
Oh lord
Hold up
sure
% Openglobe %
There it is
do I have to do it that way
That’s an alternate way
that looks like chain rule
LOL
yeah
mf never taught us about reverse chain rule
ty
at least now I know what he did
This “u” stuff is confusing
@lyric mountain Has your question been resolved?
Yeah
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what are we talking here about ? it is permutation right?
no, the n things are all the same. So the number of values of r is n+1
so there are n+1 ways to choose r things from n identical things
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p & q are alike objects and s is distinct object... in how many ways can we select object in this ?? i know when one group are alike the eq is (f+1)(h+1)-1 and when distinct it is (p+q)!/p! * q!
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did i do this right?
<@&286206848099549185>
why 0?
Wait
Cross product gives you a vector that is perpendicular to the plane of the crossing vector i.e p and r here
Shouldn't it be up the plane?
In my diagram, no
Why not?
Taking dot of 2 perpendicular vectors give 0
Oh nvm its the right hand rule
Im dum enough to repeat the same mistake over n over again
im not just doing cross product the question asks me to do a dot product of r too
Happened with me couple of times.
Practice made it go away
Yes
Here
oh so is there no calculations needed then?
so i did my cross product wrong then?
Let me check
since if i do the dot product with r it has to equal 0
is my method bad? it's what was taught in my lesson
It looks good but you can space out to avoid confusion
actually it would be 3i+2j+k
Can you kindly point out the mistake in my image?
(4-1)i
you have done right . you just did minor mistake in j part
ok what was it?
1 X 0-(-2 X 1) that will be 0+2=2
ohh i see it thanks
real dumb mistake my bad
thanks for the help guys have a good night
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I'm going through some solutions to a past paper (at uni) and I don't understand the solution given
Let $\chi$ be a non-trivial Dirichlet character modulo an integer $m > 1.$ Prove that the sum of the values of $\chi$ at the first m non-negative integers equals 0
LeftySam
Solution:
Since $\chi$ is non-trivial there exists an invertible $b$ such that $\chi(b) \neq 1$
LeftySam
(this is the first step, not the whole solution); I don't get this? Why is this true?
@velvet phoenix Has your question been resolved?
Why is n non-invertible if gcd(n,m) > 1?
bezouts lemma
or well, thats the other direction
if gcd(n, m)>1 then it is clearly a zero divisor
Idk what that means
I'm confused what we're even talking about with regards to invertible here too
has a multiplicative inverse
LeftySam
It's mod m no?
same thing
I don't get what you mean here
Or why that implies the result
if m=dk with d=gcd(m,n) and n=dt, then nk=dtk=mt=0 mod m
an element can only be a zero divisor or invertible
exclusive or
Why wouldn't this method work for gcd(n,m) = 1. I.e. if m = k and n = t then nk = tk = tm = 0 mod m
then k=m=0
so you are multiplying by 0
which isn't interesting
but if d>1 then k is nonzero so you are multiplying by a nonzero element and get 0
which means zero divisor
Okay, the next is
As $a$ runs through all residue classes modulo $p,$ so does $c = ab$ as $c = ab$ has a unique solution in $a$ for every given $c.$ Hence $$\sum_{c=0}^{m-1} \chi(c) = \sum_{a=0}^{m-1} \chi(ab) = \chi(b) \cdot \sum_{a=0}^{m-1} \chi(a)$$ shows that $\sum_{a=0}^{m-1} \chi(a) = 0.$
LeftySam
So a i'm assuming is what? A generator?
No I get that, but I don't get the wordy bit
What does it mean that "a runs through all residue classes modulo p" anyway? A generator? Contained in the set {1,2,...,p-1}?
if you let a be every element mod m, then also c=ab will hit every element
not sure why you switched to mod p now?
this is an easy question
Seems unnecessarily difficult
no offense but you dont seem to know any basics
I'm in third year
It's just "a runs through all residue classes" is a very vague statement to me at least
it's a very classic math statement
just look how its used in the sum
you also say that sums run over some numbers
every number from 0 to m-1 is used
for a
and then also for c because b is invertible
Does it mean a generates the group mod m {1,2,3,...,m-1}?
So what does it mean, you have a in {1,2,3,...,m-1} mod m and you sum over each possible a?
do you know how sum notation works
Yes
Sure, then include 0 in that, is that correct?
yes
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- Water flows through a cylindrical pipe of internal diameter 7cm at 5m per second. Calculate:
i) The volume in litres, of water discharged by the pipe in 1 minute.
Here's what I'm doing
π * 300 * 3.5
11545.35/1000
11.545
consider volume of water that flows in one second
It should be a cylinder of definite length
@hallow garden Has your question been resolved?
@hallow garden Has your question been resolved?
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i need help with this
im kinda stumped
i did ratio thing
for first one
i got mod x <1
so r is 1
?
@neon iron Has your question been resolved?
help
@neon iron Has your question been resolved?
help
yeah looks like left one is r=1
what do you reckon right one is
main ideas are there, presentation can be more formalised
yeah seems so
ty
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ok I have geometric equations, I'm at Tn=6600(0.825)^n-1 to model the value of a machine after n years of depreciation, how much was the machine originally worth
It hasn't been 15 min yet
Oh sorry, I didn't see the time
It's 11:28 already
OK let's see}
Is this your equation
find the value when n=0?
$T_n = 6600 \cdot (0.825)^{n-1}$
Max Hetfield
yes
What is the n?
i mean for the initial value 1 ??
n is the years of depreciation
If the machine is new, how many years of depreciation have passed?
