#help-17
1 messages · Page 193 of 1
They are saying sub (5) into (4)
They are substituting into f_x and equating to 0?
the rest is just finding partial derivatives
Like, into (3)
Yeah but they wrote (4) which is a typo so rip
Yeah
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Problem from discrete math:
f(n,k) is a function that counts all permutation from S_n that have exactly k fixed points
so the problem doesn't require me to find the explicit solution to this but still i was wondering if this is correct
ok nvm im wrong
ok how would i get the number of permutation with NO fixed points?
then if I had that i could just do $f(n,k) = \binom{n}{k}*(permutations with no fixed points)$
OHHELLNAH
Note that when with k fixed points, the rest of the permutation can be presented as a permutation of (n - k) elements
yeah but if i just do $\binom{n}{k} * (n-k)!$ i could get more than k fixed points
OHHELLNAH
i need exactly k fixed
Yeah, that should be it
Why do you think this is overcounting?
Ah
yes
Do you want at least k fixed points or exactly k fixed points?
exactly
thats why i wanted to find the number of permutations with no fixed points
and my idea was to to find permutations with Atleast one fixed and then subtract that from all permutations but i ust 0 for some reason:
$n! - \binom{n}{1}(n-1)!$
OHHELLNAH
i just learned there is no formula for this
its called Dearangments and the solution is n!/e rounded to nearest integer
I remember the problem about counting permutations with k non-fixed points
There is no closed form to the solution, it's presented as a sum
However you can derive the recursive formula by picking some non-fixed element x and considering two cases on phi(phi(x)) where phi is the permutation (the cases are phi(phi(x)) = x or phi(phi(x)) ≠ x)
Yeah, exactly
There is, it's just that the formula isn't a closed form
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not sure where the 1/4 came from ? It was never brought up in other problems
for example f(x) could be defined like f(x) = 1/2 * x^{1/2}
oh no, I'm asking where the 1/4 slope came from
wdym where it come from?
Its just that the derivative of the function f in a is 1/4
the slope of the linear function that aproximates f in a is 1/4
well the original problem only have us the 1/2 and a=1, this is Quizlet and it kinda just gave me the number
gave**
well they introduced the value of the derivative in this step
do you want to see the first two?
Ok but whats the problem
just a sec
no problem
ok im back
wb!
The function given
💀
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Can anyone help with #2
<@&286206848099549185>
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<@&286206848099549185>
@vast shale Has your question been resolved?
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step by step please
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how do you get to that last step from the 2nd last
i havent done this in a while and i forgot
you can apply tan^-1 or arctan to both sides
to isolate F
so if you put a calculator in degree mode and type tan^-1(0.82759), you should get that answer
how do you apply ir
it
i asumed
but idk how you enter that into your calc
like tan-1*.82
oro what
there should be a tan^-1 ( on your calculator
it might even be the same key as where tan is, you might have to press 2nd or alpha or something to select it
u put the right side in the brackets
can you type in the chat
what ytou mean
Tan^-1
i got that in my calc
how do i tell it
my number
so it would be tan^-1 ( opp/adj ) to get the angle
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arc tan
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what all work would i need to show
just tan^-15.8/4.8
or would i need to show
tan deg = 5.8/4.8 first
sorry let me reword
so you can solve into the decimal first (as the worked soloution does) and do arctan of the answer, however i sometimes find it easier to just do it in one equation
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???
do you remember formula for average rate of change
y2-y1/x2-x1
ohh
so does the slope decrease or increase
ohh it becomes less negative
maybe you realized the magnitude of the slope was decreasing
but yeah being less negative means it's technically increasing
even though the changes are getting smaller
i was thinking of this
decreasing at a decreasing rate
i'll keep that in note
thanks guys
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Vertex is the max or the min of the parabola
Axis of symetry is the y axis of the parabola
Stretch or compression is determined by the value
A value
As it is 1-1a 2-2a
Like one space right one space down if it is inverted
Direction of opening determines on negative a value
Either upwards or downwards
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I won't solve it ( I mean give tyou the answer). Think, or recall, what is a perpendicular bisector? Does this construction seem like one?
alr can u do another problem then?
Its no right
because the lines are not straight
so you cant make a right angle
Fair enough. But, you meant the lines are not perpendicular since they do not form a right angle? Because I see all these lines are straight.
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In a chess tournament 2 guys played each of them playd 3 games and then left. In the whole tournament 84 games where played how many people where at the tournament and did the original two guys play each other
Not clear
Can you send original question
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good job, now theta is the angle forming the arc
so assuming the gondolas are equally spaced out, and you have 360 degrees in an entire circle, how many degrees separates each gondola?
ohhhhh
like the formula S = r * theta only works if theta is in radians
so you'd have to convert your angle into radians to plug it in
the other way i'd think about this is that the circumference is 2pi * r, and you're chopping the circumference into 42 different arc lengths
so you'd just divide 2pi * r / 42
Yeah I tried it that way, but it doesn’t follow the s=rtheta formula they want us to use
oh okay if they insist you use the formula then that works
just instead of 360 / 42, it'd be 2pi / 42
Is this good?
yeah that looks right
Could you check my Answrrs I don’t have an answer key
So this s=rtheta formula, theta MUST be in rad?
Yea, if you want it in degrees it would be (theta/180)(pi)(r)
Could u check if my answers r correct?
Yea everything seems alright
So we know that the unit circle has a radius of 1, where the right triangle formed using the radius as its hypotenuse has side lengths sinx and cosx
yes because soh cah toa?
And because tan45 = 1?
So since cos 45/sin45 = 1 my coordinates r sin 45 and cos45?
Wow you got that quick but yea essentially that's what it's asking for
But while the answer is correct, i just noticed that you wrote tan45 = 1, what exactly do you mean by that
I was referring to the unit circle
Tan 45 is 1
On the unit circle
The chart associated with the unit circle
Ykwim
Yea it is, but i dont really see how tan 45 relates to the question
Ok i think we should go back and revise a little
So the unit circle has a radius of 1
So sinx = opp/hyp, but because hyp is 1, sinx = opp
Same thing for cosx = adj/hyp, so cosx = adj
So the side lengths of the triangle are sinx and cosx
Meaning that p(45) = cos45,sin45
3 o clock i think
Am?
Pm
Nah
It’s 12 am for me and I have a big final test in the morning right, it’s on trig, I still need to learn how to find equations from graphs, how to graph when given equations, and how to write equations from words
Do you think you could potentially stick with me for a couple hours maybe and teach me these things?
Let me send you pictures
Yea i guess so why not
Thank you so much, you’re a life saver!!!!
Should I just read through all the material quickly and return in 15 mins?
Sure
Ok I’ll be back in 15, thank you so much ur a life saver!!
@distant saffron Has your question been resolved?
@urban snow hi bro check your messages (dms)
@distant saffron Has your question been resolved?
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what happened to -1?
negative x negative = positive
I figured all this out when I was 14 playing around with desmos
can't solve it lmao
trust me bro its all piss-easy if you can add and multiply
im still learning pre algebruh
so maybe soon
how you got into math?
school
💀 then y do you have to learn this
graphics programming?
oh..
i envy you first ngl
knowing so much math requires alot of time
but soon i will learn i guess, fundamentals are needed
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Need help on how to solve these optimal price questions
@still summit Has your question been resolved?
try writing the total revenue for the hall as a relationship between price and the amount of people
This good?
First bracket being 30 dollars per person and -1.5
And second being for the amount of people
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if you add those two expressions and simplified by combining like terms, what would you get
-4x^2?
yes
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How do I convert the slope to parrarel
Try plotting the graph of y=-x+3
You only need two points to plot a line
So take any 2 random values of x and calculate y for them
Plot the points and join them
Yes
The other side or opposite
what do 2 parallel lines have in common
The same line
Or slope
so which line has the same slope
C?
the slope is -1
I just wanna know how to convert it to thr pararrel one
So it’s decreasin
yes
the -x means the slope is -1
Yep
so what line is the one parallel
D?
yes
Ohh
Aight thanks
no
np
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Can someone help with a
dr du
lmao nice
Yes but my brain malfunctions when it sees proofs
instead of factorng a^2, b^2 and c^2, factor a, b, and c, so that you have terms of the form a^2+b^2
np
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I’m supposed to show that 0 =< Un =< Un+1 =< 1
With Un+1 = f(Un)
U0 = 0,1
f(x) = 2xe^-x
And i dunno if it’s good
I recommend to divide it into cases, it can be challenging otherwise.\
- Prove that $U_m \geq 0$\
- Prove that $U_{m+1} \leq 1$\
- Prove that $U_m\leq U_{m+1}$
Crystopher
You probably can use induction and/or some reasoning involving properties of real valued functions.
@lethal quartz Has your question been resolved?
What is this?
Like I told you, you can divide the inequality into pieces.
You don't have to do as you did in the image you sent.
If go into the logic behind it, if you write $$a<b<c$$ it is the same as $$a<b \land b<c$$
So proving that $$a<b<c$$ is equivalent to proving $$a<b \land b<c$$ being true, which in turn holds if $a<b$ and $b<c$ are true by themselves (as per the significance of the $\land$ operator.
Crystopher
If you still are not convinced/don't like the idea of splitting up the inequality, well I find it hard to help since I myself wouldn't know how to do it as you do.
???😭
Wait, you don't see this?
In short, it is valid to split up the inequality, if you don't wanna, well, I can't do much about it, can I?
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Im not understanding a)
here
!spoonfeed
ohh well i am still explaining
not really
hmm wdym?
I was tryna say that you could replace the value of d this way and solve the equations to reach this result
they are just tryna give u the value which u had to substitute
Please delete this
So i just write what u wrote
Let's not give people answers
okk
But basically thats it tho
no
replace the d with a+c in the equation and simplify
well it is
but technically you cant explain it that way in this server so here you go
!nosols
As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.
you can say maybe, "find a way to write the right hand side in terms of (a + c)^2"
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ohh i see okk
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yup
@flint topaz Has your question been resolved?
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x=2^[2^(y)]
can I log_2() both sides?
yes
ty mate
I see, ty
do you know what I can do when I have:
log_2[log_2(x)]=y?
well what do you want to do what x and y
I want to simplify the equation for y on one side alone
you did it
I need help😭
but can't I simply further?
no
oh
Open your own channel
How?
!help
To ask for mathematics help on this server, please open your own help channel or help thread. See #❓how-to-get-help for instructions.
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The famous (infamous?) "windmill" problem on the 2011 IMO
Help fund future projects: https://www.patreon.com/3blue1brown
An equally valuable form of support is to simply share some of the videos.
Special thanks to these supporters: http://3b1b.co/windmillthanks
Home page: https://www.3blue1brown.com
The author of this problem was Geoff Smith. ...
np
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Hey, my homework kinda randomly includes using Excel to approximate the sum of an infinite series, but I genuinely have no idea how I'm supposed to do this.
this pic is an example of them doing something similar in the textbook
I've got the solutions to my homework but they kinda just show the equation with the sum from n=1 to n=infinity and then go "we put the first 144 terms into excel and get the answer"
Just make a column in excel where each row is one of the terms in the series and use =SUM to add them up.
@crimson flower Has your question been resolved?
I really hope this is right lol
You’ll have an easier time parsing it if you make columns for different parts of summand and put it together in the last column
Well I kinda tried but I've been working on this assignment for over 12 hours straight and my brain barely works at this point lol
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I'll try to look up excel formatting tips or something to figure out how to make this work for 144 terms
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1+1
pee
11 and please stop trolling
Is 2
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Im not that type of person that keeps trolling
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am i on the right track?
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having trouble figuring out how this works with powers
the former
so their both squared?
yes
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Here's my question; but aren't only 105 and 106 within the range?
this question is atrocious
I should've given context: It's supposed to be about using SRS to gather opinions on racial profiling of the Hispanic Population of Denver
Also I'm legitimately terrible at math; I need to pass this course for the degree requirement, so any help would be appreciated
<@&286206848099549185>
oh okay so begin with what you do understand about the problem
So, certain sets of the random digits listed equate to a housing label, which should be between 0001 and 9552
With that being said, doesn't that mean only 105 and 106 are within that range? I'm not sure if I'm misunderstanding, or this has been worded badly or whatnot
in my perspective of which I don't really know much about this topic, the simple random sample of 200 mailing addresses, include line 105 and 106 in being part of the mailing addresses or am I wrong?
yes, that's what I'm saying
But then, how can I know what the fourth, let alone third household equates to when those are the only options that fit the range?
will this be the answer or am I just being dumb? 😭
I don't think so
yeah it would be too straight forward lol
would the fourth household be 0004? orr
wait so 105 and 106 lines is the simple random sample that are fixed numbers. it's a random digit table. there's a total of 9552. All of your possibility of choices can actually have the same chance of getting picked so if the last digits are 4 digits, then the first digits will be 4 digits too.
no offense taken but I GOT THISSS
sorry, walk me through this? so, it can be anything above 106 then?
am I getting that right?
106 is the line with randomized digits
the range is 0001-9552
yes, but I meant within that range it can be anything above 106?
chose whatever line number that the problem told you for the sample to be a randomized which is 105 in this case
in the range of 0001-9552, yes. but the number 106 doesn't matter because it's suppose to be randomized with the amount of random number 105 LINE gave us
it said to start with line 105
still trying to figure this out
they already numbered it for us by 0001-9552. number 200. 9559 doesn't work because it isn't in the range of 0001-9552. but 2940 does work because it's in range 0001-9552. do you understand that?
yeeeeessssss
okay
Now it makes sense
thanks, and sorry for doubting you haha
this is the first line but we also have to do this for the second line 106
do you think you can do 106 on your own?
Yep, I think so
nah it's totally alright, I doubt myself too sometimes 😭
line 106
Line 105
2940, 0769, 1481, 6077, 9537, 9117, 2975, 9335,
Line 106
6841, 7350, 1313, 5297, 2765, 8508, 6750, 2114, 7487
@wary tulip these were the answers I got, were they any different to the ones you got?
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The Hispanic resident's households is labeled from 0001-9552 (total of 9552 homes), to get a simple random sample of 200 mailing addresses (200 randomly selected mailing addresses having an equal probability of being chosen). Our numbers are grouped 0001-9552 so we're going to group the numbers from the random digit table in four digits too. Anything above 9552 is not included in the numbers and any repeats are skipped (not any in this case). The simple random sample are the numbers selected above, the fourth one in line 105 being 6077. In my cognitive opinion, I believe this is the fourth household in this SRS sample. but idk tho
Lowk feels racist
it's about this bro 😭
I was giving my answer to the person that needed in this channel before but this channel got closed after I was able to give my complete answer on the problem 😭 😭
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thewizardofOU
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for this binomial distribution question.
p = 0.3
n = 10
x = 9, 10
1-p = 0.7
and I solve for
P(9 <= X <= 10) right?
Seems alright to me.
thee re c'rrect brot'r
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literally cannot tell if this if x at -3 is removable idek
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try first looking up
removeable discontinuity
jump discontinuity
infinite discontinuity
i watched the khan academy video lol but im not really sure because for the removable one at the point where it dne, it has another point somewhere else but for this one it doesnt
would x=-3 be considered jump discontinuity? oh wait maybe because it doesnt have a two sided limit
so would it just be x=-6?
yes
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$\sin^2(2x+\frac{\pi}{6})-\cos^2(x+\frac{\pi}{3})=0\implies (\sin(2x+\frac{\pi}{6})+\cos(x+\frac{\pi}{3})(\sin(2x+\frac{\pi}{6})-\cos(x+\frac{\pi}{3}))=0\implies\sin(2x+\frac{\pi}{6}+\frac{\pi}{2}-\frac{\pi}{2})+\cos(x+\frac{\pi}{3})=0$ or $\sin(2x+\frac{\pi}{6}+\frac{\pi}{2}-\frac{\pi}{2})-\cos(x+\frac{\pi}{3})=0$
pirateking0723
Maybe use this to write the sum of sine and cosine as a sine function, which should be easier to solve I reckon.
hmm, otherwise expanding the terms of sin and cosine will leave a mess I think.
so from here $\cos(2x-\frac{\pi}{3})=\cos(x+\frac{\pi}{3})$ or $\cos(2x-\frac{\pi}{3})=\cos(\pi+x+\frac{\pi}{3})$
no need to do messy expansions
this form here is reached without messy expansions as above
pirateking0723
now $x\in [-\frac{\pi}{2},\frac{\pi}{2}]$ so $2x-\frac{\pi}{3}=x+\frac{\pi}{3}+2k\pi$ or $2x-\frac{\pi}{3}=-x-\frac{\pi}{3}+2k\pi$ or $2x-\frac{\pi}{3}=x+\frac{4\pi}{3}+2k\pi$ or $2x-\frac{\pi}{3}=-x-\frac{4\pi}{3}+2k\pi$ where $k\in\mathbb{Z}$
each must have a +2kπ where k is an integer
not a problem
i am trying to find the x that make this true
i am not saying that they are always equal
just like here plot the RHS and the LHS they wont be the same
because they are not
they just intersect at some points (infinitely many points in fact)
pirateking0723
okay, a bit doubtful of your approach but I'll let you cook until you are done.
tysm
now from here we get $x=\frac{2\pi}{3}+2k\pi$ or $x=\frac{2k\pi}{3}$ or $x=\frac{5\pi}{3}+2k\pi$ or $x=\frac{(2k-1)\pi}{3}$
pirateking0723
i am not sure if i have some calculation mistakes at the end
but i am pretty sure about my steps
i am done cooking if i have any mistakes or if you have any doubts please tell me to correct or explain myself
ah wait before that
i am not done yet i still need to follow the restriction on x
$-\frac{\pi}{2}\leq\frac{2\pi}{3}+2k\pi\leq\frac{\pi}{2}\implies -\frac{7}{6}\leq k\leq-\frac{1}{3}$
pirateking0723
so the 1st gives no k now for the 2nd one will give $k=0$ the 3rd will not give a k and the 4th will give $k=0$ pr $k=1$ so $x=0$ or $x=-\frac{\pi}{3}$ or $x=\frac{\pi}{3}$
pirateking0723
@onyx marsh Has your question been resolved?
-pi/3 isnt the solution because it is outside [-pi/2;pi/2]
i am missing one more solution i have a mistake up there
no, it is correct
probably a calculation mistake
The problem is I see x=0 is a solution but I don't see it in your calculations.
Yes, i see now. Probably missed a $\pm$ somewhere
Crystopher
i think ik where i went wrong
i have to add kpi not 2kpi
because originally cos and sin are ^2
so adding a pi wont affect it
because the negative sign will vanish due to the ^2
From $x=\frac{(2k-1)\pi}{3}$ you should've gotten
$-\frac{\pi}{2}\leq\frac{(2k-1)\pi}{3}\leq \frac{\pi}{2} $\
$-\frac{1}{2}\leq\frac{(2k-1)}{3}\leq \frac{1}{2} $\
$-\frac{3}{2}\leq (2k-1)\leq \frac{3}{2} $\
$-\frac{1}{2}\leq 2k\leq \frac{5}{2} $\
$-\frac{1}{4}\leq k\leq \frac{5}{4} $\
Where $k=1$ was included.
Crystopher
ohh yes
i have a question
since x is restricted to lie in [-pi/2;pi/2] then sinx is bijective here right
Yes, there are no two different $x$ values in the interval that give the same $y$ since it is monotone in that interval, so it is injective. Then the codomain is $[-1,1]$ and the function is surjective since for each value $y$ in codomain there is at least one $x$ such that $\sin x = y$. This can be proven using the intermediate value theorem.
Crystopher
@onyx marsh Has your question been resolved?
but that doesnt mean that $\sin^2(2x+\frac{\pi}{6})$ is bijective in fact it isnt right
thats why we couldnt just use arcsin here
or arccos
pirateking0723
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✅
are they different from these
or is there any solution that i added
also why npi not 2npi
cos = sin is pi periodic so it's npi
why does it have a period pi
have you solved it or you still searching ?
i reached these
if i replace 2kpi by kpi will they be correct
and why is the this the period of that
i thought that kpi will be the period because of cos^2 and sin^2
because adding kpi may lead to a negative sign but with the ^2 it will vanish
i'll try the problem
ok
if you want check the steps above to save yourself the trouble of solving it again
and if you want solve it and compare
so from this
the period for cos^2=sin^2 is pi/2
how do you know
also wdym by period of sin^2=cos^2
i mean this is not a function
this is an equation
talking about the solution
although wolfram doesnt add kpi/2 but adds kpi instead
and i'm trying to figure out why with you, but i'm clueless for now
how did you reach this
this will give the answer
cos²(x) = sin²x
cos²x - sin²x = 0
cos(2x) = 0
x = pi/4 + kpi/2
no
i did mistake ?
x=pi/4+kpi
nah kpi/2
because then 2x=pi/2+2kpi
no it's 2x = pi/2 + kpi
so that cos(2x)=cos(pi/2+2kpi)=0
ah yes because cos(pi/2)=cos(-pi/2)=0
exaclty
so this is the answer you were looking for ?
we still didnt reach our destiny
what you did here works only when the input of sin and cos is the same
but our problem doesnt have this
the only way to explain the npi is that cos and sin are ^2 so that adding odd multiples of pi to the input of cos which makes it -cos the input will also be cos(input)^2
same for sin ig
there is a slight difference
because sin(pi+x)=-sinx while sin(pi-x)=sinx while cos(pi+x)=cos(pi-x)=-cosx
so these are correct if i replace each 2kpi by kpi ?
idk, maybe someone else could find the trick, sorry
oh ok tysm np
<@&286206848099549185> can anybody check if my answers are the same as wolfram's
Okay
so what did you find
how are they equivalent to wolfram's results
can you explain to me to know how
@onyx marsh Has your question been resolved?
<@&286206848099549185>
Seems a lot happened since I was last around here. What's the issue?
i want to check how my solution is the same as wolfram's
so how are they the same
thats the issue
Crystopher
You mean these solutions?
yes
if these are the same as wolfram's or no
if they are not then i have some mistakes
we can see if they both contain the same elements in a group of arithmetic sequences
if they are then how are they
can we equate them to each other
and then find n in terms of k
and take the natural n from that
if n turns out to be any integer then they are the same
other wise it is not
like if we get n=k
then they will be equivalent
for instance, all of wolphrams solutions entails all $x = \frac{\pi}{3}n$, $n \in \mathbb Z$
Crystopher
i am not sure if this is efficient
although npi doesnt
We can mark the solutions in the unit circle and see where they land
I meant together
because n is an integer
ohh
how can we check algebraically
without resorting to graphs and so on
is that possible somehow
I think I have tried to do that before, but my reasoning was half-baked, it would be hard for me at least. Like we need to prove that the union of the three arithmetic sequences given by Wolframs solutions is the same as the union of your solutions.
$x=\frac{2\pi}{3}+k\pi$ or $x=\frac{k\pi}{3}$ or $x=\frac{5\pi}{3}+k\pi$ or $x=\frac{(k-1)\pi}{3}$
pirateking0723
these are the correct solutions
i changed each 2kpi to kpi
because of cos^2 and sin^2
so i am trying to check if these are equivalent to wolfram's
One thing I can say about your solutions is that $x = \frac{2\pi}{3} + k\pi$ is redundant since $x = \frac{k\pi}{3}$ contains all of the solutions given by the aforementioned.
Crystopher
yes
because you can make a common denominator
so you only have one solution
now we need to prove that the union of Wolframs solutions is the same.
the same goes for these
all of these are just kpi/3
but that doesnt prove it right
exactly, I don't know how strict do you have to be in your solution.
hmmm
you could assume that every solution from wolfram can be written as $\frac{\pi}{3}n$ and prove it, but then the problem becomes that you also need to prove that there are no more solutions than that.
Crystopher
i can take it as something granted
given that wolfram produced the result
but the real problem is to show that my and wolfram's solutions are exactly the same
that there no solutions i included which arent in wolfram's and vice versa
idk how to do this
I think I have something. We can 'scale' the sequences given by Wolfram. Let's say that we expect a sequence $x = \frac{\pi}{3}n$ from all of Wolframs solutions together. Then, from the sequence given by $\frac{3x}{\pi}$ we can expect all integers, so we expect this new sequence to contain $\mathbb Z$. We can do the same scaling to Wolfram's solutions. For $x = \pi n$ we can have $\frac{3x}{\pi} = 3n$, for $x = \pi n - \frac{2\pi}{3}$ we have $\frac{3x}{\pi} = 3n-2$ and for $x = \pi n - \frac{4\pi}{3}$ we have $\frac{3x}{\pi} = 3n-4$. We notice that each of these are the sequences of modular classes modulo 3, which means that they together form $\mathbb Z$. So they would be the same, we can then 'convert back' if you want and we should see that they are the same.
Crystopher
or we can find the 4 solutions that i got modulo 3 and it will turn out that they will together form Z right
also this shows that they are exactly Z not just that they contain Z
because every n is in Z and 3x/pi for example generates only all of these n
not anything more
Ye probably, I was thinking that the sequence contains all integers, so they contain $\mathbb Z$, I don't know really if a sequence is really a set.
Crystopher
on the other hand you could construct them as a set I think, so maybe they can be considered sets.
i have a question which is unrelated
is there something as non integers modulo integers
you might find the top answer here useful:
https://math.stackexchange.com/questions/586595/finding-modular-of-a-fraction
though it seems to be only for rationals
yes, I find it hard, or rather unnecesary to define them on reals.
there might be a notion of repeatedly adding or subtracting
like pi mod 2 might be pi - 2 = 1.14159...
but that seems too hand-wavey
ye, I don't know how useful that would be
Like the closest to a modular function to the reals I can think of is wave functions like sine
this talks about fractions
but not about irrational numbers
^
oh so there is nothing like that for irrationals
so you are still unsure if they are equivalent
but ig it is a set because you can define the sequence x_n=npi/3 where n is an integer
If we look at Wikipedia (maybe not the best source ik), they are not the same
cant you define the sequence from integers ?
I think a key difference is that in a set order does not matter while in a sequence it does.
432 x 3
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find the number of solutions to this equsion:
x1 + x2 + ... + xn = k, such the the even xi's are even natural numbers, and the odd xi's are odd natural numbers
(even natural numbers include 0)
so how do i start?
so we need n/2 even numbers and n/2 odd numbers that sum to k
if i had to approach this i would probably start by splitting k into two numbers, a and b, where a + b = k and a is the sum of all the even xi numbers and b is the sum of all odd xi numbers
yeah
is there a way without a summation?
well actually fuck that i dont have time
so
if were doing this approach
to get to a from even numbers the number of ways is s(n/2, a/2)
right?
now we need n/2 odd number than sum up to k-a
yeah
i think so ?
and then the sum from a=0 to k?
yeah
the thing is the question says to assume (k-n/2) is even
so im supposed to use that somewhere
but i didnt in this solution
thats a weird condition
oh
it makes sense
that just means that if n/2 is odd then there must be an odd amount of odd numbers being added up meaning that k will also be odd
and if n/2 is even there is an even amount of odd numbers being added up so k will be even
well its just an assumption you have to make otherwise it wouldnt make any sense
if you think you need to use that somewhere in your solution you can just state why it is a necessary condition for the problem to make sense
but why is it an assumption?
i mean like
that must be true
why did they state it
like you cant not assume that
thats like saying given an even number n blabla assume that n is divisible by 2
stars and bars
wat
lets start with a simpler version of the problem: how many solutions are there when xn must be a natural number (no constraint about even or odd)? you can think of this as having k "stars" and distributing n - 1 "bars" to divide the stars. for example 1 + 2 + 3 = 6 corresponds to the picture i gave below
then the number of solutions to x1 + x2 + x3 = 6 just becomes the number of ways to arrange the stars and bars
exactly. so you apple the same logic
but we have constraints here
well the problem is the constraints themselved
its that there are 2 kinds of constraints
in the same equation
thats why i split into cases and did the summation
the summation shouldnt be too bad, i think
yeah i did that already
i was wondering how to do it without a summation
thats what i got
maybe you can think of it as dropping stars into boxes two at a time
even numbers that add up to 2i, odd numbers that add up to k-2i
yeah thats what i did with s(n/2, i)
mhm im not sure how youd do it without a summation
and nice bio my friend
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So for this integration by partial fractions, for problems that basically need us to create systems of equations how can we tell which system of equation to use to find our B?
so for this picture for example, I created a system of equations where A+B=0, 4A-B-C=3, and 4A-2B-C=9
when I solve for A+B=0, I get B=2/3, when I solve for 4A-B-C=3, I get B=32/3, and when I solve for 4A-2B-C=9, I get 2/3
A+B=0 and 4A-2B-C=9 both give me 2/3 which is the right answer when I look at the answer key that my professor provides but 4A-B-C=3 doesnt
how do I know if I should use A+B=0, 4A-B-C=3, or 4A-2B-C=9 to get B?
<@&286206848099549185> ?
@fresh tide Has your question been resolved?
<@&286206848099549185>
ChatGpt 4 Wolfram Alpha plugin
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X^(n)=y
Is there n that satisfies this equation
?
Uhm- i can help you
is n an integer?
n must be complex
yep
$a^z = -b^2 => z\ln(a) = \ln(-b^2) => z = \frac{\ln(b^2) + \ln(-1)}{\ln(a)}$
Obotron
$\ln$ denotes the complex logarithm.
Obotron
Kk ty
$\ln(-1) = \ln(e^{i\pi \pm 2ki\pi}) = i\pi \pm 2ki\pi$
Obotron
x <= 5
it's just looking where the sqrt function is defined
i know the denominator is never 0 since sqrt is always positive
so i just look at the inside of the sqrt function and analyse where it is defined
essentially im solving: 5 - x >= 0
(Brb)
X is equal to or less than 5
But like
The denominator
Cannot be 0
Why didnt u consider tbat
Oh
Omg right
Gj! Ty
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Help !
I need help on an exercise about SIGMA ALGEBRA
