#precalculus
1 messages Ā· Page 37 of 1
4.0 straight a's but physically cannot take ap classes (in freshamn)
oof
what aps u taking next year
ap calc ab/bc (im gonna request to change my course load to ap calc ab and ap pysc instead tho), ap us gov, ap csp
how ap chem?
its what all the sophomores take
nah my school u can take regular honors or ap chem but if u fck up, u fck up
taking summer school honors chem tho
ok bye
with life
you 2
bye
byee
hiii can someone help me?
pleaseee
how would i graph this if the radius has a square root?
what are you trying to do here
are you graphing a circle at center (4, 1) with radius 2 sqrt(2)?
2 sqrt(2) is just a constant
you would graph it the same way as anything else
except it's kinda pointless to do it by hand since there won't be much accuracy
np lil dawg
yea im forced to
or else sheāll give me a 0
your teacher?
i mean there are grid points at distance 2sqrt(2) from (4,1)
so at least you can get those exactly
and eyeball the rest
2 sqrt(2) is a little bit less than 3
does 5 c(3,1) here?
also this is not a question for #probability-statistics ?
why precalculus?
Idk, I'm taking precalc honors and this is a hw assignment from that class
Could I uh
Get some help with these
Still a little lost :(
Sure let me read them
6 is a combi?
for permutations order matters i believe
Yes
I need to go to sleep. Sorry I couldn't help more. gn
gn sleep well scraxzt
Its ok, sleep well
Thanks
@willow bear I'm sorry for pinging you - if you'd prefer that I don't just lmk and I won't do it again but I'm so lost on this hw, I need to go to bed, and I really, really need help
which one(s)
5-10
these?
ok, do you have progress on any one of these? if you do, share your progress and we'll start with that. otherwise we will go through them in order.
I mean, I know the functions for permutations and combinations
I know that permutations means order matters
I just don't know how to determine which is which
im talking about these specific problems -- do you or do you not have progress on at least one of them?
No, I don't
ok
for some of these you dont need to know permutations/combinations and just need to know shit like the multiplication principle
which may go by many names or none at all
but let me give you a different setup as an example
have you ever seen, or held in your hands, a deck of cards? @compact spade
Yes
like regular poker cards
ok
so you know that the cards come in 4 suits and within each suit there are 13 ranks
Yes
and there's exactly one card for each suit-rank combination
for a total of 4 * 13 = 52 cards
the same principle applies to problem 5, in which you choose from 3 different albums and 2 different formats (the choice counts being independent of each other)
do you see what i'm talking about here?
Yes!
ok great
problems 5, 6, 8 and 10 can be done with this method more or less directly
we'll come back to 7 and 9 in a moment
ok sure
you can ping me when that happens
(but you will have to remind me cause i might forget this)
(like just tell me the problems you're following up on or w/e)
Onto 9! We can do 7 also but I figured that one out by just writing them down
@willow bear
alright
so for 7 you can also apply the multiplication principle in a similar way
carlos has:
- 3 subjects to choose from as his first
- 2 subjects to choose from as his second (because one has already been done as the first)
- 1 subject to choose from as his last
for 3 * 2 * 1 = 3! = 6 ways
for 9 proceed in a similar fashion but place the dictionary first
ohhhhhh ok
that's really easy thank you
can i like
pay you??
you've helped me with my math homework like 5 times now and i feel like i should do something back idk
i mean uh
all the shit i do on here i do pro bono
if any money were to change hands we would not want to do it on here bc rules
that's true
hey sorry for replying to this message but is PNC tough ? we have this on our syllabus & our sir told it will be done at end since rarely qs come from it
sorry for replying to this message
could have just pinged me
anyway all toughness is relative
so i cant answer that
Depends on how deep your syllabus is. Once you understand where to use either and practise questions, it becomes fairly trivial. In cases like special arrangements on chessboards, dearrangements etc., it becomes quite demanding.
thnx, our syllabus is pretty simple but the qs are made quite tough to check the aptitude
Jee right
no CAT, JEE is way beyond this š
people in calc chat prob even better ngl
you should prob just post ur problem tho
I tried several time no one helps i have to do it before tomorrow and i have to sleep its literally 2:00 AM
where did you post the problem?
Here
And in disscution / prealg / geometry
The problem is that the exercise isn't that hard
try to stick to just one channel
and uh yeah i dont know series that well
Is anyone free to help me study chapter 3
3.1 to 3.5. I have a study guide.
You still haven't told anyone which book.
102 Lecture Notes
Can someone please help me visualize this. Iām not sure if i did it correctly
Can someone explain why x is 16 even though k = 1/2
Shouldnt the x value be 4 since the original is 8?
I did the graph on desmos, but graph g seems to be compressed
Someone explain pls
Nvm
this would be a correct visualization (im taking the lighthouse to be a single point as we donāt know about any internal details regarding the lighthouse at all)
Hey y'all, I don't take pre-calc, but I am currently teaching myself as it was something that I "skipped" over. I have had mixed opinions on skipping pre-calc and going straight to calc 1. Looking for some opinions here, anything is appreciated!
yo i was using my calculator on the test
and it said -1^2
was -1
am i buggin
or what
how
shouldn'[t it be 1
by convention, we define the order of operations to say that
[ -1^2 = -(1^2) \ne (-1)^2 ]
cloud
HOW DO I TRANSLATE THIS to summation notation
If i had a penny that doubled each time per day, how many would i get in 30 days
2^30 ?
1 + 2 + 2² + 2³ + ... + 2³ā°
This is the closed formula
In your case it's 1ā¢(1 - 2^31)/(1-2), which is 2³¹ - 1
op admitted that the problem is one he made up himself
but also as-written it doesn't suggest that sum
we have a magical penny that clones itself every night, not a money machine that starts out paying you a penny a day and then pays twice as much every day as it did the last
am i just too dumb or should the answer he wants be 2^29 instead?
the problem is stated too vaguely
true
Perhaps I should revise the question, so, If I had a penny (0.01$) that doubled each day for 30 days, by day 2 (0.02), by day 3(0.04), next(0.08), and so on, so, how much would I get in 30 days? In this time in terms of VALUE, not the quantity of pennies. How would i put it in summation notation form?
why do you specifically need this "in summation notation form"?
you yourself said the question is made up by you.
"summation notation" is not a panacea, and is not a thing you should be trying to shoehorn into every single problem you see or think of
anyway, with this more precise statement, your penny undergoes 29 doublings, so you end up with 2^29 = 536870912 pennies, or $5,368,709.12 at the end of it.
This algebra video tutorial provides a basic introduction into factoring trinomials and factoring polynomials. It contains plenty of examples on how to factor quadratic equations.
How To Factor Trinomials: https://www.youtube.com/watch?v=-4jANGlJRSY
The Greatest Common Factor:
http...
first hit on youtube search for "ochem tutor simple factoring"
yt videos js show the factored function automatically
do you have a particular problem or problems that you are having a hard time with?
could u tell me the formula for it
- avoiding the question
- there is no "formula"
having problem with it in general
what abt the steps
ive been having problems with factoring since 1st sem
post specific problems you have an issue with
4x^2 + 8x
= 2 * 2* x * x + 2 * 2 * 2 * x
you're multiplying all these factors, if you are adding two terms then you can take common factors out of the two terms
you can see that both terms have two 2s and one x in common, so you can "factor" these out of both terms.
you can take out, 2 * 2 * x, and the remainder is (x + 2)
so, it equals
2 * 2 * x * (x+2)
= 4x(x+2)
this ^ is the factored form, because it took all the common factors in each term out, and now you're multiplying by whatevers left
are you proving for all numbers {0,1,2,3,ā¦} or {1,2,3,4,ā¦}?
Divide into cases according to whether n is 3k or 3k+1 or 3k-1 for some k.
Oops, didn't see you wanted induction.
There is no formula, but, thetre is a first step to factkring which is takibg the gcf of all terms, so say, 4x+2x has (2x) as the gcf, so if you ffactor it, you will get 2x(2+1) basically you reverse foil method
Does it really matter 0+0=0
The question asks to āprove n^3 + 2n is divisible by 3ā, but itās not clear what ānā is
It's true for all n in Z.
hi can someone help me because i wasnāt here for math today
what is foci?
so the center, vertices, covertices, and foci (plural for focus) are all points, so your answer for each of them will be ordered pairs
i gtg sorry someone else should be able to explain hopefully
ur good thanks
How do I solve this? I have been trying for like 30 minutes but I donāt even know
try taking log of both sides
I already did
What do I do after I get: (3x)log6=(2x-3)log2
I tried dividing by log 6 on both sides but I donāt know
factor it out
it might have been better if you divided by log2 instead but what ur doing works as well
Factor what out?
sorry i meant distribute š
i don't know why i say factor instead of distribute š
i can't think of the word distribute lol
is there any part of this you still need assistance with?
no but i still need help with this problem
like how to graph vertices if one is a square root
since the instructions just say āsketchā, you should be fine to estimate, just treat sqrt(12) like itās 3.5, since thatās what it is approximately
thanks so much
why you think hes here genius šæ
Can you help me with this?
do you know the cos(a+b) identity
yes
can you write it out?
cosacosB-sinasinB
ok, so make a table:
\begin{tabular}{r||c|c}
&$\alpha$&$\beta$\
\hline\hline
cos & & \
\hline
sin & &
\end{tabular}
|Annā©
fill it out based on the given data
bc you're gonna need all four numbers in it to find cos(α) cos(β) - sin(α) sin(β)
oh ik it
@devout bison so you want someone to give you a worksheet of basic summation notation problems?
?
(cont'd from #multivariable-calculus )
this is cos(a+b)
you said you wanted some summation questions to practice, right?
a is alpha b is betha
while finding the limit by direct substitution how does b/0 (where bā 0) denote an asymptote?
You can't divide by 0
@devout bison here you go
it means the function behaves similar to 1/x near your limit point
but 0/0 doesn't denote asymptote
but u can in infinity
when k/x xgoes to infinity y goes to 0
0/0 is a special case
Sometimes it's a removeable discontinuity so the limit has to exist, and other times it's not going to have a limit at all cause it's not continuous
Yes
0/0 can still be an asymptote
it's just that it doesn't have to be one, it depends on the functions
what's 1/x here?
the function y = 1/x
the green one is like y = 1/x around x = 0
@devout bison if you want you can DM me your work for any of these problems in the worksheet, but with two rules:
- include the questions themselves in your DM.
- show work and not only answers. i won't accept answers without work, even if they are right.
is there a quick way for1)b)
define quick?
quick compared to what?
1 +4+9 etc
the sum in 1b) has length 4. i want you to do it longhand.
i have even instructed you as such.
also look more carefully at the notation.
got it. thanks.
np
@devout bison i made the sums in Q1 short on purpose, so that working them out in some kind of "smart" way would take more effort than just doing as i instructed.
okay
q2 is 1 ig
q1)a)70
the number on the up means that u will go as much as that or until that
work, not only answers.
or until that
indeed i used quick method
you have to write out your work properly and show it
until then i will not accept any answers.
i dont have a phone am on pc not sure if cam will see it
my problems, my rules.
as in you don't have a phone at all, or that you don't have it on your person at the moment?
bruh ok
well, you're gonna have to figure out how to write it nicely.
cause im still not gonna accept answers without work.
can u help me out on 4th @willow skiff
@willow bear
a quick method
wait
exactly like the graphics right
idk what you mean by "the graphics"
functions
but we only take complete numbers here
and thats a big problem
that explains precisely nothing...
idk what on earth you are trying to say there sorry
are you trying to ask me something, or are you trying to bounce an idea off of me?
can u pls give me a certain method that i could apply in all of these
all 4 questions?
no just a method for all summations
especially 4th
1 and 3 were the same and method written
you want a panacea
?
what you're asking me for is a "solve everything" method
such a method does not exist
solve every summation
?
for example in functions there is
1 method we apply to find areal of all these
okay so how will 4th be
@willow skiff
<@&286206848099549185>
@willow bear
how will 4th be
work out the first few terms, and see if you notice a pattern.
nope there wasnt
i did all
except for
1)c)
and 4th
@everyone do u know a certain method to find out summation
a method that could be applied for all summations
don't ping everyone. it's incredibly rude.
ok then write out the first 8 terms of the summation $\sum_{k=0}^{85} \cos(k\pi/2)$ right here and now. not their sum, but the first 8 terms themselves.
|Annā©
0 1 2 3 45 6 7 8
cos0
cos90
oh i see
it is cos90k
which is either 0 0r 1 0r -1
and they keep on each other
no. 0, 1, 2, 3, 45, 6, 7 and 8 are not the first eight terms of my summation.
wrong answer, and it is unsupported by work.
why wrong
(for future answers that you don't give work for, i will simply say "no work" no matter if you get it right or not.)
impossible to tell without working.
i worked in my mind
not acceptable.
why to write down on paper
by the way u won't even see what i write
and
yeah i see
it was wrong
make a word document and write your work there. it has an equation editor.
and send screenshots of that.
answers without working are not accepted.
they roll into same after4th number
and when we reach 85th
they rolled
but one still left and that is 85pi*k/2=1
oh wait
you are expressing yourself poorly.
that is 0 either
what is your native language?
could u be more respective
what u have as a knowledge doesnt give u the right of boasting on others because
nothing we have is actually gained by our own
it is a gift
i am not boasting on anybody.
"you are expressing yourself poorly" is the most polite way i know to convey that point.
i am 24, if that matters at all.
yeah it matters becuz at that age don't u think it is more impolite to insult someone smaller than u
i am not insulting you.
or you could tell me what i said that you took as an insult.
ok, then what was it?
1
i said u already that i dont have a phone to img
and this is kinda so rude
ok, so maybe i should have suggested the alternative of "make a word doc and type shit there with equation editor" then and there.
yeah
and i honestly don't see how "my problems, my rules" is rude. these are my problems that i made -- and i get to dictate what i want to see in response to them.
if you don't like that, you don't have to do my problems.
then can u say like
i am not forcing you.
i wanna see how uu do it
you want me to see how i do #4?
yeah
no
i did 4th
i only need a way for 3)c and and 1)c
by the way i already did 4th and explained the way i did upwards
i wanna see how uu do it- i typed it that u could talk like that since it is kinda more soft u see
for 1c, just as for 1a and 1b, write the thing out longhand. it is only 5 terms.
okay
i am still interested in knowing what your native language is
there is a chance we can communicate better in your language
well it is turkish
ok, nevermind
such a method does not exist
not equations but summations i wanted to say
for 3c, my first step would be to split the summation like this: $$\sum_{n=0}^{15} n^2 + \sum_{n=0}^{15} 6n,$$ and also realize you can replace the starting index 0 with 1 in both summations (because $6\cdot 0=0$ and $0^2=0$)
|Annā©
ohwait sorry
i mistyped
i don't need 3c
okay i did all
now i wanna ask u some questions
did u know something so called e^ix=cos (x)+i*sin(x)
what is the provement of this
?
@willow skiff @willow bear <@&286206848099549185>
i mean where did it come from
the word is "proof", not "provement"
stop pinging so many people so often.
it is 200 times more rude than anything i have done.
okay
anyway
so
one idea you could think about is that if you look at the function f(x) = cos(x) + i sin(x) [where we don't know what e^ix should mean yet], it satisfies the law f(x+y) = f(x) * f(y)
so it should behave like an exponential function, i.e. e^(kx) for some constant k
(because all exponential functions satisfy the same law)
if you take the derivative of our function, you will find f'(x) = -sin(x) + i cos(x) = i*f(x)
while the derivative of e^(kx) is k e^(kx), so k is the ratio of the function's derivative to itself
in our case this ratio will be i, so our function could be written as e^(ix)
(this is not rigorous. this is meant as one possible kind of intuition for euler's formula.)
(to make a fully rigorous proof, we would need to dig into the definitions of e^z, sin(z) and cos(z).)
? my question
yes
i gave you my best attempt at something that explains why it is true, but without being heavy
bc i think you don't want the heavy shit
(it'll involve series, which are like summations but infinitely long -- and you are only beginning with finite ones!)
sorry the message wasnt loaded so i typed again
f(x+y) = f(x) * f(y) is this always true?
it is true for the function f(x) = cos(x) + i sin(x), and for all functions of the form f(x) = e^(kx).
and here is something how can we draw these functions
with numbers that dont exist in reality
"don't exist in reality" is almost a derogatory way to refer to complex numbers.
just because they aren't real does not mean they do not exist as mathematical objects.
ik they exist in math
and a very
essential part
inclluding a miracle
the fractals like one u see in my prophile
unfortunately, it is not easy to draw graphs of functions where the input or output (or both) is complex.
so what we do
for a function with real input and complex output, or complex input and real output, you can make a 3 dimensional sort of graph
with 2 axes for the complex variable and 1 for the real
it'll be a surface or a curve
but for complex->complex you would need 4 dimensions to do it like that
so kinda like fractals but more complicated
so usually for those functions, if they are plotted at all, they do something more sophisticated like colors
nothing to do with fractals.
u know how we draw fractals right?
?
what do u mean by 4dimensions
and why did we use 2 axes for complex
no
bruh
you have a Mandelbrot set on your avatar and you talk about fractals but you don't even know basics of complex numbers?
i only know what they are
i am mid school
and i searched how fractals work but idk what u say the complex surface
ok well heres the issue
if you ask about stuff like euler's formula like you did above
people are going to assume you are familiar with some basics of complex numbers
so you should go learn that
ik the euler number
and what it is
((x+1)/x)^x=y when x goes to infinity y goes to e
ik basics
but not the "complex surface"
can u send a video orexplain it
can i ask combinatorics here
what is ur question
jamies dad allows him to choose 8 cars for his birthday
jamie's dad has 6 aventadors , 5 r8s , 4 bmws
in how many ways can jamie pick such that there're an equal ammount of r8s and aventadors
@devout bison
so i think the pssibility for each will be
6P1*5P1
6P2*5P2
6P3*5P3
6P4*5P4
6!*5!
<@&286206848099549185>
sum these
divide by
15P8
wanna get explanation
?
sum these- this will give u the n of possibilities where number of r8 and avendator equal
when u divide itwill give u the possibility
uh can u explain the first part
u see
u have 6 cars from that type
your ability of taking random u have 6 chances
u took one
u r left with 5 chances
one more take one minus chance
now for each single choice u can make on first run which is equal to 6
in the next run u have 5 different choices
but these willl change
it is like a timeline game
where u control the timeline
as u made a choice
u entered an alternate timeline where
u can make 5 different choices
with each next choice
u type that timeline more
but still
u have other timelines either
@everyone how can i put images there
now if u start with 5 cars
there are 5 possibilities
u made one
now u have 4 possibilities
but imagine
u could have made another choices
and ur next generation possibilities would have changed
if the order doesnt matter
instead of permutation we use combination
4P3 means
u start from 4
and each single time multiply it to -1 number
until the amount of numbers is 3
so 4P3=4 * 3 * 2
see 3 numbers
started from 4
and multiplyed them to each other
@static mesa
?
could u do it
also i made a mistake if u saw
i had to use the combination
so it will be
@static mesa
?
so instead of p u will right C ig
there is only 1 difference between c and p
u divide p into the number of timeline generations(the number on the right)
this is a chat gpt explaining
i tought it will be more accurate so i sent this one
the previous was mine
Please do not trust ChatGPT or similar AI tools for mathematical tasks, as they often generate output which "sounds correct" but has numerous factual or logical errors. Use of these AI tools to answer other people's help questions is strictly against server rules (see #rules).
yup
u divide p into the number of timeline generations(the number on the right) and get c
so called the combination
u use permutation when choice order(timeline order) matters
Thereās a couple more corrections to make. you canāt make all these cases, and youāve got to complete your process. I donāt think You can ignore the ways of choosing the BMWs
i don't need bmw possibilities am not asked for that
i sent the other bot explanation for accuracy
For example the 1A , 1R case is not possible as you need 6 BMWs(we only have 4) to choose 8 choose
who said that
i don't remember anything like that in my explain
chatGPT output should not be trusted.
ever.
zero exceptions. if you can verify it without chatGPT then it means you never needed chatGPT in the first place.
well i sent it only cuz i tought my explain was mindmixing
chatgpt doesnt know what the hell it is talking about
also the one in file is ai generated
You did this case, then you asked them to replace permutation by combination, by which I inferred that you meant do 5C1 * 6C1? Did I misinterpret you?
it is a language model. it is designed to create coherent sentences, it is not your google
the writings upwards are mine
your explanation was very "mind-mixing", but chatgpt would not help that at all.
yeah which would make no difference at al
since 1!=1
what's the problem there
also i counted several mistakes in my own
so i simply gave the idea of the way of possibilities
anyways
@static mesa u can ask again
there are more people
more miinds
oh damn' man
am gonna delete chat gpt
what the hell is this
word of advice: if you are not 120% confident that you know how to solve a problem, then it's better not to try to help at all.
this metaphor will be unpleasant but it needs to be said:
what you have taken is basically the textual equivalent of a huge pile of shit, and we now have to live with it and smell it all.
my mission was to give the idea of doing it
and somehow shovel it all away.
instead of talking maybe u help them
also u can't say the idea was wrong
so ig he kinda understood the method and
here we wait for u
there may be a grain of truth there but it's buried under a pile of shit
what is ur explain
this is the original problem:
jamies dad allows him to choose 8 cars for his birthday
jamie's dad has 6 aventadors , 5 r8s , 4 bmws
in how many ways can jamie pick such that there're an equal ammount of r8s and aventadors
yeah
we are choosing 8 cars from this set with the condition that the number of R8's and aventadors
if we choose a aventadors, b r8's and c BMW's, the number of choices will be C(6, a) * C(5, b) * C(4, c). it remains to be seen what values of a, b and c are possible.
we know that a=b and that a+b+c=8, leaving us with the following possibilities:
- (0,0,8) -- rejected: not enough BMWs
- (1,1,6) -- rejected: not enough BMWs
- (2,2,4) -- possible
- (3,3,2) -- possible
- (4,4,0) -- possible
so u done?
(Not that relevant to the problem but doing it as if all the cars are unique would be a fun exercise)
thats exactly what we do. we look onto each as unique
i stopped one step short of the solution.
Nope like in bmws they are numbered bmw 1 bmw 2... bmw4
if OP cares about solving the problem and understanding it, they will complete the last step
if not, they will not
c'mon seemingly u couldn't huh
???
thats what i said bruh
Rude ppl argh
Thats not what we are doing rn though?
not with u
We are considering all bmws as one, all r8s as one and all aventadors as one
she has that behavior that plagues me also she didnt help just blab
And thats what we should do considering this problem statement
Bro shes so helpful seriously
nooooooooo
exactly
i gave you everything needed to get the answer yourself
the fact you're choosing to pester me for the last step is entitlement on your part
Exactlt
Yes we are?
you know the saying "you can take a horse to water but you cannot make it drink"
You guys are getting out of control.
Also doesnt this belong in #competition-math anyways
a grain of truth in
a pile of blabbing
this is not mine but
@static mesa is probably on exam
he said he only needed combinations
Th? Why are we even helping them in that case?
Someones begging to be banned
what is a ping spam
what you just did
@devout bison please stop repeatedly spamming and pinging Ann
also u typed on ur own upwards that u could be pinged
okay
she said that she could be pinged
anyways
<@&286206848099549185>
No one needs to be pinged 4 times in a row
may be instead of blabbing <@&286206848099549185> help them
since this is a math server
not blabbing course
They got it already bruh
still that is a math site not blabbing
Soo?
Ann has laid out a substantial amount of help for the OP. We don't just straight up give out answers here so idk what you're waiting for, you are currently the one blabbing
by just typing down what has given? and even so, what's the case with ann anyways
Stop
i pinged her for the answer u said don't and that's all but what's the case of urs anyways
i did not "just type what was given".
anyways thats none of the stuff but ig someone needs help in #help-44ļ½stanley-š²-v2-dans
does that apply to trinomials too
Can I ask a high school calc question here?
I don't need help here but I enjoyed this problem
strict inequality is not a concern here
sure you could say these inequalities are strict. but (a) nobody gives a shit and (b) there is no obligation to write a statement that is as strong as humanly possible
take reciprocal of everything
does it change the sign?
it flips the sign
example of what?
how the flipping happens
are you asking why 0 < a <= b implies 1/a >= 1/b...?
yeah
like the formal proof?
yes.
a <= b implies b - a >= 0
1/a - 1/b = (b-a)/(ab) = (b-a) * 1/a * 1/b >= 0
b-a >= 0, while 1/a and 1/b are each positive
thus 1/a - 1/b >= 0
is this what you wanted
yes
i didn't understand what you did here in this line
are 1/a and 1/b positive because both a and b are greater than zero?
yes
The conclusion isn't even true if a and b have different signs.
hey, sorry to interrupt but if i have the quadratic approximation (second order taylor expansion) of cos(x)
how do i find the quadratic approximation of cos^(1000) x?
approximately
If a and b are both negative, the conclusion is true again, but we'd need some modifications to the reasoning Ann showed.
Binomial theorem, I'd say.
i thought of that but it didn't work out
cos(x) = 1- x^2 + x^4/4! + ... right?
(1 - x^2 + x^4/4! + ...)^1000 = ?
it's a bit hard
Or perhaps just wing it:
If you imagine multiplying out (1 - x^2/2 + o(x^2))^1000, there will be some times that contain one or more factors of o(x^2). You're not interested in them; they'll have too high degree to matter for your quadratic approximation. Then there will be terms containing factors of 1 and factors of -x^2/2. There you're interested in exactly those that have one factor of -x^2/2 and 999 factors of 1. How many of those are there?
yeah i think i'm aware of it but i'm probably missing something basic of what i should be doing
like can we try with sin(x) for example?
what am i looking to do exactly
I don't think I have any better explanation ready than what I just said.
no it's not about your explanation, but i think it just didn't "click" for me
I agree with the extra O(x^2) term part
every terms of higher degree gives you an even higher degree so we don't care
But the last sentence i'm not sure how to put to practice
So you agree that the quadratic approximation you're looking for will also be the quadratic approximation of (1-½x²)^1000?
whta about the O(x^2)? do we still not keep it there just so that after our expansio we have something ike O(x^1004)?
which we don't care for but yeah, do we still not leave it there regardless?
Oh, I thought those were the ones you jsut agreed could be ignored.
Yes well technically i can ignore, i just thought formally you'd write O(x^2) as well right?
but yes i agree
so just 1 - 1000 (1) ( x^2) + ...?
wait so just x^2
wait i'm being stupid probably lol
okay nvm
Okay, so let's write that out with the binomial theorem:
$$ (1 + \tfrac12 x^2)^{1000} = \sum_{k=0}^{1000} \binom{n}{k} 1^{n-k} \left( \frac{x^{2k}}{2^k}\right) $$
Troposphere
true
okay i think this part is fine
what about more termst hough
let me think of a question
So there's now only one term left, namely the k=1 term.
okay so what about for sin(x)
this time it's a cubic approximation for anything meaningful
because it has no quadratic term
Yes, this is right. (Sorry, didn't see it while I was typing).
well shouldn't the second coeffficient be like 500?
Ah, right. Sorry.
anyway no problem i get the idea i think my main problem is "more terms" in the expansion
by more terms i mean
multinomial expansion i guess not binomial anymore
this is why i was curious how we'd do it with say O(x^3) formally put into this
Do you know multinomia expansion (which would make it easier) or were you just guessing the word?
cos(x) = 1 - x^2/2 + O(x^3)
i'm curious what would be the right way to write out: (cos(x))^1000 = 1 - 500(x^2) + O(x^3)
i've heard of it lol
but not too familiar
That looks right.
but like if i were to reason this out
it'd be: (1 - x^2/2 + O(x^3))^ (1000) right?
how do you deal with that?
I'm confused. Wasn't that was we just did?
Or you're asking for a formal justification for ignoring the O(x³) terms?
i know but our argument was that we can just ignore O(x^3)
which is sound yes
but like what if you just want to incorporate that into our expansion
instead of outright deleting it
so instead of writing $\qty ( 1 - \frac{x^2}{2})^{1000}$, how would we do it with the presence of $\qty ( 1 - \frac{x^2}{2} + o(x^3))^{1000}$
!Kiz__
Hmm, let's define f(x) = 1 - x^2/2 for brevity.
Then we're looking at (f(x) + O(x^3)) ^ 1000, and we want to argue that this is f(x)^1000 + O(x^3).
Binomial theorem again: $$ (f(x) + O(x^3))^{1000} = \sum_{k=0}^{1000} \binom{1000}{k} f(x)^{1000-k} O(x^3)^k $$
oh i see, so we can always just turn it into a binomial
Troposphere
Indeed.
okay nice thanks, but wait my actual context is to use taylor on limits
therefore i know something like sin(x) approximates to x - x^3/6 + o(x^5) right?
O(x^5) not o(x^5)
would small o notation not be the same as big O notation here?
Or alternatively ... + o(x^4).
oh
No -- for example, x^5 is O(x^5) but is not o(x^5).
okay then i don't know what little o notation is
can u briefly explain it then?
why o(x^5) isn't x^5?
We say that f(x) is o(g(x)) if f(x)/g(x) goes to 0 as x->0.
We say that f(x) is O(g(x)) if f(x)/g(x) is bounded near x=0.
In other words, o(x^5) stands for a function that goes to 0 strictly faster than x^5 does.
But O(x^5) means one what goes to 0 at least as fast as x^5 does.
Oh i see, i get it
nice
okay so i think back to my question
sin(x) = x - x^3/6 + o(x^4)
how does this follow:
that's from stackexchange (https://math.stackexchange.com/questions/1786112/how-to-calculate-lim-x-to-0-fracx6000-sin-x6000x2-sin-x)
oh great, thanks!
what modifications?
I'm too lazy to go through and figure out exactly where they are, but I imagine there might be some signs that need adjusting.
And instead of "because 1/x and 1/y are both positive" we'd need to say "because 1/x and 1/y are both negative, their product is positive, ad therefore ..."
Not deep changes, just pesky.
well they are deep if you have zero familiarity with proofs or zero familiarity with inequality manipulations
Fair.
Wouldnt anyone trying precalc have a good enough knowledge of inequalities anyways?
not me
Thats a fucking lie lmao
We were taught inequalitirs the first day we started jee prep
I'm not him
I'm himm
Ahem is there smthn else to do?-
Not considering like the triangle inequality or am-gm shit
u can't do that
(x-2)/(x-4) > (x-6)/(x-4)
then u have to take any one to the other side
U can't just cancel out the denominator
You could just cancel? As long as x-4 is positive anyways
If its not you can still cancel
Just change the sign
Ig
U can't
Uh?
nuh uh
Lmao okay
nuh uh
Anyone have a good strategy for review the AP test
hi! im on highschool and i love maths. i like functions but the content on the highschool lessons seems very easy and i want to learn more about calculus. I learnt limits and derivatives by the textbook by my own, but the book doesnt explain integrals. Can someone tell me how can i learn integrals and that kind of things? thank you
Thomas/stewart etc etc are all good books since you can learn from books on your own
Plan A would be to ask your teacher if they can recommend some material. Schools sometimes have old advanced textbooks sitting on a dusty shelf somewhere.
If you're working that far ahead, you might consider if you should be looking at some proof-based real analysis instead of just forging ahead to integrals.
Proff leonard is a good one
I see mathisfun.com being recommended to ppl a lot too but havent used it personally so cant comment on its quality
what is proof-based real analysis?
Limits, derivatives, etc, but presented with theorems and rigorous proofs of everything instead of "here's the steps you must follow".
For all I know, that might actually be what you've already read -- it varies a lot between parts of the world whether one even distinguishes between "calculus" and "real analysis" in this way.
that seems nice
As a quick touchstone example, do you know what the intermediate value theorem says -- and would you have an idea of what would be necessary to start proving it?
oh, i dont know it
Good, that means what you've been learning is not proof-based real analysis yet, and my suggestion to look into that won't waste your time. :-)
This is a topic where you'll pretty much need to use books rather than videos as your learning materials, though.
If you're on good terms with your teacher (and the teacher is somewhat competent), I'll repeat my suggestion to ask them. The teacher knows you better than we do, and can make a more educated guess at whether you should just be thrown straight at Baby Rudin or find a softer-and-friendlier introduction instead.
If that doesn't pan out, ask for concrete recommendations in #calculus or #book-recommendations.
using this bc I couldn't find a channel dedicated to geometric series
is this correct?
its the evaluation of this sum
!nogpt
Please do not trust ChatGPT or similar AI tools for mathematical tasks, as they often generate output which "sounds correct" but has numerous factual or logical errors. Use of these AI tools to answer other people's help questions is strictly against server rules (see #rules).
In this case I don't immediately see any error, though.
yeah it was incorrect
i got the correct one now haha
i think this is the one
$S = \frac{15}{2} \left(1 - \left(\frac{3}{5}\right)^n\right)$
uh
If I set n=1 there I get S=3, which does not seem to match what you said you're evaluating.
How hehe
huh
shit I'm gonna have to do it again now
anyone any idea how i'd go about evaluating this
are you 110% sure that you wrote it correctly and made zero typos?
@urban stream
asking because the probably-intended meaning of the sum doesn't align with the sum as it is written right now: $$\sum_{r=1}^n \frac{15}{4} \cdot \paren{\frac{3}{5}}^n$$
|Annā©
(What Ann is saying is that it looks extremely likely that the n'th power in that formula should have been an r'th power instead).
no i think its incorrect
OH
FUCK
ok so then can you post the correct sum
the sum of the terms are \sum_{r=1}^{n}\frac{15}{4}\left(\frac{3}{5}\right)^{r}-1
$\sum_{r=1}^{n}\frac{15}{4}\left(\frac{3}{5}\right)^{r}-1$
the -1 is gonna be with the r, couldn't type it on with latex
$\sum_{r=1}^{n}\frac{15}{4}\left(\frac{3}{5}\right)^{r-1}$
uh
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
2
the question later on says to find the least value of n for which sum of infinity - sum of nth terms <0.045
Hey people someone told me to come to this channel maybe i will find what i want but promise you will not laugh after i say my request? I really need it but dont ask why, ok?
no need to be ashamed
Is there any function that has like one point like for example (1;3) and that's it no more points?
Many qustions cannot be answered well without knowing why, though.
I just need it
How do I calculate the area of this pool using calculus?
this goes in #calculus
Aight
Struggling with C
you could pretend its 2 curves, put it on a coordinate axis, and use riemann sum to guess
you really don't have any lengths or units tho
soo
imposibleh
XD
How do I solve this?
Didn't you already ask that yesterday?
And if you keep asking the same question, people will just keep giving you the same answer that you didn't find helpful the previous times.
Would you be able to solve this equation: 3Ā·xĀ·1.792 = (2x-3)Ā·0.693?
Yeah
I got -0.52
Thatās the same answer for the question I asked
So you got me the correct answer but I donāt know what you did
The previous times you asked, you got to
3xĀ·log(6) = (2x-3)Ā·log(2)
and then got stuck.
Yeah
I simply calculated the values of the logarithms: log(6) = 1.792 and log(2) = 0.693.
(Though now I see I should probably have used the base-10 logarithm instead of the natural one, sorry).
Hmm, without a calculator, I don't think there's any reasonable way to reach the value -0.52 as an answer.
(I'm assuming you don't have a slide rule or a log table either ...)
Nope
No, you're misapplying some log rules there. The next step would be to rearrange as
(3Ā·log6) x = (2Ā·log2)x - 3Ā·log2
they prob want you to distribute and solve for the exact value of x
Yeah I already did that
But I skipped a step
And just showed what I thought might have been the next step
its not
I know I thought so
2xlog2 - 3log2 isn't that
I tried using these
you should subtract 2xlog2 from both sides instead
Okay
that only works if its M or N inside the log
use log6(6)³^x in both sides
2x and 3 are both outside the log function
no wait why
I imagine when you solved my version with decimal numbers, your next step was to combine all the terms with x in a single term.
oh nah that step was wrong in the first place
Yeah
then factor out x
and then divide by everything thats left
to solve for x
So the point here is that log(6) and log(2) are just two particular numbers. They behave the same in an equation as 42 and 18827 would have done.
it's correct
3x = 2log6(2)x - 3log6(2)
So what you should be thinking first when you see
(3Ā·log6) x = (2Ā·log2)x - 3Ā·log2
is not "uh oh there's a logarithm there, I need find and use a log rule", but instead "ho hum, there's some constant number there, it doesn't affect how I solve the equation precisely what the constant is".
thats correct...
Okay
idk what this is tho
It looks pretty incorrect to me. For example, if you plug in x=0 it claims that 0 = -3log(6)Ā·2.
oh ur right its not nvm šæ
what u get
I just factored out the x and then did (-3log2)/(3log6-2log2) and then I got -0.5213
Perfect.
yeh
Thanks
[3-2log6(2)]x = -3log6(2)
x = - (3log6(2)/3-2log6(2))
x = - (3log6(2)/log6(6³)-2log6(2))
x=-(3log6(2)/log6(6^3.2^-3))
doing that u got:
x=-(3log6(2)/log6(27.2))
x=-(3log6(2)/log6(54)
x=-3log54(2)
x=-0,5213
How do I solve this?
I tried the same method
But it wonāt work this time
I keep getting the incorrect answer
The same general approach should work. Can you walk us through your steps that give an incorrect answer?
Smaller steps, please?