#help-38
1 messages · Page 82 of 1
so you just multiply and divide by positive numbers if n is even
therefore the entire expression is positive in that case
if n is odd however, we multiply by a negative number, so LHS is negative and 0<LHS<1 is not true.
I don’t get the inequality part
What are they implying be restricting it between 0 and 1?
oh nvm I switched it
only if n is odd, then we multiply by a positive number
so it'd be if 0<LHS<1, then n is odd.
The full question is also about the n is odd with the restriction being 1<LHS<2
So even n is 0<LHS<1 and odd n is 1<LHS<2
hm no, because if n is even then LHS is negative
then LHS<0
try a value
n = 0 for example
then we have 30 * (-1) / (1 * 5)
= -6
is not between 0 and 1
you can take n=2 too
I see what you mean
it'll still be negative
It’s wrong isn’t it
yeha
Why
Why did they ask me to explain why as if they are right?
Is this a trick?
And instead I have to explain why it is not?
idk
since they used the sum notation wrongly
I'm not sure what they had in mind
Yeah seems to be they wrote it wrongly for the second part!
Ok thank you so much!!
Are you gonna be on this discord later?
if it's from a class or course, maybe ask for the correctly put task, because this isn't properly written lol
I wanna attempt the remaining questions before asking( pretty sure will have some questions but would like to try to solve first)
time to time, you can dm me if you want, otherwise I'm sure other wanderers will come by here to guide :)
sure np
I might not be available, so you can just put them here and in dms once you're unsure or stuck
This is indeed from a class textbook although it’s not assigned, I’m trying to do questions as extra practices
kk
Sure! Thank you so much!!!:))
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I need help with part b
i saw that coming 

math jokes
no jokes here
only compactness
@granite cove 😂 is banned on my messages. please purchase nitro to be able to use 
?
you've gone too far this time
@dawn dune Has your question been resolved?
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Can i get some guidance with this
im not sure how to show the first part of their hint
What is your doubt?
.
ok i got the idea
.close
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Glad I could help
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mind
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nyxie9151
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@astral ore ?
yeah that was my question but i'll reopen
but what's the question
it's on my other channel
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what do i need to study to be able to answer this? i been doing online classes for 3 years and played games most of the time and now i am clueless on what to study to be able to solve these
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this will teach me?
okay thank you! ill do it now
.close
np
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I have a quick question regarding the semantics of first-order-condition (FOC / necessary condition) and second-order-condition (SOC / sufficient condition) when evaluating stationary points of functions.
I am quite sure that I do understand the difference between necessary and sufficient.
I am a bit confused as to why the FOC (f'(x)=0) is only necessary and not sufficient? Is it not that when f'(x) = 0 there is ALWAYS a stationary point? As I understand, that would make the condition sufficient (in addition to being necessary already).
Also, is it correct to assume that SOC (f''(x) > 0, in case of maximum) is only sufficient and not necessary because there are some cases like the function x^2 where we have a minimum at x=0 despite f''(x) !> 0? Or is there another reason?
think about f(x) = x^3, is its derivative 0 anywhere?
Yes, at x=0. And it is a stationary point / inflection point.
But I fail to see the what you are trying to convey Im afraid
sorry, maybe i'm confused by terminology here, i'm not used to stationary point, does that mean a local extremum or something else?
yes
As I was taught, a stationary point can be a global/local maximum/minimum or an inflection point.
derivative = 0
gotcha
and again, i've just seen different terminology in textbooks i'm familiar with, but what does first order condition refer to, is that related to first derivative test?
I just looked up inflection point and what I wrote doesnt make any sense, sec
they explained it as necessity, 2nd order being sufficiency
What I meant with "inflection point" is a saddle point. Somehow the latter is named as the former in the class notes.
"I am a bit confused as to why the FOC (f'(x)=0) is only necessary and not sufficient?"
when you are asking this, are you asking whether it is only necessary and not sufficient for what exactly? I'm looking a bit at the definitions so it is sufficient to call it a stationary point since that's the definition of a stationary point, but it is not sufficient to call it a turning point (local extremum)
i think the right question is why f'=0 is necessary but not sufficient for a local extreme
turns out neither necessary nor sufficient, yall should try to find examples
Yes you understood me right. But the way you phrased it makes me realize that you might be correct in the sense that is sufficient to determine a stationary point, but not sufficient to determine what type of stationary point is at hand. That might be the reason.
How is it not necessary?
before proceeding, a stationary point is defined at f'=0
well it's necessary if we are only limiting ourselves to talking about differentiable functions, but an extremum can also occur at an undifferentiable spot (i.e. absolute value function)
by definition f'=0 is sufficient and necessary for a stationary point
so thats not the right question
What did you mean by "turns out neither necessary nor sufficient, yall should try to find examples" then?
i think the right question is why f'=0 is necessary but not sufficient for a local extreme
Yes, but how is it neither necessary nor sufficient?
Julian, can you plz ask a specific question on the point of confusion you are now having, if this hasn't answered your question? And specify "necessary and sufficient" for what?
i can give examples to show that but i invite you to try finding some yourself first
Necessary and sufficient to determine a local extreme I assume. The conditions are named necessary/sufficient in the class notes but "necessary/sufficient for what" is not explicitly stated, hence I am wondering aswell in which context the conditions are necessary/sufficient. But as you already pointed out earlier you might be correct that the context is "for local extreme" which would in turn make sense that f'(x)=0 is only necessary and not sufficient. Right now I am still a bit confused about the input of roketsune though.
If we assume a non-limited and differentiable function I cant think of any so Id be thankful if you could provide one.
what are we assuming about the function in the discussion? is it differentiable? or are we only assuming continuity?
because that changes the conditions
the kicker is we need not assume differentiable!
This was not really specified, but most likely we can assume that both apply since thats the standard case for the level Im at.
Oh okay I get it then I think.
yes but maybe his class discussion concerns only differentiable functions, it sounds to me like this might be more like calc in an economics context?
Haha yes it is economics
thought so
even so i think its highly instructive to see what we can get away with vs what we cant by assuming certain conditions
well in short: local extremes can occur potentially at either places where the derivative is 0 or when it isn't defined. so if the function in discussion IS differentiable then yes we can conclude that it's necessary for the derivative to be = 0 for an extremum since the undifferentiable option is no longer an option
as an aside ive not met many calc students who know the math versions of necessity and sufficiency
so you kinda have to decide what properties of the function you are discussing are, otherwise you can't really make any conclusions
simplest example: absolute value function, continous for all real numbers, differentiable for all real numbers except x = 0, has a local (and global) minimum at x = 0, so that minimum occurs where it is undifferentiable
so that example shows it's not necessary to have f' = 0 for an extremum, but this is only if we are including undifferentiable functions in the discussions
And in turn I think your take that it is not sufficient because f'(x) = 0 does not allow us to determine the type of the extremum is correct.
Thats a good example, thanks.
it doesn't allow us to determine if an extremum is even happening
that was the example of f(x) = x^3, it has a horizontal tangent at x = 0, but f is increasing for all nonzero x, both to the left and the right
It is also far from important in the class context but it bugged me that the terms are always used to refer to these conditions without a lot of explanation.
So I guess the following conclusion would be correct?
- f'(x)=0 is necessary if we try to determine the type of a local extreme on a differentiable and unlimited function
- f'(x)=0 is necessary and sufficient if we try to determine a stationary point on a differentiable and unlimited function
what does unlimited mean
I lack the terminology, but what I mean is that we assume that x-values for -inf to +inf are allowed. Otherwise it would be possible to have an extreme at the end of the function where f'(x) would not necessarily be 0 right
what does f'(x) is necessary mean?
Necessary = If X is true, Y has to be true aswell (Y necessary for X)
Sufficient = If Y is true, X must be true aswell. But there might be other causes than Y that lead to X (Y is sufficient to assume X)
yeah but literally what does f'(x) is necessary mean
ah I meant f'(x) = 0
it means I slacked
lemme see how we can summarize:
i think youre trying to say that the limit of f at +/- infty need not be finite?
in which case that has no relevance here
the thing about stationary points is boring. we DECLARE c to be a stationary point if and only if f'(c)=0, ie necessity and sufficiency is there already
if f is differentiable at c then f'(c)=0 is necessary but not sufficient for c to be a local extreme
Not suffcient because...?
you were already given a example to show that, f(x)=x^3
assuming f(x) is a differentiable function on some interval [p, q]. For local extremes in (p, q) the following is true:
- f'(x) = 0 is a necessary condition, but not sufficient, but this condition can be used to find "potential x values" which can be tested using either first derivative test or 2nd derivative test as below:
- first derivative test: if x = c is the potential x value examined, if there is some open interval (a, c) where f'(x) > 0 and some open interval (c, b) where f'(x) < 0 then x = c is a local max. (similar situation with local min with signs switched)
- alternatively you can do 2nd derivative test: if there is some open interval (a, b) where a < c < b and f''(x) > 0 on (a, b) then you have a local minimum
if f''(x) < 0 on (a,b) then you have a local maximum
f'(0)=0 but c=0 is not a local extreme
so basically the first derivative test is: are the signs of the derivative opposite on either side of the potential point?
2nd derivative test is it concave up or concave down on both sides of the potential point?
Okay so not sufficient for local extreme, but sufficient for stationary point.
I think that sums it up yes.
stationary point is just a useless and unnecessary term that means derivative is 0, nothing else
just say f' = 0 instead of needless terms imo, but i guess that's what economics classes like to do : (
you can read many calculus textbooks without even coming across that needless term
this question is a prime example of how it just introduces needless confusion to begin with by introducing unnecessary terms
It is a bit weird yeah but luckily not relevant at all to what we are doing in the end
But still wanted to dig a bit cause it bugged me
you can remember it just means derivative is 0 if you think about problems that come up often in calculus where you have some function of position, usually s(t) and then the derivative of that is velocity v(t) and well when v(t) = 0 you are stationary, not moving because your velocity is 0
i guess
Also the lack of context probably makes this task of exploring the terms quite a bit more daunting than it actually would be
Thanks
@tepid hamlet
@willow urchin
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What do you think x and y should be?
yes
May I see your progress?
no
yes
sorry
its 40 x for oinion and y is 75 for chicken
like you have to multiply the quantity of chicken wings to the calories
which gives 75y
75y = chicken wings
and 40x is onion rings
x and y are undefined which will have to be found
yes also this is off topic but ima need ur pfp
im gonna send it to Ukraine to bump up moral and let them know theyll just go back to lobby if they get hit
yes indeed we shall
yes
and all together there are 19 onion rings and chicken wings combined
yes
and then you add all of these together to get a combined calory total of 970
so
40x + 75y =970
is that equation
Instead of just giving him the answer, maybe help him understand why a 2-variable system requires two equations to solve
no i got it
final question do you know how to substitute algebra
no
like you can make x the subject
idk
umm multiplying
yeah
so what would x equal
onion
ok
that is the number of onions
so I am assuming you don't know how to rearrange a formula
no not at all
ok
are you meant to solve for x and y or are you trying to just get the equasions
just getting equations
nah just eqautions
ok so the q has been solved
the q?
question
but theres two boxs
you gave me 40x+75y=970
x+y=970
can you eat 970 chicken wings and onion rings?
nickacadoavacado can
nice
I said 'combining'
wait wait wait would 970 be at the begging
970 is the amount of calories
not the amount of food
we are talking abt the number of rings and wings
okay so were finding the amount of food
so 19
good
x+y=19
yes but don't mix up what x is or y
like x is the rings
y is the wings
that should be it
okay
send a screenie before submitting
it was wrong
how?
i have one more chance
What happened?
bro
..
got it mixed
wait what
oh mb
yes
nice try
come onnn
40 x 75 y
40 or 75
so which one should be x and which one should be y
read the question
@rough citrus I'm losing you
75x 40y
=970
Were I you, I would definitely give him the answer directly 😂
ok
It has taken too long and he doesn’t seem ambitious
Congrats
yes
💀
now look at your answers and tell me it's wron
wrong
I think we should close this channel
@rough citrus
you can tell your teacher you got it correct
wait i put x and y when it should have been r and c
it says any letters can be used
wait fr
💀
i can make a case about this
they got my back fr
uhhhhh 2025
what?
no its 2024 lol
do you even go to school
yes im in ninth
grade?
and im only failing algebra
okaythank you for the help today
lol i need help agian
ye x and y
okay
let's x be small boxes and y be large boxes
okay lets define those
to find how many bars you get from the small box
what do you have to do to get the total number of bars in let's say 5 small boxes
@rough citrus
5 x8
okay
replace 1 number with x to find the total number of bars
okay x=8
x8
y=12
not equals
olay
72
8x+12y=72
good
now
in the problem it says there are 3 time as many small boxes as large boxes
how do we make an equasion out of that
what do you think it should be
@rough citrus
one sec lemme see if I'm right
ok
if I have 6 small boxes and 2 large boxes
idk how to word it
yea
no
no
might have to ping the helpers because idk how to help you without giving the answer
<@&286206848099549185> how do you teach ratios to a person to help them in this question
to find the relations with the boxes
just give answers
you need to learn not cheat
?
read the question and you will see where I'm going
WHO HAS THE DUMB
me
nah don't be mean
What's the question
I am too lazy to read it....someone will do it
bro
So you are basically asking helpers to help how to teach a person so you can help them
here
yes
I'm so stuck
first time teaching and I'm still learning
so far i got this
U forgot there are 3 times small boxes
U already know number of gran per box
yes 12 and 8
So u took x wrong
oh
8x + 12y = 72
that is what he put
3y = x
.
wrong way round
Score good marks✅
3x=y
Bruh
okay so i put 3y=x
.
okay
Just take type what I am sating
that was close
Don't waste more time
good
You still there?
🥶cold
maybe try switch around the equasions into different boxes
because I am corrct
correct
@rough citrus
I know I am
Can you explain why you wrote that equation
wdym
What logic went into that equation?
Why did you write 8x + 12y = 72
What is "x"
What is "y"
x is amount of bars in small box
Maybe first correct your spelling for equation
y is amount of bars in large box
Yes
So the total number of small boxes
Is thrice the amount of large boxes yes?
If there are y number of boxes
There will be 3y small boxes
x = 3y
,w x - 3y = 0,8x + 12y = 72
surely it's the other way round
That would be wrong
so i will put x=3y
Yes
see how that goes
U guys still at it
and 8x +12y= 72
yes
x = 3y
let's see what it says
We all know what it is going to say
❎
🫵💀
You still haven't corrected equasions
@rough citrus just change the x and y
Bruh
Anyways gtg
equations
@rough citrus what does it say
now what
submit
Submit
alt f4
The fu
surely x and y are supposed to be the number of boxes
not the number of granola bars in the boxes
y=2
nice one
YOU GOT THE FIRST TWO ANSWERS WRONG THAT'S WHY
ik
thats y i said lets define the variables
yeah
Bruh
nvm
well done
x=6, y=2
we are not solving
Thanks a lot cedric
we are just finding equasions
ooh
my bad

5
lol thats how we all feel with this algebra
we have 5 more questions
hi
Child I have more work to do
soldiers prepare
fair
u summoned me?
idk
When you forgave math work and you have to do 3 problems in 5 minutes
how much time can you spare
help the enemy is here
this took 30 minutes for one question
when is this die by
sdue
due
@rough citrus
When the enemy is too strong, you gotta flee and come back strong to fight it again 
unless this is the last opportunity
its past due
this type of problems let me on my mathematics competition. I had to do 25 problems in 90 minutes
7s + 14l = 252
bro
s + l = 21
you're a teach
thank you
💀
,w 7s + 14l = 252,s + l = 21
Go for it
what are the variables
Who exactly
how did you get the helpful role
Oh
bro how are variables defiend
Perhaps I have helped people too much now
fair
@rough citrus
yes
🥱
thank you
lol hw won the war but the second wave is coming in perpare
You know what s and l stand for right?
nah
What are the options for the variable?
They denote the volumes
but you have already define volumes in the 1st equation
Volume of each small and large box respectively
nah
no way
am I going to go thru with this
it's the number of small boxes shipped and number of large boxes shipped respectively
If you consider
which is 7s
look at the second equastion
Not s
s+l=21
But s would be defined as the volume of each box?
And also the number of small boxes shipped?
s is the number and 7 is the volume
@rough citrus put this in
as defining
TRUST ME😭
okay
so which is s small or large
s is small
Well I get what you are trying to say
Because it even asks the number of small and large boxes shipped
So it would make sense
it was @low verge who i went with
To find s and l as number of small box and large box
lol
It also would be correct to say s and l is the volume of each small and large box respectively
wait do u hear that
I've been here for 2 and a half hrs
Great work btw
I'm Asian I can do math for a long time
So am I
im american i can grill
really!
Ofcourse!
and do unspeakable thing to you sibling
any way
let's get on with this work
no i race win wars and grill and shoot guns
ok bro
I see percentages😭 (those are the juggernauts)
can you give me 10 minutes
I need a break
I'm back
let's define the algebra
let's do x and y respectively
@rough citrus
and show me the options for defining the alsgebra
ok
I'm British
idk what commission is
can you explain it to me @rough citrus
is that profit
idk
it's is profit
I think
average american\
Commission is money you earn after making a sale e.g selling a house earns a percentage of the sales as commision
so in the context it is profit
thank you
let's start with the first equation
for profit
you will have to add the percentage onto the original price
@rough citrus
what is 9% as a decimal
ok
dude this isnt china u can not listen and still pass
I'm sorry
lol
I'm just tired
same
I'mma just give you the answers
please
isn't it like 10 am in America
where do you live
nice
yo wassup
yeah
I'm in England rn
wspppp
no way a recruit
Hw you guys ?
shellshocked
bro were at war with algebra
Oh
we get through 1 question in 30 minutes and it is supposed to be easy
x is the number of dollars in phone sales
@low verge is mathing
Going for 3hrs straight
yessie
Dedicated
wit i hear nuke warning
Are you asking in general?
Oh sorry
okay
0.09x+0.06y=135
YESSSS
I THINK I'M RIGHT
but
don't submit yet
I'm not even teaching at this pint
point
You are understanding how this is being solved right?
he doesn't have a clue
135
lol
135 instead of 165
jk jk jk jk jk jk jk jk jk
What is the question?
Is this like your mutual improvement math study channel session
not supposed to give out answers guys
hahahah
But you understood that part right
yes i understand it alll
Then try making
lol
Equations yourself this time
enter it in to see if it is right
@rough citrus can we do this all later
algebra teacher rn
bro I'm giving up
now close this channel and we can rest
.close
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@sullen sable Has your question been resolved?
weeks
okay thank you! and are the other ones correct
seems good to me
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Is my calculation correct?
rhs of first line equals -21I, not 21I
and then the 21 disappeared when you went from line 2 to line 3
aside from that, the idea is right
I need to divide 21 to right side?
yes
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Greetings, given this system i must discuss for the non trivial solution, i tried to solve the problem using gaussian elemination but i am running into problems in the last part because i am left with two unknowns, how do i proceed? even if the calculations are incorrect how would one proceed here? thanks 🙂
you have 4 variables but only 3 equations
you won't be able to eliminate them all
so having 2 variables remaining is correct
okay but how would i then solve for the other unknowns? i dont understand
so we have -9z = 10w, which you can rewrite to w = -9z/10
then replace w in all the other equations using that
then keep eliminating variables and get everything in terms of z
and that will parametrise the line of solutions
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hello! currently i am doing trigonometry inverses with a calculator, however i have no idea how to solve for sec(x)=undefined
try rewriting sec(x) in terms of sin(x) or cos(x)
like cos-1(x)=und?
we usually write it as 1/cos(x), to not confuse it with the inverse function, but yes
when would that be undefined?
im assuming infinity?
we're dividing 1 by cos(x). when we divide by a number, when would that division be undefined?
whenever the denominator is 0?
yes
however 1/cos(0) just comes out as 1
What's $\cos(\frac{\pi}{2})$?
ColdTee
@lone elbow Has your question been resolved?
0.9996
,w \cos(\frac{\pi}{2}
what
Also you can easily solve this if you know the range of sec(x)
i have a paper with the ranges of tan/cos/sin for graphs
,w cos(1.57deg)
but pretty sure i lost it somewhere
oh that’s probably why
this problem has to be in deg mode
Radian
sec(x) is defined for all x in $R - (2n+1)\frac{\pi}{2},n \in Z$
It's range however is $\sec(x) \geq 1$ or $\sec(x) \leq -1$
ColdTee
$(-\infty,-1] \cup [1,\infty)$ in interval notation
ColdTee
Notice 0 doesn't lie in the range
does that mean i would need to plug in any value between $\sec(x) \geq 1$ or $\sec(x) \leq -1$?
jupiter
ColdTee
No that's the range
What is $\sec(x)$ in terms of $\cos(x)$?
ColdTee
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$R - (2n+1)\frac{\pi}{2},n \in Z$
ColdTee
$\sec(x) = \frac{1}{\cos(x)}$
ColdTee
And $\cos(x) = 0 \implies x = (2n+1)\frac{\pi}{2}, n \in Z$
oh yeah also that
ColdTee
Put in any integer for n
You will always get 0
Since 1/0 is not defined
Therefore the domain won't contain those values of x when cos(x) = 0
would that mean cos(x) = 1/0??