#help-13
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so you need to apply some rules
but just do it in order and go as slow as you need to keep track of things
,rotate -90
,w D[x^3 cos(1/x), x]
oh should be + because of - sinx
you lost the x^3
you should do this problem more slowly 
its less time to do just do it right the first time
its harder to find mistakes than avoid them
FWIW
yeaa my math teacher always says to slow it down
this is a good one to practice on maybe
but ur perogative
oh its spelled prerogative 
,rotate -90
jan Niku
$y' = x^3 \dv x \csc 6x + \csc 6x \dv x x^3$
did the first step
$y' = x^3 \qty(\dv t \csc t)\bigg \vert _{t=6x}\qty(\dv x 6x) + \csc 6x \qty(\dv x x^3)$
still havent applied any derivatives
do you know all of the derivatives here?
hmm lemme edit here
cscx is -cscx*cotx
maybe this is more clear
jan Niku
$y' = x^3 \qty(\dv t \csc t)\bigg \vert _{t=6x}\qty(\dv x 6x) + \csc 6x \qty(\dv x x^3)$
im just trying to distinguish between the derivative of csc(6x), and after we've applied the chain rule
once we apply the chain rule, were free to just differentiate csc t
but its still evaluated at t=6x
ohhh okay
(6x remains the argument of the derivative)
yeah yeah
so if you know the derivative of csc t off teh top of your head
lets do more steps
maybe we'll break it out
$\dv t \csc t = \dv t \qty( \qty( \sin t) ^{-1} )$
would it be -csc t * cot t
jan Niku
$\dv t \csc t = \dv t \qty( \qty( \sin t) ^{-1} )$
$\dv t \csc t = \dv t \qty( \qty( \sin t) ^{-1} ) = \dv t (\sin t) \cdot \qty( \dv s \frac{1}{s} ) \bigg \vert _{s=\sin t}$
jan Niku
hmmm i think im getting it
couldnt we just do this then
you can use the quotient rule here
lemme send it
if you like it
i do like quotient
$y' = x^3 \qty(\dv t \csc t)\bigg \vert _{t=6x}\qty(\dv x 6x) + \csc 6x \qty(\dv x x^3)$
jan Niku
were back here
yea so just hit (1/sinx) with quotient rule
maybe thats what u did
yea we learnt the rules on how to find the derivatives i just wasn’t sure what i would do with the 6x
hopefully the way i wrote it makes it make sense 🙏
and isnt just more confusing
in a way you ignore it
but you arent allowed to forget it entirely
,w D[ csc(6x) ]
because we learnt if we have y=cos(f(x)) then d’y/dx is -f’(x)sin(f(x))
sorry it takes a bit to type out haha
sure, yea
i was just kinda wondering what that would be for csc and those
well, if you apply quotient rule, you'd get to use this, right?
not ignoring it don’t worry, it’s helping a lot!!!
ohhh yeah
$\dv x \frac{1}{\sin 6x} = \frac{ \sin 6x \cdot \dv x 1 - 1 \cdot \dv x \sin 6x }{ (\sin 6x)^2 }$
jan Niku
something like this?
then you can apply this rule right in-place
OHHHH
yes yes that looks right
its really whatever is easiest for you
$y' = x^3 \qty(\dv x \csc 6x) + \qty(\csc 6x) \dv x x^3$
jan Niku
maybe you get to here and just go oh man that csc6x derivative is gonna be hairy or whatever
ill do it on the side
why is there a cosx on the bottom
you were working on this right?
oh!!
yea this looks better
sorry about all the questions by the way we just started the unit on wednesday 😭
do you see how to group this all out?
no worries if you can master derivatives your life will be easy 
at least mathematically
that’s all i need!!
yea
then you leave behind a 1/sin6x
you do have a constant floating around
wouldn’t it be 1/sin6x
ye
oh a plus or minus
go back here
jan Niku
this is $\dots - 1 \cdot \qty( 6 \cos (6x) )$
jan Niku
ohhhh okay
OHHH OKAU oops
thank you
just forgot it i went a bit too fast again
ORETTY SURE
oh yeah 😅
,w D[x^3 * csc(6x) ]
yea up to your prof but conventionally
factor out as much as you can
dont right factor like wolfram did here
lol
just my own personal taste
okay yeah
maybe its trying to keep all the trig functions close together idk
lemme do it rn and i’ll take another pic
probably
idk this is just tough because we started the unit wednesday and we have a test wednesday
it is a test about being careful 
1 week to learn it all including eulers number haha
if it was i would get a 60 hahaha
i have one week to write a 10 page paper 
do not pay any attention it was assigned in january
that is not important
oh gotta get that started soon then right
these trig problems are good
you know you can generalize these if you wanted but idk how good practice it is
trig ones are good because you really have to know quotient and not lose signs
yeaaa i know quotient good i just forget signs sometimes
just solve $\dv x \qty( f(x) \cdot g\qty(h(x)) )$
jan Niku
or something like this
my last calc test went great though!
i dont think its helpful
but possible 
dont let me waste a bunch of your time prattling about nothing
haha i’m not don’t worry
applications in calc was fun though, just wished we got more time to practice for this unit
mind if i try the last question and send you what i got?
okay
my calc exam is next tuesday 
I believe in you 
i’ll do my best!
hopefully it’ll raise my grade
starting the problem now just had to grab a snack
no problem feel free to ping
is this as simple as this looks
SORRY FOR ALL THE WUESTIONS but also
how do i find where sinx and cosx are equal to 0? or am i just supposed to memorized?
you should have pinged me in channel haha
ah i feel bad!
a cat… 😭😭
oh
jan Niku
why do you need to solve where things are = 0?
,rotate -90
lol
it helps to know identities but its in a week so who cares
you should know some
$2 \sin x \cos x = \sin 2x$
jan Niku
BUT you dont have to know this
cosine is 0 at pi/2, 3pi/2, 5pi/2, ...
sin is 0 at 0, pi, 2pi, 3pi, ...
and cos is like
i know this
i don’t remember how to like word it but it’s like kpi/2 where k is an odd number
i mean its periodicity
because $\cos(x) = \cos(x+\pi)$
jan Niku
so if $0 = \cos \frac \pi 2 = \cos \qty( \frac \pi 2 + \pi) = \dots$
jan Niku
yup
so the problem is like
remember the unit circle
perfect okay, is there any way to like show that though
it gives you infinitely many solutions
then, use the constraints of the problem to pick some out
inclusive, yea
so, you want either cosx =0 or sinx = 0
since that makes the product 0
and then the derivative 0
you have a formula for where these happen
or you remember your unit circle
yea
I wouldnt give too much ceremony about it unless your professor is especially picky
nice
thank you very much for all of your help
and sorry if i distracted you from other work
i dont wanna work today lol
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Well, one could say f is approximated by 2(x-1)⁴/4!
Tbh, isn't "local extremum" just f'(1) = 0 though? We already have that.
But the approximation should make the function's behavior pretty clear
@copper sky
we are looking for local min or local max or neither
so the derivatives dont give us that directly i believe
Luckily we can approximate with Taylor's theorem
yes
but in taylors theorem we have the fourth derivative at some point c
so i dont see what to do with that
on nvm got it
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I believe I made a mistake but I can’t seem to find it.
its correct
Would I leave it as cosx/1 or is just cosx?
i'd write cosx
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Hey could someone teach me how to graph these?
do you know about curve sketching?
using differentiation to sketch graphs
I do not know how to do that
then plot the graph
put values of x solve for y and vice versa and get coordinates
then plot it
isnt this just asking for when f(x)=0?
Yes
When the graph crosses the x axis
have u already solved it algebraically?
aight guess that works
I got some weird decimal numbers so I just drew a rough sketch using them
How to do these 2?
@silver oxide
at that rate just sub in values and plot the points
How do I do the bottom 2?
D and e?
@silver oxide
Pls teach me how to do the bottom 2
@silver oxide
@silver oxide
!noping
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how would I go about solving this?
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I understood the first part
But I didn't like using manual counting to find all the sample space
Is there any other intuitive way to find the answer
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What is the minimum number of books required to ensure that we have at least 18 books of the same genre (all 18 books being from one genre), if there are a total of 31 genres?
-17 ?
because we ensure atleast 1 genre is repeated atleast 18 times
31*18 is nothing
not sure tho
thats the answer i guessed but its wrong.
it's 31*17+1
not -17
should be 528 (558-30)
that's the right answer. But i don't know what's the thought process to get it
basically 31*17 is for 17 books for all genres
now it says you should have atleast 1 genre with 18 books
so if you pick a book of any genre you'll fulfill the condition
so you add +1
oh mb -30 because 31 genres
yeah
I counted the books it seems
can we start from the beginning? I don't even understand the question. What do they mean by "ensure that we have at least 18 books of the same genre"?
okay, so
there are 31 genres
now it asking you the minimum number of books you must have so that at least one genre out of 31 has 18 books in it
got it?
but they never tell us how many books are in each genre or how many books are there total
im still confused, sorry
there arent any books in total
you need to find the number of books
lets say you're building a library, you can fill in books with 3 genres
now u have to find the minimum number of books you must fill so that atleast 1 genre has 2 books
now in this case you take the worst possible scenario
that you get 1 book of each genre first
now since you need atleast 1 genre with 2 books in it and the total number of books should be minimum
so you just get 1 more book now, regardless of its genre you'll have 1 genre with 2 books in it
fulfilling the condition
now just repeat this but with 31 genres and 18 books in atleast 1 genre
is this what u mean by your library example:
yes
so the minimum number of books required to ensure that we have at least 2 books of the same genre, if there are 3 genres, is 4
now repeat this thought process for 18 books of same genre if there are 31 genres
i think we going too far ahead. what do we add or multiply in the library example
wdym
assuming we add or multiply to get 4, what numbers do we add or multiply and why?
3*1 + 1
3 for the 3 genres multiplied by 1 for the first book in all three of them and then add +1 to fulfill the condition of having atleast 2 books of the same genre
so 3*1 because there's 1 book for 3 genres each, and then that 1 is added so that one of the genres has 2 books?
yes
@quaint sunthere's 31 genres in existence, like any book at all is definitely one of those, and no book is 2 genres
that's the assumption
there's some magical number of books that you can be sure you have 18 of the same genre in them (and it's the smallest such number)
it would be impossible if for example we wanted 2 genres at the same time, 18+18
take a million books, they could all be from genre 1, so we don't have 2 times 18, so we can never be sure
but if we only want one genre there's no problem
527 books could be not enough (31×17) but one more book makes it certain
"it would be impossible if for example we wanted 2 genres at the same time, 18+18"
i like this counterexample, it really makes the problem clearer.
"take a million books, they could all be from genre 1, so we don't have 2 times 18, so we can never be sure"
I don't understand this though
Re-thinking this problem on my own. I've arrived at a different answer (but its not the right answer).
Since there are 31 genres. Since one of them has 18 books, then the minimum book case is where 30 genres have 1 book each: 30*1 = 30 books. Then add 18 books from that 31st genre: 30 + 18 = 48.
Why is this wrong??
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What happened to the -1/j from the second line to the third line? My answer is the same with the third line except with a -1/j multiplied to it
Is it just a typo or am I missing a rule or smth
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Given a vertical prism ABCD.A'B'C'D' with B'D = 3a, the base of ABCD is a rhombus with AB = a, BAD=60⁰
a) What is the volume of prism ABCD.A'B'C'D'?
b) Let d be the measure of the dihedral plane angle [A', BD, C]. Calculate d?
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A wagon with a mass of 120 kg moves at a speed of 6 m/s. After a person with a mass of 80 kg jumped from it at an angle of 60° to the direction of movement, the speed of the wagon became 5 m/s. Find the speed of the person during the jump.
@indigo cove Has your question been resolved?
n p
oh sorry
i dont have enough time rn to correct this
anyway, I wish you good luck in your search for help.
it makes me feel bad that I can't help you, I'm really sorry.
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this question is driving me crazy idk how to do it
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Can someone help?
open () not []
Why are the others []?
inf aren't numbers, there is no bound
and tan(x) is undefined at pi/2,-pi/2
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hi i know its very simple but i have a test tomorrow and this is one of the only questions im confused on im just stuck on what the other angles are
i think if the quadrilateral is circumscribed then opposite angles are supplementary
ooohhhhh
that makes so much more sense
so just do 91-180 and i have my answer for W?
ok i got it tysm
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<@&286206848099549185>
@light temple Based on that table we need to answer.Right?
See the table if one person is voted in the last election the probability will be 0.23 and so on.
oh yea I got that but I have another question
Tell
for this question
The 5% on the graph should be shaded right
But idk how to determine if it’s on the left or the right
KingDanger
What these three things means here? @light temple
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(dont actually need to solve) but i want to know how would i go about checking if they collide at the same time?
is it just comparing to see if t and u are the same?
in this case they are not the same so they dont collide?
like if the u and t are the same at (1,5,0)? yea it's not simultaneous since you can just check it doesn't work for x=1
so in the future if i get a problem about asking if they intersect at the same time, i just compare t and u?
im a bit confused by the differing notation
yeah im just a bit confused why it's u
so u also denotes time
alright thanks
so both systems are still time
i thought u meant something different
the t and u variable
uh
calculus 3
lines and planes
yeah variables not i j or k
i just wasnt sure if u also denoted time
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hello!
i am struggling with tle last part.
the last espression we have is (r/k +c_2)delta(t)
but that is zero on 0+ and 0-
so the solution would be just 0 and r
I don't understand what should i compare
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<@&286206848099549185> someone knows this stuff? it's Unit Step and Unit Impulse Response for differential equations
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hi I need a counterexample of Barrow's Proof of the Fundamental Theorem of Calculus when function f is not continuos
As continuity in [a,b] for f: [a,b] --->R is required
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I’m having trouble proving this identity, it seems true but I can’t find a path to proving it. I’ve tried looking at its relation to Pascal’s triangle and some algebra but nothing really jumps out to me
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Help
<@&286206848099549185>
Yes could you provide me with an answer plz
Ok thanks
Ur supposed to find d^2y/dx^2 at the point (1,-3)
So the fraction
Yes
Np
Hopefully you're good with finding the first derivative. If not, we can focus on that instead
Once you have the first derivative, solve for it. Then take the derivative in terms of x again.
It's lengthy, sadly.
I believe the first derivative is 2 could u help me answer the other half
Sorry I don't mean the first derivative at that point
You'll need the general first derivative
So -1/x-y/x that doesn’t seem right to me
That's right
Can u answer the rest of the problem and show the work so I can see how to do the rest
Not my style sorry. Hopefully someone else can help
Ok can u atleast help me
What do I do after I have the first derivative
@glossy sierra did u get an answer?
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how to solve
i don't see it telescope
i didn't find a way to express it in a general expression for nth term
or i'm high
the denominators increase by 5 for each term
yeah
that should be enough for you to get started
add 5 to the 4 and add 5 to the 9 right?
yes
i mean i thought of a way already
but i don't think it's right bcs it's 10 seconds
i fucking hate orals0
i get you man, but trying to do every question as fast as you can is not a good way to learn it
some question youd get faster some slower
coming back, i can write this as 1/(4+5)(9+5)
from second to third it would be 1/(4+5+5)(9+5+5)=1/(4+2* 5)(9+2* 5)
how can i express it as n?
do you see the pattern?
a
you still dont see how to express it?
i see now
and you can obv simplify this afterwards
what you got brother?
hmm, i dont have time so cant really help you
thx
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<@&286206848099549185>
what is it that you struggle with
you need to construct a linear function
the input is t and output is d
imagine t was time and d distance
for every 5 minutes you travel 2km for example
ok
now you want to know how much you travelled after 10min for example
or basically want to always know how much you travelled
that would be 4km?
yea how did you do that?
times 5 by 2 to get 10 which represents 10 mins then got 4 and multiplyed it by 2
you basically just did
what your function line would do for you
so basically
a multiply of 5 minutes gives us a multiply of 2km
we can also say
basically you have
i have it like this
d/2 = t/5
ok
so like this?
not quite
think
this functions says
at 5 minutes i travelled 0km
and at 10 you would be in the negative
but it's the opposite
as time progresses your distance increases
so it goes up
not it's worse
it still goes down
from left to right
it has to go through your points
(5,2) and (10,4)
ok 10 is not on the axis
but it goes through (0,0) the origin
at 0 minutes you travelled 0 km
nope
im stupid frfr
this line means you didn't travel for example
at 5 minutes you are at 2km
and after 8min you are still at 2km
it has to go through (0,0) and (5,2)
im so lost
what is the problem
so make it like this?
To explain how we came up with the function:
For some time you traveled some distance.
5min -> 2km
10min -> 4km
So for every 5 minutes your km increases by 2.
You have a ratio of 2/5 which describes you rate of change
2km per 5 minutes
not quiet
i suck at this
your two points
now draw the line through thes
it says for one unit
oh okay lol tysm and im sorry
no ig not
haha
i wasted ur time though lol
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You have 6
identical dice. What are the total number of outcomes?
Note that cases like (1,5,5,2,3)
and (3,5,2,1,5)
are considered the same outcomes since the dice are identical.
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I've been having this problem for a long time.
Translation: Problem 3. How many subsets of S = {1, 2, 3, ..., 33} have the property that the sum of their elements is greater than 280?
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Show your work, and if possible, explain where you are stuck.
I achieved basically nothing. I know it's a combinatorial problem. From subsets that add up to 561 to 528 I had gotten the number of possibilities, but I realized that the method was humanly impossible later.
I noticed that the difference between the sum of all the elements is 561, which divided by two basically gives 280.
the sum being 561 is not a coincidence btw
definitely
but ur pretty much done once u realize that
honestly i dont know how to proceed
number of subsets that sum to 0 = number of subsets that sum to 561
number of subsets that sum to 1 = number of subsets that sum to 560
...
etc
i cant prove it, but i think that the number of subsets that sum to a number has a pattern
sum to 561 = 1 probability
sum to 560 = 1
sum to 559 = 1
sum to 558 = 2
sum to 557 = 2
sum to 556 = 3
sum to 555 = 3
and this will continue at least until 528
but this should go half
but I can't really prove this, and for the exercise in question, I would actually need to prove
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This is 1/4^3
Yes
nice
for this example since you have the negitive in brackets
it means that you do the 6th power
with it in brackets
but if the negitive was on the outside you would just ignor the negitive and add it back on in the end right?
Yes
You can just replace the minus sign by multiplying by -1
It is really just shorthand for that
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how do I start 5a (ii)
so do you know what you are trying to find exactly?
ratios for sin cos and tan
yeah
how☹️
so the 15 degrees angle is what you call a reference angle. Are you familiar with those
i think so ya !
,,, right so your first objective is to find
\e{align*}{
\6\sin{\0b\theta} &= \0r{{???}} \
\6\cos{\0b\theta} &= \0r{{???}} \
\6\tan{\0b\theta} &= \0r{{???}}
}
ooooo ya (wait that’s texit thing so cool)
hope the colour coding helps. What im trying to say is can you represent the blue theta angle trig ratios in terms of the red (15 degrees) trig ratios?
um um um I don’t know😭
,,,
\e{align*}{
\6\sin{\0b\theta} &= {???}(\0r{15\degrees}) \
\6\cos{\0b\theta} &= {???}(\0r{15\degrees}) \
\6\tan{\0b\theta} &= {???}(\0r{15\degrees})
}
hopefully this is better?
the ???s can be sin, cos, tan, -sin, -cos, or -tan
so do I just solve for theta using the inverse(15)?
no haha i think you are overcomplicating things
so basically like how reference angles work is like
in all of those situations you can have a reference angle, and that reference angle has a very nice property
the trig ratios of the green theta (the main angle in the picture) are equal to the trig ratios of the red theta (the reference angle) BUT with a small catch that they might have a - attached next to them
to know if they have a - attached, just remember that cos is negative in the 2nd and 3rd quadrant, and sin is negative in the 3rd and 4th quadrant
oh the CAST rule?
as an example
[
\cos(120 \degrees) = -\cos(60\degrees)
]
yeah!
so here 120 degrees is in the second quadrant and cos is negative there
the reference angle to 120 degrees is 60 degrees from the negative x axis
so the two are equal with a -
hope this is understandable in some way?
yaaaaa that makes sense ty
oki so going back to this
first; what quadrant is the blue theta angle in?
q2
yeahh
is it also in q1
nop! can only be in one at a time
so cos is negative and so is tan right?
oh oh sorry ignore what I’m saying lol
yaaaa
yeyeyey so now, the reference angle is 15 degrees
ya ya
so knowing all of this what are the ???
165
the ??? can be sin, cos, tan with a potential - attached
oh wait the theta is 165 right then the ??? is sin, -cos, -tan
YESSSS! good job!
ok so
,,,
\e{align*}{
\6\sin{\0b\theta} &= \sin(\0r{15\degrees}) \
\6\cos{\0b\theta} &= -\cos(\0r{15\degrees}) \
\6\tan{\0b\theta} &= -\tan(\0r{15\degrees})
}
yaaaaaaa!
now we wanna calculate those on the right
do u have any ideas on how to calculate something like sin(15 degrees)
do i take the inverse of sin then multiply it by that
no haha that doesn't work
aw☹️
as a hint, think of sin(a + b) for example
can i just plug in sin(15) into my calculator lol
idk ur teacher but i dont think they want u to do that 😅
,align
\6\sin{a\pm b} &= \6\sin a \6\cos b \pm \6\sin b \6\cos a \
\6\cos{a\pm b} &= \6\cos a \6\cos b \mp \6\sin a \6\sin b
oh☹️
you can use this here tho
do u know about this
no this is my first time seeing this
mmmm
tytho
what trig identities do yk
we didn’t learn trig identities yet
i think we start that next monday
hmmm okii i guess u cant do this one manually then
you can use a calculator then
ooooooo yay ok !!
TYSM for the help 😊
no worries good luck!
sorry I’m like terrible at math lol
tyyy
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nah it's ok
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for a, do i just take the f_x (x - x0) + f_y(y - y0) equation and do it s and t?
for b, i assume I take an integral, but how to set it up I'm a bit lost
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<@&286206848099549185>
@polar flame Has your question been resolved?
for a
r(2,3,1) + gradient of r(3,2,1) • <x-2, y-3, z-1>
for b
geometrically, what shape does the restriction make? if you understand that, it will help with setting up the bounds
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would P(1-r/100)^n be the same as P-P(r)^n in exponential decay when p is decreased by r%, n times
are you asking if P(1-r/100)^n = P-Pr^n? if so, no
the second one factors as P(1-r^n) with the ^n inside the brackets
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i was doing an exercise related with find and draw the domain and from log(y-x^2+4) which they give us the value of 1 (idk in english how its call but in the question we say cotes), the thing is why from y-x^2+4 = 1 it changes to y-x^2+4=10
Guys what's 1+1
2, broken window, 11, window
?
$$\log (y-x^2 + 4) = 1 \cdot 1$$
i think here the base of log is 10 , so the question becomes
$$ \log_{10} (y-x^2+4) = 1 \cdot log_{10} 10$$
if u didnt know then $log_{a}a = 1$
Taking anit log u get
$$ y-x^2+4 = 10$$
JustToPro
i see, in the question is like this
yeah usually log written like that has base 10
unless if base is different , then base is mentioned
if doesnt says anything more
yeah log has base 10 , ln has base e and if base is different then its mentioned
if the exercise was with ln
usually yeah
but in this case it doesn't rlly matter
you'd just get 1*log_e(e) or whatever
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Help with d pls
,rotate
There is an interesting number theory result that if u add up the digits of a number and the sum is divisible by three, then the number is also divisible by three
Might be helpful
Oh wait, my bad, I was looking at e not d.
Well, for it to be greater than 3000, you know that the first digit has to be either 3 or 4 and the last digit has to be either 1 or 3. So how many numbers work with those restrictions. It should just be counting 😭 after this.
@random raptor Has your question been resolved?
Yea I did 2 x 2 x 1 x 2 over total amount
Is that right?
Pretty sure the answer is 6.
Consider 2 case
Case 1 ( first digit is 3):
Then the last digit is 1. So the middle digits are either 2 or 4.
So case 1 has 2 options
Case 2 ( first digit is 4):
Then the last digit is either 3 or 1
So between the last 3 digits there are 2x2 so 4
So 6 total
I think where u went wrong is u multiplied the first 2 rather than adding them
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Ive factored the bottom to (x+1)(x-1), i've got a feeling i need to use substitution, but as x approaches 1, i cant use a standard limit, and so i dont know where to go
I also can't use Lhopitals and only standard limits
can you use the series
You mean taylor series? I believe so but i've had a little trouble understanding it
i cant find other ways of solving it rn, sry
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f(x) can't be increasing if f'(x) = 0 right
it just isn't doing either
i'm so fucking confused
it can be
if f'(x) is 0 at point c
how does that make sense intuitively
if the rate of change at c is 0, how can it be increasing
here shouldn't the increasing interval be equivalent to the interval above
no
acc to the definition
why
if f(x-h) < f (x) < f(x+h) then its inc at X
f(2-h) < f(2)
so inc at 2
okay
