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428200 messages · Page 489 of 429
Yep, that simplifies further
+2x
Oh ya
Then the h cancels out on top and bottom
Yep
Dam
That's nice
But some proofs use h^2=0
As an approximate
Would that mean
Those proofs are wrong
Which proofs
wait i read somewhere, that it's approximations but with a really small error(?)
@bold hinge s point is also convincing
heres the source im not sure since im no mathematician i just wanted to understand this
https://www.askamathematician.com/2014/08/q-since-it-involves-limits-is-calculus-always-an-approximation/#:~:text=Calculus is exact.,always feel a little incomplete.
wait which point
His way of defining derivative as a limit
And solving a limit instead
i dont understand what this means
I think u haven't been taught limits uet
yes i jus started this subject T__T
It's taught later ig
wait, what do i need to learn to understand this please
Limits
like...how?
U need to understand limits which is also a part of calculus
alright, what are limits and how do they relate to the question? since all i know is that there's a limit, we have to get as close to it but not actually be the limit(?)
There are many ways to solve a limit
One way is by factoring
Wait
I am also getting confused
💀
How do we even know that limit isn't a approximation
The moment we cancel out h we know that h=0 and 0 dosent cancel out
How do even show it approaches
Some value
By factoring
oof endtimes gotta get back in here
Ya
it's not an approximation because you let the error go to 0. emphasis on "go to" rather than "be equal to"
the whole point of taking the derivative is finding the slope of the tangent line at a given point on a curve
here's an example problem for you:
you are in a car undergoing a constant acceleration. your position as a function of time is x(t) = 5t^2. how fast are you going after 2 seconds?
its not an approximation because you let the error go to 0
How are we approaching something
When we just factored it
And thought that 0/0=1
Even when we use lhoptal while computing limits as x approaches 0 we compute the function at x very close to 0
Not exactly at 0
We don't approach anything
We just compute at the place closest to 0
Yet not 0
Which again brings back dx
we never said that 0/0 = 1
Then how did we cancel out h
And h=0
right, and that's why we have to take the limit
for all h arbitrarily close to 0, h/h = 1
yes
Which is dx/dx and not 0/0
?
I think I got it in a different way
Nvm
x/x approaches 1 as x approaches 0
This way
Ig
yes
that's the same statement
lim x->0 x/x = 1, yes
Yup makes sense
when we take limits, we do not care about what the function actually does at that point
it doesn't matter what 0/0 actually is, or whether it is defined
the only thing that matters is the behavior of the function in some arbitrarily small interval surrounding 0, but not at 0 itself
My point is that " As for values of x very very very close to 0 x/x is 1 " Is not reason the limit is 1 it's because the "x/x approach 1 as x approaches 0"?
And they are different things ig
But ya I am convinced that calculus is exact
these both mean the same thing
No they don't ig
If I think of it very deeply
f(dx) = f(0) [ this is what the first line says ]
While second line says
f(1) = 1
f(0.5) = 1
f(0.25) = 1
.....
Approaches 1
They are totally different
I mean f(0) should be close to f(dx)
f(x) = x/x
we want to find the limit as x approaches 0, so we let x equal 0 and find the limit for some arbitrarily small change in x, dx
f(0+dx) = (0+dx)/(0+dx)
then we have:
lim dx->0 dx/dx
this is how we formalize the concept of closeness, by introducing an error term that we make arbitrarily small
you should look at the epsilon delta definition
And arbitary small brings approximatations
Again
right, it does. but as the error in measurement gets smaller, so does the error in the result
Ya but it will not be 0 or exact
but we are still able to get an exact result in this case because the expression simplifies to a simpler one for all x in the neighborhood of 0
look at the epsilon delta definition of the limit
I am thinking of it in terms of that
Makes sense thanks for ur time
It's always better to think approach in terms of epsilon and delta
Makes much more sense
idk7 can u explain it 4 me TwT i got nothing im too noob
Wait until someone explains to u limits in terms of epsilon and delta
Then it might make sense
I started making silly blunder when I didn't thought of it in terms of epsilon and delta
how far off is epsilon n delta, its not in our syllabus
https://youtu.be/kfF40MiS7zA this is enough don't watch the lhoptal part
Formal derivatives, the epsilon-delta definition, and why L'Hôpital's rule works.
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As I doubt u will understand it
aight imma watch it
lemme jus ask idk7, is calculus approximate or exact? based on what you got from endtimes?
Exact
aight ill take u guys words 4 it till get on the epsilon thing then imma ask again if i dont get it thanks
i think this worked...
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@bold hinge @marble bone can i dm u guys or smth once i get a higher calc degree to ask abt my question again?
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do we have to take log in this question?
or else how to calculate since the first 1 was in 12 but thete is no such option
You have 2⁵ and 2¹⁰, just check which of the options have both
oh i guess i know the answer now thanks for the explaination
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hello what is the hight and width of the triangle to get the biggest surface?
count the blocks
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u are calculating the roots z^1/n so you have n roots, the k is the number of the root
it goes from 0 to n-1 which gives n roots in total
you could try it for example for a 4th root, and when you draw it it creats a square inside the trigonometric circle of radius given by the 4th root of the modulus of the original number
and in general it shows as an n-gon, so you are dividing the circle in n parts
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Hello, I think you forgot the minus sign of u in the first line
well it is there
he has e^ln(u + 1/2)^-1 = 1/(u + 1/2)
it is correct
(that line)
look at the line before that
last line from the first screenshot?
yea
n*ln(x) = ln(x)^n
$\int \frac{1}{-u+1/2}, du =-\ln |-u+1/2|$
leonardogtf
i think i made a mistake in the second to last or third to last line in the first screenshot
oh you mean the line before that
yes, that's exactly what I said 😅
im sorry
ohh
now i see it too
ok will fix it and try again. can i leave this thread open or close for now?
you can leave it open if you will try again
just in case
but when you're done, close it
checked it with a calculator. there is no minus behind the x after integrating. (substitute it with u) <
but i dont get the last step
how do you simplify it like that? 😕
nobody? 😦
<@&286206848099549185>
Rewrite C as ln2 + C, since C is an arbitrary constant, the step is valid
Then combine the logarithms
wdym by
which one i take
ideally you'd simplify as much as possible
ok will try it with the simplified version
They explained it here
Valid meaning the two formulas are equal
@sick crest Has your question been resolved?
solved it
i wrote -ln(|x+(1/2)|)+C but as you can see from the calculator the right integration is: -ln(|x-(1/2)|)+C
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Hi would anyone mind checking my number 6 thank you very much its for my exam in the next few days
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Your number 6 is correct.
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can someone check if this proof is good please
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What is your trouble?
$\lim_{x\to\infty} 4^{-x} = 0$
Remavas
It's quite easy actually, but I'll wait for the op to answer my question.
Consider that you need any function with an asymptote at x = -4, and which does not have a finite limit as x goes to infinity
Hmm
@eternal comet Is it just (x + 4)^x
,w plot (x + 4)^x
Bruuuu
TF?
Seems like it will work
A much easier option
I immediately just thought of $\frac{1}{x+4} + x$
Remavas
Hm
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Thanks! Sry i was sleeping
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Say it?
Is it asking the minimum number of members needed for the condition to yield?
I see
Hint :- Just let the number of members needed to be x
And try to see if u can come up with a formula
Like when the costs at both places are equal
That has to be the threshold
Just looking at the ice rink case "Lizzy would pay $40 plus $18.25 per person" what is a very obvious word we can replace with a math symbol such as (+, -, *, /)
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Just a question, if A Cone and A Cylinder were combined into one shape and I was asked for the surface area, it would be (2 x pi x r x h) + (pi x r x l) but if it were only the cylinder and I was asked to find the surface area, it would be 2 x pi x r x h + 2 x pi x r^2 right
@deep flicker Has your question been resolved?
no, if they're combined you still need to add the area of the base that isn't covered by the cone
Oh yea I forgot about that thanks!
Imma do the first for you
You do the rest
f(x) = 9x-3
Let y=f(x)
y=9x-3
y+3 = 9x
(y+3)/9 =x
Thus f-¹(x) = (x+3)/9
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In -x³ if x=10 do i do it like -(10)³=-(-1000)=1000 or (-10)³=-1000?
It will be -1000.
-(10)^3
-(1000)
-1000
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A company's profit is determined by the function P(x)=-x(x-10)(x-30) where P=profit x=branches operated
Do i first turn -x(x-10)(x-30) into -x³+40x-300?
If so then if x=10 would the answer be -900 meaning the company lost -900 profit?
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A company's profit is determined by the function P(x)=-x(x-10)(x-30) where P=profit x=branches operated
Do i first turn -x(x-10)(x-30) into -x³+40x-300?
If so then if x=10 would the answer be -900 meaning the company lost -900 profit?
that is not a complete question
you have simply stated something about a company
what problem are you trying to solve?
Oh
math questions aren't some random language
they're English or whatever native language you want
just stating
A company's profit is determined by the function P(x)=-x(x-10)(x-30) where P=profit x=branches operated
doesn't tell anyone what you're trying to do or why this matters
If someone walked up to you and said "Apple made over $100 billion last year," you'd be like "okay, why are you telling me this?"
the same applies here
Oh
you do mathematical manipulations / mathematical steps to achieve a particular goal
Sorry
Do i first turn -x(x-10)(x-30) into -x³+40x-300 so i can find out what the result is if x=10?
Or do i just substitute 10 into -x(x-10)(x-30)
again
you haven't stated a complete math problem
To go back to my example about Apple, what you're doing here is saying something like "Apple made 162.75B in the 12 months of 2021," and then asking, "do I write that number as $162,750,000,000.00 or do I write it in scientific notation, or do I subtract 40% from it?"
A company's profit is determined by the function P(x)=-x(x-10)(x-30) where P=profit x=branches operated
Evaluate the polynomial function for x=10?
what is the actual question being asked
like if you have an actual screenshot of it, it would be much easier
okay I hope you realize that this bottom part is very important
it tells you what you actually have to do
just pasting the top part means nothing by itself
would've saved a good 5 minutes if you had pasted the bottom part
Sorry
to do part 1, all you have to do is plug in 10 for x
So no need to turn -x(x-10)(x-30) into x³+40x-300?
If i solve it through plugging in 10 for x in -x(x-10)(x-30) it results in 0?
If i plug in 10 for x in -x³+40x-300 it results in -900?
,w expand -x(x-10)(x-30)
First of all, you have not expanded it correctly
Oh i missed x²
and the x
Second, these are two ways of writing the exact same thing
Ah
Sometimes i solve using both so that i can be sure my answer is correct
Its 0?
So the company doesnt get any profit if they operate 10 branches
yes
And if x=20 its 2000
yeah
And because it says "a company's profit in thousands of pesos..." Its 2,000,000?
Alright thank you
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Like when we intregate nested functions
The derivate of the second one is divided below
🤡
And if we can't whats the reason behind it
Shii
Opposite
idu what u mean
me neither
Blurred
must be a new type of integration

then substitution, afterwards ibp, then partial decompision, and then u have to use a special integral
Isnt there a chain rule for intreagation
Can we use it on log like this?
no
no
do u mean integral of logxsinx
Yes
because log(sinx) is not an elementary function
K thnx for the terms
Will learn about them rn
K
it's big
beautiful
F
it's doable except first term if u don't know special integral Li
this one's a famous one tho
you can creatively use the bounds to find the integral
you dont need to do the ususal indefinite integral then plug in bounds
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shoundnt it be (cos 2 pi/n)^2+sin(2 * pi/n)^2
and not whole sqaure
how is it whole square?
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try looking up de moivre
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hi there i am stuck on proving the statement in blue
i know that for c=1 and n>=5 or 4, the statement is obviously true but how do i rigorously show that?
i tried to work with logarithms but that didn't really lead anywhere
any thoughts?
i looked up a similar proof on mathstackexchange but i am confused by the answer on there
What about some induction? Show that the statement is true with n+1 by asserting that it is already proven for n, and you can show all of it with just one real calculation.
interesting. i didn't consider using induction
actually yeah now that i think about it, this would b easier to prove with induction
but how do i determine when or when not to use induction lmao?
Intuition 
If you have some always-repeating thing, like >, so valid "to infinity", induction is usable. No idea when it makes sense/doesn't make sense to use though.
lol got it
i was having a real hard time proving this directly. been trying it for more than 50 mins smh
but thanks for clearing up the confusion
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this is the formula for the sum of n roots?
that one yes
ahhh
so we jsut used geomtric progression formula and we arrived with this?
cool thanks guys
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Hey there
I have a question in sets theory
It's this one:
"a set A in R will be called bounded if there exists M in R s.t. for every a in A : |a| <= M.
Let B be the set of bounded sets. Prove that B ~ P(P(N))
So using cantor's theorem we have to show 2 one to one functions
one is easy: |B| <= |P(R)|
but the other side.
idk how to do that
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hey can you please help me finding these differential equations
Do you know how to solve a first order DE?
And what form you need it in
Qs 2 3 and 4 give you a good hint towards how you need to manipulate Q1
unfortunately dunno
That seems pretty important knowledge for this piece of homework 🙁
No
can you help me if you have time
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I like this series on DEs. Covers everything you would need to know for first order in A-Level Further Maths here in England - should be applicable to yours too
Basically there is a process to follow and it usually just pops out nicely. I'm not going to do your questions for you though, but I am happy to check your work
I am watching them now
Sounds good
so for the firsy q will I take integral of sqrt(1-y^2)/xsqrt(x^2-1)
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@glossy mist hey! If you are available can you check my question cause I am still struggling
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@elfin hemlock help
read #❓how-to-get-help
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Hi everyone how do i find the partial derivatives of (-15,30) ?
that doesn't seem to be something you can find the partial derivative of
you need a function
can’t i use the definition?
There must be a way since there is an answer
Its 1.3
it seems they want you to estimate the derivative
Yea
so, yeah go to that point and try out the smallest h you can try given your table
What does that mean ?
go to (-15, 30) on your table, that's f(x, y)
find values that are f(x+h, y) for small h that are in your table
What is h ?
some number
I don’t understand
what values do you have in your table that are f(-15+h, 30) for |h| small?
Is -33 good ?
yeah, nearby values are good
Then what do I do?
apply the definition
It gives me 1
how did you get 1
-33+26/7
where did you get 7 from
Its h
h is the change in temperature right?
Is this right ?
this isn't the change in temperature, it's the change in the output of the function
Then how do you find h ?
h is a change in the input
How do i find the change in inpout
-33-(-26) is a change in the output of the function
Whats input ?
what values you put into the function
-15,30 ?
-33+26/-5
=1.4 its still not 1.3
because its smaller ?
well, it's as far apart as the first one
6 and not 7 ?
so maybe it's worth trying out to see as well
(-10, 30) and (-20, 30) are "equally far" from (-15, 30) so maybe both should be used to calculate the result
Was my calculation good ?
The other gives me 1.2
@tranquil oracle do i make the average?
1.2+1.4/2
Ok thanks
Btw do you know how to solve this limit
do i apply the same strategy?
well, it depends on how f is defined
This question is related to the previous
same f as previous function?
try out those difference quotients for big v
i did the same as the last problem but got -0,15
what did you do exactly?
the answer is 0
or technically you can argue physically and say that the answer is undefined
Well last time we dis question a) but we only did half the question only for T
I repeated what u told me and got -0,15 for v
But doesnt f decrease by 0,15 degree for every 1km/h of wind
so why is the answer 0 ?
okay from a "just try out the table" approach, try doing it for bigger and bigger v
because there's the lim v->infinity
so i use f(any T, big v) ?
where did you try it out?
On (-15,50)
Ughhhhhhh i hate this problem
ok
I got -0,1
So we assume it decreases to infinity
To 0
that's what they want you to think
but velocities are capped by the speed of light
so the limit is not defined
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Der
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hello! In the case of the denominators for geometric sequences, you use 1-r in the case that r is greater than one, and r-1 in the case that r is less than negative one? I'm really sorry, but I can't find my notes confirming or denying
i'm not sure what you are mentioning exactly, are you trying to expand out (1/(1-r)) in powers of 1/r?
sorry! to clarify- the sum of geometric sequences
in the formula for that, the denominator?
the formula can be the same in both cases
$\sum_{i=0}^kr^k=\frac{1-r^{k+1}}{1-r}=\frac{r^{k+1}-1}{r-1}$
Element118
wait okay sorry one second just checking bc the answer key alternates using both and I was confused
ohh
okay thank you so much!!
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Hi, i don't get why these two expressions are the exact same.
the result?
Show the whole graph
The function
Like the functions it graphs
Unless you're asking if they're the same exact function
Well yeah I also graphed it, and I'll tell you why
Factor out the 2, but because you're factoring from an argument that is being squared, square 2
And you get 4
Esssentially, you're dissecting the function:
(2x - 1)^2 = 2^2 • (x - 1/2)^2
The other thing you can do is, expand each one and you'll see that they are the same
@lucid bolt you understand exponent properties right
Ohhhhh I see. You factor our the two. But can you write out 2^2 outside the paranthesis?
4(-1/2)^2
1^2 = 1
Yeah
That Also works. Yeah.
Thanks guys. This was very helpful!
you can close the channel if you are done
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No problem
Is this open?
alr
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I'd like the formula and while im trying to answer it, please let me know if im doing my solution right
yes but i want the formula on how to get the ratio
okay im sorry, how do i solve it?
Using ratios
@elfin cypress lmao this dude
thats exactly my problem..
As I questioned, do you know what a ratio is?
yes i do but how exactly will you find the height?
You wanna help, feel free. I got stuff to do
assuming volume is linear in height and base area, then the ratio FigA:FigB will be 2.1:1 since 42.25/20.25=2.1
so the volume of A if B is 50 is 50*2.1 = 104.3
if volume of A costs 216 then volume B wiill cost 216/2.1 = 102.8
did i get it right?
<@&286206848099549185>
Hmm
No no
Let’s do (a) first
It’s actually an interesting question, despite the boring problem context
so i got something wrong?
enlighten me
Honestly I’m not like 100% sure but I’m pretty sure
Okay let’s go on a little side trip
(Gimme a sec)
thank u
Let’s say we’ve got two squares here
The small square has a side length of 1, and the big square has a length of 2. So the ratio between these lengths is 2 : 1, or simply 2.
What are the areas of these squares? @elfin cypress
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hello! i don't know why my answer was wrong. please let me know if there's a part of my solution that i should fix (to be fair, it is kinda weird that the volume was 0...)
@steady salmon Has your question been resolved?
consider 3x+5y+2z for your points
wait where do i use this for??
oh i see lemme check
all of them resulted to 5 :0
how did you get that equation??
well, I tried to figure which plane ax+by+cz=d they all lie on
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$\int_0^{2\pi}\int_0^{\pi}\int_0^{\infty}r^2(C\frac{r}{a_0} exp(\frac{-r}{4a_0} \cos\theta))^2 \sin\theta dr d\theta d\phi=1$
Trenton
I am solving this equation
So normally I will solve the boxed part first :
$\int_0^{2\pi}\int_0^{\pi}\boxed{\int_0^{\infty}r^2(C\frac{r}{a_0} exp(\frac{-r}{4a_0} \cos\theta))^2 \sin\theta dr} d\theta d\phi=1$
Trenton
But my lecture notes solve the outer part first
And I am not quite follow what is happening in the fourth line
Can anyone tell me what happens?
And why can we do that ?
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@tough osprey Has your question been resolved?
from the 4th line to 5th line ?
if so
the outer integral is dr therefore everything that doesn't have a r is a constant to this integral
so he takes out all those terms that don't have a r which is that cos^2 * sin
Ok thank you
Can I do similar thing for this?
yes
Ok thank you, I will continue
Umm can anyone help me to have a look please
You can check by plugging C into your original integral
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@tough osprey Has your question been resolved?
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@tough osprey Has your question been resolved?
Does continuity imply differentiability?
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I guess same for single variable case?
you can rule out several of these by the fact that they are not even true for n=1
ok but is it true that ABCDEG all correct? At least I cant find any counter examples
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✅
Nothing, it says "the answer above is NOT correct" 🤣
Sorry
So I am asking about what is wrong lol
answer above
That is typo for the web page I think
It's not a typo, because if I remember correctly, that site displays your answer above as well
Oic ok
But can you tell me what is wrong in my choice of answers?
No
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If all first partial derivatives of $f$ exist on $D\subset R^n$ and are continuous at $\vec{x_0}$, then does it imply that $f$ is differentiable at $\vec{x_0}$?
Trenton
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If $f$ is differentiable at $\vec{x_0}$, does that implies all first partial derivatives of $f$ at $\vec{x_0}$ exist?
Trenton
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V =ah
But I don’t know what face area are they referring to.
And do I times that by the perpendicular height which is 6+6+6
Ye ok
your cake is composed of 3 cylindrical pieces
find the volume of each and add them up
just as you would find the volume of any other 'composite' shape
Instead of using the volume formula?
Wdym? You will require the volume formula to calculate the volume of each cylinder.
Yes but I mean v=ah
Yes.
That's what Ann said too.
That would work perfectly.
Yh that’s also what I meant ok
Alright great then.
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I don’t understand how to do this question
I subtracted 5 from all sides and then calculated the volume but I’m still getting it incorrect so maybe my technique is wrong
Then what should I do?
Water is filled 5cm below the top
No change with the other two dimensions.
Oh
Imagine a tank, which is not fully filled.
If you're filling a bottle till 3cm below it's limit, do you have empty gaps in the sides or the base of the bottle?
Only the height then
No
That means the change is the height
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@leaden snow
R u free rn man?
sup
I'll post question
Do u mind if i @ u for help sometimes. I really liked ur explanation
But here is the tant from yesterday
cos^2(x)?
does tant not just go to sec^2?
post the full problem
yeah
So I got a thanks to u
but tan is a bit different cause my first is 0 and my 2nd is 1 and my 3rd is 0
@azure magnet You could also find the first few terms using the Maclaurin series for sin and cos
If the derivatives get too nasty for tan
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Wait a min
amn't I meant to divide by n! here
on each term
@leaden snow
I just used a differential calculator
But I gotta divide by N! on each term then????????
@azure magnet
$$\tan(x) = \sum_{n=0}^\infty \frac{f^{(n)}(0)}{n!} x^n$$
So yes, you have to
Oh shit
Navix
You should have calculated
$$f^{(0)}(0)$$
$$f^{(3)}(0)$$
$$f^{(5)}(0)$$
Navix
So one is for n=0, one is for n=3 and one for n=5
thanks
and for
I use the first 3 terms only
right that should work out nicelt
I got one more question for u man
this
so I use I hopital I diff the top and bottem (2nd fraction)
and end up with picospix/1
if I sub in 0 I get the answer to be 1
It seems a bit too easy for 4 marks each roughly (both fractions)
Yeah
L hopital
pi sin pix /1
and u sub in 0
but Idk if the answer is 1 or pi
I wish I could write in latex
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can anyone help me with this physics qn?
@gaunt lake So work is Force * Distance right.
Essentially you want to estimate the area under the curve
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uh yes but how do I estimate it
do I use a triangle?
it also asked me to explain how I made my estimate
so how do I explain why I used a triangle as a formula
@leaden snow
@gaunt lake Has your question been resolved?
@gaunt lake You could use a bunch of trapezoids
or a bunch of rectangles
or a triangle, even
sounds super long 💀
Explain how you decomposed the area under the curve into triangles
For example you could give the coordinates of the points of the triangle
Decompose it into a right triangle and a rectangle below it
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can anyoni confirm if my proof is correct?
STATEMENTS
1. AC bisects ∠A and ∠C
2. ∠ABC ≅ ∠ADC
3. ∠AC ≅ ∠AC
4. ⊿ABC ≅ ⊿ADC
REASONS
1. Given
2. Definition of Bisector
3. Reflexive Property
4. By SSS
is incorrect
∠ACB ≅ ∠ACD
is it
that would be more appropriate
ohh why is it
∠AC ≅ ∠AC
using two letters to denote an angle is also nonsense
oh fuck uh
that's a line right
so there must be a macron on top
ĀC ≅ ĀC
something similae
$\overline{AC} \cong \overline{AC}$
ℝamonov
so i got only two stuff incorrect?