#help-39
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Your algebra looks good
I'll trust that the calculation was right
Oke thank u for help
Is it okay if I can ask u one more question on related rates?
If ur unable to I understand
It's question number 3
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write r in terms of h, replace so you get V = f(h), differentiate and solve
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ā
So u would basically solve for the rate of the radius?
yeah, my bad, thought you wanted the rate of the height
same gist, write h in terms of r, and then replace h by that in the volume equation
differentiate everything wrt time and solve for dr/dt
So the equation would be
dh/dt = 1/3(3.14)(2.5)^2 (dr/dt)?
you made a mistake in your derivative
Huh?
Sorry for missing your question 
Firstly, you want to get volume in terms of r, not height. This is because you are given dV/dt, but not dh/dt
It's oke bro ur good lol
excuse me!?!? What's the triangle projection?š
Ooh wait nvm it just registered to my brain
Basically as you fill the conical tank, the height and radius increase in tandem, looking at this from a horizontal angle (the "triangular" projection), you'll see a 2d triangle slowly growing. The height and base (radius) of this triangle is always proportionate
Oke I was low-key freaking out bc u said h=3r and I'm like where was the 3 fromš
yeah, miswrote that haha, its 4r
Oke so the equation would be like this then?
close, but you shouldn't plug in for r before getting the derivative
cause that'll just give you the volume at a given value of r, which isn't useful for you
Would I take the derivate of 1/3pi?
No, the derivative of any constant (including pi) is zero. You would first write volume in terms of radius, so that would be V = 4/3 pi r^3. Afterwards, you would take the derivative of both sides of the equation with respect to time.
Ooh wait would it be 2= 1/3(3.14)(2.5)^2(4r)?
Always take the derivative before plugging in any numbers (apart from cosntants liek 1/3 and pi) when doing a rr problem
So something like this then?
Did you take the derivative (of both sides of the equation) before plugging in r = 2.5?
I low-key don't know if I did my brain is so slow rn
You first need to find an equation for the volume in terms of the radius r
which you did correctly, V = 4/3 pi r^3
So would the equation be V= 4/3(3.14)(3r^2) before plugging in 2.5?
close, chain rule.
Since you want to find the rate of change of the readius with respect to time, you want to differentiate both sides of that equation with respect to time
since both r and V are functions of time (they change as time passes, duh), the left hand side would become dV/dt (rate of change of volume with respect to time)
the right hand side will become (4/3)(pi)(3r^2)*dr/dt
Ooh yeah that rights
the dr/dt appears because of the chain rule, since you're differentiating with respect to t, not r
Now I would plug in 2.5 for r and 2 for dv/dt and solve algebraically?
yes, that would give you dr/dt, which is the rate of change of the radius when the radius is 2.5 and rate of change of volume is 2
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Prove that every countably infinite set has a well-ordering.
I have trouble to prove this problem.
what does countably infinite mean
a countable set with infinite elements
I have a Theorem that: Let $\preq '$ be a well-ordering on the set $B$. Suppose that $h: A \rightarrow B$ is one-to-one. Define the relation $\preq$ on $A$ on by $x \preq y$ if and only if $h(x) \preq ' h(y)$, for all $x$ and $y$ in $A$. Then, $\preq$ is a well-ordering on $A$.
Silly Cyn
Compile Error! Click the
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gimme a sec..
Let $\preceq '$ be a well-ordering on the set $B$. Suppose that $h: A \rightarrow B$ is one-to-one. Define the relation $\preceq$ on $A$ on by $x \preceq y$ if and only if $h(x) \preceq ' h(y)$, for all $x$ and $y$ in $A$. Then, $\preceq$ is a well-ordering on $A$.
Silly Cyn
This is a hint to prove that problem.
what does it mean to be a countable set
A set A is countable if and only if there exists a one-to-one function $f: A \rightarrow \omega$.
Silly Cyn
So {1} is countable?
Since every finite sets are countable, yes.
true.
So there is a function
Oh no
That isnt even nessesary with the form the hint is written in
Surprisingly, only a textbook provides that theorem as main hint to prove.
So with this
yes
Do you have a well ordering on that?
Yes
it does.
So can you see how can you use it here?
It is still vague..
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We learned statistics a while ago in maths, and I can never remember the stuff because I feel like I canāt logically understand it like I can with the other topics.
For example, why is it that the normal distribution should be e^-x^2 (ignoring the constants, I figured out where they come from)? I saw a cool 3Blue1Brown video about it, and while it was interesting, I donāt feel like it gave me a wholistic understanding of where it actually came from. There are also formulae to do with like the error of a proportion and mean that I donāt fully understand, but Iām guessing Iād be able to figure them out if I knew where the e^-x^2 came from. Any help is appreciated, or resources youād recommend!
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those who know
rude
what is rude, exactly? I'm confused by what omega said, but not seeing how rude.
we'll never know š
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ok literally
how do you not get an erf when u try to solve the LHS
okay
i give up
lol
someone help me tmr
ā¤ļø
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Well you get erf but they're asking for an upper bound for that.
Lhs is 1 - erf(a), of course
ack
how are we supposed to know that without a calcualtor
or are we just supposed to recognize it
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I was having an argument saying thereās a pretty easy way to do this
Is this handwavey at all?
Iām legit getting brainrot because one partyās saying it doesnāt work and to say Ax=0 has a non-trivial solution (vector of all 1s)
For reference, I got asked this, I have the solution to the matter Iām just being told my way doesnāt work and it makes 0 sense to me at all how it doesnāt work
it does work absolutely, well I would say that the columns are linearly dependent since you added up the numbers in each row to be 0, so each entry of the column sum becomes 0
Thatās exactly what I was thinking
if you would use the same permutation in every row, then summing the rows does not give 0, but summing the columns does
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,tex .exp rules
riemann
3 = 6/2 and 6-1 = 5
this is using the quotient rule?

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Hello I wanted to ask if this is correct
Expand the function š(š„)=š^(š„^2ā1); š„ā[0,1] in the neighborhood of š„_0 = 0 into a fourth-order polynomial and estimate the maximum error between the function š(š„) and the fourth-order approximation polynomial using the Lagrangian remainder.
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why is b negative
if you move up parallel to the y-axis from point b you go from level set 5 to level set 4, which is a decrease
Yeah I was gonna say look at reasoning you did in question below that
Or what is D_yf(b) equivalent to
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how would i solve this?
when i find the divergence, and sum up all of the partial derrivatives, they equate to zero
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,w divergence [x^2z,4-2xyz-3y+x^2y,3z-x^2z]
You appear to be correct on the divergence
The divergence theorem only applies to closed surfaces, the surface you are asked to integrate over appears to be open. If you can relate the surface in the question to an appropriate closed surface, then you may apply the div theorem
how would I make the surface in question closed?
By attaching any surface which shares the same boundary as the original, there's an infinite # of ways to do this but for example you could consider the whole sphere instead of just the hemisphere with y>0
Most ways of choosing this surface will not make the computation easier, but there should be an 'obvious' surface to chose which does make the computation easier
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why did the restirction on the integral change?
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how do I solve this?
<@&286206848099549185>
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hi
do you have any question?

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how do you do this question? (correct answer circled) how do you find function f
do you know the average value of an interval formula
is it mean value theorem
f(a)-f(b)/a-b = f'(c) theres this formula
it's basically the same as the mean value theorem for integrals
not for derivatives
yes
so what's the avg value of the function over [2,4]?
(using the formula ofc, we already know its actually 3)
do you just do this
ohh wait the integral is just the area
yep
why did they say f(x)ā„0 for all x in [2,4] in the question though (is that relevant to solving the problem)
it's probably just to remove any unnecessary complications with sign of area
if f(x)ā„0 for all x in [2,4] then we know the area is greater than or equal to 0
and we don't have to worry about signed area of anything ig
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Hey Iām fish. Im 21 and trying to study up for my Picat verification test. I need help with some factoring problems, specifically
5x^2+20x+30
Im literally on the verge of tears please help
Heyo, first to remember is deep breaths, you got this!
are you familiar with what a discriminant is in math?
You can factor out a 5 to start well
No I am not
That's alright! Here's the formulas
D is Discriminant, using it we can solve most problems where there is x^2
Very cool so leave brother
Alright
Sure
Alright gotchu
Will this method not work for this equation?
The first thing we gotta do with 5x^2+20x+30 is equal it to 0
Alright, whats the most efficient way to do this? Imma start on a new piece of paper
||this has no roots||
No, since we have x and x^2
Basically an equation that has two unknowns, X and x^2
This means we have to use either Discriminant or another method which doesn't always work, so I'll show you how to use D
The most efficient way doesn't always work, so it's best to practice with D a bit to know how to do it quickly
Alright, Iām listening
So we've got this now
5x^2+20x+30=0
Another thing worth mentioning, we always put a x^2 first, then x, then the number (when dealing with such problems, where there is X and x^2)
This is called the commutative property
We've already done that so we're good to go
If you already know which value is a b and c, then please write them out here so I know we're on the same page
If not, lmk and I'll explain how to find them
So the B value would be 20x and the C would be 30 yea?
Yep!
Awesome
And value a iss
5
Yep!
Or would it be 5x^2?
Getting to that part, the important thing is you already know where to look to find out what is a b and c
Going back to this
We see that D=b^2+4ac
When dealing with a b and c, we only take the actual number, not x
So for example we have b=20
(If this was a case where nothing was next to x, not to worry, we just use/know that one is next to x; but this does not apply to our problem as each value has a number next to it)
Yes, we're looking for D
So the end bit of that equation would come out like
0=20x^2+4ā¢5ā¢30
Fucking asterisks bleh
No need to rush!
This is what we've got for now
Right now we're at putting in values (numbers) instead of a b and c
Oh! Okay so the equation we have no is literally just like that
Now we know that when taking a b and c, we don't take x, just the actual number
So what would we take for b again?
20
Okk
-4 is part of the formula, so we just rewrite it
We've got to find out what value a and c are
What does a=
And
c=
A is 5 and C would be 30
Yep!
Or devide everything by five first
400
Yes, there are many ways of solving equations, this is the one I decided to show!)
Ah sorry
Yep, and 4ā¢5ā¢30?
No worries, thanks for looking out)
600
Yep
Ohh okay
Hopefully this makes sense
We've just calculated 20^2, and 4ā¢5ā¢30
The minus stayed from the formula of D
So what does D equal from here?
Yes yes, I understand where weāre getting that from
200
So our D value is 200
Sorry
-200?
No need to apologise
Yep
Okay, awsome
Lemme jot it down and find it, one moment please
Well, just a moment^^
We see that the formulas for x both require the square root of D
And our D is..
-200
Mhm! So we know that our D is less than 0
When D turns out to be less than 0, the problem has no solutions, since we cannot find a normal root for a negative number
And we need the square root of D to find x1 and X2, which we cannot do (get the square root)
So in the answer, we'd write like so:
This symbol means that there are no solutions
Sometimes yes, there are problems that don't have solutions!
If this was a bit confusing, we could try using the other method, but we'll end up with the same outcome (no solutions)
Well
There wont be an option for no solution on my test, I took the practice and the answer option that it shown as correct came out as
5(x^2+4x+6)
Iām guessing it was to simplify š¦ Iāve been told by like 20 people I have to factor the equation to get the answer and ive been so lost
No wonder I couldnt figure it out
Alright, so you don't get how we got this, right?
Let's look at our equation
5x^2+20x+30
This part is a bit tricky
What do 5 20 and 30 have in common
(Clue: the smallest number apart from 1 they're divisible by is..)
we've got to make sure it's a whole number
So if we divide 5:2=2,5 (not a whole number)
Oh shit yea youre right
Well then it would be 5 correct? Since 5 isnt a prime number
Yep!
From here, we can put 5 in front the brackets
Doing so means everything in the brackets has to be multiplied by what's outside of the brackets
Remember the ^2 only applied to x
Yep
So 5x^2:5=
Basically if we take away 5 from both sides what are we left with
Everything is correct apart from 5(5x^2)
Hm okay so can we rewind a second. Im a little lost
Weād just divide 5 by itself
Yep
So we realise that all the numbers are divisible by 5, meaning that's why we put 5 in front of the bracket
Now that we did that we have to divide everything by 5
So we have 5x^2 which we need to divide by 5
(See picture I attached)
Ohhhhh
Yes! That leaves us with...
(If we completely remove 5 from what I wrote we are left with...)
Okay I see what you mean
It leaves us with 1
Iām going in the complete wrong direction arent I?
It leaves us with 1x^2
We usually don't write the one, since we know that multiplying anything by one just gives us the same value
Which would mean
Yep
And by putting it into our bracket it looks like so (since we just take away the one):
Oh alright yea
Divide it by 5
Yep!
4x
Yess
Lemme take some notes, Iāll read the next but momentarily
Alright no worries!
And our last number in the bracket would be...
6!!
It does! A lot actually
Glad I could help then
And will this method work with every equation I have to simplify?
Yep! You just have to figure out what all the numbers/values have in common
And if they dont all have something in common then it is unsolvable! Awesome thank you so much
Well you've got to be careful with that one
I'll set an example one sec
Okay
Let me know if there's a part that confuses you here
What I mean to show by this, is that it doesn't always have to be a number
It could be a value, such as x
In this case, x^2
Hm
Lemme look it over
Okay so
X would be set to 1x^2
Since you dont show the number when you have a lone variable
So it would be 1x^2ā¢3=3x2
My A value would be x^2
=3x^2 yes
What are you trying to solve it by?
The same method you showed me, so that way I can understand why it wont work
We can't use Discriminant here, since we don't have a 'c' value
This is just for simplification
Not solving/finding solutions/roots
Okay, so how would you solve the third equation? That seems the easiest to solve
Simplify *
Oh those aren't the equations they're just steps to show how I solved what's next to 1)
So sorry if that caused confusion!
- is that base equation (first step, rewriting the equation)
- second step (putting what's in common in front of the brackets)
- third step (calculating)
Would you be opposed to a voice chat? I feel like it might be easier for me to grasp some of this if I heard it
I'm not opposed to it however Im not sure for how long I can chat
Thats okay! Id just need a little to understand
Alright one second
Take your time Iām around
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Okay so we back, were struggling we absolutely braindead
Gotta solve linear equations, and the one im working on now is
5n-3=7n-5
If anyone can help me please ping me. Voice calling preferably, but text will work too
I dont know where to even start, and I know if I look it up on google it will just tell me how and not explain how and why to do it that way
could also help here but i only got abt 7 mins
Nono, youre all good!! You did plenty for me and I appreciate your time so much
You get some rest or get ready to go to work or whatever you gotta do
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can someone help me how did they get that last statement ?
@rapid halo Has your question been resolved?
<@&286206848099549185>
man, x^6 gives you 1. revise complex numbers
no ik that but like where are the rest of the terms and how did they take the 6 common
from this 3B1B video btw, https://www.youtube.com/watch?v=bOXCLR3Wric
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So I have trouble understanding this inequality
(6x-x^2) >= 0
I tried to factor it as
x(6-x) >= 0
and then proceeded to draw this to see how I can control x, but the book says that the left side is positive when x is an element in [0, 6], and not the other way like I did
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Why AB and BA are similar if one of them is invertible? Is there any intuitively explanation? Why is it only "one of them" instead of " Both of them"?
recall the definition of similarity
I know the definitionš„²
then which one is it?
Hmm wdym which one?
S^-1 P S = Q?
Yes
rbit
suppose B is invertible, what would you choose for S?
$B^{-1}S^{-1}ABS= A$
is that if A is invertible?
Cryolite
but no I mean, choose some value for S so that the equation holds
Ooh uhm S might be B^-1
right
then it cancels the B on the right and introduces a B on the left
and if A is invertible instead?
S will be A^-1
almost
$S^{-1}ABSA^{-1} = B$
Cryolite
Ok S will be A
right
so in either case, be it A invertible or B invertible, you can satisfy the equation
if both of them are invertible, it doesn't really matter which one you choose
Btw is there any geometric interpretation for this maybe?
@fringe raft where did you goš
not that I can think of rn
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prograce
!xy
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
@rapid wagon Has your question been resolved?
It's not in English
"Prove using the definition of boundedness and limit only that the sequence $a_{n}=n^{((-1)^n)}$ is not bounded and yet does not approach an infinite limit"
Is the exact translation
Oh omg
prograce
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Omg
Anyeays I proved it doesn't converge to infinity I'm struggling wjth boundness please
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I'm not 100% clear on what they're asking me to do, could somebody possibly walk me through the first row in the table? :o
in the text, the 2 solutions of f'(x)=0 are calculated.
Those points are where the function f changes monotony.
oo right, I remember the professor talking abt that
The points are 5 and 9; that means between -inf and 5, for example, function f has same monotony.
either increasing or decreasing.
f is increasing if and only if f' is positive on that interval.
decreasing <=> f' < 0 on interval.
you take an x within interval; compute f' (x); see sign (+ or -); say the behaviour.
since there's 2 roots, there's 3 intervals. if there were n roots, there would be ... intervals
aaaa ok, I can work with that. Thank you :)
You're welcome.
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any idea on what method to do this?
whem in doubt use l hopital
my school doesnt allow lhopital š
um
try a substitution to get rid of all the roots
and see if you can factor amything
alright
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im struggling with normal distribution
Result:
3.3333333333333
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Solve the trigonometric equation sin(3x) - sin(6x) = 0 within the domain of [0, 2pi]
can someone help me w this
i got to
3sinxcosx - 6sinxcosx = 0
i can factor 3sinxcosx
3sinxcosx(1-2)
so u left with -3sinxcosx
what exactly do u do next
well, if that's the result you got, then that happens when either sinx or cosx is 0.
since it's a product
-3sinxcosx=0 if and only if sinx=0 or cosx=0 (since -3 is definitely not 0)
although I am not 100% sure the result should look like that...
did you write sin(3x) as sin(2x+x), used the formula, and switched every sin(2x) and cos(2x) with the correct formulas?
oh
isnt sin(3x) = 3sincos
š
afraid not. sin(2x)=2sinxcosx, but that's simply because of the formula sin(x+y)
oh right
it doesn't happen to look exactly same for sin(3x)
but it can be deduced.
eventually you should be able to express sin(3x) and sin(6x) using only sinx and cosx.
so for sin(6x) i need to do sin (3x+3x)
yea, that's the quickest approach, since you'll already find formula for sin(3x)
will also need for cos(3x) before sin(3x+3x)
sin(a+b)=sin(a)cos(b)+sin(b)cos(a)
cos(a+b)=cos(a)cos(b)-sin(a)sin(b)
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So for i1 I make y and z all the opposite signs?
And i2 all y and z the opposite sign?
@spring crystal Has your question been resolved?
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Is this the correct notation?
Yes
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guys how is 7pi/5 - pi = to 2pi/5
pi = 5pi/5
pi=pie
3=6
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Why mine wrong
did you substitute back in u = e^x
and its 1/2 u not 1/2 x
how did you get rid of cos^2?
its correct, its cosine double angle
yup
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heres my work:
thnxs ):
like even if i converted that answer to kj its still wrong š¦
the answer issupposed to be 79.8 kj/mol
can you rotate and send?
Ok sry about that
@gusty prism Has your question been resolved?
š
you calculated the energy of a single photon
to get the energy of a mole of photons, you have to multiply by avogadro's number
@gusty prism Has your question been resolved?
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If a number ends in zeros, the zeros are called terminal zeros. For example, 520,000 has four terminal zeros, but 502,000 has just three terminal zeros. Let $N$ equal the product of all counting numbers from 1 through 20:$$
N=1\times2\times3\times4\times\dots\times20.
$$How many terminal zeros will $N$ have when it is written in standard form?
938c2cc0dcc05f2b68c4287040cfcf71
So youāre given lots of factors of N.
What kind of factors do you expect might give a 0 at the end?
hi guys, Could someone help me with this exercise?
@stoic imp Has your question been resolved?
yeah maybe find the prime factorization of 20!
how?
help me raphaelo
donatello
well let's see, we can write
1*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*20
actually it will be pretty annoying to find the whole prime factorization
but we only need to collect factors of 2 and 5
how to do it
in 1, there are zero factors of 2
yes
in 2, only one
yes
in 3, zero factors of 2
in 4, two factors of 2
in 5, zero factors of 2
in 6 one factor of 2
in 7 zero factors of 2
in 8 three factors of 2
do I need to count up to 20?
or use wolfram
in 9 zero factors of 2
in 10 one factors of 2
in 11 zero factors of 2
in 12 two factors of 2
in 13 zero factors of 2
in 14 one factors of 2
in 15 zero factors of 2
in 16 four factors of 2
in 17 zero factors of 2
in 18 one factors of 2
in 19 zero factors of 2
in 20 two factors of 2
there are 2 in 20
,calc 0 + 2 + 0 + 1 + 0 + 3 + 0 + 1 + 0 + 2 + 0+ 1 + 0+ 4+0+ 1 + 0 + 2
Result:
17
i think you missed the first two
they will all have 0 except 5, 10, 15, and 20
okay, good
how many in 5, 10, 15, and 20?
5 has 1 factor of 5
10 has 1 factor of 5
15 has 1 factor of 5
20 has 1 factor of 5
four in total
so 20! = 2^18 * 5^4 * x
with some number x that isn't divisible by 2 or 5
,calc 2^18 * 5^4
Result:
1.6384e+8
so 20! = 10^4 * y
with some number y that isn't divisible by 10
$20!=2^{18}5^{4}x=2^{4}5^{4}2^{14}x=(2\cdot5)^{4}y=10^{4}y$
Axe
where did 2^14 go
y ate it

Result:
10000
yes so there are 4 zeros

š
.solved
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Yea just keep solving
Yep, just make sure you add the +C *right after *the integration
1/arctan does not equal arccot
Use arctan arcsin and arccos from now on so you didn't confuse yourself
I did the reciprocal
Yes I see. 1/thing is reciprocal of thing
So where I do that
You're missing the +C here
You didn't do this appropriately
i added it after
but when im doing y(0) im getting 1=undefined
i added the step after that
That's incorrect then
?? what
Read this more carefully
ok so its -c
What is "it"
You need parentheses
Then you're not doing this
bruh i dont get it
That's not correct
This was your last correct step
Just plug in the initial condition there
whats wrong with the recriprocal
also i thought i had to get y by itself so i did that
Result:
1.5
Use parentheses to fix this
And the identically placed parentheses to fix this
You can do that after finding C
im confused what u mean
Did you understand this
so i change c to 1/c?
No
Do this
ok its y=-1/(arctanx+c)
so its 1= -1/c?
c=-1
so the answer is y= -1/(arctanx -1)
??
,w solve dy/dx = y^2/(1+x^2), y(0)=1
Is that the same
they're the same actually!
try multiplying top and bottom by -1
(-1)/(-1) = 1 so you are multiplying by 1
Just because functions look different, doesn't mean they are
Use plotting software to check your answers if you're not familiar with the algebra
Desmos and GeoGebra my beloved
but this appears really really often
@spring crystal Has your question been resolved?
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Hi do i have any errors in my calculations?
I don't see how anyone can answer your question without much more context
Oh like in my conversions - are my conversions good.
im getting an error in sig figs i think
i mean scientific notation
i think wolfram or something of that sort would do you better.
@lusty pier Has your question been resolved?
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Equilateral triangle ABC, AH is perpendicular to BC at H. M is a point in ABC. MP, MQ MR is perpendicular to BC, AC, AB at P, Q,R. Proves that MP + MQ + MR = AH.
I don't have an idea on how to do it.
this is vivianis theorem
i have an idea but im not sure if its the solution
therss many proofs online
nevermind you can do vivianis theorem then
one way is by segmenting the large trisngle into 3 smaller ones, with EQ ER EP as their heights
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could someone explain how to do this question ?
i did part a and b im having trouble with the last two
@fierce snow Has your question been resolved?
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Let $a<b$ be real numbers, and consider $T= \Q \cap [a,b]$. Prove $sup(T)=b$
Ę(Why am. I here)=I don't Know
why should you need cases?
Q do not verify sup propriety
what is the sup propriety?
I know, I mean if b is in Q than the largest element in the intersection is b
That was just a thought
Least upperbound proprety
So Here I just attempt to use the defn of the supremum ?
yes
rationals dense in reals.
noted
planning on using that here
thanks
$Sup(T) <b \implies x<sup(T) ,\forall x \in \Q \cap [a,b] < sup(T)$.However, as the rationals are dense in $\R$, , there exists a rational, between $sup(T) and b$ , which would lie in the intersection. Therefore $sup(T) \geq b$.
Ę(Why am. I here)=I don't Know
Not sure what to do from here
I mean I know I now have to show all upper bounds are more than 2
just not too sure of how to do that
<@&286206848099549185>
did you show is an upper bound yet?
yeah, here
that doesn't show b is an upper bound
hmm
don't think too complicated about it
b is by definition an upper bound.
yes
using this idea, you can also do a contradiction. assume that b is not a supremum and that there is a different supremum, say c. then c<b. then use the density to show that there is a number in between c and b, contradicting that fact that c is a supremum
oh yeah, forgot that
Let $c$ be the suprmeum, $c<b$, but by the density of rationals, a rational can be inserted between $c$ and $b$ , but as this rational is less than $b$, it's in the interesection, contradicting our assumption that $c$ is the supremum, thus there is no upper bound less than $b$, and b is teh supremum
Ę(Why am. I here)=I don't Know
this.
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\textbf{3.-} Find all $z \in \mathbb{C}$ such that
$64z^3 = (1 + \sqrt{3}i)^7 \overline{z}^2$.
938c2cc0dcc05f2b68c4287040cfcf71
Do you know angle and magnitude?
angle is argument
ok so suppose $z=(r,\theta)$
Arnavutkƶy
then can you tell me what $z^3$ is?
Arnavutkƶy
in terms of $r$ and $\theta$
Arnavutkƶy
yes
,, z^3 = |z|^3 \left(\cos(3\theta) + i\sin(3\theta)\right)
938c2cc0dcc05f2b68c4287040cfcf71
,, z = a + bi \ |z| = \sqrt{a^2 + b^2}
938c2cc0dcc05f2b68c4287040cfcf71
right? or am I missing something?
yes
i will use coordinates to represent this to keep track
so if $z=(r,\theta)$, where $r$ represents magnitude
Arnavutkƶy
Then, $z^3=(r^3,3\theta)$, right?
Arnavutkƶy
sure
And $64z^3=(64r^3,3\theta)$
Arnavutkƶy
Btw using these parenthesis is called polar coordinates and is considered common notation
Okay, can you tell me $(1+\sqrt{3}i)$ in terms of angle and magnitude?
Arnavutkƶy
magnitude of that is $\sqrt{1^2 + 3} = 2$
938c2cc0dcc05f2b68c4287040cfcf71
the argument, idk
Think of inverse tan
938c2cc0dcc05f2b68c4287040cfcf71
ty
Np
Re(1 + sqrt(3)i) = 1
Im(1 + sqrt(3)i) = sqrt(3)
both Real and Imaginary parts are in first quadrant, so this is correct
do you know what $\arctan(\sqrt{3})$ is?
Arnavutkƶy
Ļ/3 + 2kĻ with k in Z