#help-10
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Trying to understand this solution. This is a problem from survival analysis but my issue is with the calculus
I'm struggling to understand how we go from the first red line to the second red line (using integration by parts)
I've tried writing this out in the usual \int uv' = uv - \int u'v notation but I think I'm misunderstanding how to handle the v' (i.e. dS(t))
@mental vector Has your question been resolved?
@mental vector Has your question been resolved?
@mental vector Has your question been resolved?
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allo calc question on the jacobian
change of variables from cartesian -> spherical
heres the math stack exchange post
i had the exact same question
can someone further explain this person's answer?
why can i just take the absolute value of a jacobian?
The sign of the Jacobian is telling you whether or not the change of variables preserves (if the sign is positive) or reverses (if the sign is negative) the orientation of space
like
its the difference between saying
oh frick i forgor
ohh
so if i want to preserve the orientation of space
and my jacobian is negative
i can just take abs() value of it
does it mean that other than the sign, the determinant of a jacobian matrix always has the same value?
even if i move the columns/rows around?
yes
LOL
sorry i experienced brain damage remembering this 

,, \mat[v]{a &b \ c &d} \tss{and} \mat[v]{b &a \d&c}
yes i see u have swapped the columns!
okay but people use | | to denote det, and also absolute value
so how many do you want there 

tis ok iget the msg
,, \mat[V]{a &b \ c &d} \textss{and} \mat[V]{b &a \d&c}
6
big, Big, BIG, large, Large, LARGE
if u r swapping columns/rows in a det u r just changing the sign in the det
i mean it doesnt matter if it gives a negative just abs it
yeah just abs it
i mean yeah you can justify why interchanging columns in a determinant makes it negative
yes its always true
Column flipping is a multiplication by permutation matrix with determinant -1

magical human always answering my q's
whether 2am at night
or 10 am in the morning
wtf
i only answered your probability question the other day
no ive seen u before more
i username changed so u prob dont remember
but remember u
really?
what
like twice more
you remmeber
my old account
so did he 

hes 83 years old
i will go back to studying byebye and ty!!
this is his retirement plan
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Closed by @outer siren
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very 老
HAHhwha

and very wise
yes
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A cone has a radius of 4cm and a slant height of 10cm. What is the perpendicular height?
Use the Pythagoras theorem
@orchid warren Has your question been resolved?
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I started Modulus Functions and I still cant seem to get the hang of it
I dont get why its wrong
Oh i think I do actually
No i dont
I would understand if you cant have negative Y values
as its reflected off X axis the | asdsd |
?
@stuck olive Channel is occupied
Create a help channel and post ur problem
Don't post ur problem in an occupied help channel
And dont forget the 15 min rule
@graceful marten Has your question been resolved?
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@graceful marten Has your question been resolved?
if u gonna draw graph, u will see y= mod( 3x + 4) and y= x will never meet, so there is no solution of this, but if u want to know whats wrong in this solution, then I will say, over here question is wrong, probably it would have to mod( 3x + 4) = mod(x) that make sense, since if u take any value of x then it is impossible to get a positive and negative value of that same x , and this question will also make sense if it was mod( 3x +4) = y , since u gonna get , two straight lines
so in short question is wrong over here
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i know that when 2 radiuses are different the radius of the sum of the 2 series is equal to the smallest of the 2 radiuses
but is this rule still valid in the case when we take a linear combination of the 2 series such as in this case?
please tag me if you answer
im not sure
What happens if you multiply each term by a constant?
Either in the series of a_n or b_n
Does the convergence radius change?
It doesn't
If a_nx^n converges for some x, then multiplying each term by a constant would still converge
is there a reason for that?
I mean, it's just multiplying by a constant...
Not sure how to explain it
If the series converged to L, it would now converge to cL if you multiplied each term by c
The partial sums are c times bigger.
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5(x+y)=xy help pls
what do u have to do with that
x,y are integers?
yes
u'll get x-5Xy-5 = 25
asks for the answer range of x and y in response
@low spade
.
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Does anyone know how to solve this integral. Its from a length of a cardioid curve i applied the formula but im stuck on this integral
If it had a 4 instead of 5 it would be easy but i dont know how to solve it like this
Over the given interval, sin theta > 0
So you can use sin theta = sqrt 1- cos^theta
Try u = sqrt 5 + 4 cos theta
Or just u=5+4cos
Although it may still be impossible with special functions
,w antiderivative of sqrt (5 + 4cos theta)
Oh
F
XD
And this was on my analysis 1 final 😂
LMAO
The integral is definite tho
True
But definite integrals may have nice values
Without standard anti derivatives
agreed
I think the prof made a mistake tho
,w integrate sqrt (5 + 4 cos theta) from 0 to pi
does that look familiar @lilac flame ? i got no clue
Nothing off the top of my head
try taking 4 common from inside the root
What is Ε(θ/2|8/9)
Elliptic something
you would get 5/4 ( an angle in a right angled triangle)
write it in terms of cos
then
Literally all fractions can represent ratio of sides of right angled triangles
yeah so ?
But 5/4 isn't cosine of any real value
yeah it isnt
....
ik
???
...how?
this one is a single term
Do you want to go to C (complex)
So whats c
nah c is that value
5/4
cosine
C is
not complex lmao
Cos ^-1(5/4)?
yeah
mhm
Anyway i think the professor made a mistake there is no way anyone could have solved this
In analysis 1 at least
You sure you set up the integral right
It was question 2
Sory its in greek
But the function is r=1+2cosθ
So i just took the formula r^2 + (dr/dθ)^2
Sqrt
Of that i mean
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@timid silo Have you tried what I told you?
take 2 common from the denominator
Show your work
multiply divide denominator by x^2
@timid silo Stop
Don't give out solutions
sorry bud
I can see where you are going with this, but let's allow him to try it for himself
All good
;-; okay
Good
Keep simplifying
Ok good. Now try to manipulate this, so that you can use the limit of sin(x)/x.
Why is there an x in the denominator at the first line?
And where did the x^2 go to in the second line?
Make sure you didn't forget anything, but yes good progress
Same thing for sin^2(x/2)
That's sin(x/2) * sin(x/2)
I'd say that's overcomplicating it
The trick to solve this limit of adding terms we need is very useful for other limits
A good thing to learn
No i get that
Just asking
Intuitively you may notice that the denominator has a higher degree than the numerator
So you expect it to diverge
So you can't get rid of all the terms in the denominator
So try to get rid of the numerator
Tell you are left with something like 1/x or 1/sin x etc
Also u sub could help
Try to see if you can get rid of the x in the numerator too
You know you can destroy x's using sines
And there are 2 sines in the denominator
So that's nice
You can simplify the x/2 if you want
With u sub
How can u make the limit of sinu/u here
It will be more complicated that way
There is an easier way
Also
U didnt square the 2
Its (2u)²
(Ignore this, I misread)
The constants don't really matter
Just thik of it as u^2/sin^2 u
Now
If it was just u/ sin u, could you do it?
Yes
W8 u need to prove that right?
Only sinx/x is known
Okay
Try diving with something so you can make those limits
Yup
Think of something simpler
If you have (sinx/x)²
Its the same thing right
Its just 1²
And you have the sin²x
Look at the denomination
sin²u same thing
Its the same thing
You just have (x/sinx)²
Just dont look at the ^2
You have x/sinx
And you know x can not be equal to 0 because it is approaching 0
So you dont need to worry diving by 0
If x cant be 0
You can divide by x
And not worry abou it being 0
Try doing it
You have x/sinx
If you divide both top and bottom by x
What is the result
Yes
Can you solve it now?
Yup
Closed by @buoyant gull
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Npnp
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kisnar
try it with x=0 to see that it's not equivalent
monotone increasing or decreasing?
Pain
kisnar
Why are you just turning the e^ into a log
Can you explain the step you're performing here
I saw the equation that you're trying to solve
I swear I replied
discord app gaslighting me
hmm
so I think the way to think about it here is to think about taking the ln of both sides
rather than just applying the definition of ln
then you use the fact that ln is an increasing function
So if x>y, then ln(x)>ln(y)
And in that sense, the inequality really isn't flipping
Very understandable source of confusion though
Yeah that's correct
kisnar
Nice
Wolfram and some other places use "log" as ln
And then specify log_10 when taking base 10
That's because ln comes up a lot more in advanced math then log_10
Yeah it is
I've made that mistake before too
Np!
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by applying l,hospital in these
in the part where you get
"2x+1/1"
how did it turn to 3
woudlnt it be 2 since both derivatives of those ones are zero since they are both constants aswell
why not factor ?
what do you mean how did it turn to 3, you are taking the limit as x->1
(2x+1)/1 is 3 when x=1
im having a hard time
wait
first is x^2+x-2/x-1
then 2x+1/1
so you mean ill only apply the derivative thingy on 2x?
,
yes
yea you can't do that
oh why
you can only apply it when the limit in the num and denom are both 0 or both infinite
in this case that's not true, the denom is 1, you can't apply l'h anymore
no i mean (2x+1)/1 is no longer 0/0
it's 3/1
which is the limit
you have to stop applying l'h when you get something that's not 0/0
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hello idk the English term of this subject but i need to know how to solve these 2 tasks
@crude jasper Has your question been resolved?
What you refer to as route is known as a line segment in English.
,tex $$\triangle SA \prime B\prime \sim \triangle SBA$$
@atomic umbra
(This is for part A)
SB’ corresponds to SB the same way SA corresponds to SA’
SA/SA’ = 4/6
Therefore, SB/SB’ 4/6
SB’ = 6 * SB / 4
SB’ = 6 * 5 / 4
SB’ = 7.5
The length of SB’ is 7 cm
@crude jasper Has your question been resolved?
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I did it wrong but how am i supposed to do it
It wanted you to graph both lines and see where they intercept
Put them into the form y=mx + c
do both lines meet at 3,-4?
the line i drew is y=4/-3x +0
and the second one is y=5/-3x +1?
Nearly
+1?
-1?
since its 3/-3
so they meet at -3,4?
would this be the correct graph?
would -3,4 be the solution?
would it be (-3,4) or [-3,4]?
ok
thank you so i think my mistake was mostly a silly mistake and i only did one of the lines
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i got the value for F'(x) right, but im not sure what to do for the other parts
so what can you tell about first derivative
what do you mean?
like what does F'(x) tell you
or you know what
because first derivative is slope
and its increasing
the slope has to be positive
so F'(x) has to be > 0
you just solve for x
yeah
oh wait
i see what you mean
oh wait
so if you graph it
you will notice there is a VA
so what you will do is try to figure out where that is, which is pretty easy, and then find the interval from there
vertical asymptote?
yeah
isnt the VA at 1/3
oh ok
thats the answer?
oh oop
aren't you supposed to type infinity instead of inf or is that acceptable
oh im dumb
its greater than 6
oh
so it would be 6 to infinity
so [6, inf)
yeah
what about the last one though
is it none
oh yeah
it is
thank you foryour help!
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Is there a way to factor $$ x^2 - 17x + 72 $$?
JusticeIroquois
8 and 9?
yes
what do I do with the -17?
ah, I see it now
I knew I was having a big block here. Thanks
$$can it be either (x-8)(x+9) or (x+8)(x-9)$$
JusticeIroquois
@timber osprey Has your question been resolved?
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Can someone help me with this?
where is the question?
do you know how to move a graph on the x axis?
Kinda
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Help with part ii Im stuck.
@grizzled perch Has your question been resolved?
<@&286206848099549185>
are you using power series for part (ii)?
i mean here
Yes
that's a good approach
if you continue with the remaining 2 fractions with power Series up to x² term, you should get the answer
I want to ask about the 4(2-x)^-1 and 8(x-2)^-2
How do i bring out the 2 properly
i see i see
4(2-x)^(-1) need some specific alegebra, while 8(x-2)^(-2) youll need differentiation
and sorry for the slow reply, I'm on the streets
its alright
I can't read a thing on the screen with the bright sun lol
is it alright if you show me how?
i just realised (x-2)^-1 i cant rotate the sign because its not commutative
oops
yes, finally some shade for me lol
4(2-x)^(-1)
2(1-x/2)^(-1)
and then
8(x-2)^(-2)
= 8(2-x)^(-2)
=2(1-x/2)^(-2)
and do you know the power series for (1-x)^(-2)
wait we call it binomial expansion not power series i never learnt power series before
i see
so 2^-1 is 1/2 and i multiply 4 by 1/2 and it becomes 2?
but i bet you have learnt that expasion for (1-x)^(-2)?
correct
yes im fine with the expansions just confused with the algebra
i got it now thank you
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not sure how to do this
$\frac{\orange{\frac1b-\frac1a}}{b-a}$
hayley!
simplify the orange part into one fraction first
i think i may be the opposite of a math prodigy
bc i cant figure out how to do that
:D!!
the common denominator would be ab
.
i keep thinking
they gotta multiply by the same number for some reason
idk why
a/ab-b/ab
/
b-a
okay so if we combine those two orange ones together?
a-b/ab
$\frac{\orange{\frac{a-b}{ab}}}{b-a}$
hayley!
we can write this as $\orange{\frac{a-b}{ab}}\cdot\frac1{b-a}$
hayley!
yes
and then a-b and b-a have a very special relationship with each other
hmm
how about you try some examples
pick random values for a and b
and calculate a-b and b-a
no, not multiplyint
oops
do you have a theory as to the relationship between a-b and b-a?
opposites sure, we might say in math that one is the negative of the other
which we can write like
a-b = -(b-a)
can you use this to finish simplifying this expression?
maybe?
i do not trust myself with math atp
if that isnt it then no idea what it is :DDDD
yes, that seems to be correct
this comes up a lot btw
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How to proof this? Is it true
Ok, I am trying to find the therom to proof it
Ok i got it
Thanks a lot
How can i use modular arithmetic to get the remainder 37*16! - 1753^99 is divided by 17
this is fun, what have you tired?
@grizzled lagoon Has your question been resolved?
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excuse me
can someone plz explain what my teacher did for this proof
he used a conditional statement
Which part is unclear?
can u walk me through it?
to be honest all of it looks confusing
why did he do x+y - 2sqrt(xy)?
\begin{align*}
\frac{a + b}{2} & \geq \sqrt{ab} \
a + b & \geq 2\sqrt{ab} \
a - 2\sqrt{ab} + b & \geq 0\
\sqrt{a}^2 - 2 \sqrt{ab} + \sqrt{b}^2 & \geq 0 \
(\sqrt{a} - \sqrt{b})^2 & \geq 0
\end{align*}
casework
When you copy make sure u copy it correct
is it not correct
he used a conditional statement and took away the inequality
im confused
Because AM - GM is equivelent to square inequality
At least for the basr case for n = 2. Then later you do induction
what is induction sorry?
is this different to his method?
Irrelevant right now
Well you know tha classic inequality $x^2 \geq 0$
casework
hmm yes
for the symbol there does it mean they both rely on each other
It means that they are basically equivelant
ah ok
casework
This is probably better way to write it
One implies the other
ahh
casework
how about the grass is wet, it's raining?
If its raining water is falling from the clouds and if water is falling from the clouds its raining (i assume so)
In that case
$\text{its raining} \implies \text{grass is wet}$
casework
yea :/
So just because its wet we cant say that its raining
Yes we cant say $\iff$
casework
but we can only do the one arrow facing to the right?
Is this what you want to teach him
Yea basically
But im just giving examples rn
first day back at school and i am mind boggled
ah ok
What is that?
Oh ok so basically you do proofs
idk
I wanted to say you dont really need logic if you wont be doing proofs
I mean its good to know logic but a typical person doesnt need it in life
yes u do hahaha
By logic i mean "logic"
like math logic?
Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or logical truths. It studies how conclusions follow from premises due to the structure of arguments alone, independent of their topic and content. Informal logic is associated with informal fallacies, ...
...
Yes
So... any questions?
hmm yeah
how does it turn into (sqrt(a) - sqrt(b))^2?
You know the identity
$(x - y)^2 = x^2 - 2xy + y^2$
casework
$(x - y)^2 = (x - y)(x - y)$
casework
oh
Thats what the square means
ohhhh
ok let me try the question again :P
btw did u do it different to my teacher?
he did this here highlighted,
Its same thing
Its ok
my classmate said it is faulty
Oh i see i mean its not xyxy but xy + xy
But the idea is ok
he said
it is true that (x-y)^2 greater than or equal 0 it is faulty because we cannot prove that the result is true by assuming the result is true
which sounds like non sense
is he right?
Ask him where did you assume the result is true
he says
u started with the original equation
and u are trying to provei t
so u dont know if its true or not
Classic
In proving inequalities it is very common to start with original inequalitie. You just need to make sure all your steps are reversible
Not really but he has a point basically you just put $\iff$ after every line
casework
Like this
\begin{align*}
\frac{a + b}{2} & \geq \sqrt{ab} \
a + b & \geq 2\sqrt{ab} \
a - 2\sqrt{ab} + b & \geq 0\
\sqrt{a}^2 - 2 \sqrt{ab} + \sqrt{b}^2 & \geq 0 \
(\sqrt{a} - \sqrt{b})^2 & \geq 0
\end{align*}
casework
Someone could argue this is wrong
But just make sure you put this in proof
\begin{align*}
& \ \ \ \frac{a + b}{2} \geq \sqrt{ab} \
& \iff a + b \geq 2\sqrt{ab} \
& \iff a - 2\sqrt{ab} + b \geq 0\
& \iff \sqrt{a}^2 - 2 \sqrt{ab} + \sqrt{b}^2 \geq 0 \
& \iff (\sqrt{a} - \sqrt{b})^2 \geq 0
\end{align*}
oh so now this is correct?
Yeah basically put that symbol like that to write that every step is reversible
casework
I cant get the spacing quite right
Its important to mention not everything is reversible
This is 1 example
Note that the reason you can square it is because you are working with numbers in R^+
In that case $a \geq b \iff a^2 \geq b^2$
casework
why not?
$-3 > -5 \implies 9 > 25$
casework
casework
Squaring positive on one side and negative on other is well it depends on the absolute value
I mean this is supposed to be a contradiction i dont know how to do not implies in latex
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w=1/z +i and z=1+i. find w in polar form
please
what'd you try?
not really 😭
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how I can work out if there are any similar numbers in two sequences (2^n, 5+ 2^n)
I think it's more like 2^a vs 5 + 2^b
wdym by "similar"
Any same numbers
n is a natural number right?
You can just see one of them is always even while the other is always odd (when n is not 0)
11?
yeah
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If A is a set with 71 elements and < is a partial order in A, then which of these statements are correct:
- If A has 70 minimal elements, then in A there's 70 maximal elements.
- If A has 71 minimal elements, then in A there's 71 maximal elements.
- In A there's at least 2 maximal elements.
- In A there's a minimal element.
Need help concluding the answers
so, right off the bat, Ik that there's a minimal element
so 4)
nvm
confused minimal with least biggest
minimal would be least element. If all elements are the same they would all be minimal/maximal
but we don't know if they are the same
If A has 71 minimal elements, then in A there's 71 maximal elements.
The keyword is if
so that's true for sure
but can't claim 1), because it's about 71
Yes that is correct
can't say that there's at least 2 maximal elements
so we exclude 3) as well
since it's about <
whereas there would be 1 maximal
Ig?
correct
so 2) for sure, but I kind of am unsure about 4)
There will be least 1 maximal
Why are you unsure about 4
the formal definition is
for a minimal element
Image if we had a set of number. {1, 2, 7, 3, 9}. No matter what set we construct there is always going to be a least element.
yes, but aren't least and minimal different?
No to the best of my knowledge. How would you define them?
I just remember that in lectures they told us to know that there's a difference
oh I have the formal definition
this is for least
minimal
I am afraid I can't help you
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I believe I've got all parts sorted except for e. I'm not sure what half would be
@vivid mirage Has your question been resolved?
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!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
1 @pine sail
ok... i thought you didn't see so i pinged you
Continuity would imply the limit of f as x approaches 0 = f(0)
Can you solve for the limit?
no... i am a complete new to this
i wanted to solve it with steps but i am not sure where to start
A function 'f' is continuous at x = a, iff\
$\lim_{x \to a} f(x) = f(a)$
In your case, a is 0.
You want to find
ok
$\lim_{x \to 0} \f{\sin(4x)}{9x}$
! What the hell am I doing here?
ok
Now do it.
should i use the f(x)+f(x+h) formula?
Which formula?
one sec i am solving it...]
i solved this and got 4/9
That's correct.
! What the hell am I doing here?
so this is the answer?
And you know this.
It's not.
oh
yeah
0?
there is no x in k so..0?
Wait what?
sorry!! the thing is i only know how to solve it if it is in this form
yeah
But try to understand what it means for a function to be continuous.
Like I said previously.
Now you know the limit.
And it is known that f(0) is k^2
how ?
ok
My bad, I've edited that.
Which means, the limit is equal to f(0)
You can solve for k from there.
0?
How?