#help-26
1 messages · Page 43 of 1
$\forall x\in \bR^n, |x| < 1$, $|\partial^\alpha\varphi(x)| \leq \frac{2^{d/2}\sup_{|x'|<1}|\partial^\alpha\varphi(x')|}{(1+|x|^2)^{d/2}} \leq \frac{C_{d,\alpha}}{(1+|x|^2)^{d/2}}$
rafilou2003
what happened to the 2^d/2 for the C_d,alpha
oh it's inside
ok before i ask where the middle term came in here
we have C_d,alpha = max(p*, 2^d/2 thing)
and p* = max(thing1, thing2)
so we have 2 maxes going on
C and Cdalpha are different, remember that
$C = \sup_{|x'|<1}|\partial^\alpha\varphi(x')|$
rafilou2003
it's this C here
what's the '
so that we don't get confused with x, already being used
so we use a different dummy variable
mainly the x used here
ah it's just used to descibred the furthest (\partial^\beta \varphi(x)) can take us
Frosst
thats just this
right it's not really a varaible since we take hte sup of that
so really there's only "1" value that gives us the sup
or maybe a bunch of them that gives the same sup either way
it's not a variable
yes
ok still trying to comprehend this here
So for $|x|<1$, $|\partial^\alpha\varphi(x)| \leq C$
rafilou2003
by definition of sup, right?
true
but we showed this
ah
that's also true
so you bound that C by the thing on the right
with another C
that's indeed true again
and that's the middle term
and that in turn is yet smaller than the C_d, alpha
ah
because it is at leas thte same as the middle term
because if that was the biggest we'd have pikcedi t
if p* was bigger then of course it's bigger
$b\leq \max(a,b)$
rafilou2003
indeed
so giving us the final inequality
$\forall x\in \bR^n, |x| < 1$, $|\partial^\alpha\varphi(x)| \leq \frac{C_{d,\alpha}}{(1+|x|^2)^{d/2}}$
but that's only for |x| < 1
Yes, now we need to prove it for |x| >=1
oh dear
rafilou2003
that's a lot of steps they've hidden in 1 line
For $|x| \geq 1$, we know by definition that $|x|^d|\partial^\alpha\varphi(x)|\leq p^*_{d,\alpha}(\varphi)$ right?
rafilou2003
definition of supremum
from here?
well yes
yes
so now we divide this inequality by |x|^d
if the left one is bigger
what happens
then |x| >=1 is bounded by the same bound as for |x| < 1
ok that makes sense
that would be like the e^-x^2 example
the overall upper bound is in |x| < 1 and for |x| > 1 it's still bounded by the upper bound of |x| < 1
ok now if the right one is bigger
then we indeed have this inequality sure
either we took the left one and p* is bigger
or we take the right one and we are at equality
ok good
all good?
now we can do this good thing
so now we have $|\partial^\alpha\varphi(x)|\leq \frac{p_{d,\alpha}^*(\varphi)}{|x|^d}$
Frosst
so now we just need to find a constant to bring us back to the denominator we want
but we wanna make the left side still big right
we want to show that the right side is smaller than the right side here
Now $1\leq |x|$ right?
rafilou2003
that is true
So $(1+|x|^2)^{d/2} \leq 2^{d/2}|x|^d$
rafilou2003
is that from before
yeah but we need to change it because |x| >= 1
so we had this
$1+|x|^2 \leq 2|x|^2$, is that alright?
rafilou2003
now you multiply it but something thats > 1 on the right
true
that inequality will still hold
so now we raise this inequality to the power d/2
wait does that work
gives this
we're on |x|>=1 now
this comes from the fact that |x| >= 1 right
yes
ok sure
we added |x|^2 to both sides
now we raise both sides to d/2
ah
that is indeed true
ok good
we do get this
So uh I didn't anticipate this but I'll have to change Cdalpha a bit
will it change the stuff from before?
$C_{d,\alpha} = \max(2^{d/2}p^*{d,\alpha}(\varphi),2^{d/2}\sup{|x|<1}|\partial^\alpha\varphi(x)|)$
rafilou2003
no because we only change the left term
ah
and we used the right term on what we did before
here we divide both sides by 2^d/2
So from this, $\frac{1}{|x|^d}\leq ?$
rafilou2003
then we sub that in for the denominator
uh huh
very clever
$|\partial^\alpha\varphi(x)|\leq \frac{p_{d,\alpha}^(\varphi)}{|x|^d} \leq \frac{p_{d,\alpha}^(\varphi)}{\frac{(1+|x|^2)^{d/2}}{2^{d/2}}}$
Frosst
so we have this now
$|\partial^\alpha\varphi(x)|\leq \frac{p{d,\alpha}^(\varphi)}{|x|^d} \leq \frac{2^{d/2}p_{d,\alpha}^(\varphi)}{(1+|x|^2)^{d/2}}$
Frosst
aha
yep that's good enough
that's the other part of our C_d,alpha
So $\forall x\in \bR^n, |x| \geq 1$, $|\partial^\alpha\varphi(x)| \leq \frac{C_{d,\alpha}}{(1+|x|^2)^{d/2}}$
rafilou2003
done
that is a lot of stuff
well, the other guy did hope i could get to page 3
alright thank you so much for your patience
i will look through this again in the morning
good luck
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how do i
answer
A looks like simple multiplication since 3000 every year, so total money is 3000×7. 7yr for 19 to 25th birthday
B is Geometric progression with
a = 400
r = 2
Sum of Geometric B= a(r^n-1)/(r-1) i think
And tabular form smth like this probably
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I need help in finding the domain of this function
You just need to make sure that x^2 - x - 2 is not equal to 0 as 0^-1 is undefined (Assuming you are asked to find the maximal domain within reals)
oh so all I need to do is solve x^2-x-2≠0 ?
Yeah
but I don't understand why it can't be equal to 0
Because 0^-1 is undefined
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|x-3| < 2|x|
how do i solve this linear inequality? do i first divide by x to get it to the other side?
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Hello there, I'd like to know what is the procedure to getting the inverse function of f(x)= 1/x+2, which is (1/x)-2
it's not the correct reverse
You mean $\frac1{x+2}$?
for real?
A Lonely Bean
yes
ah ok
my bad
is it possible to move 2 out of the division by changing its sign to negative?
sadly, no
english isn't my native language so I'm not very familiar with terminology in english
from what I understand, you get the inverse by swapping x with y
you mean to say that the inverse of x+2 is y-2?
I'm starting to think I wasn't taught how to get inverse functions properly, or that there is something I don't know about reciprocal functions
As i was taught, you start by expressing the function as y = 1/(x+2)
and when you get the inverse, you swap y with x
I'm more curious about how 2 is out of the division in the inverse, and I don't see how swapping x with y explains how the 2 is changed
ok, I understand that, what I don't understand is how 2 is adding to x in the division on f(x) but on the inverse it's outside of the division
the problem is more related to algebra here I think
each day I realize how blind I can be from seeing things
I was brainstorming on this for hours yesterday
not really
for like an hour and a half prob
but damn do I suck at algebra
Yea, don't know how to thank you
sorry for any annoyance
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Guys, I have a confusion. in a complex number of the form: a+bi. a is the real part and b is the imaginary part, however b is not an imaginary number(when squared will produce a negative) b is a real number what makes it imaginary is i. So why do we refer to be as the imaginary part? Why do we not consider the imaginary part as bi because b itself is not an imaginary number. Or am I wrong?
I think you meant to write in a help channel rather than an already existing channel for me
i don 't see the point ....the immaginary part is the real in front of i
but why is it imaginary? imaginary part=imaginary number?
yeah but b is a real number, then why do we call it the imaginary part?
we just call it imaginary part because it is in front of the i
its not supposed to be imaginary itself
in fact its nice that it is real because then we can treat it like we can treat any real number
no
just b
I'm saying that only i is imaginary, b is real so why do we refer to is specifically "imaginary part"
its the definition !
I can also call it orange part but that would be an even worse name
gabe if you want b immaginary then immaginary part of -1=i*i would be i ...that doesn t make sense
yeah that's fair enough, I was just confused that whether b is an imaginary number itself
exactly
because it is attached to the i
hmm yeah that make sense, i was only confused by the fact that whether b is an imaginary number, but as it turns out it is a real number but considered as the "imaginary part" of the complex number only because it is the coefficient of an imaginary number.
chatgpt best math teacher ,,,
!nogpt
Please do not trust ChatGPT or similar AI tools for mathematical tasks, as they often generate output which "sounds correct" but has numerous factual or logical errors. Use of these AI tools to answer other people's help questions is strictly against server rules (see #rules).
am I right above?
well specifically it is the coefficient of i
like if you had a+b*(2i) then the imaginary part would be 2b
yeah but itself is a real number, only its called imaginary part because it is the coefficient of i
I was just stupidly thought that imaginary part=imaginary number, which made this whole confusion but now it's clear
well I wouldnt say so, it can make you VERY confused
i was ironic
ohh, I thought you were making a statement, my bad 🙂
an ironic statement
yeah
"dog"?
wow, I never would have guessed that you use an animal to describe that something is bad.
Anyway thanks guys for your help, I appreciate it
its like "you are an animal!"
it s an insult
which is definitely totally related to the animal
greatest of all time?
I've never heard anyone saying: "you are dog at maths" or smth
Its def not Irish 😄 I'd guess its american
ohh 😄
well speaking for Ireland I've never heard anyone saying it
ohh so thats why I never heard it then 😄
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I need help
This is where Im stuck, cant seem to match the left hand side with right hand side
induction?
Yeah
wow beautiful sigma symbol
Haha thanks
ok got it
Im stressed ok
yeah it's a bit too wide imo
it looks like you traced it with a ruler
anyway lets see whats up
I dont know if Ive done the steps incorrectly or if IM just too dumb to see the answer
some typographical alignment issues here
$\sum_{k=0}^{n-1}(k+2)2^{k+1}=n2^{n-1}+\sum_{k=0}^{n-2}(k+2)2^{k+1}$ right?
ok so uh
everg
lets just rewrite this into a more manageable form
$\sum_{k=0}^n (k+2) \cdot 2^{k+1} = (n+1) \cdot 2^{n+2}$ by the looks of it
AnnGhost
So that part is p-2 right hand side + p-1 left hand side
should equal to p-1 right hand side
we want to show $(p-2) \cdot 2^{p-1} - (p-3) \cdot 2^{p-2} = (p+1) \cdot 2^p$ by the looks of it
AnnGhost
That doesnt look right
Yeah I know, first time Ive stumbled upon one
But I assume that if the sum equals to p-2 for an example during the assuming part, all N = to p-2
Is that correct?
@topaz panther Has your question been resolved?
Nein
Have you tried induction?
If that's what you were doing in the paper you sent please forgive. You can use your induction hypothesis to substitute the left-hand-side for the right-hand-sight when you do the inductive step, and then simplify from there
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yo
how do you go about calculating the edge of a graph that has an edge like where the equation has a root in it
for example here
and this being the formula
find the point where the value under the root becomes negative
basically what are the coords
ohhh right
domain
soo here that would be
-2x^2 = -12
x^2 = 6
yes
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Can i get help on this question:
Please don't occupy multiple help channels.
oo this is fun
let's look at an example term
but as n tends to infinity, 1 / n^p tends to zero but n! tends to infinity
mb
i know it diverges
but i dont know how to show it
ah
because the numerator tends to infinity at a faster pace than the denominator tends to infinity
so it goes to infinity but that is a very short explanation
indeed, I'm thinking of a good way to show it
The idea is you can write out the two equations, n(n-1)(n-2)...(3)(2)(1) and n*n ...p times... n
the factorial term can have a growing number of factors
id say showing that it monotonically increases is sufficient
while the n^p term has only ever p factors
so, at a point in the sequence when n! has more than p factors which are all ~n in size, then the numerator will grow faster
as it will have a higher degree in n
monotonically meaning it is always increasing right but i wouldnt know how to do that for all n (would i have to differentiate a factorial?)
oh ok
im trying to understand sorry if im taking some time
yeah thats my problem with that method lol
possible but a lot of work
in particular, if look at a factorial n(n-1)(n-2)...(3)(2)(1), we can always truncate to get a strictly smaller number
ahhh
so, as long as n is larger than 6
diverges
factorial is basically unlimited whereas n^p is limited right
why 6 tho?
exactly!
we then can write out the first terms we can write as (n)(n-1)(n-2)(n-3)(n-4)(n-5) of our sequence and it will be smaller than n!
so in particular, n! is larger than a 6th degree polynomial
yes i figured that out by intuition just need to explain it
thats just with 6 as an example
$\frac{n!}{n^p}=\frac{n}{n}\frac{n-1}{n}...\frac{n-p+1}{n}\frac{(n-p)!}{1}$
everg
you could instead choose larger than p
oh i didnt know that
to then get something that is degree p+1 in the numerator and p in the denominator
so the limit would go to infinity
It's pretty cool! it shows that n! grows faster than ANY polynomial in n
at least asymptotically
expect for n^n right because it tends to zero if p = n
yeah!, (n^n) is larger than degree n though since its degree becomes unbounded as n gets larger
In general we have a heirarchy of polynomial< exponential like (2^n or 3^n) < (n!) < (n^n)
i dont understand how you have formed the terms above the fraction, is n! = n * n-1 * ... * (n-p+1) * (n-p)! ?
n! is by definition n(n-1)(n-2)...(2)1
yh that makes sense, i learnt this in big O notation
now I expanded only the first p terms
its exactly the same thing! the big O dertermines how it behaves in limits at infinity
now its more like small o
Thank you all for helping, i believe Ive got a good explanation now. I appreciate all the help!
what does that f emoji mean lol?
nvm now ive got to get back to work. Special thanks to @north spruce for explaining the concepts thoroughly!
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what a pen!
I'm trying to isolate y. Is there a natural log rule I'm forgetting?
$e^{ln(x)}=x$
AℤØ
so y(x)=kx
wait
oh okay
So, help me recall this rule. If I multipy both sides by e, would I be able to rewrite it as e^ln(y) = e^(ln(x) ) + e^C
e^ln(y) = e^(ln(x) ) * e^C (times e^C)
then y = x * e^C but since e^c is just a constant you can write y = x * A => y = Ax
wait I'm not sure I follow this part
e^c is a constant and I follow that part
youre not multiplying by e
no, youre making each side an exponent of e
$$e^{ln(y)}=e^{ln(x)+c}$$
AℤØ
you can split the right side by the fact x^a * x^b= x^(a+b)
why not
times e^c man
thats like saying if i have 5=3+2 then 2^5=2^3+2^2, 32=8+4
is it correct now then?
this is fine
just simplify
and replace the constant with some simpler notation if you want
k!
I will use K!
Stewarts book uses k
so it's y = xk!
ughhhhh math is so much nicer when it's not for hw
ty ty both
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I'm confused on this
the teacher explained us and I understood most, but the things underlined in cyan
is what's confusing me
like how did the teacher get those variables
the shortest distance between a point and a line, is the length of line (perpendicular to the main line) that joins them
the slope of the main line is 1
so the slope of our joining line is -1 since theyre perpendicular
(main line is y=x, joining line is CP)
it's always gonna be -1
or only for this question?
not necessarily no
but the product of the slopes will always be -1
like if the main line was y=1/2 x, the slope of the joining line would be -2
y = -x - 2 the teacher wanted a line that's at a right angle perpendicular to y=x so they flipped the slope to -1 but when they plugged in the point (5.5,1.5) to get the equation they made a mistake It should be y = -x + 7 not y = -x - 2
'b' is where the line crosses the y-axis and the teacher was trying to find it but got it wrong for the point (5.5 1.5) b should be 7 not 6
its (-3,5), not 5.5
y-1.5=-(x--3.5)
y-1.5=-x-3.5
y=-x-2
ohh, and did it mention the slope in the question?
where
so the y= -x + 7?
the slope was from the fact the main line is y=x, so the slope is 1
no
or was the teachers work correct
it is y=-x-2
but they said
they were mistaken
they read the point C wrong
y=x is given in the question
ohhh
its the yellow line of this diagram
so could I also have used elimination?
or only substitution
you mean to find the intersection?
like the teacher here used substitution
could I have used elimination instead
if you wanted to use elimination, feel free to
okay thanks
yes
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seems like greedy on highest urgency?
?
question is above
oh mb
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what did they do in this step? why does 8y+2x become 4y+x
i know it’s divided by 2, but why?
They multiplied both sides of the equality by 8y+2x. So it cancels out on the LHS and becomes 1/2(8y+2x) = 4y+x on the RHS.
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I'm trying to show that the function f:(-1,1)-> R f=x/(1-x^2) is bijective. For surjectivity, I got the quadratic equation: 1+-sqrt(1+4a^2)/2a but I'm not sure how to show that one of these is in (-1,1)
I'm trying to show that the function $f:(-1,1)\to\mathbb{R}, f=\frac{x}{(1-x^2)} {}$ is bijective. For surjectivity, I got the quadratic equation: ${} x=\frac{1\pm\sqrt{ (1+4a^2) }}{2a} {}$ but I'm not sure how to show that one of these is in (-1,1)
Jesses
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<@&286206848099549185>
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Here is a few tips:
You want to show that the absolute value of your expression is less than 1.
Since |a+b>|a-b| for all positive a and b, you want to consider the version with a neqative sign
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Describe the sequence of rigid transformations that shows ABC is congruent to A’B’C’ ?
A (5,7), A' (-2,7)
B (0,2) , B' (3, 2)
C' (7,4), C' (1,9)
I tried to do this but it was too difficult for me I need somebody to help me out
What I did was
I was already kinda out of ideas so I just reflected onto the y axis
But then I can’t translate point C correctly
So that idea was wrong
And now I’m stuck
Uh
<@&286206848099549185> sorry, could you please help me out here?
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can someone help me with this
i just started integrals
i dont understand how they got that'
we know that the maximum value of the interval is 2
yes
we dont know what the true area of under the graph of that region is
but we know that i cant exceed 6
yes
2*3
let me draw you a graph
yea
is if the value of the function between 0-3 is constant (2)
oh ok makes sense
also
it cant be A or B cuz we dont know what the graph looks like and dont know if its increasing or decreasing right
or no?
yup
@silver trench
it could be c, since it has a max value of 2
so we cant rule it out
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What have you tried
i am clueless right now
is the perpendicular 0.45m?
Do you know this?
Yes
Yes
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trying to solve this ode with these initial conditions but im lost
this is what i got so far but idk if it is right
i dont think it makes sense to me because wouldnt i need to find e^pi?
e^pi is just a number
,calc e^pi
Result:
23.140692632779
hm
it still does not fit the answer (i have the key for it) im just lost on how to get to it
as c1 is 1, c2 os -1
i got c1 as 1
i got this
i am so tupid i did the derivative wrong
i got derivative e^x in then product rule as multiplying another e^x, for some reason
ty
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I don't know where to start
i don't want the answer
i just don't know where to start
@neon iron Has your question been resolved?
you should start by writing the numers that use only th edigits 1,2,3,5 and 7
then look at the first 31 numbers which are divisible by 5
add those numbers up
and ur done
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I think I got it, just need someone to point up my mistake
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.solved
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is there any part of your question which makes you confused?
@barren garnet Has your question been resolved?
I tried to solve it with formula but it is so lengthy is there any short method?
ofc
Please guide
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,w plot |x|
Why does the graph have negative values
it doesnt tho
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\def \P{\mathrm P}
Does [
\map \P{\overline A \cap \overline B} = 1 - \map \P{A\cup B}
]
just a quick question
yes (by de morgan)
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If each coded item in a catalog begins with 2 distinct letters followed by 3 distinct nonzero digits, find the probability of randomly selecting one of these coded items with the first letter a vowel and the last digit even.
i have [
\map \P A = \f{25\cdot 8 \cdot 4 \cdot 5 \cdot 4}{26 \cdot 25 \cdot 9 \cdot 8 \cdot 7}
]
would this be true perhaps
hmm
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.close
Q6
AnnGhost
Number of roots of the equation x2 – 2x – log2 | 1 – x | = 3 is
this is your equation and you want to find how many roots it has, yes?
yes
umm yes
!show
Show your work, and if possible, explain where you are stuck.
i dont have a phone rn
i can tell
got 3 in rhs
lhs*
then completed the square
then simplified a bit
and what did you end up with
2^(x+1)(x-3) + x = 1 ,,,, for x <1
2^(x+1)(x-3) = x -1 ,,,,, for x >1
this is suspicious
@neon iron Has your question been resolved?
?
@neon iron Has your question been resolved?
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can anyone help me with this i was absent from school when we learnt it and dont understand it
A force of 200N acts over the area of 40cm^2 calculate the pressure
can any one help me
this isn't your channel, find an unclaimed one up top
look up law of cosines
YE CANT UNDERSTAND IT
oh sorry
i am new in this server
okay, please stop shouting. perhaps you might find a video lecture useful? there are plenty available
i tried calculating 4x but my answers were all wrong
This looks more like a law of sines problem.
can someone help?
@neon iron Has your question been resolved?
@neon iron Has your question been resolved?
no
sin rule states that sinA/a = sinB/b = sinC/c, a being the length opposite to angle A. essentially it's just plugging in numbers... that would give you a basic angle (which, in this case doesn't happen to be obtuse). use the ASTC quadrants to find an obtuse value of C. the quadrants part might be a bit more difficult to understand, i'd recommend consolidating with your teacher or watching a video explanation for that
this is the quadrant thing i'm referring to. apologies if i'm not using the correct terminology
man.. im sorry
where is the question
Hello?
@neon iron Has your question been resolved?
@neon iron Show us the question
Have you learned sine rule?
$$\frac{\sin(A)}{A} = \frac{\sin(B)}{B}$$
Ratatatat
Use this to solve the problem. Remember the angle is obtuse
@neon iron Has your question been resolved?
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I'd say start from scratch again since that's not the correct approach
Have you learned about this limit?
$\lim_{x \to 0} \frac{\sin x}{x}$
RedstonePlayz09
@toxic stirrup
@toxic stirrup Has your question been resolved?
I’m not sure how I could to that
You want sin(something)/something
Just keep the value of the expression the same, but move it and manipulate it in such a way, so that you have sin(?)/?
If whatever is inside the sin and in the denominator approaches 0, the limit of that part will be 1
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Can some please help me in this? Is it correct? If not please tell me what is the correct answer and explain it please
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dude like atleast give them some time to even read your question
@violet current Has your question been resolved?
Okay sure why not (read the English part)
Sorry
it is correct
Sure? Then which are the f’’ (second derivative)?
Which represents
f'' on the first picture is the red graph
f'' on the second picture is the blue one
whenever a graph is decreasing, the derivative is negative
So basically, the lower the graph, the more the derivative is increasing, like going from the first to second derivative, right?
could you clarify what you mean by "the lower graph"
sorry my english isnt perfect
Like in the first picture, I can see that the red line is going more straighter/lower, so it means that it is the second derivative
Like when the graph is being more straight does that mean it going through more the derivatives?
f’ straight, and f” more straight
It’s totally fine
So am I right and got the idea?
i look at these problems by trying find f(x) first. The (simple) definition of a derivative is a rate of change, so when a function is increaing, that means its rate of change is positive, which means the derivative becomes positive there. If you look at the first picture, the blue curve begins increasing at x=-1. you can notice that the black curve becomes positive at x=-1, so therefore, the black curve is the derivative of the blue curve. notice how when the black curve begins decreasing at x=1.5, the red curve becomes negative, so therefore, on the first picture, the red curve is the derivative of the black curve.
when the graph of a function becomes straight (horizontal), its rate of change (slope) is 0, so the derivative of the function is at y=0
this is a way to think about it, but its not necessarily correct. I think that you are thinking that the derivative function of a polynomial is one degree lower (for example, the derivative of x^2 is 2x) which does make it look straighter in most cases. I wouldn't use that for this type of question though, because you only get to see the graph of the functions, not the equations of the functions itself
Hmmmmm, that was an excellent explanation tbh. I got the idea mate
Tysm for helping
🤝
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Confused about this, only question I really dont know lol
@rare jewel Has your question been resolved?
@rare jewel Has your question been resolved?
the population proportion is just X/n, or the amount of people that think they dont need a television divided by the total amount of people surveyed
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hello
when i type the -3.5 for X in my calculator is error sadly
is this undefined or something like that
how did you type it
i take pic 1 sec
idk i did the same format for the other ones i guess this one is different
huh weird
Return ur calculator
never used one of those calculators lol, always used a casio
I tried that and still error
maybe
i just got it tho
is this something possible without calculator
or its too much
@graceful leaf u can simplify first using exponent laws:
(1/5) ^ (-2.5)
= ((1/5) ^ (-1)) ^ (2.5)
= 5^2.5
the error probabably has to do with it having trouble doing negative exponents so if u do that by hand u should be able to type it in now
or try using negative sign (left of enter) instead of subtraction sign in ur exponent
@graceful leaf Has your question been resolved?
wow thnxs very much
let me try ok
i forgot to put
whole thing
tahts why the error
Lol
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i'm struggling to understand what the logic from 'inspect these summations further...' and how this changes the indices on the summations so you change the sum to n into a sum to infinity
basically, how does n>=k warrant the step that comes after?
it might help to write out the first few terms of all the sum notations
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Hello, I have the following logistic regression definition
it's clear to me, that we can basically treat it as a probability and use it for classification problems.
yet I'm confused by $P(Y=y | x;\theta) = \sigma(y\mathbf{x}\cdot\mathbf{\theta})$.
resp. confused by how the loss is defined.
if we e.g. look up the logistic unit we see
so why do we have the y in the argument of our sigmoid?
Pascal
hmm I guess mathematically it kinda makes sense, just somewhat weirdly notated (at least for me) but I still don't understand what's going on exactly.
re pascal
to go back to hyperplanes
we're trying to do binary classification here, i.e. we're trying to see where the points x with y=1 are located in space, and same for the x's with y=-1
the way we're doing that here is with a hyperplane
the hyperplane splits the x-space in 2
on one of the half-spaces you'll consider that y=1
on the other one you'll consider that y=-1
that's just basic binary classification
now logistic regression tries to add some probability info
the closer you are to the hyperplane, the less sure you are about the result (1 or -1)
and conversely the farther you are, the more sure you are about the result
just trying to give a very high level view of what's going on here
yeah I get that mostly but I fail to properly interpret the math here.
you want to say something else or no ?
We have a bunch of data points with labels and we draw a line that separates them (in a 2D case) i.e. we tune theta. Right? Now how do we tune theta, we do that by defining a loss function and then solveing the resulting optimization problem. In our case, the loss function is the cross entropy i.e.
H(p;q) = - sum_i( p_i* log(q_i)) (iirc)
Now p is basically the "distrbution of our labels" i.e. "y". We only have i=1 so we get -y*log(q_i)
hmm i remember that yesterday, when I looked at that I didn't fully get the connection which is probably why I struggle now.
I guess I'd rather bother a TA with that.
I really wanna see it being derived properly
they have to 😄
otherwise math stackoverflow 😛
I'll force them to, whatever the cost
the ultimate answer
just wondering, what's that book you got ?
ah just lecture notes from a deep learning course
ah okey
alright alright
maybe
Logistic regression is basically just taking a linear assumption e.g. f(x) = x * theta and then defining a loss function lik e.g.
- Perceptron
- least squares
- log loss
and then optimizing theta, right?
well ultimately yes that's the goal
funny how I probably did all that stuff a shit ton of times but never really tried to understnad the math behind if properly.
to seperate the -1 and +1 classes in the nicest way
nicest being defined by the loss here
yes
thanks you too
anyway I have to leave. thanks again.
have a nice day you two
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Just a quick log question. Log10(3)=m, log10(5)=n Q:find log15(30) in m and n
@wintry oar Has your question been resolved?
<@&286206848099549185>
hi
Hi
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How do i solve (-2/cot^2(3t)), i need to derivate.
@drifting stream Has your question been resolved?
u need derivative of that right
-2 tan^2(3t)?
yes now use chain rule
in chain rule we follow the rule power function angle
first we do derivative of power of tan^2(3t)
so it will be 2tan(3t) right
Oh yes yes
then we do deriivative of function that is tan3t as sec^2(3t)
then we do derivative of 3t
-2*2 sec^2(3t)?
-4 sec^2(3)?
Thats the final answer?
yes
derivative of 3t
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how did they get h= sqrt 3 L/2
either trig or pythagoras
you can split the equilateral triangle in half with an altitude
it'll have hypotenuse L and legs L/2 and h
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Why is arg(z^25)=arg z=(i-1)
what is z
X+yi
