#elementary-number-theory
1 messages · Page 59 of 1
i stared at it for like 2, 3 mins and i got nothing
what happens when you get to
is there something useful when looking at element raised to the divisor of its order?
$a^{k \frac{p-1}{k}}$?
Zopherus:
indeed
yep
and since a has order p-1
everything before k does not repeat
hmm did i do something stupid with my examples?
,rotate
like, for 17 and 19, something repeats before kth element
oh
i didn't start with a^((p-1)/k)

thank you zoph
any time
i have a pretty baby question but i cant see how to make any progress on it. i'm supposed to find the least residue of $10^{2019}$ mod 1009. it's pretty easy to factor out a 3 and show that this is the same as $(-9)^{673}$ mod 1009, but i'm not sure where to go from here
the problem is written in a way that makes it seem like 1009 being prime is important, but im not sure how to use that information
Fermat's little theorem
oh
we havent learned that but i can probably work through the proof in my solution
So Fermat's little theorem states that if $p$ is prime and if $\gcd(a,p)=1$, then $a^{p-1}\equiv1\pmod{p}$
Whoever:
Yeah there’s no way to do this w/o fermat
There is always another way
indeed there is
u manually calculate (-9)^673 first
in Z
and then take the mod
ez
the only alternative I'd consider legitimately is writing 673 in base 2 and then work out by repeated squaring but even then 🤢
This is more #discrete-math
sorry
if we have f(x) = 1988x^2 + bx + 8891, and g(x) = 8891x^2 + bx + 1988, why is it that any factor of g or f must be a factor of g(x) - f(x)
i think i may be missing the obvious here
its not obvious
you have to use the fact that the polynomials are kind of symmetric to one another
so if the quadratic and constant coefficients were different, this would be not true?
yes you're right
its only because you get the polynomials from switching the constnat and quadratic terms that this works
if it said that any factor of g and f must be a factor of g - f
then this is always true, regardless of g and f
what if it said some (or more) factors of g must be factors of f
but not necessarily all?
well what about what @fervent crest said
I guess its always true since 1 is a factor of g, and is always a factor of f
before they deleted it
it was something like
f(x) = q(x) * h(x) and g(x) = p(x) * h(x)
lol i deleted because it wasn't the question
then g(x) - f(x) = h(x)(p(x) - q(x))
okay so the original polynomial difference was g(x) - f(x) = 6903x^2 - 6903 = 6903(x^2 - 1)
so i suppose i'm a little bit unclear on why this means x^2 - 1 is a factor or something?
Now I don't think the statement is true tbh
If it is a factor of f or g, and a factor of g-f, then it is a factor of the other
Implies f and g has the same roots?
But they dont have the same roots..
i am just really lost right now ngl
yeah, this isn't true
what is not true?
your original statement
"that any factor of g or f must be a factor of g(x) - f(x)"
sorry
it's missing 1 important word
"any common factor of g and f must be a factor of g(x) - f(x)"
oh
so now it's true?
yes
okay. could you explain why?
h is anything that is a common factor of g and f
anyone know how to solve this its driving me crazy
alright thanks
welp
what do you know about these types of problems
that's not what i thought that was going to happen
{ }
i know euler's function
3^(71)^82
and i guess i know like how to find inverses with like
euler's function?
like phi
where it gives like the # of coprime numbers less than it
And why do you think that helps you here?
maybe like
reduce down the 82 first
by doing (3^71)^82 (mod phi(23))
where im modding the 82
idk if that's a word
And why would this help?
bc maybe then i would get a smaller number to work with so i could just brute force it lol?
23 is already prime
Does this preserve your original number though?
i think?
how do you know that $3^{72^{82}} \pmod{ 23} = 3^{72^{82}} \pmod {\phi(23)}$?
Zopherus:
well the exponent gets modded by phi(23) but the number sa a whole is modded by 23 still
by the way, $\phi(23) = 22$ since 23 is prime
Zopherus:
yeah

Yeah okay, that's the right idea
So we can reduce down the exponent, which is $72^{82} \pmod{\phi(23)}$
Zopherus:
This is called Euler's theorem by the way
oh okay
tbh idk after that point :/
well okay, we know that $\phi(23) = 22$ so its just
ive been trying just random brute force stuff for an hour lol 😅
Zopherus:
$72^{82} \pmod{22}$
Zopherus:
what's one way we can simplify this? How would you simplify $72 \pmod{22}$?
Zopherus:
You can do better than that
And why can we do that?
Can we reduce down the exponent mod 22? Are we allowed to do that?
yes bc of euler's theorem?
What does Euler's theorem say
I.e., what did we do earlier?
Did we reduce the exponent mod 23?
So what do we need to do here, to reduce the exponent
and thats what we're reducing the exponent by?
But the exponent is $72^{82}$
Zopherus:
so we're trying to find $72^{82} \pmod{22}$
Zopherus:
oh
and we need to reduce this somehow
ohhhh
and it'd be nice if we could reduce the exponent of this
im not entirely sure how to do that ik the bottom is 6^82
but now i see that we can't just do the euler's stuff to the power
and why not?
Does that matter?
Yeah
So we want to split this into things so it is coprime
Do you know of anything that could help us with that
can't we just do 3^82 * 2^82
but are those both coprime to 22?
no i thought we'd just do one of them and worry about the other one later lol
in that case i have no clue :/
3
and what do we get when we do it
uh, how'd you get that?
how'd you reduce it down to 3^16?
and then squared it and put it through mod 22 again
oh
oh right
phi(22) is 10
3^2
so its 9 mod 22
mb
uhh
if we write that $x = 2^{82} \pmod{22}$
Zopherus:
then we know that $x = 2^{82} + 22k$ for some integer $k$ right?
Zopherus:
well okay, is there anything you notice about x here?
Like some condition x has to satisfy?
it has to be even ig?
Zopherus:
Zopherus:
now y= 2^81 + 11k
so that's uh y = 2^81 (mod 11)
and then its like uh 2
bc 81 mod phi(11) (which is 10)
wait but how i have a 9 mod 22 and a 2 mod 11
but $y = 2$ so what is $x$
Zopherus:
$x = 2y$
Zopherus:
(x had to be even remember)
yeah smh im stupid mb lmao
so 36 in the exponent which reduces down to 14
bc the exponent was mod 22
so now we have 3^14
and im good from there i think
thanks!
sorry for being a bit slow lol
you're fine
i haven't had the time to focus on number theory bc my discrete and multivar classes were harder than i thought they would be B(
but thank u very much for the help
any time
hey, I have a doubt regarding definitions: does a prime element always has to be irreducible as well?
I know that in an integral domain that's always the case, but it is not strictly required by definition, right??
Yes
okay, thanks!!
I solved the a part by proving b and c part
I wanted to know if there is a way to directly prove the a part
(also because that's what the author wanted us to do)
how did you do part b and c?
for part b, as any field with 0 characteristic has subring isomorphic to Z, and so will have a subfield isomorphic Z's field of fractions, Q
for c I used the map :
$\phi (x) = 1.x$
mega:
where x element of $Z_p$
mega:
hm, what's the definition of prime subfield?
a prime field is one which has no proper subfields
a prime subfield is one which has no proper sub-subfields
ah okay
Well I guess one problem would be that you haven't done part (a) in showing that this is the unique prime subfield
ah okay, you mean I have shown only existence, not uniqueness?
yeah
I think it can be proved that's it's unique in the sense that all other subfields will have to contain the subfield formed from the image of the mapping
I mean all subfields will have 1, and thus will have 1, 1+1, 1+1+1...
yeah
does this help in anyway in proving part a) ?
wdym?
I wanted to know anyway to directly prove part a) without first proving part b) and c)
I proved only existence for part c) but now also got to uniqueness
does this help in part a)?
i tried it with x^4=-1(p) but i don't know how to argue that (p-1, 4) = 4, i tried to assume that it equals to 2 and get a counter example but that didn't really worked out
@light flicker my nt papa help pls
okay, well if (p-1,4) = 2, then you know that p is 1 mod 4 right
yes
so you just have to show its not 5 mod 8
actually, if i pick p=7 then that breaks it?
wdym breaks it
the implication (p-1, 4) = 2 implies p = 1(4)
logic is not my strong suit
so you just have to show its not 5 mod 8
p != 5(8)?
i don't understand how you arrived at that
the statement (p-1,4) = 2 is the same as (p-1,2) = 2, and so it just becomes the first part
if p is 1 mod 4, then it is either 1 mod 8 or 5 mod 8
oh
hmm
alright let me see if i can prove that
uhh idk man,
if i assume (p-1, 4) = 2
then that's iff p = 1(4)
and i'm suppose to show that this implies(iff?) to p = 1(8)
indeed
Again, p = 1(4) iff p = 1 (8) or p = 5(8)
can a prime p satisfy both p = 5(8) and (p-1,4) = 2?
hmm probably not, let me try to prove that
4 does not divide p-1 hence 4 does not divide p-5, hence 8 does not divide p-5
sounds ok..?
wops
uh
i'm eating rn, sorry but maybe i should finish eating first
yeah, that's right
how can i figure out $x^7\equiv2(49)$ has any solution without solving it?
Publius:
@light flicker 
so i was trying to use this but p = 7, and 7 divides 7
i don't know if there are any other theorems out there
i dont think its easy
i mean i'd just say
that x^42=1 so 2^6 must =1 which is contradiction, but this doesnt generalize that nicely i think
2 and 6 are small numbers here
hmm
oh no thats nice
wow
that's a pro fucking gamer move
wait actually i don't quite understand why x^42 = 1
oh wait phi(49)=42
nice
actually, how do you know x^42 = 1? i thought i need prime to apply FLT @winter bear
wops
eulers theorem
am retarded
looks like Hensel's lemma
yeah, my next question is apply hensel's lemma to calculate some stuff
anyway... new question
so i'm trying to do the same for $x^7\equiv18(49)$\
i rise both sides to 6th power and since $18^6\equiv1(49)$, i get $x^{42}\equiv1(49)$, which is true by euler's theorem, this means i can pick any $x$ that is co prime to 49 and it'll work
Publius:
but it doesn't
the pattern seems to be +7, which is the power
what is going on 
this garuntees the existence of a solution
so basically use the fact that Z/49Z* is cyclic
i mean if you want the explicit solutions sure
to show existence/number of sols u dont need that
i know, but know more is better than know less
can you explain why this won't give me solution?
did i alter the congruence when i rise both sides by 6
i guess i surely did
um suppose g is a generator of the multiplicative group
uh huh
your implications are basically going backwards
we are saying that since 18^6= 1(49), that this thing has a solution right, cause 18=g^n for some n and g^(6n) = 1 which means 7|n
just because x^42 = (18)^6 doesn't mean you can just take 6th roots
and say that x^7 = 18 for all x
yeah
okay let me digest john's message, i'm big dumb at algebra
thats proof of existence btw
gotcha
hmm alright
how does the logic work here if i'm going backwards?
i showed that that congruence leads to euler's theorem
uhh...? but F => T is still true
yeah that wont work here, which is why i wrote that thing

if 18=g^n and since 18^6=1, then g^6n = 1 which means 7|n as order of g is 42. this means 18 is a 7th power
the fact that these groups are cyclic are very powerful for precisely this kind of manipulaitons
yes, since 18 \equiv x^7 right
if 18 is the 7th power then there exist some x such that x^7 = 18
oh then that's it?!
there exists that x
like generalize it to $x^n\equiv a(p^e)$
Publius:
so pick a generator of Z/p^eZ*
suppose $d|\phi(p^k)$, show $x^d= a (p^k)$ is solvable iff $a^{\phi(p^k)/d}=1 (p^k)$
oh hmm
JohnDoeSmith:
just generalize both arguments we made
yeah take ur time
I'm trying to figure out how many solutions there will be to a^2 \equiv 1 (mod 195) and I know the solutions to this will be the same as the solutions to the system of congruences of a^2 \equiv 1 (mod all the prime factors of 195) and I know that each of these prime factors will have two answers a= plus or minus 1 (mod some prime factor) but idk how to account for double counting solutions solutions?
like in the case of 35 i have the system of congruences a^2 \equiv 1 (mod 5) and a^2 \equiv 1 (mod 7)
and i'll double count 6 as a solution
idk if that makes any sense
you would not double count 6 as a solution
infact there would never be any double counting, courtesy of chinese remainder theorem
fuck
you're right
im stupid
idk how i thought 6 was the solution to two things
two system of congruences
-6 is a solution too
yeah
prolly messed it up there
is what i wrote full of garbage or
i know we just went over an example but i'm dumb
so a few things
a^x=1 means ord(a)|x
np
not the other way around which is what u seem to have there
also umm yeah the other implicition needs to be done
i can't even do one implication how can i do both lmao
this makes sense?
aight go ahead do that, keeping in mind that a^x=1 means ord(a)|x
np
(btw try continuing this to when d doesnt divide n, use gcd)
so the question im trying to answer is how many solutions to a^2 \equiv 1 (mod 2^e) where e is any natural number (not zero)
from test cases it seems that a \equiv plus or minus 1 (mod 2^e) and (mod 2^(e-1))
so when e > 2 theres 4 solutions, else there are 2 solutions
i started proving this but uh i realized i my proof would also show that any odd number should also work
so i have no clue how to solve this or if my conjecture(?) is even right
nvm got it
yep it's true if you want me to check your proof or whatever
i think i got it
its just not very rigorous bc its 5:50 am
and im too lazy
but i just said a^2 \equiv 1 (mod 2^e) equivalent to the system of congruences a^2 \equiv 1 (mod 2^(e-1)) .... a^2 \equiv 1 (mod 2)
which is the same as just doing a^2 \equiv 1 (mod 2^(e-1)) (which i proved in words lol)
and then i just showed that applying this to different cases with different values for e give me what my conjecture(?) was
Merosity:
then look at which e this could be equal to 1
and then go back and determine what xs were allowed
ughhh
im sure that's better
i just don't know if its worth it at this point
im just so drained
does what im saying have a semblance of truth
so i can justify putting what i just said down
also i have no idea where u got that from
well you said some stuff and said "which you proved in words" and I didn't see what you said so
I really have nothing to go on
lol yeah :(
you sound like you just need to sleep and come back when you're fresh
I was terse in what I said
lol
aint no rest for the wicked or something like that
but yeah
thanks i appreciate the help
just try to reason why every a that's a solution is of the form 1+(2^b)*x for some b, x
then by squaring it you end up with some more concrete restrictions mod 2^e
well that's just cuz you can just represent it as 1 + 2^(e-1)*(2k)
so x = 2k and b = e-1
oh wait im dumb
still thinking
yeah i can't figure it out
ill just turn in the homework as is i guess
no you restricted x too much
that's not the reason why you're sorta working the opposite direction
$a=1+2^bx \mod 2^e$
Merosity:
we're supposing we know nothing about b and x except that b>0 and x is an integer
but we know that squaring gets us 1
$1 = 1 + 2*2^bx +2^{2b}x^2 \mod 2^e$
Merosity:
can't we get something larger than 1 leftover since we don't know if b is divisible by e
$0 = 2^{b+1}x ( 1+2^{b-1}x) \mod 2^e$
Merosity:
yeah so you can start to see what are the minimum constraints to force this to be 0 mod 2^e
b+1=e would do it but that doesn't force x=2k
you just have to be careful about what b is when it's small which is where it switches over, right?
is this clear or do you not see where to take it from here
because it's the most generic choice I could make
it has to be either a=0+2^b*x or a=1+2^b*x
for b>0
either it's even or odd, that's really all I'm saying
the 2^b is just saying there are some number of 0s (possibly none) up until this value times x
err written in base 2
sorry I implicitly assume I'm working in base 2 when thinking about stuff mod 2^e
since each e basically chops off a further digit, it's just cleaner
it's not too serious if that's confusing to you
either a=0+2^b*x or a=1+2^b*x
this is just a generic representation for some b>=1 and integer x
and we can assume x=1 mod 2
yeah i get that
it's just a way to force it more cleanly
ive just never seen that representation of even and odd numbers
$a= a_0+a_12+a_22^2+a_32^3+\cdots$
Merosity:
basically looking at its base 2 expansion and then saying, there's some number of 0s
yeah yeah you get it I guess I forget this isn't so common to see
specifically working in the 2-adics is working with numbers mod 2^e for all e simultaneously
so I got used to that, which is where I'm kind of coming from
take your time I've got nothing better to do right now
im sorry i just can't
i wanna cry
i've pulled an all nighter
and i just can't figure it out

I'm just here to talk about math ideas, time limits and morale problems are out of my sphere sorry
$\left(\frac{\cdot}{p}\right):(\mathbb Z/p\mathbb Z)^\times \to {\pm1}$
Publius:
how would i show that this is a homomorphism..?
kinda lost
this is legendre symbol btw
by proving it
love you
so prove it
i guess i can try harder, i'll report back if i fail
actually
could i just map the quadratic residues to 1 and non residue to -1... uhh
i know that there are equal amount of them..
I mean
That's the definition of the legendre symbol yes
The legendre symbol is a function from (Z/pZ)* to {\pm 1}
$\left(\frac{ab}{p}\right)=\left(\frac{a}{p}\right)\left(\frac{b}{p}\right)$
this proves it..?
for a and b in (Z/pZ)*
Publius:
true
very cool, thank you
any time
yeah this one I dont think is easy to prove
its not particularly difficult, Ireland Rosen does it in like 3 lines
(ab)^n = a^n b^n
lol
I mean, he's not wrong
At least, the way Ireland Rosen proves it is to show that
(a/p) = a^((p-1)/2) (mod p)
And then you can use the fact that exponents split
most of it can be done just fine
but showing product of two non-residues is a residue is not as simple as the rest
the rest are like one line contradiction or construction
Hello
Can anyone help me prove Brocards theorem using induction?
Will be thankful to anyone who helps
,rotate
the problem just wants you to just check a few cases by hand
proving the general statement is an unsolved problem
ya it's just 8 cases (if we include 0)
Oh so i have to just put the values and check?
When does the equation $$x^k\equiv a\pmod{m}$$ have a solution in $x$?
Whoever:
when you can find $x$ for every $p|m$ such that $|x^k-a|_p < |k x^{k-1}|_p^2$
Merosity:

once you have that, you can hensel lift up to the appropriate power of p and combine with the chinese remainder theorem
;P
I'm partly teasing
well two things
the p-adic absolute value part can be reworked into just modular arithmetic if you want to see that part,
$$f(x)\equiv 0 \mod p^{2a+1}$$ $$f'(x) \equiv 0 \mod p^a$$ $$f'(x) \not \equiv 0 \mod p^{a+1}$$
Merosity:
usually people just show the a=0 case for Hensel lifting but this is the more general circumstance when f'(x)=0 mod p
idk hopefully that's not too scary as a requirement
but in some sense I didn't really answer the original question either, I just pushed the answer back to looking at x^k=a mod individual small powers of primes
🙃 Take in mind that I don't know a lot about p-adic
ok ok back up have you seen this condition for solving for x for f(x)=0 mod p^k
if you satisfy $f(x) \equiv 0 \mod p$ and $f'(x) \not \equiv 0 \mod p$ then you can lift?
Merosity:
Not the |x^k-a|_p condition you posted above
Oh
Yeah you've showed me this
I think
yeah
It was in the hensel's lemma
I didn't want to scare you too bad so I only showed you this case when f'(x) != 0
plug in a=0 and you see this second condition is f'(x)=0 mod 1 which is trivially true
it collapses back down to that, this is just so that when you look at your f(x)=x^k-a (different a from my powers whoops bad choice)
your f'(x) = kx^{k-1} might have k divisible by some power of p in common with m
which can mess things up
take gcd(k,m)=1 and your problem becomes simpler
now you really are just looking at x^k=a mod p in all circumstances
Oh
Well if gcd(k,m)=1 then I have an elementary method to solve this equation
Idk if this guarantee existence tho
yeah you need to start talking about the phi function / fermat's little theorem or something
Oh yeah
The condition isn't gcd(k,m)=1
my bad
it was gcd(phi(m),k)=1
Then you write u*k-v*phi(m)=1
somehow make u,v≥0
then
$a^u\equiv\br{x^k}^u\equiv x^{1+v\cdot\varphi(m)}\equiv x\pmod{m}$
Whoever:
But like
I don't think this shows the solution exist
Oh wait nvm it does
I'm dumb xD
But still what if gcd(phi(m),k)≠1
I stepped away for a bit
hmm what you wrote looks backwards to me, seems like you're assuming a=x^k
?
So I assumed gcd(phi(m),k)=1, then write u*k-v*phi(m)=1 where u,v≥1, then you have that x=a^u is a solution
your first equals sign, how do you make this substitution:
$a^u\equiv (x^k)^u \pmod{m}$
Merosity:
aren't you assuming a=x^k here?
yeah
i realized that
but it's also really easy to show that a^u is a solution
$\br{a^u}^k \equiv a^{uk}\equiv a^{1+v\cdot\varphi(m)}\equiv a\pmod{m}$
Whoever:
oh ok
I guess the next thing is if gcd(k,phi(m))>1 to split off the offending powers of primes from m so that we have the simple cases taken care of
and then specifically look at gcd(k, p^{n-1}(p-1)) > 1
Hm ok
kind of distracted but I got a handful of results for some cases
if k isn't divisible by p, then you just need to have x^k=a mod p
i k is divisible by p, and p>2 then you need the numerator of (a-1)/k divisible by p once
if k is divisible by p and p=2 then you need the numerator of (a-1)/k divisible by p twice
that's enough to guarantee you have a solution but there could be some weaker conditions I'm pretty sure
@fervent crest tell me if these are obvious or not I have tunnel vision
I'm not sure what you meant by offending powers of prime
oh
gcd(k, phi(m)) > 1
so you factor m into two parts m=r*s such that gcd(k, phi(r))=1 and gcd(k, phi(s))>1
then we look only at the powers of primes in s
and look at just these cases for the sake of gluing them back together with the chinese remainder theorem
because phi is multiplicative and I'm picking gcd(r,s)=1 for m=r*s
Ok
gcd(k, phi(m)) = gcd(k, phi(r)*phi(s)) but
the idea was to pick them such that this splits as well, that's what I meant by offending
Hmmm ok
has anyone used the chinese remainder theorem before
to solve a system of congruence
What are you confused about?
trying to solve this system
i got an answer but it doesnt check out with the second congruence 3(mod 5)
Maybe show your work?
yeah I get 2(mod 5) when I check it so ik that’s wrong
Yeah, so check your calculations for b2 again
what's 252 * 2 (mod 5)?
4
but what do you need it to be
1
so what do you need b2 to be instead
3
yes
oh ok lol
thx im a silly goose
yeah I was just kinda following another example without even thinking
I noticed that
15/154 = 9.7%
10/149 = 6.7%
is that a coincidence?
15-1/3 * 15 = 10
9-1/3 * 9 = 6
?
there's no pattern here
likewise 20/159 = 12.6%
what
10/149 = 6.7%
15/154 = 9.7%
20/159 = 12.6%
25/164 = 15.2%
30/169 = 17.7%
35/174 = 20.1%
it seems to me like you can roughly approximate the %
10/149 = 6.7
12/151 = 7.9
14/153 = 9.1
16/155 = 10.3
obv few jumps like 15.2 to 17.7 and you'd be off by quite a bit
but it's still better than nothing
im guessing your claim is that the approximate increase is by 3% at each turn?
$\dfrac{n}{x+n} = \dfrac{n}{x} \dfrac{1}{1+\dfrac{n}{x}} = \dfrac{n}{x}-\dfrac{n^2}{x^2}+\mathcal{O}((n/x)^3)$
JohnDoeSmith:
with x>>n
this approximation should show why its increasing at about a 3% rate when ur numbers are small enough
what's that letter at the end
big O notation
when do you learn it
just google it, the defination is p easy to understand
also what does the >> mean
much greater than
thanks
im using some taylor series approximation, if your familiar with those
cause thats what your problem essentially breaks down to
you are seeing the linear term in the expansion dominate for small values of n
thanks for that, I'll try to read some wiki pages on it
Any books u would recommend for number theory?
I had maths in my alevels but now am in first year of uni
Having trouble with modular arithmetic and stuff
hm, you could look at Silverman's A Friendly Introduction to Number Theory
But, if you just want to understand the stuff you're struggling with, you can just ask here, or there are videos online
More of a book guy tbh
Yeah I mean, trying to read a book just to figure out modular arithmetic probably won't be the most efficient
As in, this book goes over some unrelated stuff before talking about modular arithmetic and you might not be able to skip that stuff
Ahh i see alright I’ll look into this stuff tbh and if encounter any problem will get back to u
I could always just try explaining stuff to you too
Thanks bud
why is the flipping rule allowed with (1001/9907) even tho 1001 is not a prime?
i know that the Legendre smbol is defined for (a/p) a need not be a prime
but what confuses me is why can i flip without a being a prime too since the law says q and p both ood prime
pls come to rescue zoph papa @light flicker
The situation for the Jacobi symbol is a bit different. Jacobi symbols don’t always detect QRs properly, but they will always detect QNRs (if the Jacobi symbol is -1, you have a nonresidue).
right, i understand that, but not what i'm asking, sorry for my shit wording above
the one on the left is a Legendre symbol, yes?
Jacobi symbols are equal to legendre symbols when the "denominator" is prime
quadratic reciprocity
Look at property 6 on that wiki page
Since the Jacobi symbol matches with Legendre symbol in prime case, it’s always right
It has the do with the number of QRs modulo n in general
oh huh, so since the LHR is both Legendre and Jacobi, i just treat it like Jacobi and get 1 in the end
The Jacobi symbol takes permutation signs so it is half +1 and half -1 always while quadratic residues mod composite moduli are much rarer in general
Yeah
Pub is that u???
ain't that a coincidence lmao
fermats little theorem is basically useless with p=2 right
I mean if you have to state it in that way
im just trying to solve a problem using flt but it would rely on 2 actually doing something
now i have to do extra work 
happens very often in nt that 2 is a special cas
let's kick 2 out of the prime club
fundamental theorem of arithmetic is only for chad odd numbers
228
What remainder is left after dividing by that number
$232\equiv 4(\text{mod }x)$ is same as saying\
$232=4+xn$ for some integer $n$
Publius:
@rigid loom
Ohhh
~~yeah alright throw him some ideals lmao
~~
always generalize stuff in Z to rings smh
i'm not far enough in nt to see why that'll be very useful
nice new pfp btw, it was one of my favs
thx
in proving a^(p^k) = a mod p, induction is fine, right
mhm

can someone tell me if this logic is flawed
i dont want to have to do induction again, but this just seems kinda cheeky
I got an assignment to solve a problem using newtons method for multiple variables
sat all day coding in matlab and i thought it would work but didnt
and when I debug I notice that for some reason f1 and f2 become the same value after the first iteration has passed
function NewtMultiVar
function newtMulti = newtMulti(xk)
u = xk(1);
v = xk(2);
function f1 = f1()
f1 = ((93-u)^2)-((63-v)^2)-(55.1^2);
disp(['f1 : ',num2str(f1)])
end
function f2 = f2()
f2 = ((6-u)^2)-((16-v)^2)-(46.2^2);
disp(['f2 : ',num2str(f2)])
end
function df1u = df1u()
df1u = -2*(93-u);
end
function df1v = df1v()
df1v = 2*(63-v);
end
function df2u = df2u()
df2u = -2*(6-u);
end
function df2v = df2v()
df2v = 2*(16-v);
end
function S = S()
s1 = sym('s1');
s2 = sym('s2');
E = [(df1u()*s1)+(df1v()*s2) == -f1(), (df2u()*s1)+(df2v()*s2)==-f2()];
X = solve(E,s1,s2);
S = [X.s1 X.s2];
S = double(S);
end
newtMulti = xk + S();
end
The disp is just to debug
I dont get what im doing wrong, (in the body i call this iteratively but thats irrelevant, this is the function that calculates)
After one iteration f1 and f2 turn out the same
and my results just spasm out of control
I'm going insane, spent entire day on this and Im pulling my hair out, defeated
Ill give my first born child to anyone who can help, i'm at a total loss..
<@&286206848099549185> if possible
can someone help me with this problem, i've broken it into modulo 2 and 5, giving
x = 1 mod 2, which is obvious, but idk what to do for modulo 5
i know that (x^4)^250 = x^1000, but dont know how to apply FLT
do i assume that x has an inverse and is a unit? or what...
nvm
I got 1, 3, 7, 9
yes
x=0 mod 5 gives contradiction, then just have to solve the 4 other cong. when x = 1, 2, 3, 4 mod 5
You can do it with euler’s theorem
i.e. x^(φ(n))=1 (mod n) if x is coprime with n, where φ(n) is the euler totient function
Euler totient of 10 is 4, therefore automatically 1, 3, 7, 9 are solutions
Then for 0, 2, 4, 6, 8, when you raise them to arbitrary power it’s always even therefore never 1
For 5, when you raise that to any power it’s always congruent to 0 or 5 (actually it should always be 5), so it’s also never 1
What is a word salad?
I imagine the lecturer was wanking himself off while writing this thinking hes a genius
it's clearly not parsable
I think the lecturer just wanted to direct you to other related topics to explore
this is supposed to be a solvable question
Also, it isn't really unreadable, at least it isn't a mess of symbols
okay please enlighten me
On?
what is the question asking?
The first sentence?
yes, the question
can you put it in words that humans understand?
how is it "producing" said sequence
he's a fucking charlatan
I don't get it upon further examination, sorry downtown
Idk man
Probably equivalent to that anyway
This is weird
Is it showing that a^n is periodic (as a function of n)?
such a fucking fraud
I’m out I can’t read it
Sorry, downtown
I can’t give a definitive answer as to what he wants
can we see the whole problemset @sacred junco
maybe theres some context in other problems?
I'd rather just call it out publicly
eh bad move, man controls your grade, just give him the feedback that he made a mistake
everyone makes mistakes lol, doesnt mean they should be shamed for it right
no it's pretty consistent
he's a charlatan who thinks he knows what he's talking about
wait what do you guys not understand lmao
he's writing a book that is riddled with mistakes
its just asking you to show there's always a primitive root
and not even for F_{p^n}, its just F_p
i mean thats what i guessed, but it really doesnt say that?
I hate this guy, he's a total pseudointellectual
it's a computer science course and this is his attempt to teach mathematics
but he's failing since he doesn't know any
I mean, it says to show that if you take a primitive root, then it'll produce such a sequence
I mean, its pretty clear he does know mathematics lmao, this is fine
I mean, he might be a terrible teacher, but thats different
nah the wording is still p bad, most of us guessed he meant show its cyclic but still
you think this is good evidence that he knows mathematics? a word salad with words he doesn't even understand?
I can’t read this right, but I wouldn’t go so far as to say he’s a charlatan
i mean he doesnt use any particularly big words
It's not a word salad lmao, it makes mathematical sense
And it's correct math as well
my problem is that he just didnt phrase it well enough
I mean, maybe he just copied it from somewhere and he doesn't know the stuff, but its correct mathematically
his construction of the real numbers was $\mathbb{R} = \overline{\mathbb{Q}} \cup \mathbb{Q}$
downtown:
Doesn’t seem like he hides behind terminology, it’s just I can’t read it
in his great book that we all get to read
yeah rifts, its like missing a sentence i feel like
I'm a math major taking his course
i mean i think by that he means like the completion of Q?
Lol it sounds like he is confused. But maybe the theorem he's trying to get at is that for every prime, there exists a primitive root.
no, he was saying that the real numbers are the rational numbers with the rationals
which is blatantly wrong
You mean the irrationals?
yeah
Because that's correct?
...
lmao
Irrationals are literally defined as the real numbers that aren't rational
So maybe this might be circular, but its definitely not wrong
And there are plenty of other ways to define the irrationals
I don’t see what exactly would make that wrong per se, tho idk what kinda closure that overline refers to
$\mathbb{Q}$ is the algebraic numbers, not the irrationals.
4c:
if you mean \bar{\bQ}
sorry. meant to put a bar.
this notation is used for both
just because algebraic numbers come up more, you see that used more frequently
Anyways, its clear that he meant irrational here and thats not the confusion
Like, is the bar for a metric closure, algebraic, etc?
it’s annoying hoe stuff gets reused
set complement
@sacred junco so uh, have you figured out why this is right yet
It’s right but wow I don’t like it
I mean, its probably the most common notation for denoting irrationals
not that people do that often but
Anyways, your professor is right, it's not "blatantly wrong"
Whether its a good way of defining the reals is another question
I still think he's a charlatan
Idk, you just seem mad at this guy and are trying to blame him for everything, including you not understanding any of this
I don’t know enough to reliably talk about his skill & knowledge, but I certainly can’t say that he is an imbecile
nah I just don't have time to decipher this stupid question
Clearly he knows something
yeah, as i said he prolly just forgot to put a sentence into that question
I mean again, its not stupid just because you can't understand it
@light flicker that's not the reason I think it's stupid
Then why do you think its stupid
It's a fine exercise that introduces important number theoretical ideas
because it's phrased in such a way that no reasonable person should be expected to be capable of being able to decipher it
I mean, I understood it fine
If you understand what primitive roots are and fermat's little theorem is, you should be able to understand this
I couldn’t decipher it but I am an imbecile
@light flicker could you rephrase the question?
Do you understand what Fermat's little thoerem says?
theres a lot of smart ppl here 
yes
And what does it say
if $a$ is not divisible by prime $p$ then $a^{p-1} = 1 \pmod p$
downtown:
Okay, and do you understand what primitive roots are
no
Then you should try to understand that?
Not knowing one of the terms in the problem will obviously make the problem confusing
where is "primitive root" a term in the problem
for the record there is no expectation of understanding primitive roots before attempting this question
"The \alpha here is known as a primitive root"
ok i got that
Why does he say there's a "unique" sequence? Different primitive roots can give different sequences.
Yeah, it means unique as in choosing different alpha will give you different sequences
okay so I choose alpha = 5, what is the sequence given
As an example, if p = 5, 2 and 3 are primitive roots because they give 2, 4, 3, 1 and 3, 4, 2, 1 resp., but 4 is not because it goes 4, 1, 4, 1, etc.
The sequence here is the powers of \alpha
for when p = 5, \alpha = 2, the sequence is 2, 2^2, 2^3, 2^4
up to p-1
which you can see reduces (mod 5) to be what he described
so how do I prove the uniqueness?
This is also a pretty hard problem to do without any hints. An outline is, you define the order of an element z to be the least d for which $z^d = 1$. A primitive root is one whose order is p-1. Now you can show that the order must divide p-1 by FLiT. Then you show that for each d, there are at most phi(d) guys with order d. Then you use the fact that every element has an order and the fact that $\sum_{d|p-1}\phi(d) = p-1$ to show that this implies that in fact, there are $\phi(d)$ guys with order $d$. In particular, there are $\phi(p-1)$ primitive roots.
4c:
I still don't understand what "uniqueness" really means here.


