#help-17
1 messages · Page 269 of 1
cos would work
wait so how do i start the question aft drawing
idk what to find 1srt
Omg nvm i see
wheres the right angle tho
im lowk tweasking out over this question

The channel was just lost, huh !
but how do u know if its a eright angle tho
You just need to find angle ABD
idk the tangent rule thing 😭
Tangent
A tangent to a curve is always perpendicular to the radially outwards vector
Okk?
Wlcmm
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$(E-F)\cup (F-E)\iff (x\in E\land x\notin F)\lor (x\in F\land x\notin E)\iff [(x\in E\land x\notin F)\lor (x\in F)]\land [(x\in E\land x\notin F)\lor (x\notin E)]\iff [(x\in E\lor x\in F)\land (x\in F\lor x\notin F)]\land [(x\in E\lor x\notin E)\land (x\notin F\lor x\notin E)]\iff (x\in E\lor x\in F)\land (x\notin F\lor x\notin E)\iff (x\in E\cup F)\land (x\notin E\cap F)\iff x\in (E\cup F)-(E\cap F)$
pirateking0723
is this correct

$(E-F)\cup (F-E)\
\iff (x\in E\land x\notin F)\lor (x\in F\land x\notin E)\
\iff [(x\in E\land x\notin F)\lor (x\in F)]\land [(x\in E\land x\notin F)\lor (x\notin E)]\
\iff [(x\in E\lor x\in F)\land (x\in F\lor x\notin F)]\land [(x\in E\lor x\notin E)\land (x\notin F\lor x\notin E)]\
\iff (x\in E\lor x\in F)\land (x\notin F\lor x\notin E)\
\iff (x\in E\cup F)\land (x\notin E\cap F)\
\iff x\in (E\cup F)-(E\cap F)$
artemetra
looks correct.. the only way i see how to simplify this further is by writing it as symmetric difference
$E \triangle F$
artemetra
finally lol
wdym by simplify further
to let it take fewer steps to reach the other side ?
yes
yeah it's what your final expression is equivalent to
in fact i am trying to prove that $E\Delta F=(E\cup F)-(E\cap F)$
huh
pirateking0723
given that $E\Delta F=(E-F)\cup (F-E)$
pirateking0723

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The question is about the calculation of a basis of the kernel of a linear function - ker(l)
I dont understand what's the link between the the solution of the system and the two vectors that make up the basis
after solving for all the entries a vector in the kernel can be written as (-x5,0,0,x4,x5)
yes?
i dont see why x4 and x5 are inclued in the end though
x5 can be chosen arbitrarily
as long as x1 is chosen as -x5
similarly x4 can also be chosen arbitrarily
well they were moved right because of it
so kind of the other way around
(and moving them to the right is a bit of an odd step imo, you dont need to do that)
i copied this from a solution sheet made by my prof
i got here now
so how do I get those two column vectors as the basis
i dont see it
ok
but I still dont get why they're being separated
and the first -x5 doesnt appear in the first vector
I chose to split them up that way instead of another way
another way would also be valid but not as useful
now I have two vectors, one with only x4 and the other with only x5
which means I can move those factors out
and get this
aha ok
you chose to split them like that to make it tidier
variable segregation
let's say
but if we now look at this from a different perspective, this means that any vector in the kernel can be written as (some number)*(0,0,0,1,0)+(some other number)*(-1,0,0,0,1)
(english isnt my first lang**)
aka as a linear combination of (0,0,0,1,0) and (-1,0,0,0,1)
and those vectors are obviously linearly independent
can I ping you just in case?
so therefore they are a basis of the kernel
I dont know if I will still be there
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Can somebody tell me if this is correct?
yes thats a correct basis
stay on the server
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Help
𝔸dωn𝓲²s
list all the elements
Z_12 is cyclic so the other one would also have to be
what could a generator be?
what do you know about homomorphisms and generators?
1 generates Z_12 and my guess is (1,2) has to generate Z_3 x Z_4 cause the others don't seem to
you sure?
either (2,1) or (1,2)
well look at what happens to the second slot as you keep on adding (1,2) with itself and then argue why it cant be a gen
(2,3) should work?
ok it doesnt generate 2,2
hmm yea prob that then
there is a much easier generator
if (a,b) generates Z3 x Z4, then a needs to generate Z3 and b needs to generate Z4
at the very least
just necessary
are you aware of the chinese remained theorem? by any chance?
okay dont mind that but as denascite said there is a very obvious generator which for some reason you didnt try, and it will justify why your map is an isomorphism
1,3?
is that really the first thing you thought of
whats the most naive guess you can make
as if it was really 1,1
it is
no way
why dont you check
,w Table[{n mod 3, n mod 4}, {n, 0, 11}]
my first intial thought was 1 from Z_12 is a generator and would map to (1,1)
and it does
but (1,1) I thought I would only get pairs like (1,1) (2,2) and (0,0) for some reason
in fact if you trusted your map this should be the first generator you find
f(a,b)->a+b isn't onto
f(a, b) = a + b isn't well-defined
what does well defined mean
it means that the definition actually makes sense
it is better if you define your map in the reverse direction but you can make this work too
how can you make it well-defined?
there are several ways to write the element (a,b) in Z3 x Z4
by not defining it that way
not all of them would give the same value for f
for example, (1,3)=(4,3) but they have different sums

f(a, b) = the solution x to x = a mod 3, x = b mod 4
whenever you have some object which came from some equivalence relation you have to make sure that the way you write an element does not influence the value of the function
and how is it defined
Z_12 -> Z_3 has an "obvious" map which is the mod 3 map
Z_12 -> Z_4 has an "obvious" map which is the mod 4 map
that should be your first choice really
two maps??
to map into a product, you need two maps
making them into one is why you producted them(the groups)
one to each component
𝔸dωn𝓲²s
(note that this is well defined, if you take a or a+12 or any other way to write the same element of Z_12 then f(a) still has the same value)
which is important because if you want to check that its a homomorphism then you have f(a+b) where a+b could be "bigger" than 12 and if you then had to make sure that you took the "correct" representative it would be a huge pain
@bitter pilot Has your question been resolved?
your proof of surjectivity is not a proof but the good part is you dont need it. also why does 3n = 4m imply n=m=0
i can have n = 4 and m = 3 for example
did nobody tell you that a homomorphism is injective iff its kernel is 0
when you do algebra, nobody ever checks f(x) = f(y)
its always f(x) = 0, prove x = 0
and here it is especially easy to check this condition. (just check every element)
yeah
but then the homomorphism needs also to be surjective in order for it to be an isomorphism
for finite sets, injective, surjective, bijective are all equivalent
right..
in fact, that is how you can characterise finiteness of a set
you're assuming the sets are of the same size, right?
endos
no
endos?
,w endomorphism
that's also necessary
yeah i just meant this statement only holds if the sets are of the same size
or do you mean the thing about injective bijective surjective being equiv
that statement was for endomorphisms
in my mind i had already identified the two sets 
and x = 0 mod 12 implies x = 0 because x is in Z_12 so the only solution is {0} got it
T
I have to see whether [ (\mathbb{Z}_{12}^, \cdot) \cong (\mathbb{Z}_3^ \times \mathbb{Z}_4^*, \cdot). ]
I have the feeling it is, I will get soon to it!
𝔸dωn𝓲²s
@bitter pilot Has your question been resolved?
𝔸dωn𝓲²s
𝔸dωn𝓲²s
yea it worked out but i still wonder if the above is sufficient
you have to check that it's a homomorphism
you can't just write down a random map like this and call it a day
well it's based on that map
yeah so then you have to check it's a homomorphism
𝔸dωn𝓲²s
yeah
those in the know would just say that Z_12 and Z_3 x Z_4 are isomorphic as rings
but now the bijectivity is shown
yes
and that makes Z_12* isomorphic to Z_3* x Z_4* ?
yes
Is there an explanation for that
a unit of R x S is an element of R* x S*
Ok, so to understand it, Z_12* does not only denote the set of all integers mod 12 and g(x, 12) = 1 but it also denotes the set of all units of Z_12?
That being said Z_12* acts like a subset of Z_12. Same with Z_3* x Z_4* being a subset to Z_3 x Z_4.
If we consider them as rings (meaning we have both addition and multiplication), then it is clear that the structure in the units is therefore also persevered?
Them being isomorphic is proven by proving an isomorphism exists
yea that's trivial
i just wanted to get the intuition behind this
those in the know would just say that Z_12 and Z_3 x Z_4 are isomorphic as rings
that this implies immediately that Z_12* and Z_3* x Z_4* are isomorphic
You'd have to prove that the rings are isomorphic idk if that is any better
hmm ok
In this exercise we explicitly considered them as groups actually not rings, so I am not quiet sure if I would be allowed to use Blake's argument but just for the sake of understanding, I think it makes sense
I proved that there is an isomorphism between Z_12 and Z_3 x Z_4 previously
as groups tho
And now you have to do it for the multiplicative versions?
yes
I did that too
wait
I did that here
Mod is addition
Can you elaborate?
Let p be 5
Actually
Not a prime
8
Then 2 * 4 is not an element of the multiplicative group if it is mod 8
But that only happens because you consider Z_8 not Z_8*
It wouldn't be a group in the first place because it wouldn't be closed
idk
lmao
😭
1st task and it's been 3 hours already
i believe this proof is fine to show isomorphism. what exactly is the problem you are having with it? the map is defined properly and is an isomorphism
I believe the proofs are fine (snow would otherwise say something) so I am gonna mark it as solved
thanks to all! ❤️
.solved
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how do i do iii and iv)
What's the sum of all 5 roots
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hello
!show
Show your work, and if possible, explain where you are stuck.
Your exercise looks wrong in the middle
Your steps looks correct but idk what u wrote
Step 2 and step 3 is what u have to do but the outcome is not correct
@neon crypt
L2 -> L2 -2L1 is equal to 0, 1/2, -2, -2
!occupied
Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).
And L3-> L3-5L1 should be equal to 0, -3/4, 1, -7
@neon crypt Has your question been resolved?
why 1/2 in the L2 ?
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Does anyone have any advice for this task, because I haven't found anything similar on the internet. I simply can't find A and B after division, which is the remainder.
See if you can write x^3 + 5x^2 - 12x + 3 in the form p(x^2 - 6x + 10)(ax + b) + c
wolfram says long division
@tawdry stirrup Has your question been resolved?
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Hi, can someone check the proof?
𝔸dωn𝓲²s
how have you used that a,b are coprime
I forgot it
its a very essential condition
the problem is that the order of (1,1) is not always ab
you need that they are coprime
but here you just claimed it
well is $\mathbb{Z}_4 \cong \mathbb{Z}_2 \times \mathbb{Z}_2$?
artemetra
Yea here [(1,1)] = {(0,0), (1,1)} only so it wouldn't be ab
@bitter pilot Has your question been resolved?
I don't know how to show that based on the fact gcd(a,b) = 1 it is ord(1,1) = ab
ok for example
k(1,1) = (0,0) then k = 0 mod a and k = 0 mod b so that would mean if k != 0 then the smallest next possible must be lcm(a,b)
Axe
ye
am I on the right track
i was thinking along those lines, and
lcm(a,b) = |ab| / gcd(a,b)
yah it's ok except typo at the end lcd should be lcm
ok ye
gcd(a,b) = 1 implies lcm(a,b) = ab
😭
and you ended up proving something better
the order of a general element in the product is lcm of the orders of the components.
also before you get the wrong idea I've been helping you cause we played minecraft together, I've been helping anyone that I've seen from the server lol
hmm ok
well i basically helped Cyrenux, who built everything, on most projects, we even have a base together
but cool lol
then yeah I definitely benefitted from the stuff you built, so this my way of saying thanks
i see, thank you too
np
and now i have shown it too 
thank you guys ❤️
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I'm looking for some help on sports betting statistics. I currently have an app that gives as much info on each sports bet as it can (record, avg,etc). I show the win percent of bets which is just the record of that bet happening as well as a weighted chance of happeing which is this formula: a(1-b)/(a(1-b) + b(1-a)). This takes into account the other teams liklyhood of winning the bet as well which I like. So team A has an 80% chance of winning a game based on their record, playing team B that has a 40% chance of winning. We could assume that team A has a greater than 80% of winning because team B is not good, so the above formula would come out to 85.7% chance. I use this same formula for other bets such as spread and total. What I need help on is how can I use a formula like this that adjusts team A based on team B and use it for player bets. So if I have a player that has a bet of getting over X shots, their chance of that happening is 72%, but some teams average allowing less shots per game and some on average all more per game. How can I use this in a similar way as the formula above to calculate the adjusted number for a player?
@warm vector Has your question been resolved?
@warm vector Has your question been resolved?
@warm vector Has your question been resolved?
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how am i supposed to find this
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Can I set this up as a proportion?
I did 27/63 =x/1.75
got 63x=47.25
Now x= .75
Point .75 of 36 is 27 which is the answer.
But I can’t work out in my head why it works.
The speeds are in a 4:3 ratio, so the times are in a 3:4 ratio
Ohh, true. I didn’t realize that
so 3/7 is the proportion of the time the first trip took to the total
in other words the first trip took (3/7)*(1hr 45min) = 45 minutes
and the second trip takes 1 hour
the second trip is the easier one to calculate the distance for, of course
I think what you did works by pure coincidence and it wouldn't work if you changed the numbers
How would you set up the problem if you saw it? Without using a calculator.
Sorry, I’m really stupid. Is that systems of equations? Or two different operations?
I just can’t imagine how that looks on paper
Distance = 36*t1 = 27*t2
is
Distance = 36*t1
Distance = 27*t2
Yea it is system of equation
I must be stupid
.close
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can anyone help me solve these derivatives using limit definition instead of the table? thats how the professor wants it
27 and 28
!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
2
may we see what you've done so far ?
i tried this but idk if it leads anywhere
i have no clue how to get a h out and simplify
or should i multiply by 1/h and
idk man
@full fox Has your question been resolved?
<@&286206848099549185> ?
@full fox Has your question been resolved?
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(a+b)^2=a^2+2ab+b^2
why do you beleive (2/5)^2?
its the same 3/4 -> 3/8
take the half as you have taken form 3/4 -> 3/8.
3/4 divided by 2 is 3/8. 2/5 divides by 2 is 1/5.
no. (a+b)^2 = a^2 + 2ab+b^2, so if oyu have something like x^2+2/5x and you wanna have a complete square like (a-b)^2 it means that 2/5x is 2 a b, so a = x and you hav to half the rest to get b.
the technique you wanna use is called "completing the square". you have a quadratic term like x^2+10x +3 you can write it as (x^2+10x + 25)-25+3 which gives you (x+5)^2-22
10x = 2ab, use a = x -> 10 = 2b -> b = 5
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how to solve 2/3 power 2/3?
Wdym with solve? It's not an equation. Do you mean compute?
Do you require a decimal approximation for this?
,w simplify (2/3)^(2/3)
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the first thing i did was multiply the first and last equation by two, but the book's answer decided to subtract the first from the last, if I subtracted the last from the first, the same answer would be achieved?
as long as the operation is valid i guess
there are many ways to solve systems of equations
the main thing is knowing that you got the right answer by plugging everything back in
if you have different methods and get the same (correct) answer, then it doesnt matter
alright, because i added the first with the third and the last with the third, but i got a different answer at the end
So the problem probably isn't that, but something a did wrong later right
yeah probably
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yo
simple question
it's $\hat i$
aPlatypus
oh thanks
okay yeah so 2 vectors
$A = a \hat i + b \hat j + c\hat k$ and $B = a' \hat i + b' \hat j + c' \hat k$ such that $a,b,c,a',b',c' \neq 0$
rak³en
What does $A \cross B$ correspond to?
rak³en
Like it makes sense for stuff like $6 \hat i \cross 7\hat j$
rak³en
but how do you a squeeze a third perpendicular vector out of this?? i'd love a diagram with an example, if someone has
Its euclids axiom. Two lines make a plane
ig its like how two sides make a closed plane in geometry?
You can imagine the two vectors to be lines thru the origin
A X B is how much a vector "helps the other turn clockwise" so to speak
counterclockwise
alr makes sense to me
i love conventions
ik how to find it bruh
so you want an intuition behind it?
hm?
yes
they're talking about something like torque in mechanics I guess, which is a cross product
thats an application, I believe
but yeah wait it makes sense to me now
if i treat the vectors as lines in 3D euclidian space
then the two lines will two planes
and the line that is perpendicular to the plane
the two lines will make one plane
is the cross product (line version)
sure whatever
why? 1 plane after the point of intersection and another behind it
thats exactly what I did 💀
they will lie flat on your desk
"after the point of intersection" what's that supposed to mean
like the pencils form an x right (u cant form a v with lines cus then they'd have to intersect at infinity)
so the upper portion is 1 plane, and the bottom portion is another right? or are they part of the same plane
what about the left and right portions too
both sides of the plane make one plane
now we have 4 planes 
erm
okay so all of that is 1 plane
its plane and simple
the right hand rule is a big helper in understanding what A does vs B
A stays in place and B does the turning
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Let $\mathbb{H}_1 = {\mathbf{x} \in \mathbb{R}^4 \mid x_1 - x_2 + x_3 - x_4 = 0}$, $\mathbb{H}_2 = {\mathbf{x} \in \mathbb{R}^4 \mid x_1 + x_3 = 0}$, and $\mathbb{S} = \langle (0, 1, 1, 2), (1, 1, 1, 0) \rangle$. Determine whether it is possible to find a projection $p: \mathbb{R}^4 \to \mathbb{R}^4$ such that $\text{Ker}(p) = \mathbb{S}$ and $p(\mathbb{H}_1) \subset \mathbb{H}_2$.
938c2cc0dcc05f2b68c4287040cfcf71
H1: x1-x2+x3-x4=0
x1=x2-x3+x4
(x1,x2,x3,x4)=(x2-x3+x4,x2,x3,x4)
x2(1,1,0,0)+x3(-1,0,1,0)+x4(1,0,0,1)
H1=<(1,1,0,0),(-1,0,1,0),(1,0,0,1)>
H2: x1+x3=0
x1=-x3
(x1,x2,x3,x4)=(-x3,x2,x3,x4)
x3(-1,0,1,0)+x2(0,1,0,0)+x4(0,0,0,1)
H2=<(-1,0,1,0),(0,1,0,0),(0,0,0,1)>
@left portal Has your question been resolved?
<@&286206848099549185>
Ker(p) ⊕ Im(p) = R^4
<@&286206848099549185>
there arent going to be many people who can help you with this problem i would try going to the math channel, but pinging continuously isnt gonna change much, sorry
What is the question?
this @blissful badge
@left portal Has your question been resolved?
Hi, one second
So I think that you can answer this question by answering the slightly easier question of "what is the dimension of the intersection of H1 and S?"
nobody never helps me at lin algebra channel, I am going to be honest, maybe because this exercises are lengthy and very much involved tbh, people don't have the time to help with a lengthy exercise
If the answer to the above question is "1" then it should be possible to construct p.
If it is 2, then it is not
why
Well, the kernel of p is the set of all vectors that get mapped to 0 by the transform
Wait
Hmmm.... No sorry, upon reflection the above may not be true, give me a moment to think
(not about the kernel obviously)
It should be possible regardless?
S = <(0,1,1,2),(1,1,1,0)>
s in S, a,b in R
s = a(0,1,1,2)+b(1,1,1,0)
s = (0,a,a,2a)+(b,b,b,0)
s = (b,a+b,a+b,2a)
(x1,x2,x3,x4)= (b,a+b,a+b,2a)
H1 : x1-x2+x3-x4=0
b-(a+b)+(a+b)-2a=0
b-a-b+a+b-2a=0
b(1-1+1)+a(-1+1-2)=0
b-2a=0
b=2a
(b,a+b,a+b,2a)=(2a,a+2a,a+2a,2a)
(2a,3a,3a,2a)=a(2,3,3,2)
H1 ∩ S = <(2,3,3,2)>
Ok cool
So if we find H1 perp (H1 cap S), this is the basis set we need to map to somewhere in H2
We can construct this with a similarity transformation
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in all this exercises is always possible, because they haven't taught us proofs, so being it impossible we would need to provide proof of why is impossible :(
Ok here's a way you can construct this
We do a similarity transformation
We have a change of basis matrix which contains {S, H1 perp (H1 cap S)} (as column vectors)
I know and understand.
Then we have a mapping matrix internally which is {0, 0, v1, v2} where v1 and v2 are destination vectors that map somewhere into the H2 subspace as expressed in this basis
If our change of basis matrix is D and our mapping matrix is Q then p is D Q D^(-1)
Note that the choice of v1 and v2 is not unique
We just need to make sure they are linearly independent
And not in S
H1 =<(1,1,0,0),(-1,0,1,0),(1,0,0,1)>
v = (x1,x2,x3,x4)
- v.(1,1,0,0)=0 <==> x1+x2=0
- -x1+x3=0
- x1 + x4=0
x1 = x1
x2 = -x1
x3 = x1
x4 = -x1
H1 perp = <(1,-1,1,-1)>
By H1 perp (H1 cap S) I mean the portion of H1 that is perpendicular to the intersection of H1 and S
Though I guess it's more simply expressed as H1 perp S
so the intersection between H1 and the orthogonal complement of H1 ∩ S
Yes exactly.
To find v1 and v2 you'll want to also find the same thing, but for H2 and S
(and then feed it through the change of basis matrix)
But before you get to number crunching, does it at least make conceptual sense?
I'd like you to double check my work
Just to make sure I haven't made a mistake and we're on the same page
H1 ∩ S = <(2,3,3,2)>
v . (2,3,3,2)=0
2x1+3x2+3x3+2x4=0
2x1 = -3x2-3x3-2x4
x1 = (-3/2)x2 + (-3/2)x3 - x4
(x1,x2,x3,x4)=((-3/2)x2 + (-3/2)x3 - x4, x2,x3,x4)
x2((-3/2),1,0,0) + x3((-3/2),0,1,0) + x4(-1,0,0,1)
so the orthogonal complement of
H1 ∩ S is <(-3/2),1,0,0),(-3/2),0,1,0),(-1,0,0,1)>
=<(-3,2,0,0),(-3,0,2,0),(-1,0,0,1)>
You can check mine also, if it's shown to you.
@left portal as mentioned it will probably be less work overall to find the orthogonal complement of S instead.
Because H1 perp (H1 cap S) = H1 perp S. And because you'll need to also calculate H2 perp (H2 cap S) = H2 perp S
So if you have the orthogonal complement of S you can simply reuse it later
(In long and complicated problems it is generally beneficial to make a "roadmap" of the solution, so that you can try to minimize the amount of work you need to do by hand. This is one example where it saves a little bit of effort.)
H1 cap S I can understand why we look for that
H1 is part of the preimages of p same with S, it's part of the preimages of p
the dimension of H1 cap S has to be >= 1 otherwise is impossible to define a projector p such that the conditions hold
there is a property that to uniquely define a linear transformation, and thus, a projection operator
we need to define it wrt to a basis
Well, the dimension of H1 cap S must be >= 1 by virtue of being in R^4
Because dim(H1)=3 and dim(S)=2
ye and R5 is bigger than the domain R4
we found H1 cap S, I got a bit lost with the change of basis approach and the orthogonal complements tbh
That's fair!
Ok so, we want p to have a kernel equal to S
So that will mean that in your theorem above, two of the v_i will be a basis for S
And they map to the 0 vector because kernel
And the other two will need to be in H1 but not in S
And will need to map somewhere into H2
I guess I was wrong though, anywhere into H2 works, doesn't matter if it's in S or not
problem is H1 is dim(3)
the real problem then is H2 is dim 3
S=<s1,s2>
H1 but not in S = <v1,v2>
p(s1)=0
p(s2)=0
p(v1) = ?
p(v2) = ?
Also not a problem.
We can just choose two vectors in H2
The choice isn't unique
But the problem doesn't specify it has to be
We can just pick 2 of the 3 basis vectors
what is the subspace H1 but not in S?
H1 ∩ S perp
Yeah $H_1 \cap S^{\perp}$
OmnipotentEntity
Which I've been writing as H1 perp S as a sort of shorthand.
ok, let me find the orthogonal complement of S
S = <(0,1,1,2),(1,1,1,0)>
v = (x1,x2,x3,x4)
v . (0,1,1,2) = 0 <==> x2+x3+2x4=0
v . (1,1,1,0) = 0 <==> x1 + x2 + x3 =0
i) x2 = -x3 - 2x4
ii) x1 = -x2 - x3
x1 = x3 + 2x4 - x3 ==> x1 = 2x4
x2 = -x3 -2x4
(x1,x2,x3,x4)=(2x4,-x3-2x4,x3,x4)
x4(2,-2,0,1) + x3(0,-1,1,0)
S perp = <(2,-2,0,1),(0,-1,1,0)>
v in S perp
a,b in R
v = a(2,-2,0,1)+b(0,-1,1,0)
v = (2a,-2a-b,b,a)
equation of plane H1
x1-x2+x3-x4=0
2a-(-2a-b)+b-a=0
2a+2a+b+b-a=0
3a+2b=0
a = (-2/3)b
(2a,-2a-b,b,a) = ( 2(-2/3)b, -2(-2/3)b - (3/3)b, b , (-2/3)b )
b( -4/3, 1/3, 1, -2/3)
H1 ∩ S perp = <(-4/3, 1/3, 1, -2/3)>
=<(-4,1,3,-2)>
dim 1 unless I meased up

Well, you found H1 cap S, and it was dim 1, right?
yeah
If H1 is dim(3) it would stand to reason that H1 cap S perp is dim(2)
Because (H1 cap S) cup (H1 cap S perp) = H1
Hmm oh my
I found the orthogonal complement of S correctly it seems because
S + S perp = R^4
Excellent
but maybe I messed up the intersection
Maybe double check both intersections?
🍎🍎
@left portal sorry, give me a second, I went AFK
I'll work this problem now and compare notes afterwards
@left portal Has your question been resolved?
I appreciate the effort, I am still trying to find the projection operator that matches, I got time so don't worry about time, time is the only thing I got these days, hopefully I manage to pass this, I feel motivated, we got this
Sometimes I think profesor doesn't want us to pass, but I will manage somehow, someway, I study a lot
This is a mistake btw.
I'm still working through the problem.
@left portal
The dimension of H1 cap S perp is definitely 1.
it's the subspace sum of the two that is 3 dimensional.
Ye A union B is most of the cases never a subspace because it's not closed under addition
Usually A + B is more appropriate
,, \cup
938c2cc0dcc05f2b68c4287040cfcf71
yeah
So ok
we can just select v1 to be the basis of H1 cap S perp, (4, -1, -3, 2). And then v2 is some linear combination of the basis of H1 cap S perp and H1 cap S, I just chose (1, 1): which gives (6, 2, 0, 4)
these two vectors are in H1, but not in H1 cap S.
and they are linearly independent.
so we have our two vectors we map into H2.
Your work was correct btw.
Or at least it matches mine
Ignore the bit at the very top, a different problem.
yeah, as in, we just want some vector off of H1 cap S
so a (non-zero) linear combination of these two spaces suffices.
Also H2 = H i pressume
Ok
Edited.
S=<s1,s2>
H1 cap S perp = <v1,v2>
p(s1)=0
p(s2)=0
p(v1) = ?
p(v2) = ?
p(v1) = a basis for H2
p(v2) = a different basis for H2
i guess they don't have to be different, or even bases, just two vectors in H2.
Yeah
Exactly
Elaborate
So if they were linearly dependent, then the kernel of p would be larger,
but yeah, any two linearly independent vectors in H2
it's easy enough to just choose two of the bases.
H2: x1+x3=0
x1=-x3
(x1,x2,x3,x4)=(-x3,x2,x3,x4)
x3(-1,0,1,0)+x2(0,1,0,0)+x4(0,0,0,1)
H2=<(-1,0,1,0),(0,1,0,0),(0,0,0,1)>
Wdym?
Basis vector
we can choose (-1, 0, 1, 0) and (0, 1, 0, 0), or we can choose (0, 1, 0, 0) and (0, 0, 0, 1), etc.
a basis vector can be called a basis for short. And then I pluralized it to "bases" which pluralizes like that because it's a greek derived word ending in "sis"
S=<s1,s2>
H1 cap S perp = <v1,v2>
H2 = <v3,v4,v5>
p(s1)=0
p(s2)=0
p(v1) = v3
p(v2) = v4
well, not quite
S=<s1,s2>
H1 cap S = <v1>
H1 cap S perp = <v2>
H2 = <v3,v4,v5>
p(s1)=0
p(s2)=0
p(v1 + v2) = v3
p(v2) = v4
x = v1+v2
Is x linearly independent to v2?
Because
We need to define it on a basis of R4
If {s1,s2,v1+v2,v2} forms a basis of dim 4 then it's fine
x and v2 are independent, because if we let ax + bv2 = 0, then we have a(v1 + v2) + bv2 = 0, giving a = -b and a = 0 as the requirements for the solution
which gives the only solution at (0, 0)
oh, good point.
I don't think the entire collection is linearly independent.
I guess we need to adjoin v2 with a basis of H1 linearly independent to it and not in S.
rather than with v1.
we have (1, 1, 0, 0) which is linearly indepenent of (4, -1, -3, 2) and S.
which is just the first basis vector of H that I have in my set.
Okay good
so {s1, s2, h11, v2} should be linearly indepedent, but let's double check just to make sure.
I'll use a computer for this though
(1,1,0,0) is in H1 and linearly independent to S and linearly independent from the vector of Sperp cap H1
Yeah i forgot H1 cap S perp is dim 1, my bad
So the determinant of the above matrix is -12, so we're good!
so honestly, this is done, you've proven that there exists a linear transform satisfying the problem
And it doesn't say to find the linear transform
The original exercise says find a projection such that
Is just that i wrongly translated
described here
our mapping matrix is going to be {0, 0, v3, v4}
H1=<(1,1,0,0),(-1,0,1,0),(1,0,0,1)>
S=<(0,1,1,2),(1,1,1,0)>
and D is {s1, s2, h11, v2}
so now you just have some troublesome calculations ahead.
involving inverting D and then doing a couple of matrix multiplications
and then double checking your result.
H1 cap S perp =<(4,-1,-3,2)>
p(0,1,1,2)=0
p(1,1,1,0)=0
p(1,1,0,0) = (-1,0,1,0)
p(4,-1,-3,2) = (0,1,0,0)
Should be the projection
Ker(p) ⊕ Im(p) = R^4 aswell
As long as it's correct is fine leaving it defined like this
In 4 equations
We can find the p(x1,x2,x3,x4) = something
With some couple extra steps tho
Let me give an example
In the example 5
938c2cc0dcc05f2b68c4287040cfcf71
oh, thanks for the translation
No problem :') you have helped me a ton
Hopefully our projection satisfies the kernel not having intersection with the image other than trivial intersection
jfyi, it's doing the exact same thing I did above just with a handful more steps
I'm getting:
[
\frac1{6}
\begin{bmatrix}
2 & 4 & -6 & 1 \
-4 & 10 & -6 & -2 \
-6 & 12 & -6 & -3 \
0 & 0 & 0 & 0
\end{bmatrix}
]
OmnipotentEntity
It maps S to 0, as required, but it doesn't map H1 to H2, I'm getting that for any vector (a, b, c) written in the basis of H1, it maps to (a -4b/3 + c/2, a - b/3 - c, a - 3c/2, 0)
which is only in H2 sometimes.
specifically when b = 3c/2
which means we've made a mistake regarding the whole perp S stuff
maybe we need only find a basis of H1 that includes one vector in S?
(and map that vector to 0)
Basis for H1 cap S is <(2,3,3,2)>
So we have
p(0, 1, 1, 2) = 0
p(2, 3, 3, 2) = 0
and now we need two more vectors in H1 that are linearly independent of (2, 3, 3, 2)
we can select two of the bases, probably
p(1, 1, 0, 0) = (-1, 0, 1, 0),
p(1, 0, 0, 1) = (0, 1, 0, 0)
let's check to make sure our vectors are linearly independent
they are
,w det {{1,1,0,0},{1,0,0,1},{0,1,1,2},{2,3,3,2}}
Its tricky to work with projections, there are some properties i didn't mentioned
Like p(v)=v if v in Im(p)
ah, so you're saying that we need to find two vectors in H1, not in S and not in H2?
H being H1
Nah if they are in H1 they should be mapped to vectors contained in H2, p(H1) should map to vectors in H2
The above I definitely did
sorry, my dumb that final line should be a plus rather than a minus
but it's still non-zero
oh good lord
I'm a moron, I know what I'm doing wrong.
what happened
is that mathematica
this is the solution, but is in spanish let me translate that
There, I was missing a key step
I needed to change the mapping matrix to be relative to the basis of H1
There's probably a less yick way to do this on the mathematica side.
but it works
938c2cc0dcc05f2b68c4287040cfcf71
why are they doing H1 n H2
we prolly defined a linear transformation correctly but since is a projection, is prolly tricky with the image
oh, ok, that works too
I completely missed the fact that p was supposed to be a projection all of this time
I thought it was merely supposed to be a general linear transformation.
ok ok ok
the reason why they do H1 cap H2 is because if the vector is already in H2 (and not in S) we don't want the vector to change.
it's the definition of a projection.
so we need to find the set of all vectors where this is the case.
and those are the intersection

I feel like a moron now.
anyway
you are good, this is real good practice
most people are never taught linear transformations like that
it's honestly why I help.
learn new ways of approaching things, and keep myself sharp
I appreciate the help, we did a lott
like i also have to do the same for linear transformations and with projections
so is good practice still, but now that I look at the solution, projections are a bit easier
because p(v) = v if v in Im(p)
yeah
yeah exactly 🙂
I cannot thank you enough though, everyone ignored me, I really appreciate it omni
it's not that everyone ignored you, it's just a large commitment to help with a problem like this, and there are a smaller than average number of users who can
The other guy just shat some chatgpt garbage at you, which honestly I think is infinitely worse
anyway, yo, glad we got this sorted.
sorry for leading you down a false path because I misunderstood the question at a basic level :x
You are really smart, and you are a wonderful helper Omni, I appreciate it, I know it was a big commitment to help, but people also were reluctant to help in lin alg channel, I wan to be like that when I grow older, when you get older you stop learning and who that stops learning stops living. I appreciate it, we practiced linear maps aswell, thank you so much for taking the time
You're very welcome
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Whoever can solve (b) shall get 1:1 succ
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The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.
also don't be gross
I've tried for an hour doebeit
o wait
i forgot to post my progres soz
I've plateud right here
ignore strat on the right side
what if the question is broken
https://www.youtube.com/watch?v=zNYdkpAcP-g here's a guide btw
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Just try harder bro!
Oh my heckin science is this it? Is person 3# undeterminable? And that's why d is 50%
@vast shale Has your question been resolved?
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Can someone show me how to draw this?
draw a circle and mark its center point as T
Done
Draw a random point anywhere (except at T), and label it K
Ok done
Draw the straight line KT. It will intersect with circle (twice). Mark a point at either intersection at label it Y
oh hol up
one thing
It says that K will have a tangent to the circle, which means that the point K must be outside of the circle
Ok i did it ouside
Done
the segment KT will intersect the circle at just a single point now. Mark that intersection and label it Y
The first or second intersection
there should be only one in the segment KT (not the infinite line)
You also need to draw a line that goes through K and is tangent to your circle
there are two possible lines that could be drawn, but you only need to choose one
Something like this?
No. That line is not tangent to your cirlce
yes
yes
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Hello
Can somebody check my proof?
𝔸dωn𝓲²s
Is that last line necessarily true? Regardless, I think the implication in that direction follows in a far simpler way (choosing your n wisely)
Like x = y^n?
I mean that there’s one n from which the conclusion follows trivially
what do you mean one n?
Since the assumption holds for all n, it in particular holds for some particular n
Yep
a^1 in R is the same as a in R
I also see you’re up quite late (not that I’m any better)
yea
honestly i am amazed how I struggled with the <= more than =>
anyway thanks again!
No problem
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is my answer correct for this question?
seems about right
I made the whole graph +1 up to simply integrate it with respect to x but also converse the distance of revolving radius. That's correct approach right?
how do they solve it without geometrically shifting it?
is there another formula or something?
there exists the shell method too but that requires a change of variables
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Anyone knows how to do just question a as an example? I don’t really know how to do it in word form like is it all real numbers greater than -6 smth like that?
Alright so I think I understood
Ok so consider 2a)
Do u know how to write line equation?
Oh nvm they didn't ask for equation
So basically if u see the graph for a)
x starts at what and ends at what
3 and -6?
Ah nop
Ok so
If u have arrows
It means it is a line i.e., goes all the way from -infinity to infinity
If u have 1 dot and 1 arrow, it is a ray
If u have 2 dots then it means u have a line segment, which is a small part of the line
So now say
x means the point corresponding to line on x axis
@snow knot
Yeah so like the arrows mean it’s like never ending or sort of an undetermined number outside of the range of the graph right
Y is the same? Or is it different
Consider that C has only 1 line the middle (it means belongs)
Yes same
Kk, I think I’ve got it, thanks :)
Anytime!
I type .close right?
Yep
Closed by @snow knot
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how to start
$\left(\left(2^{-2^{x-1}}\right)^{4}+2^{-2^{x-1}}\right)^{2^{-x}}$ it's the same thing as this I think
MæthIsAlwaysRight
$\left(\frac{\left(2^{-2^{x-1}}\right)^{3}+1}{2^{2^{x-1}}}\right)^{2^{-x}}$ which is same thing as this
MæthIsAlwaysRight
how do u know
Oh, I sort of prepared for the exam
how do u solve this though
See what @peak matrix is doing
and then make a substitution to simplify the probelm
I think i just got a better method
$\frac{1}{\sqrt{2}}\left(\left(2^{-2^{x-1}}\right)^{3}+1\right)^{2^{-x}}$
MæthIsAlwaysRight