#help-42
1 messages · Page 124 of 1
I repeated the wrong vector lmao
again
f(1,0,1,-1) = (-1,0,0,1)
f(0,1,0,0) = (0,0,1,0)
f(0,0,1,0) = 0
f(0,0,0,1) = (0,0,1,0)
Im(f)=<(-1,0,0,1),(0,0,1,0)>
Ker(f)=<(0,0,1,0)>
S =<(-1,0,0,1),(0,1,0,0),(0,0,1,0)>
Ker(f) ⊆ Im(f) ⊆ S
now we need to check if (1,0,1,-1) not in Im(f)
and if {(1,0,1,-1),(0,1,0,0),(0,0,1,0),(0,0,0,1)} is a basis of R4
I repeated the wrong vector
again
f(1,0,1,-1) = (-1,0,0,1)
f(0,1,0,0) = (0,0,0,1)
f(0,0,1,0) = (0,0,0,1)
f(0,0,0,1) = 0
Ker(f) = <(0,0,0,1)>
Im(f) = <(-1,0,0,1),(0,0,0,1)>
S =<(-1,0,0,1),(0,1,0,0),(0,0,1,0)>
Ker(f) ⊆ Im(f) ⊆ S
again bro
I repeated wrong vector
f(1,0,1,-1) = (-1,0,0,1)
f(0,1,0,0) = 0
f(0,0,1,0) = (0,1,0,0)
f(0,0,0,1) = (0,1,0,0)
ker(f) = <(0,1,0,0)>
im(f)=<(-1,0,0,1),(0,1,0,0)>
S =<(-1,0,0,1),(0,1,0,0),(0,0,1,0)>
Ker(f) ⊆ Im(f) ⊆ S
yes bro
now we need to check
(1,0,1,-1) not in Im(f)
(1,0,1,-1)=a(-1,0,0,1)+b(0,1,0,0)
i) 1 = -a
ii) 0 = b
iii) 1 = 0 + 0
iv) -1 = a
we did it
let's check if {(1,0,1,-1),(0,1,0,0),(0,0,1,0),(0,0,0,1)} it's a basis of R4
,w rank {{1,0,1,-1},{0,1,0,0},{0,0,1,0},{0,0,0,1}}
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let $\mathbb{H} = { x \in \mathbb{R}^4 \mid x_1 + x_2 -2x_4 = 0 }$ and $\mathbb{S} = \langle (1,0,1,0),(0,1,2,-1) \rangle$ Define a linear transformation $f : \mathbb{R}^4 \to \mathbb{R}^4$ such that $\operatorname{Im}(f) = \mathbb{H}$ and $\mathbb{S} \subseteq \operatorname{Ker}(f \circ f)$
i wanna b this intelligent but am only 16 💔
intelligence doesnt come with age, knowledge does
(generally)
very bad at maths and dk where to start
938c2cc0dcc05f2b68c4287040cfcf71
first step is to not intrude onto other's help channels
x1 = -x2 + 2x4
!help or chat a bit in #discussion
To ask for mathematics help on this server, please open your own help channel or help thread. See #❓how-to-get-help for instructions.
<@&268886789983436800>
(x1,x2,x3,x4)=(-x2+2x4,x2,x3,x4)
x2(-1,1,0,0)+x3(0,0,1,0)+x4(2,0,0,1)
H = <(-1,1,0,0),(0,0,1,0),(2,0,0,1)>
f(v1)=w1
f(v2)=w2
f(v3)=w3
f(v4)=w4
im(f) = H
S ⊆ ker(fof)
this kernel of fof condition is tripping me up
that's all v such that
f(f(v))=0
ker(f) ⊆ ker(fof)
but ker fof is bigger than ker f
is it me or ker(fof) = ker(f)??
yeah i guess that was the trick
im(f)=H and S ⊆ ker(f)
f(v1)=w1
f(v2)=w2
f(v3)=w3
f(v4)=w4
f(v1)=(-1,1,0,0)
f(v2)=(0,0,1,0)
f(v3)=(2,0,0,1)
f(v4)=0
f(v1)=(-1,1,0,0)
f(v2)=(0,0,1,0)
f(v3)=0
f(v4)=0
S = <(1,0,1,0),(0,1,2,-1)>
f(v1)=(-1,1,0,0)
f(v2)=(0,0,1,0)
f(1,0,1,0)=0
f(0,1,2,-1)=0
ker(f(f(x)) all x st f(f(x))=0
ker f(x) all x such that f(x)=0
f(x) = a
f(a) = 0
stop tripping, ker fof = ker f
period
anyways
Im(f) = H
S ⊆ ker(f)
@simple musk Has your question been resolved?
I need some help proving ker(fof) = ker(f)
@simple musk Has your question been resolved?
@simple musk Has your question been resolved?
@simple musk Has your question been resolved?
f(0,1,0,0) = (-1,1,0,0)
f(0,0,1,0) = (0,0,1,0)
f(0,0,0,1) = (2,0,0,1)
f(1,0,1,0) = 0
@simple musk Has your question been resolved?
@simple musk Has your question been resolved?
thats not true
yeah
do u know rank-nullity?
only ker f ⊂ ker fof
yeah, dim(im) + dim(ker) = dim(dom)
yeah
so what should the nullity(f) be?
and whats nullity(f^2)?
f^2 = f compose f btw
dim ker = 1
so?
thats >= 2
how ?
bro, please elaboratee
well do u know of the identity dimker(ST)<=dimkerS+dimkerT?
is something I just realized is true, though Is still an inequality
but what does it say for ur current problem?
for our purpouses
dim(ker(fof)) <= dim(ker(f)) + dim(ker(f))
and dim(ker(f)) = 1
so dim(ker(fof)) <= 2
and we also know S ⊂ ker fof
dim(S) <= dim(ker(fof))
2 <= dim(ker(fof))
dim(ker(fof)) >= 2
hahah
and since we know dim(ker(fof)) >= 2 and dim(ker(fof)) <= 2
that must be only possible if dim(ker(fof))=2
so?
can u say anything more about ker(f^2) and S?
they are equal
since their dimensions are equal they describe the same subspace
or maybe not, just give me a sec to think
S ⊂ ker fof
but they are same dimension
they must be equal
but unless ker fof ⊂ S we will never know
well what is the definition of the dimension of a vector space?
the length of the basis, so?
as it says, any two bases of a finite-dimensional vector space are of the same length
moreover, if i have a basis and a linearly independent set with the same length, what can u say about the linearly independent set?
what do you want me to say? they are equal to each other?
so that proves this
actually no
its that the set is also a basis
thats what proves ur claim
okay
so u know ker(f^2)=S
S = <(1,0,1,0),(0,1,2,-1)> = ker(fof)
and ur idea so far has to find a basis and define the elements f maps this basis to
yeah exactly
any ideas?
u can construct a basis one vector at a time
u probably first want to describe a basis of ker(f) right?
well
which basis vector I send to 0
S = ker fof
what about ker f?
again, whats its dimension?
dim ker f = 1
what about it
so any basis of ker f should be just 1 vector
but what properties does this vector have to satisfy?
it cant be any arbitrary vector, right?
well
since Ker(fof)=S
and ker(f) ⊂ ker(fof)
then ker(f) ⊂ S
should be in S
problem is, which vector in S to map to 0
v1 ∈ S
why not the angle notation <
idk i thought u used axler
but wtv
i can use angle notation
can u think of something v1,v2 should span?
like what subspace makes sense next
cuz in the end u want a basis v1,v2,v3,v4 of R^4
and u want to know f(v1) to f(v4)
rn u know f(v1)=0
no
and u have subspaces kerf, S=kerf^2, H of R^4
currently kerf=<v1>
dimS = 2
and dimH = 3
also kerf is a subset of S
if i have an element of S\kerf, what should f map it to?
S\kerf?
to H
yes
why did u brought up fof
so if v2 is in S\kerf, u know f(v2) is in imf=H, but also, f(f(v2))=0
I thought we were over with fof
so what else do u know about f(v2)?
f(v2) ∈ Ker(f) = <v1>
great
so maybe lets just say f(v2)=v1
since i can scale v1 arbitrarily
but then f(v2) is in H intersection ker(f), so what new condition does v1 have to satisfy
before we only said v1 is nonzero and in ker(f)
and also H intersection S
what can u say about H intersection S in ur original problem?
S = ker(fof)
ie what does it equal
why
how does kerf relate to S?
idk, is prolly dim 1
we would need to find it
H ∩ S = <v1>
well numerically, using the vectors given in the question
how
so I find the intersection between S and H or no?
you just gotta write S as a generic point in R4 and make it satisfy equation in H to find the constraint and put the constraint back into the generic point of S
s in S, a,b in R
s = a(1,0,1,0) + b(0,1,2,-1)
s = (a,b,a+2b,-b)
H : x1 + x2 -2x4 = 0
a + b -2(-b) = 0
a+b+2b=0
a+3b=0
a = -3b
s = (-3b,b,2b-3b,-b)
H ∩ S = <(-3,1,-1,-1)>
(-3,1,-1,-1) = -3(1,0,1,0) + (0,1,2,-1)
(-3,1,-1,-1) = (-3,0,-3,0) + (0,1,2,-1)
M8 u gotta start thinking for urself
U have 2 vectors v1,v2 for which u know their image from f, ie f(v1)=0, f(v2)=v1
And u know v1 is in <(3,1,-1,-1)>
U just need to find v3, v4
The last condition u need to satisfy is for H=im f
So think about that
And figure it out
v3 = e1, v4 = e2
you can just use standard basis vectors
as for the image
f(3,1,-1,-1) = 0
f(h3) = (3,1,-1,-1)
f(e1) = h1
f(e2) = h2
where H = <h1,h2,h3>
I am trying, is just hard exercise bro
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hlep please
there is not asolution
online
I ended up getting 3/91
but there is not answer choice for that
I baseically did 6 choose 2 * 4 choose 2 and divided that by 2 and then divided all of that by 15 choose 4
is there a mistake in my thinking
the 15 choose 4 is essentially choosing 4 chords from the 15
and 6 choose 2 is choosing 2 of the points of the 6
and then another 2 for the 4 choose 2
so then we can just find those two choords, and the rest will connect themselves. as in we find two, and the other two are decided
and then divide by 2 for repetition
what is wrong with my answer
is it just simply a computational error?
help would be much appreciated
thank you
this is where you are making a mistake
you see to account for repitition or indistinguishable chord sets...it has to be divided by 3!
Let me explain u with small examples
Say you have 4 people A,B,C,D and you have to create 2 teams with 2 members each ...you go on with (4C2*2C2) / 2! ....we divided the whole by 2! because whether we select A,B with 4C2 or we select C,D with 4C2 , both results in same distribution of teams...teams here are indistinguishable to each other
Similarly say now you have A,B,C,D,E,F 6 people and you have to create 3 teams of 2 members each...you will do (6C2*4C2) /3! ....we divide by 3! here to account for 3 indistinguishable teams here
NOW another case which is more valid and directly links to the Q is if out of 6 people, we need to create 2 teams of 2 members each...last 2 would be left behind...this still doesn't change the answer as we want all 3 groups (2 teams and the group of 2 people left out) to be indistinguishable so we still do the same thing i.e (6C2*4C2)/3!
huh
thats weird
interesting
so how might I go about thinking about this in the future
and how can I avoid mistakes like these
thank you very much for the helpful response, and taking the time to write that by the way
Just remember when, why, and how we account for indistinguishability.
so now you know which option is correct?
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anyone?
are there something missing in those boxes or it's just an indefinite integral?
never heard that lol
In integral calculus, the tangent half-angle substitution is a change of variables used for evaluating integrals, which converts a rational function of trigonometric functions of
x
{\textstyle x}
into an ordinary rational function of
t
{\textstyle t}
by setti...
you should have met this before, since this integral is very high-level
nope , never , this is a 12th grade integral
no way 
but they shouldn't be that hard
i used Wolfram Alpha to solve it and it gave me a monstrosity
never heard of it either lmao
Then it's probably the problem's fault
nope , alr checked it
it is what is given in the book
if you differentiate it it doesnt even come close
have you heard of a method , where we take a part and put it equal to a variable , then differentiate it , and then try to make its differential in the integral along with the value we chose to put in the variable
I hope this makes enough sense to you
the only way that is the answer is if the problem doesn't have the minus sign
idk bruh , i'll ask the teacher once
k
i have another one tho if you can
though, just in case, i'll solve the one without minus sign if you need
no no its fine , i'll cross check it with the teacher
alr
Hint: sin(2x)=2sin(x)cos(x), then let u = cos(x), du = -sin(x)dx
oh damn , i was doing it right then
thanks , i tend to not beleive myself sometimes lmao
np
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Need help with precalculus analytic geometry
Did you solve for where the intersection is
Well you have 2 straight line equations that intersect each other at some point (x,y)
You want to solve the equation of a third like that passes through that point
And said 3rd line has a gradient of 4
So you want to make eq1=eq2
In order to see where that intersection is
okay hold on let me try sumn
okay didnt work out
how do I find the point of intersection between the two equations
I had an idea with this
but do I need to convert the equation to y=mx+b form?
the equation for that line would be (x + 6y - 4) + k(3x - 4y + 2) = 0, make slope = 4
put slope = 4, and sub value of k
okok
so next time you might wanna save time on evaluating the intersection point and doing y = mx + b stuff
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any ideas on what to do with this
yes, thank you very much
just to clarify, we would do this if we had 3 left over right
so if it was 7 choose 2
and 5 choose 2
then would we still divide by 3!
or is it just when the amount being chosen is equal
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A square is tiled by 24 congruent rectangles. points A and B are the midpoints of a pair of opposite sides of the square on each side of the line AB, four rectangles are chosen at random and colored black. The square is then folded over line AB. compute the probabilty that exactly one pair of black rectangles is coincident.
I need help verifying my answer to this
I got 24/2475
@remote mural
I tried to use your idea
where you divide by 3!
except for this problem I tried dividing by 4 fact
so
idk
could anyone please check and lmk if the answer is correct
thanks
Do we have the rectangles configurations?
nope, thats all
they are just arranged inside it
I mean they are symmetric
from what I imagine
12 on one side
and 12 on the other
I dont quite think that it would be split down the middle
or weirdly
we still have to prove it tho
Hey
I believe it should be 20/483
favourable ways of selecting = 24* 1* 22 * 20
Total ways= 24* 23* 22* 21
P(exactly 1 pair coincide) = favourable/total =20/483
@manic pewter Has your question been resolved?
first case: 3 on one side, 1 on the other
- pick 3 rectangles on one side: 12C3
- pick 1 corresponding rectangle on the other side: 3
- we can do this in 2 ways (3 on the right & 1 on the left, or vice versa): 2
=> total for this case: 12C3 * 3 * 2
second case: 2 on each side - total pairs (both matching and not): (12C2)^2
- pick 2 on one side: 12C2
- pick 2 on the other side that don’t correspond to the first 2: 10C2
=> subtract matching cases: (12C2)^2 - 12C2 * 10C2
now, the probability: (12C3*3*2 + (12C2)^2 - 12C2 * 10C2) / 24C4
So... 41/161
hmm, i think there are 4 rect on each side of the line?
or did i misread
for your latex you should use #latex-testing or #latex-help
Oh... exactly 1 match... hang on
oh ok, ty
yeah!
$\frac{\binom{12}{1} \times \binom{11}{3} \times \binom{8}{3}}{\left(\binom{12}{4}\right)^2}$
raydohad
is this the answer?
you can model this questions like this also i think
consider you have two bags with numbers 1 to 12
you take 4 numbers from eachbag
probability that exactly 1 number is same
i think
first case: 3 on one side, 1 on the other
- pick 3 rectangles on one side: 12C3
- pick 1 corresponding rectangle on the other side: 3
- we can do this in 2 ways (3 on the right & 1 on the left, or vice versa): 2
=> total for this case: 12C3 * 3 * 2
second case: 2 on each side - total pairs (both matching and not): (12C2)^2
- pick 2 on one side: 12C2
- pick 1 on the other side that don’t correspond to the first 2: 10C2
- pick 1 corresponding rectangle on the other side: 2
=> total for this case: 12C2 * 10C2 * 2
now, the probability: (12C3*3*2 + 12C2 * 10C2 * 2) / 24C4
is this not the case? im confused by your answer @gilded atlas
there are in total 4 rect
oh
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n each side of the line AB, four rectangles are chosen at random and colored black
i think it means 4 on one side 4 on other?
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What exactly am I doing here?
You input x in g(x) then you input the the value of g(x) in f(x)
I just need to do it for one of the values in each collumn?
Yep you take g(3) then f(g(3))
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yo
How do u solve this?
I need help with b and b
Top and bottom
I'd really appreciate it
The first rule here to be exact, thx yobo
Write 12 as 3*4
And then use the first rule in the image that yoboi linked
Alr
Now what?
@glad parrot
<@&286206848099549185>
Anyone?
I need help for 2 questions asap
My exam is on Monday and I got so much to study for
Use the expansion property (the first one) and re write the log(3*4)
Idk how to do that
What's x and y?
I got 2, 3, and 4
3 numbers
2 letters
Which one is x and which one is y
Wtf is this shit
You have -log3 in the question
These two cancel each other out
And use the third property for the log4
Here
Log2(12)-log2(3) = log2(12/3)=log2(4)=log2(2^2)=2log2(2)=2
So if it's a minus Infront
3log2(2)=3
It crosses out?
Why
U guys are making me even more confused
I need one person explaining at a time
Idk who to listen to now
Basic rules
Yes you have
3log2 + log3 + log4 -log3
Just like log2(3)+log2(4)=log2(3*4)
So were left with logbase 2 4
Dont give the answer this fast
The 3rd property in the page
That says
Logbasea x^n =n logbasea x
I give up
And 4=2²
Fuck this exam
Lol
Good job
Can someone write it out cuz wtf
Or we can get someone who actually knows how to do this
And knows how to explain SIMPLY

In less than 10 mins you'll be able to solve this
Nah cuz they don't do the same question
Skip this I'll figure it out later
Can u help me out with a different question should be easier
Well you gotta learn how to solve it
Not just memorise the question
Lemme show you
I'll watch a video in a bit
The bottom one?
Wtf is that
The solution
Shit just made my day worse
I'm skipping this question as well
Ima do the easy ones
Go watch a video about the logarithms properties...
Couldn't care less
Not allowed any formulas either
The vid doesn't explain that question
This algebra video tutorial provides a basic introduction into the properties of logarithms. It explains how to evaluate logarithmic expressions without a calculator using basic properties of logarithmic functions.
Logarithms - Free Formula Sheet:
https://bit.ly/4fEwqv0
Logarithms - Video Lessons:
https://www.video-tutor.net...
Srt of x equals x^1/2
Let's do something that's not logs
Ok...
Yep
That's a
In b
You'll let the function p equal 1 million
And solve for t
In c you'll let the function p equal 2*the population given
Alr
Ok lemme try out b
Yea nvm
Idk
Do I plug in 19 as t?
Nvm idk wtf I'm doing
@wheat owl
How am I supposed to know
And we have an equation that represents the population right?
If it doesn't tell me when
Stay with me and calm
Yes
Alr
Just finished my English exam that's why I'm like this mb
So then
If we need to find the time it takes for the population to reach a million we need to make the equation that represents the population equal 1 million
And get T which is the time taken
Since as it said
T represent the time in years
You don't plug a value as t
Oh
Ohhh
And you solve for it
Oh
You have to subtract 610,000 from both sides
Then divide
By what's multiplied by t
Which is 610,000 * 0.026
Nah but like
There's 2 610ks
Which one do I get rid of?
English exam fucked me up this is from 5 lessons ago
I did this back in October I don't remember
Idk how to simplify this more
To solve for x
You make X only in one side and the other numbers in the other side
Here we have a number +T times a number = another number
So first we need t times a number in one side
Just write it out
So we will subtract the first number from both sides
I can't learn like this tbh
Ok there
U could've said this
Now we divide by 610k
6.393
610k ÷ 390k
Yo @wheat owl
Is this right?
Same thing for c I just multiply 610k by 2 and add that instead of a million
Yo u there?
@wheat owl
This exam bouta be light
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What do I do with the 0?
what about it?
every root should appear in the factored form of the polynomial
T_T is it a mark the incorrect option question?
😭 um idk
I'm doing this based off of the notes the teacher made is do
Us*
why you marked wrong on b, c
is the y - axis perhaps upside down
wait.? wont the leading coefficient be negative?
No?
This is the notes our teacher told us to write
So if the x int is -4 in the equation it becomes +4??
I'm cooked
the graph is continuously decreasing for large values of x so that's only possible when the leading coefficient is negative?
2) As x -> ± inf, your fn goes -inf but x^4 is dominating, so leading coeff should be -ve```
refer to Cid's figure
Also, for the fourth part, it's just factor theorem
Factor all of x int?
hmmm?
Idk.. I haven't understood this at all in class 😭
yeah you can even try to desmos the graph with k<0 it should be negative
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Baii
Baii
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i know that this is the formula but i dont know how to find any of the variables
try drawing a picture of the scenario :)
https://tutorial.math.lamar.edu/classes/calci/volumewithrings.aspx this also may help
In this section, the first of two sections devoted to finding the volume of a solid of revolution, we will look at the method of rings/disks to find the volume of the object we get by rotating a region bounded by two curves (one of which may be the x or y-axis) around a vertical or horizontal axis of rotation.
(this has some worked through examples)
oh those aren't 3 functions
well two of them are
x=4 is a vertical line
y=0 is a horizontal line (function)
and y=x^2 is a function
y=x^2; x=4; y=0
yes
x=4 isn't a function with respect to x
as i said, drawing a picture will help to figure out what you need. (it may even be simpler than you think)
okay so why does it say to use the washer method if there isnt a radius on the inside? because we r rotating on the x axis and the function touches the x axis
oh it says disk OR washer method
do the disk method here works best
it would seem so
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can i get some help with this exercise?
could you tell me a bit about what you've already tried or what parts are confusing you?
yep yep, so i know that b) e) and f) are wrong
but the thing is that i dont know how to prove a) c) or d)
i really dont understand how i can approach the problem of is det B equal or diff from 0
any ideas?
you're right b, e and f are indeed false when det(a) = 0
let's quick recap what it means for det(a) = 0
imagine a matrix as representing a transformation of space. The determinant tells us how much matrix scales areas (in 2D) or volumes (in 3D), and so on
If det(A) = 0, it means this transformation squishes space down in some direction, essentially collapsing dimensions
this has some important consequences for things like inverses and solutions to equations
i dont need to bend space time to know that a matrix is invertible only if det A diff 0
its pretty basic actually
How do I solve this using the graph?
not the right channel buddy
my apologies if i was going too basic there
no no
u were actually saying some really complicated stuff
that i didnt quite understand
i dont know how a matrix is squishing space into a direction
but, does it have relevance regarding this exercise?
hmm
squishing space it's a way to interpret what a determinant of zero means geometrically, but it's not directly needed to solve this problem
not really in terms of directly proving the answers
it's more background understanding
for this exercise, we really need to use the properties of determinants and matrix operations more directly, like you already know about invertibily and determinants
forget about "squishing space" and focus on what you know about determinants and matrix multiplication
a) There exists B ∈ M_n(R), with B ≠ O_n, such that AB ≠ O_n
in simpler words, this is asking "" can we find some matrix B which is not the zero matrix, such that when we multiply A by B, the result is also not the zero matrix?
think about the identity matrix
i just checked with 2 x 2 matrixes and yes it works
which would mean that c) is wrong
but how is d) wrong then
why would det B have to be 0
if det(B) ≠ 0. If det(B) is not zero, it means that matrix B is invertible
do you remember what "invertible" means for a matrix?
think about like this: with regular numbers, "invertible" is kind of like sayinh you can "undo" multiplication
let me do a example
are you trying to explain to me that B*B^-1=In?
if you multiply a number by 2, you can "undo" it by multiplying by its inverse, which is 1/2 (or dividing by 2). So, 2 and 1/2 are inverses of each other for multiplication because 2 * (1/2) = 1. And also (1/2) * 2 = 1. The number '1' is like the "identity" for multiplication
yeah
buddy
i know some stuff about matrices
i know all the theory there is to learn
i just need help understanding this exercise
not all of it, we werent taught eigen values and stuff
but i dont think its that hard
anyway
so, any idea on how to actually show why d) is wrong?
because the det B diff 0 is throwing me off
If det(B) ≠ 0 and AB = O_n, then A must be O_n. But we know A is not O_n. So, such a B cannot exiist
i cannot give an example that would work is B diff 0, so its obiously wrong, but how would u prove it
why would it have to be On
what does the determinant of B have to do with whether or not A is On
this looks like its really complex
omg
i havent even thought of this
ure amazing
thank you
what about c) tho
how would you prove that c) is wrong
oh
you can just give an example there
nvm
wow
thx
i got more matrix exercises
if you feel like u can do more, tell me
sure, just send i will help
okk wait one sec to write down the solution for this one u sent first
np
ill just type the next one for u
so
let D be a determinant different than 0; D e M3(R) and its elements can be 1 and -1. Then:
a) D=1
b) D=-1
c) |D|=1
d) |D|=2
e) |D|=4
f)D=2
are you still here?
yep
i think i got it actually
theres just 4 possible determinants
unless u just multiply the determinants by -1
bc then ud have 8
it's not quite that you multiply the determinant by -1 to get more values
the determinant itself can be positive or negative
yea i guess
for a 3x3 matrix with ±1 entries, the determinant will always be an integer
so, the possible determinants are numbers like 0, ±4, ±8, ±12, and so on multiples of 4
since we are given that det(D) ≠ 0, the smallest possible non-zero value for the magnitude or absolute value of the determint
is?
when i said "multiples of 4," I meant exactly that - any number you get by multiplying 4 by an integer (positive, negativem or zero)
anyway, the answer was indeed e so i got it
yep
Hello everyone !
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im not sure what this is asking for
This is asking you to prove that ( f\bigl(f^{-1}(D)\bigr) \subseteq D ) and then give an example where the inclusion is strict.
Samuel
I dont see how the first given function and sets help with that?
im just not even sure where to start
we did nothing like this in class but its assigned for homework
When you don't know where to start. Start writing what you have and see where it leads.
So you know D included in S what does that mean
D is a subset of S
Ok, how would you write that mathematically
every element in D is also in S
Ok good. So let x belongs to f(f-1(D))
then x belongs to f(f-1(S)) ?
Why would f(y) be an element of D ??
It's just a definition
When you dont know how to prove a causality , just write the definition of your starting point and explore where it goes (while keeping in mind the result you want to get
how did you get that y is an element of f-1(D)
Because this
if x belongs to f(H). That means x = f(something), with something belongs to H
in this case H is f^-1 (D)
You're welcome, feel free to ask if you have more linear algebra questions
oh this is linear? its for my real analysis class
so f: A -> B and Y subset of B were never used?
The whole first sentence is the definition of reverse image.
it's just to tell you (remind you) of what is the reverse image
and then they apply it to X --> S
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How do i factor the denom here
could try the rational root theorem
or maybe get lucky and notice that x=-1 is a root
oh, well it says that the only possible rational roots are 1, -1, 3, -3
and then if you try each of those, you see that only -1 works
i appreciate you jumping into it but i forgot how to apply rrt
so i needa figure that out first lol
but that's enough to get a quadratic factor
and then you can use the quadratic formula to get the other two roots
yeah, thats exactly how you do it
i dont get it
your a0 is 3
let me see if latex will let me list it
and your a_n is 1
so 3/x^3?
a_0 and a_n are coefficients here
ah
the coeff for x^3 is just 1
so 3
and i need to do that for all positive and negatives?
yep so your only possible rational roots are the factors of 3
(including the negative factors)
$\pm\qty[\frac{3,1}{1}]$
;(
yup
is that what it's saying
nonnonnono
lookie here!
okay so we need to check if 3, -3, 1, and -1 are factors?
not factors, rational roots mb
meaning i do f(3), f(-3), etc
okay but what if i have coefficients
yea its convenient that its one here
but what if it were 4x^3 - 2x^2 + 5x + 3 for example
+-3/4, +- 3/2, +- 3/5?
then you have to consider 1, 1/2, 1/4, 3, 3/2, 3/4 and also their negatives
the theorem quickly becomes less useful as the coefficients get bigger
the factors of 4 (the leading coefficient) are 1,2,4 and their negatives
the factors of 3 (the constant term) are 1,3 and their negatives
and constant, yeah
yep the coefficients of the highest power and the constant term are the only ones that play a role here
meaning x+1 is a factor
one of my factors will be (x+1)?
pretty much
damn so calculus really is like 90% algebra and the 10% is knowing how to set up the equatione
you'll still need to know how to integrate the partial fractions
but yea a fair amount of the work is finding the partial fractions to begin with
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is there a way of doing this without brute force?
isn't hard checking all possibilities tho, it's only 16
4 member:1member, 3member:2member
4 member is guaranteed to have it i believe
it's easy if two numbers and their difference is possibly 2 numebrs total
then set with 2 doesn;t have 1 and doesn't have 4
which means it has 3, 3 can't go with 1 and 4
then 5 can't go anywhere
the other intepretation idk
oh but {1,2}{3,4,5} would work if it can't be 2 numbers
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lets say a projectile is thrown perfectly horizontally, if there is a fan that is added in the direction the projectile is thrown, does that increase air time and horizontal range?
I mean ideally it would increase horizontal range but not air time ig
yes i think so
yeah thats what i was thinking as well, but how come is it that if a faster projectile is lauched then it stays in the air the same time? like if a bullet is launched perfectly horizontally it woluld have more air time then if a ball is launched horizontally
air time depends on vertical component of motion
so if the projectile is thrown perfectly horizontally
the fan will also only act in the horizontal direction (since you said its in the direction the projectile is thrown)
yea
but what abt this?
for air time
because you aren't changing the vertical component
all objects will take
rlly
the same amount of time to fall
if theyre launched at the same velocity
sorry wait are you saying
right but the vertical velocity is the same
but its thrown perfectly horizontally
so the vertical velocity is 0
right
in your scenario the fan will act the same direction as the projectile
It travels a further distance in the same time
so lets say 2 balls thrown perfectly horizontally, no y initial.
a ball travelling at 100 m/s and a ball launched at 1 m/s will hit the ground at the same time?
it's not an ideal case T_T The fan does not affect the air resistance surrounding the bullet (which is already less significant than the ball, thanks to it's mass).
Yea it's only ideally
i mean it makes sense in the sense that only vertical velocity affects air time, but logically wouldn't it make sense for a ball to hit the ground after a bullet
You can go outside and test it yourself
With like any ball ig
Won't be exact but you'll get the idea
do you assume this because of the difference in mass?
if so that's not the case even though it may seem like it
objects regardless of their mass will accelerate downwards at the same rate
hmm i see
cited by Principles of Physics
in practice though im ignoring other factors which may affect air time
If you're so interested, you can skim through 6-2 of Principles of Physics. The pdf is available online
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Seems like you got it right
Or are you having trouble understanding why 0 is right