#help-10
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i thought that there might be problem with it
do i need to use available mappings when constructing this?
what do you mean "available mappings"?
we have h(a) = a, h(b) = b, h(c) = ab
and when we want h^-1(L) we use just the last mapping
are you trying to insinuate that h(a) = a, h(b) = b and h(c) = ab are meant to be taken as definitions of 3 separate functions???
because that is not the case at all
h^-1({ab}) consists of all words w such that h(w) = ab
do you understand that h(a) = a and h(b) = b, and the fact that h is a homomorphism, together imply h(ab) = ab and so ab ∈ h^-1(L)?
so it is not mentioned that h is intended to be a homomorphism?
are you sure?
most problems you've posted so far considered only those functions between string sets that are homomorphisms.
exciplitly not
probably it would be
...can you post the full, un-cropped image just to be sure
because i am highly suspicious
of course if h is not known to be a homomorphism then you cannot say shit about h^-1(L^R) vs. [h^-1(L)]^R. they are two different sets and they have precious little to do with each other.
does it say elsewhere on the sheet anything about h
nowhere
strange.
then perhaps you SHOULD say neither inclusion holds in general, by way of malicious compliance.
$let \ w \in h^{-1}(L^R) \implies h(w) \in L^R$ by the definition on preimage, $(h(w))^R \in L$ by reverse rule
Michal
my bad
im tex noob
IF h is a homomorphism, then you can prove h^-1(L^R) subset [h^-1(L)]^R and the proof is fairly elementarty
elementary*
in fairness the fact h is a homomorphism comes into play at exactly one point
and it is when you say h(w)^R = h(w^R)
literally just definition-pushing
almost automatic
at every step there is really one choice to make
let w ∈ h^-1(L^R)
=> h(w) ∈ L^R
=> h(w)^R ∈ L
=> h(w^R) ∈ L (this is where h being a homomorphism matters!!!)
=> w^R ∈ h^-1(L)
=> w ∈ [h^-1(L)]^R
i got it, except this => h(w^R) ∈ L (this is where h being a homomorphism matters!!!)
actually. hold on.
i might have fucked that up.
h(w^R) = h(w)^R actually does not always hold
my apologies
h(w^R) = h(w)^R only holds when the image of every single character under h has length 1.
learn from my mistake, and attempt to conjure up a homomorphism for which h^-1(L^R) is not a subset of [h^-1(L)]^R
sometimes, though not always, the mistake in a failed proof can suggest a way to make a counterexample.
i will try
maybe
$L = {ab}$ and $h : {a,b,c}^* \to {a,b}^*$ defined by $h(a) = ab, h(b) = ba$
Michal
and h(c)?
or maybe next time you should not copy what i wrote without understanding it.
$L = {ab}$ and $h : {a,b}^* \to {a,b}^*$ defined by $h(a) = ab, h(b) = ba$
Michal
removed c from set
that's more like it...
ok let's take a look
h^-1(L) = {a}, L^R = {ba} and h^-1(L^R) = {b}
...yeah checks out
so neither of inclusions hold
interesting
but these problems with sets, functions and homomorphism are so difficult for me
thanks for help
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could someone plz teach me a method on how to do these kinda questions, as ive never understood how to do them
@silver plover Has your question been resolved?
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We constructed a circle around a regular triangle and a third circle that touches the other two circles. What is the ratio of the areas of the circles?
this one?
that's the one
right
i did this in paint
measured by eye
thats the lenght of the radius
so if we say area is $\pi r^2$
DanielCsocsik
as how you said
let radius be 1
so the are will be
$\pi$
$4\pi$
$16\pi$
right?
i grabbed the radius from here
cuz i dont have a ruler cuz i made this in paint
and then i grabbed the biggest one
that one
and then the smallest one
i put these next to each other so they are parallel to each other
use maths to find the other radii of the circle
isnt the answer16:4:1?
well that was epic then
radius of the circle is $a/sqrt3$, where a is the lenght of the triangle
DanielCsocsik
oh nvm this is correct but how you did it was not mathematically
lol
they wouldn't be to scale
in an actual exam
but I guess you could construct it yourself
if I can draw a perfect drawing on plaid paper
thats why i am happy that they only ask for the answer
if they ask for the answer of 1+1
or answer and proof 1+1
bruh this is painful for me as a mathematicain
please don't do that 😭
proof by eye measure lol
if you wanna solve it properly use this construction
that's your hint, you should be able to get everything from here
eye meassured 120degree
ahahah
😠
i'm dead bro
no problem
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x= 1,5 - 1/y
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How to solve number 1?
Just take out the common factor
?
Whats the GCF of 5x^2 and 50x
5x
Uhh
Like ab + ac = a(b+c)
5=a
50=b
Also, how would i solve number 2 with cmmon factor? 1?
Pure
Factor out the red bit
How?
Is there a way that woulds for all of them?
Works*
@final thunder
F.
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!help
Is this appropriate working?
1460cm -> 0.0146km
23m -> 0.023km
P = 0.0146 + 0.0146 + 0.023
P = 0.0522km
yep thats right
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I know the answer
What is it?
If 1460 = 14.60m Right?
1460 cm = 14.60m
Sure
Then do 14.60 Multiply by 23 You get 335.8 Meters If 1000 meters = 1km then the answer is 0.03358
Of course youve not got the answer yet,
They said the perimeter
I'm sorry, to find the perimeter you add the sides.
Was my answer wrong
Just say the perimeter
0.0522km
Correct ✅✅
🥳
Then do
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i really need help here i do not even understand where to start
@grave wyvern Has your question been resolved?
<@&286206848099549185>
@grave wyvern Has your question been resolved?
@grave wyvern Can you translate?
Is $0 \in \mbb{N}$ according to your book?
Sup?
Well what happens if u fix n = 0
Just fix n=0
and let m be any natural number
You will get m+0 = m, a natural number
which means, every natural number is in E
that means E contains N
hmmmmm
i see
so we have the power to make n whatever we want?
and we choose to make it =0 right?
but what will you respond if someone says what if you put n = 1 or any other number that belongs to N
You can do that
And you'll get irrationals
You have to put every natural number in place of m,n
so somewhere along the way, you have to plug n=0 and m=1,2,3,...
and this way you get all the naturals again
hmmm
so if its irrationals then N doesnt contain E
you mean E doesnt contain N?
no its not E⊂N
N ⊂ E means E contains N
E contains irrationals, but it also contains the naturals
hmmm
we have a rule in our book that confuses the living hell out of me
can i show you?
Lets say you fix m=0, you get 0 + 0sqrt(3), 0 + 1sqrt(3), 0 + 2sqrt(3), 0 + 3sqrt(3),....................
Then its time for m=1
ah
1 + 0sqrt(3), 1 + 1sqrt(3), 1 + 2sqrt(3), 1 + 3sqrt(3),..................
Then it's time for m=2
so if i were to answer the question
2 + 0sqrt(3), 2 + 1sqrt(3), 2 + 2sqrt(3), 2 + 3sqrt(3),....
i would say fix n=0
Fix n=0, let m be any natural number. This way we get m + 0sqrt(3) = m.
That means m(any natural number) is in E.
YEah this is the same
For all x belongs to E n belongs to A
To show N ⊂ E, you have to take any element in N, and show it's also in E
So for all x belongs to N, x belongs to N?
that's what we've been doing tho
Yeah it just confuses me
Take any natural number m from N.
Lemme just write an answer and see if it's good
If we fix n=0 in E, then we get m + 0sqrt(3) = m in E.
Both ways are same actually
The justification I showed above by listing elements above is correct, dw
I see
Something like this?
I wanna try to write it in the same manner as in the book
To guarantee that the teacher gives the point
Fix n=0, so we get m + 0sqrt(3) = m in E.
But since m is any natural number, that means N is in E.
Okay
so A⊂B is A is part of E
so N⊂E means that N is part of E
it confuses me and i always think E⊂N is how its supposed to be lol
since is E is just a sub-set and N is the big guy
A ⊂ B means A is a part of B, yes
N ⊂ E means E is the big guy, N is a part of E
And you can see why E is the big guy
It contains all naturals + a lot of irrationals
pi, e, and so on
Q?
Q is rationals
Q' i guess
ok so i myself understand it but i want to write it in a way that's in the lesson
im trying to figure out how to turn it into the implication that i send in the picture of the lesson
hmmm
Fix n=0, then put m=1,2,3,4..
ah
Fix n=1, then put m=1,2,3,4
1,2,3,4,5,6,7,8,9,10
Do it first
What did u do
i did it till n=4
can u show
Yeah
so if you look at the top where its written 1,2,3,4
you can see that list will go on
Yeah?
yessir
yup
okay
Looking at our list, we can see that it will appear there somewhere
indeed
OH YEAH
so N ⊂ E only if n=0
ah
But yes, you get the naturals once you fix n=0
But its not a restriction, because we know n=0 will happen
so can i write the book way and then show you?
Sure
i couldnt do it lmfao
yeah i definetly understood it but couldnt get it to work with the book way
Whats this?
the book way-
.
Yeah dont worry about that
All it tells us is that
If you take any element in N
It must also be in E.
And we did that.
okay
We took an arbitrary element from N( call it m )
We listed the elements of E.
We saw that the list of elements in E (for n=0) contains every natural number(1,2,3,4,....) and irrationals(for n other than 0)as well
And so m must also be in that list.
That means m is in E.
i see
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How do I approach this question?
this is what i have done so far
A = (2, -4, 5)
Then, I found the direction vector AP = (0, 2, -4)
Then, I am stuck
I think i need one more point, B
so i can then find the normal
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why does this turn into (-x)
maybe you have restriction x < 0?
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|x^2| = |x|^2
it's same thing, ln|x^2| = ln|x|^2
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how do i find max min sup inf of this
Yes
It's not necessarily going to be a max. It's going to be an extremum (local)
I recommend that you draw the table of signs of f'
Then use this to draw the table of variations of f
wdym table of signs
has a range of 0 and 2
So what does that say about our function?
has a max of 2?
Thats the derivative having max 2
What if I wrote this as f’(x)>=0
Can you say a property about f now?
it also has a max of 2?
What?
idk tbh
If I plug in x=4 is 4-sin(x) not greater than 2?
yh idk
it is
What does derivative tell us about a function?
tells u the gradient of a function
Okay and we have that the gradiant is >=0 always
ye
So our function is increasing?
yes?
Can’t we use that
so what would inf and min be then?
if its increasing
there is only gonna be one point such that its equal to 0
and that is gonna be min
so inf and min = 0?
yes since 0-sin(0)=0
hmm ok
gonna be honest
i found that quite hard
im a very visual student, so this logical stuff takes time to understand
(btw just because a function is increasing always doesnt mean limit is inf)
if thats why u said it
,w plot 1-1/x from 0 to 100
both are increasing but they approach a finite value
where has x -1 come from
-1<=sin(x)<=1
ive got another example question, would it be ok if we could go through that as well
got an exam monday on this so gotta make sure i get it
sure
so know how arctan(y) looks?
for this
sure go ahead
ye but only cuz u showed me above but otherwise i had forgotten
whatever the max is for 2x - x^2 - 1
will it be the same for this whole thing
ie arctan (2x - x^2 - 1)
indeed
nice
max at (1,0)
@novel knoll
so max and sup of arctan (2x - x^2 - 1) is 0?
??
@silver plover Has your question been resolved?
yes
Ok cool
Now what about inf and min
Now 2x - x ^2 - 1 doesn’t have a minimum
Does that mean that arctan (2x - x^2 - 1) doesn’t have a minimum as well?
Ie min and inf do not exist?
@silver plover Has your question been resolved?
limit of arctan x as x --> -infty is -pi/2
@silver plover Has your question been resolved?
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is this reasoning right?
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could anyone explain number 18
I would draw both the f(x) and f''(x) then go from there
@opaque thistle Has your question been resolved?
how would you draw it
@opaque thistle Has your question been resolved?
hmm
main rule is negative gradient = under the graph
that is going from f^(n)(x) -> f^(n+1)(x)
stationary points become roots
uhhh
yeah
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Need help with Basic Geometry
This is the problem
use vertical angles
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vertically opposite angles brah
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I have no clue how to do it 😭
yea they are 180
4x+9?
12y-3=6y+63
yes
Is that the final answer or is there more steps
?
they want u to find the value
of x and y
so u have to solve
to find what x=
and what y=
are u sure x is 11?
yea
This is for x
atb !
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does anyone know any resources to help with this question?
or show me the working out, i don't know if I should add the two different youngs modulus of the two materials for finding the stress
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Let Yasmin's age be x and Zayd's age be y. How can you describe Zayd's current age from the first sentence, in terms of Yasmin's age?
This but x instead of z
Yes! That's your first equation
Now, how can you describe the relation between Yasmin's age 10 years ago and Zayd's age 10 yers ago?
The first is Yasmin's age 10 years ago, yes, and the second is Zayd's 10 years ago
If you know Zayd was twice as old as Yasmin at this age, how can you describe this relation?
Okay, we'll do that
Ahh, yes, you're right
My bad. z = y + 4 is correct to describe Zayd's current age in terms of Yasmin's
We still have for the second equation that Yasmin's age 10 years ago is y - 10 and Zayd's is z - 10
You know Yasmin's age at this point in time is y - 10
And Zayd's is twice as big
Yes, that's what I meant by this point in time
Other way around
Si
Yes
take zaid age as x , then yasmin age x - 4 , 10 years ago , that is then zaid age was x - 10 and yasmin's age was x - 14 , 2(x - 10) = x - 14
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Does anyone know when do you to ether common factor a negative number or positive number? when theres a negative number in the polynomial??
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I don't get it
Is the question asking u to find the inputs and outputs using the formula?
ye
Oh okay that's cool
Just solve for whatever you want basically
Do u have any other questions tho?
im confused
so for the first boxes it would be like
40 = (20) + 20?
im confused
Yeah that's fine to be confused
Basically what u said is correct
You can also take the 20 to the other side by subtracting both sides so u have w = 40 - 20
Just think of that question as
"If you add a number with 20 and it gives you 40, what is that number? "
oh
thank you
Ofc are u confused about anything else?
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how would i approach this question?
huh what is the condition for the numbers in A... ? what is between 2022 and 2021 ?
Well, A_2 has numbers that A_1 and A_3 dont have.
A_1 and A_3 have only one number in common.
Every subset must have a prime number..
I want to brute force this lol
how would you brute force it?
well there isnt a lot of numbers in A
oh btw, the options are:
A. 6561
B. 13122
C. 19683
D. 26244
E. 39366
Jesus Christ...
@rotund rune Has your question been resolved?
Ohh, this doesn't sound too bad. You'll want to use the N choose K function
And think about giving some number of the years to A_2, and then of how many years are left, how can you give those to A_1 and A_3 such that it satisfies those conditions
The only tricky part are the last two conditions, however I think this shouldn't be too hard to account for
Essentially you can think of the 2nd to last condition as having an extra year to give out
And the final one should just require you to first consider giving out the prime numbers in A before all of the other numbers (don't forget that A_1 and A_2 could share their prime)
don't forget that A_1 and A_2 could share their prime
i thought that A_2 must not have intersections with other subsets?
Essentially you can think of the 2nd to last condition as having an extra year to give out
i dont quite understand this part
can you please elaborate?
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Sure. So say we gave 3 of the years to A_2, then from condition 1 and condition 2, there would be 7 years left to spread between A_1 and A_3
Right
wouldnt it be 8 years left for A_1 and A_3, since |A| = 11?
yes
But because |A_1| and |A_3| has to share an element, it is really that |A_1|+|A_3|=9
yes
And so rather than thinking of dividing the remaining 8 years between A_1 and A_3 with one overlapping year, we can just think about it as diving 9 years between A_1 and A_2 with no overlap
Also, if you count the number of primes in A, you will see that the common element between A_1 and A_3 is a prime
Which simplifies the problem a little
👍
I think this fact can mostly be ignored since we've realised that the shared year must be one of two primes
@rotund rune Has your question been resolved?
How is it going?
i still dont have an idea...
the subsets
A_1 = {2014, 2015, 2016, 2017}
A_2 = {2011, 2012, 2013]
A_3 = {2017, 2018, 2019, 2020, 2021}
will work but where do i go from this point
Ok, I think you're going about it from the wrong way. For this sort of problem, I find it easiest to think about the sizes of these sets
So, we know that A has 2 primes
yes
As so because A_2 must have one of these primes, A_1 and A_3 must share the other one
And so after this, we have 9 years to distribute between the 3 sets
Right?
yes
Furthermore, we can say that because A_1 and A_3 already share one number (the prime), these 9 other numbers must be distributed among these 3 sets with no overlap, right?
yes
Ok, cool
i'm following to this point
So now we're going to work sequentially distributing these 9 numbers between these sets. So first, (simple question) what are the bounds on the number of these 9 years we can give to A_1?
As in, if we just ignore that A_1 has a prime in it, what are the bounds on |A_1|?
im sorry but i dont quite understand what you mean by 'bounds'
Like, ... <= |A_1| <= ...?
oh
Let's suppose that A_2 and A_3 only have the prime in there sets so far
1 <= |A_1| <= 8 i think?
Almost, upper limit of 9 because we've already given out 2 of the 11 numbers (the primes)
Ok, hang on
Let's just ignore the primes for now
They're easy to distribute
So if we ignore the primes in A, we have 0 <= |A_1| <= 9
right
yes
Cool, so now suppose that |A_1| = n
Then how many non-prime numbers are left in A to distribute?
9-n
Cool
Now we're distributing 9-n numbers between A_2 and A_3
So again, ignoring the primes, what are the bounds on |A_2| assuming |A_3| has nothing except the prime in it?
0 <= |A_2| <= 9-n
Perfect
So now suppose that |A_2| = m
The since we have to distribute all of the non-primes between A_1, A_2, and A_3, how many non-primes must be in A_3
9 - (n + m)
Eyy, awesome
Yep
So now, if we span across the bounds on n and m, we have essentially spanned all possible combinations of |A_1|, |A_2| and |A_3|, right
yes
Cool, so we now just need to determine how many ways there are to pick n years from the non-primes in A and m years from the remaining non-primes (there's no choice as to what goes into A_3 as this is just what's left)
But we know how to do that, right?
so that would be $\binom{9}{n}+\binom{9-n}{m}$
nichoals
Umm, just about. Notice that we'll want to take their product and not sum
oh right
i forgot about multiplication rule
Yep
$\binom{9}{n}\times\binom{9-n}{m}$
nichoals
And so we just want to do that for all n and m within our bounds
So a nested double sum
aahh i see
And don't forget about about the 2 ways to distribute to two primes
Either 2011 to A_2 and 2017 to A_1 and A_3 or the other way around
that's essentially 2C1 right?
and that will be multiplied to this result?
Yep
Yeah, think about it and it should be pretty clear as to why this is the case
let me find it
^ you should be able to do the double sum with a graphics calculator or desmos
You know a regular summation, right?
Lachlan
Mmm, close
rn you're saying that 1<=n<=9 and 0<=m<=n
Which isn't correct
refer back to earlier
ah
is this correct?
oh, and just one curious question, does the order of the arguments in a double sum matter?
Why does n start at 1?
WDYM?
oh im terribly sorry
Haha, nope, it's all good
like, if i put nCr(9-n,m) before nCr(9,n) here, will it change the value?
here* i mean
Nope, it's all inside the inner sum
Multiply by 2!
thanks a bunch
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How do you evaluate the definite integral given the integral of a function f(x)?
I have attempted 2(7)+1 which would give 15x and then I did (15(9))-(15(3))= 90, and this was incorrect.
I've thought of working backwards to find f(x), but I don't know how to do that. I've also thought it might be a transformation, but it didn't seem to meet the definition of an integral transformation.
I'd like some tips on how to evaluate such an integral please.
@olive oracle it's $2\int_3^9 f(x)\dd{x} + \int_3^9 1 \dd{x}$
Ann
and the integral of 1 dx from 3 to 9 is 6, not 1
2*7+6 is what you would be looking for
also it is not possible to find f(x) anyway - there are many many functions whose integral from 3 to 9 equals 7
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@worldly parrot Has your question been resolved?
@worldly parrot alpha*beta = p/2 and alpha+beta = -3/2
square both sides in the latter
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How do I write 83521 in a base 17
well first step for writing anything in base 17 would be to compute 17^2, 17^3, 17^4, ... until you are bigger than your number
alternatively you can divide by 17 over and over again and the remainder at each step is the next digit, starting at the right
check for division of all primes from the smallest?
lol
ull get 17 is the first n lalala
it's just this
@dreamy canyon Has your question been resolved?
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I don’t get this one
.reopen
✅
Wdym next digit starting at the right
lets do a smaller example without so many 0 remainders.
lets write 431 in base 17
we divide 431 by 17 and get 431=25*17+6. so remainder 6
next we divide 25 by 17 and get 25=1*17+8, so remainder 8
and finally we divide 1 by 17 and get 1=0*17+1, so remainder 1
and now we put all these remainders together and get 186
and indeed 431 in base 17 is 186
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How can I prove this statement? Currently got this done
I'd expand the right hand side
How'd you get cos^2(theta * phi) though?
product of two cos is cos^2 no?
If they have the same argument
cosx * cosx = cos^2x
but cosx * cosy is just cosx * cosy
ah K
ah is it just this loool
thank you thank you ❤️
.close
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I have this problem:
$$\sin x = \frac{4}{5}, what's \tan x?$$
smoobles
how do I solve?
Do you know 3,4,5, triangle
I was thinking that $\sin 2/\pi = 1$ so it has to be $2/\pi - y$ or something
smoobles
nope
Ok
So you have to visualise it in a triangle
Sin 53° = 4/5
And 5^2=4^2 + B^2
B=3
Tan x = 4/3
By Pythagoras
It is lot easier than you think
It will help you to visualise
In physics we use this ∆ in lot of questions so I know everything of it
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,w plot x^2 + {y -3/4(x^2)^(1/3)}^2 = 1
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$\hat{i}$ would just be the left column, and $\hat{j}$ the right column.
3317
You do know what a linear transformation is, right?
You get the two regular bases and transform them, transforming all coordinates.
We call them $\hat{i}$ for the $x$ basis and $\hat{j}$ for the $y$ basis.
3317
A base is a set of vectors that span all of said vector space.
Say you've got the regular 2d space, $\mathbb{R}^2$
3317
The bases are $\hat{i}=[1,0]$ and $\hat{j}=[0,1]$.
3317
You can write any point in the format $a\hat{i}+b\hat{j}$.
3317
Where $a$ and $b$ are real numbers.
3317
A transformation is something that transforms those bases.
Such that there's a mapping in between the regular points and the points after the transformation.
For problem b, for instance, it asks you to draw the image of the triangle $ABC$ after the transformation. This means you should take all the coordinates of $A$, $B$ and $C$ and transform their $x$ and $y$ values according to the transformation matrix passed.
3317
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If a polynomial with fractional exponent has solutions x_1,x_2….
Does there exist a polynomial with integer exponents that has the same solutions?
yes, in general: given a finite number of solutions x_1, x_2 etc.. there will exist a polynomial with all those solutions
y = (x - x_1) * (x - x_2) * ....
polynomial with fractional exponent
uh...
Yes I know polynomials can’t have fractional exponents but I couldn’t think of a way to word it better haha
Thanks
function?
haha 69 funny. don't troll in help channels. especially if its not even your own channel
ok
@toxic hollow Has your question been resolved?
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<@&286206848099549185> I sent this yesterday but didn't get a solution
(that why i tag)
The answer is written right there
nichoals
@real acorn Has your question been resolved?
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Hello, is there any way to convert by algebra manipulation x^0.25 to something to the form x divided by something? Like x/a
