#help-0
1 messages · Page 131 of 1
i dont have the math i did before but i can just paste you some of the calculation
Im quite sure unless it's something i dont see
so
lets start with c
we know that she has 12 euros right ?
now she buys 3 mangoes
yea
no
thats the amount bought
no
k
if you have money and you buy something you have less money in your hands afterwords
so try it again
she has 12 euros and she spends 4.80 of it, how much money does she have left in her hands ?
7.10
7.2
alright so she has 7.20 euros left
right ?
do you understand that far ?
now we know that each apple is 70 cents right ?
yea
so how can she buy 17 apples prices at 70 cents if that amounts to 11.90 euros when we only have 7.20?
she would not have enough money
how many apples do you think she can buy with 7.20 euros ?
10
good
and 10 times 70 cents is 7 euros
so if she spent 7 euros and she has 7.20 euros
how much do you think she has left ?
20 cents
well
that's your answer
no
explain
i think ur wrong
explain
here ill just paste the math
alright
i only have a part of it
and i did get (i) correct
ik its correct cuz my teacher made the question
😂
chill
ok ill just put 20 cents and after my teacher corrects it ill see if u got it correct
1 mango = 1.60 , 3 mangoes = 4.80 . She has 12 euro , we remove 4.80 euro as she buys the mangoes, she is left with 7.20 euro, since 12-4.80. Now that we know 7.20 is her spending money, we know that apples are 0.70 a piece, which means she can buy 10. 10 * 0.70 is 7 euros, and now we can work out how much she has left. 7.20 - 7.00 = 0.20. that's the money she has left. 0.20 euros is how much she has left
which part are you not understanding
the answer you got which is 14 is because you worked it without removing the cost of the mangoes
🙂
why did my teacher mark it correct then
teachers make mistakes
ok ill go tell my teacher that hes wrong
if you want to workout how much change she has after buying 17 apples without the mangoes, do 17*0.7 = 11.9. 12-11.9 = 0.10 euros.
your teacher is a human
but that's not the way to work this out
@ivory pivot you agree with this ?e
ok ill try that
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Try drawing a picture
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find the least integer value of m for which the curve x(y+x)=2 meets the line y=mx-3
what have you tried so far
b^2 - 4ac
i used the discriminant thingy
it intersects or touches?
nope
so it means intersects
ohh
how do you find the x value where two linear equations intersect
not quite
all you have to do is set the two equations equal to eachother
if a = 2x + 3 and b = -4x + 7
great!
tysm omg
np
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Im kinda confused with the question. It's asking what's gonna happen if n tends to a very large number?
correct
basically as n gets bigger, what does the function tend towards
You gotta do the limit when n tends to infinity
ok
What it's asking is the same as finding the limit as n tends to inf
i think my way is valid
but yh
What is your way?
since my lecturer taught us the method i did
Right no matter how.you do it, you're still finding the limit
lemme check my mark scheme acc
Yes I'm just disputing the fact you said "we don't need to" in response to someone saying you have to find the limit
Just finished let me just check if i did it right
yh
also worth dividing the numerator and denominator by the highest power of n (which is n^9) to argue algebraically
methinks that soon you'll become very familiar with my method of finding limits
The first one tends to 0
i got this for b
You could also use lhopital if you're lazy
whats that method
bun that
thats too long
thats not for being lazy
lhopital = cringe
thats for the people who dont think
Well Yh
Putting the L in L'hopital 
why am i wrong for this?
if a limit can be solved with lh, its not hard enough 😶
Can you prove that n! Dominates
l’hopital is not for you if you are lazy lol
its an axiom ok 😶
ur welcome
but it also shouldnt be too hard to prove either
The markscheme says its 1?
we r given that axiom in our exam
yes
It is?
im joking about axiom, 'given fact'
,w lim (2^n + 3^n)/(3^n + n!), n to inf
i cba but am i not correct?
ye
Markscheme wrong
???
AGAIN
WHAT
Your markscheme is on crack
You don't know the half of it 
Get a new book bro
n! dominates the denom?
lecture notes
yes
kl
Get a new lecturer
btw
ask chartbit
this is for
all my
lecturer
notes
all modules
Can confirm, many of us can tbh 
Bc your markschemes suck
but camb is best in the world
Limit goes crazy when you start by the formal definition 💀
Idk we don't go to the best uni in the world
except whoever made those solutions 
Yh, i put 100 as n in the calculator
bruh
And it gave me 10^-112
When in doubt, try an example
No, this rule is not always true
why
If the denominator tends to 0 and the numerator a constant, it tends to infinity
Let me read
ok
In this case it's because a value is tending to infinity
You can get n as big as you want
yh
algebra of limits 
The rule is Lim of h(x), where h(x) = f(x)/g(x)/ f(x) tends to a constant and g(x) = 0, if f(x)/g(x) > 0 then the limit will tend to + infinity
If f(x)/g(x)<0 it will tend to -ininity
you can note that n < 2^n
2^n dominates what?
the denom
i said 2^n dominates the denom
n2^n might not be asymptotically equivalent to 2^n
what happened to n2^n
why did u say this then
@steady basin you were confused on whether n2^n dominates over 10^n
because it allows you to see that n2^n < 4^n < 10^n
where has 4^n come into this
Because 4^n is obviously less than 10^n
yh but
And by showing you that n2^n is less than 4^n
the ocean?
- multiply both sides of tushar's statement by 2^n
$n < 2^n \implies n2^n < 2^n \cdot 2^n$
tushar
it might be, but reasoning will always win
also good thing to note that n < x^n for all x greater than 1
sry im still over confused of ur proof showing n2^n < 10^n
but where does 4^n come from
2^n times 2^n = 4^n
$2^n \cdot 2^n = (2 \cdot 2)^n$
tushar
Yh
what did u mean by this btw?
Oh, basically remember how I used to say "you could do [insert a limit] with l'hopitals, but it doesn't mean you should"
ye
And would say e.g. divide the numerator and denominator by [something] or like that
There's a similar idea here with how you're doing these limits, you can e.g. try and manipulate these into a form where it's like limits that you can work out
yr
ye i like this methods
its leng
Yh that's a nice method. You can also use maclaurin series if your function doesn't contain a polynomial
...
See e.g. this comment here
i believe i will be coming onto that soon
10^n = 5^n.2^n
ye
Simplify that
Yh I'd agree
Yep that's fair
nice
or divide num and dom by n^4 and algebra of limits 
ye
yep
[if postedit didn't exist...]
also @pseudo ice any chance u could have a look at the mock i sent u and lmk if theres any questions i can do from it as of now, reagrding the topics ive done so far, par q4 since i asked u that yesterday
my aim is to do cauchy and other convergence power series stuff tmr
Yh you'd get (6 + 12logn/n⁴)/(3 + 1/n²). And you'd see that logn/n⁴ goes to 0 and 1/n² goes to 0 and so you're left with 6/3
which will complete real analysis content
i havent done alternating divergent sequences yet
thats the next chapter i believe
Oh damn, well fair enough I guess, getting ahead of myself 
i think q4 and q3 r the only ones i can do as of now
fair fairs
ight thats me done for today
these r the chapters i have left
gonna aim to do all of these tmr
😭
so i can do the mock sunday
The current time for chartbit is 12:10 AM (GMT) on Sat, 21/01/2023.

is cauchy stuff hard
and limits of convergence
like M-n proofs
epsilon - n
whatever theyre called
I mean, you kinda did some of the epsilon-n proofs today in a way
How did you find that?
not bad
semi
mid
the stuff i just did now
was the easiest
this kinda stuff
Cauchy sequences, at least theoretically they're not too bad to deal with (e.g. convergence implies Cauchyness, a Cauchy sequence with a convergent subsequence converges and all)
Yeah these are at least what I learned as "algebra of limits"
That stuff about finding the least N was epsilon-n convergence in disguise, in a way
looking at my mock tho, u think its all doable to understand most of it by tuesday
my aim is to do the mock sunday
i mean i want like a decent mark
like 60 % is a 2:1
and 70% is a first
I think so if you work on it, and as always if you have questions, come here and people will be happy to help you(!)
Maybe give q3 a go too for now too? or at least think about it?
[if you haven't already]
acc before we do that
lets finish off today with this
i had an exam in novemeber
and i got the proof wrong
lemme show u
lets do this
thinking
can i simplify Cn
at all?
hmmmm
@steady basin what about doing it the other way round. Is there any other way you can write e^-n
I've never done these kinda stuff. So I don't know anymore than you do.
Well i do have atleast 1 idea
@steady basin well we can start from 1 > 0
Then add e^2n on both sides
So
e^2n + 1 > e^2n
Then if we do e^n divided by those 2
We can get
e^n / (e^2n + 1) < e^n / e^2n
And e^n/e^2n = e^-n
This should be acceptable since e^n will never be negative
thats genius
but how did u recgonise to do that
thats what i find hard about real analysis
i never know how to start of
off
ygm
i recognised that e^-n is the same as e^n/e^2n
Which relates to
The e^n/(e^2n + 1)
So i just formally proved that the cn denominator is always bigger . And so the number itself is smaller
Yh it's hard to teach someone a proper algorithm for this. It's just experience and intuition i guess.
another way to do it is to multiply the top and bottom by e^-n
so u get $c_n=\frac1{e^n+e^{-n}}<\frac1{e^n}$
and thats it
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If my domain is $\mathbb{Z}$ and x is an arbitrary real integer, how do I prove x is either odd or even?
hibyehibye
or like what law states this?
hibyehibye
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real integer?
well i guess i could have jsut said integer
Not sure, but this smells of circular logic.
It would help you to have a well-defined definition of "even" and "odd" integer
so say like even is 2k and odd is 2k+1?
I guess proof by induction
sure
Let P be a predicate that is true when an integer is even and false other-
wise.
Let Q be a predicate that is true when an integer is odd and false otherwise.
should I redefine these?
so maybe
Nah those definitions seem fine
Add this as a pretext tho for definition
so like
- Define even and odd
- Define P and Q
- State your assertion
- Prove it
ah ic
It helps to use predicates to define even and odd as well
e.g. "n is even iff exists k such that 2k = n"
so like "Let an even number be a number described by 2k where k is an arbitrary integer"
oh
that sounds better
What is iff again?
if-and-only-if
yup
hibyehibye
hibyehibye
hibyehibye
Or "Q is true when P is true" if you like being abstruse
your prof/TA should know what iff means
np
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@alpine sable Don't forget to prove that even and odd are contrapositives
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urm what do you mean?
do u mean something like
$\forall x (P(x) \vee Q(x))$ is a true statement because any arbitrary real integer is either even or odd because [insert contrapositive proof here]$
hibyehibye
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Nah you need to prove that for all x, P(x) is true if and only if Q(x) is false
hm
You can't just say "an integer is either even or odd" because it has not been proven yet
It must be proven
so i have to prove by proving the contrapositive?
So far, you've defined that even and odd are properties an integer may posses, but have not proven that all integers must have only one
of $P(x) \iff Q(x)$ ?
Ah I may have used that word wrong
hibyehibye
i think im just confused what u mean
Forget I used that word. English is not my best subject
o
^ you need to prove this
okay lemme get back to u in like 5mins
ill try and prove it on my own
hm so
$ P(x) \iff \neg Q(x)$ is what im trying to prove
So like base case, of n=1
and then induction ?
@limpid turret is this the right lines
Or what about
base case 1 is odd bec its described by 2k+1
brb
wait
base case 0
number is even
cuz its 2 * 0
induction that if the number is even its described by 2k so the next number is 2k+1
and then if its odd 2k+1+1 = 2k+2 = 2(k+1)?
therefore every number is either odd or even
I think I got it TY
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ok then I had my base case as 0
oh im proving that
all positive integers are either even or odd
So 0 = 0*2 (base case)
and then induction
so
n+1 is odd or even
Question here
yea
You've proven 0 is even, but where is your proof that it is not odd?
I didnt prove that bec i didnt think it was necessary
That's the core of what you're trying to prove though
$\forall x (P(x) \vee Q(x))$ is a true statement because any arbitrary positive integer has to be either even or odd.
hibyehibye
thats what im trying to prove no?
This is where proofs are tricky. You're taking for granted what is known and what you are proving

wait so where did i go wrong
like im confused why it matter if n is not odd if its even
kk
It was your original question, wasn't it?
Prove that x must be either even or odd
even or odd
ic what u mean
ohhh
so do i just remove the either from that statement?
So you meant logical or, not exclusive or?
Ah
how should I rephrase that?
Bec the statement im trying to prove is $\forall x (P(x) \vee Q(x))$
hibyehibye
and thats logical OR
you did use \vee, so it's my mistake for missing that
o ic
so is this bit valid?
Okay I reset my brain for a second
lol all good
Clarify for me, you wanted to prove $\forall x (P(x) \vee Q(x))$ does not distribute to $\forall x P(x) \vee \forall x Q(x))$
SWR
yes
Is that what you are doing this?
mhm
yeah!
I think the proofs honestly good now
I just changed my domain to Z+ bec it made it alot easier
Okay, you're going to need the XOR quality to show this tho

That's what makes the counterexample happen
I understand it's hard, but it looks like you really want to understand it
Where does XOR come from? 😭
Yeah but like how is XOR related to distributing the universal quantifier over a disjunction?
Logically, it's P<=>!Q
Like im confused why I have to have anything related to XOR tbh
I'll start with the answer and work backwards
oki
$\forall x P(x)$ is false
SWR
I'm sure you agree there, yeah?
Same with Q(x), yeah?
yeah
one sec, gotta write this out.
Preface before you read its basically my 2nd time writing proofs so its kind of bad lol
no worries
So this is one part of what is important:
P=even and Q=odd will definitely have this property.
where did the $\forall x (P(x) \iff \neg Q(X))$ come from?
hibyehibye
We're going to prove that even and odd have this property
But I guess where I'm lost is why we need to prove that in the first place
I'm still working, so slow replies
like logically I dont understand the need to prove that P(x) \iff ~Q(x)
But I'm gonna read through your proof
oki
tysm for all the help btw
I know I'm kind of an idiot when it comes to discrete lol
In my counterexample, I need this. But maybe you don't? I'll check now
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45 -45 - 90 special triangle
How did you achieve those values?
45 -45 - 90 special triangle
Do you know that concept?
Does something like this look familiar?
I mean, does it look like something you learned?
Do you know trig?
Then I am pretty sure you learned this
That had nothing to do with angles
Do you know what kind of triangle this is?
Because it's a 45 - 45 - 90 triangle, you can apply this to find the side
Apply*
What's another name for a triangle with a 90 deg angle?
Good enough
What do we know about these right triangles?
And what tools do you have that talk about the length?
And that's what we are doing, helping you
.
Good time to investigate
If I gave you a triangle with length 3 on line segment qp and length 5 on qr, can you find length of pr?
That is, if we said the length up and down was 3 and the length left and right is 5, can you find the diagonal?
I think they are hinting to Pythagorean theorem
Try to find the diagonal length of triangle of the example given via Pythagorean theorem.
Ah this is right
Good
Yes
So what is pythagorean theorem?
What is a and b and what is c?
Conceptually
C sqrd is 34
Why is a equal to 3 and why is 5 equal b?
But why didn't you say c =5 or c =3?
drsleep
It def matters
Here
I got another better question
How
Does the pythagorean theorem relate to triangles?
I think that you don't know what how to use pythagorean theorem to solve this problem
We've essentially given you the tool
There is nothing incorrect about what has been given
Two options, you can apply that image I presented, or apply pythagorean theorem, by formulating an equation using the given info from that diagram
dldh is absolutely correct
If you choose option two, the given angles gives you a big hint on the side lengths
And you can formulate a pythagorean theorem equation based on that
We won't and no one will
No
Because that's not the purpose of the server
<@&268886789983436800> some deleted messages hint at what's going on here. I question if it's appropriate.
Oof mods you banned the op
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Use the help people gave you in your previous channel
Alright
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how is this wrong
how many millilitres is one microliter
.001
thats the number that must be here
ok and below
.
every other number is correct ig
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hi
hi
im new here
Please read #❓how-to-get-help
Not really useful
they don't really have a doubt
🤣
...
You opened the channel
...
Oh I see
could everyone just update me on everything
What
@graceful forge you want to help someone?
yea sure
dont open help channels to help others
Just read channel that starts with #help. The question is usually pinned to the channel
just go to the channels
ok
Inflation
Or also #1021175428326633542
Uhhh
srry
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uhm
.reopen
✅
so.........
Denied
Gas is back down to $4 for me!
ok
Lmao gas went up for me
3.50 where I'm at it's 
Wait so what country are yall in
Merica
Im in NZ
Hello Kiwi
but for some reason i have an american accent
since im originaly from india and moved here when i was 2
Didn't the British take over New Zealand at one point?
.
That's how you help people
If you don't know how to help, just don't comment in that channel
ok
I'm mentally unstable, if that's what you mean
what type of math do you all discuss of
🤣
All levels
no i dont mean that 👍
ok
@graceful forge you need to look at occupied math help channels not to open a help channel
We discuss a lot of things
ok
Better take this to #discussion or #chill
so bye
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ill be back in like 10-20 minutes
Fyi this server is primarily US based meaning there is more traffic in about 12 hours
That explains why there's like 50 billion channels of linear algebra
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Is there any real roots for x^3 - 15x^2 +400. When I solve this normally by taking x as common. I am getting some complex roots. When I graphed this online, It shows 3 real roots
If it has complex roots they must come in conjugate pairs. You don't need to plot to know it has a real root.
But x isn't common in all three terms
@potent plank Has your question been resolved?
@potent plank see if an odd power poly has real coefficients then min. One root is always real
Since, imaginary roots occur in conjugate pairs
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@next swan Has your question been resolved?
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can someone help?
what have you tried?
i tried inverse properties but i think thats wrong
inverse functions shouldn't be used here
if that's what you're referring to
or are you using "inverse" to mean reciprocal
no. i was first trying to find t through the first problem (cot(t) = -sqrt35/35)
then how do i find sec(t)?
$\sqrt{3}5$? \catthink
Ann
you could consider drawing a triangle / apply pythagoras and properties of the unit circle
idk if its a sqrt(35) or sqrt(3)5 btw
not sure how to do that sorry
since negative lengths aren't really a thing
you could start by drawing a reference triangle with reference angle k where cot(k) = |-sqrt(35)/35)| = sqrt(35)/35
oooh
how does this find sec(t)?
i drew the triangle yes
apply pyhtagoras
i dont know how to do that
do you know what pythagoras' theorem is
yes
following my instructions
you should have a right triangle with the lengths of two sides known
and knowing pythagoras,
that can be applied to obtain the length of the third side
ooh is sqrt35 the adj and is 35 the opp side?
yeh
so this is hyp?
35^2=1260 and sqrt35^2=35 so 1260+35=1260
and 1260 is the c^2 value aka hyp
Result:
1225
35^2 is 1225 and 1225+ 35 = 1260
oops
anyway, ideally you'd use exact form and simplify the radical instead of using a decimal approximation
anyway, after determine the hyp, use the triangle to determine sec(k)
(again keeping stuff in exact form)
what is exact form and simplifying radical?
e.g. going from $\sqrt{8}$ to $2\sqrt{2}$ instead of approximating it as 2.83
ℝamonov
so sec(t) is sqrt(1260)/sqrt(35)?
not quite
that would be sec(k)
remember that k is the reference angle of t
consider the location/quadrant of t,
and whether sec is positive or negative in that quadrant to determine whether sec(t) is sec(k) or -sec(k)
so sec(t) is sqrt(1260)/sqrt(35)?
do i rationalize denominator too?
simplify the expression as a whole, rationalising of the denominator will be involved
and you'd also need to simplify any remaining radicals
how do i know what quadrant t is?
ℝamonov
both positive so quadrant 1?
no
do you understand that (interval) notation
t is an angle between pi/2 and pi (or between 90° and 180° if you're more comfortable working with degrees)
oooooh
i see its just the radians on unit circle
so quad 2
meaning the sec(t) will be negative
so its -6?
sqrt(1260)/sqrt(35)=6 but since its quadrant 2 its negative
is this correct?
@gray isle ?
yeh
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$\varphi$ is called phi, $\psi$ is called psi, and $\Pi$ is called pi (uppercase)
Ann
which one
on the left the q looking one
?? that's phi...? didn't i just say that
the one in the middle, ∈, is called "is in" or "belongs to", if that's what you intended to ask.
so this one and this one are the same thing ?
yes they are the same Greek letter in different fonts
@viscid moat Has your question been resolved?
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There is a triangle ABC:
Find it's angles.
Can you please give me advice how to find first angle? Should I use cos theorem or dot product of vectors?
wdym by "first angle"?
you can use whatever you find easiest. both the law of cosines and the dot product will get you the answer
they both work
what ann said
many ways to skin a cat
I mean which one is simpler?
dot product seems simpler
Because when I tried dot product It got confusing
do you have work to show?
i think you went about this in a confusing/error-prone way
where are the vectors
^
write the vectors out
actually maybe that is wrong entirely
cos(A) = AB·AC/(|AB|·|AC|)
(to be clear it's an error in execution not an error in planning)
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Amy and Ben live 17.2 km apart. They cycle to meet each other. Ben travels at
12 km/h and Amy travels at 10 km/h.
a How long (in minutes) until they meet each other?
b What distance have they both travelled?
why is it minus?
and what does x represent?
yh
So 12 km/hour * x mins + 17 km/hour * x mins = 17.2km
then your equation is incorrect as written
Is that what you’re saying?
the speeds here are given in kilometers per hour not per minute
Notice that mins * 1/hour is not 1
ok lets forget that
But if you put x in hours
lets start fresh.
you are better off declaring x as the time in hours for the two friends to meet (in which case your equation will be correct),
then afterward, converting the hours into minutes
That isn't correct, they are moving towards each other so they'll meet somewhere in between and hence they won't cover the total distance of 17.2 km
I'll try solving this with taking the distance they meet at
@stoic ledge i think you're talking out of your ass rn
If they don’t cover a combined distance of 17.2km they won’t meet
the combined distance travelled will be 17.2km
My bad
So 12 km/hour * x hours + 17 km/hour * x hours = 17.2km
Continue
Notice here the hours cancel out
And you get the right units on both sides
Which usually means you’re in the right direction
ok
Amy and Ben live 17.2 km apart. They cycle to meet each other. Ben travels at
12 km/h and Amy travels at 10 km/h.
a How long (in minutes) until they meet each other?
b What distance have they both travelled?
what should i do
Well we first know that Amy and Ben travel for the same amount of time
Find the time using frosst's equation
Well we actually don’t know that they start together but it’s not solvable without that assumption
yh
So speed * time = length/time * time = length = distance
,calc 47/60*(12+10)
Result:
17.233333333333
Yeah close
so 17.23min
47 minutes
how did you get that
He did reverse calculation to check if my answer was right
Well
10x + 12x = 17.2
Solve for x
You get time in hours
Multiply by 60
what a shitshow.
ik
Now multiply the time in hours with their individual speeds and find out the distance they travelled
so far


