#help-23
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yes
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now that i look at it, i'm not sure how you brought the square down, though
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(Sub rule)
What is a quick way to know what I should sub for "u" when trying to evaluate these integrals
Well, if the numerator is the derivative of the denominator the u-sub is of course u = denom.
ohh
now that you mention it, i didnt realize the numerator was the derivative
that helps a lot
Pretty sure that's all the help i needed, thanks
.close
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Could anyone help me w q number 2
What did I do wrong asweel
Nvm I think its just best to expand the denominator
Then realise it and mod arg it
Only easy way I can think of
,rotate
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the answer is no?
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Does n! Grow faster then a^n as n tends to infinity ((a^n)/(n!) = 0)
a^n grows with a factor of a at each step
n! grows with a factor of n at each step
at some point n will be bigger than a
try making that precise
$\frac{a \cdot a \cdot ... \cdot a}{1\cdot 2\cdot ... \cdot n}$
rbit
especially the point when n > a will be interesting
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techniques of integration, regarding even powers of sin and cos
for example, consider the integral of sinx^4cosx^4, i.e. the fourth power of cos and not x^4.
now, there is a technique where one replaces each of sinx^2 and cosx^2 with some cos2x +- 1 /2, but this is infeasible for very large even powers, like 10
so the method i am reading about says to use a substitution of tan x = t
this gives a dx of 1/(1+t^2)
$\int \cos^4 x \sin^4 x dx?$
mohammed
you mean this?
and cosx^2 = 1/(1+t^2), and sinx^2 = t^2/(1+t^2)
seems like bioche's rules
yes thats correct, sorry i dont know latex yet
you should look at it
i see
i know
i'll have a look at it but i'll finish my full thing
it's for fractional polynomials of cos and sin
so this gives an integral of t^4/(1+t^2)^9 dt
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...
which doesnt seem very easy to integrate
look what i sent
yeah this is a bit different from tan(x/2) = t, i think?
just directly tanx = t
i shouldve just uploaded this img ๐ญ
anyways, if m = 4 and n = 4 i get
this
which doesnt seem easy to integrate
i will have a look at this bioche rule though
i think this is the correct section, with both p and q even, i dont really know what linearization is? i suppose i need to understand that first, then?
ye it's good to know how to do it to calculate some integrals
like with euler formula, and some basic trigs formula like cos(2x) = .. sin 2x = .. and others
i see
i'll give it a look ty
without using this, is there any way to integrate my example function except repeated expansion of cos(2nx) + 1 type terms?
ye maybe like cos(x)*sinx = sin 2x) / 2 multiply by a power 4 and you get only a sin 2x to the power 4 with that you should have it
also knowing that sin 2x is the imaginary part of exp(2ix)
yeahh i wasnt considering this solution because i gave a bad example, or one that was unrepresentative of my real problem
i guess its like p,q both even and p != q , p,q >= 4 is my actual thoughts
basically u always want to use bioche's rule and some trigs formulas when you calculate integrals with sin and cos
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How do I find the area of the shaded region?
Find the area of the white area, and then subtract this value from the area of the rectangle, which will give you the area coloured in black.
@next perch Has your question been resolved?
How do I find the white area?
it is two parallelograms with some rectangular intersection
recall the formula for the area of a parallelogram
base * height
yep
I can't think of what to do after that
base and height
it's not that simple
there's a crucial portion of the problem that has not been addressed
which one
what you're going to do about the white rectangle in the middle
it's a rectangle with sides 2 and 3
looks just rotated to me
...
hm right
the way you find the lengths of the white rectangle in the middle is by applying pythagorean theorem to find the long slanted lengths of the two white parallelograms, then applying the parallelogram area formula
my bad
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The answer is x=6 but i somehow got x=7?
can you show your work?
btw ||both values you've provided are wrong||
I did 4x+5+4x-2+x+4+4x+5
how is that leading to getting x=7
where's that coming from
Hint: The opposite sides of a rectangle are equal.
so do i do 4x-2 = x+4
Yes
yes, who said that x was 6
Ohh
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can someone help with this question?
make correspondence b <->c. And then use a standard proof that [a,b) and [a,b] have the same cardinality. Namely, first transform it into [0,1] and [0,1) by one to one map x->(x-a)/(b-a). And then just make correspondence 1/n -> 1/(n+1) for n>=1.
The idea is basically, for a map I -> I', to map a to c, (a+b)/2 to a, (a+3b)/4 to (a+b)/2, etc... and the other points mapped to themselves
more generally, create a sequence (x_n) valued in [a,b] that never repeats
and map x_0 to c
and map x_(n+1) to x_n
since there's an infinity of x_n, we never run out of x_n to fill by the next one
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is the ^2 on the outside of the log?
yes
wait what
this is equivalent to your answer wolfram is just pepega with simplifying
not if the exponent is supposed to be outside the log
yes
by using ambiguous notation?
solve with chain rule still
i dont have the time to work out the whole problem atm
nono i mean not the answer
like how would the notation be
if i had to use u'/lna.u
do you know what chain rule is?
yes
is this like a very specific restricted version of chain rule that only works when the outside function is a log
ok i give up
lol
this is supposed to be loga u = u'/lna.u
you "use" that in both cases
oh
you just use it at the beginning in the first case and not at the beginning in the other case
how should i know
yeah it's ambiguous
ah
the answer is fine, aside from the fact that there's a factor you should cancel out from both sides
there's just a 50-50 chance that it's the answer to the wrong question
well
that is the only way she taught us to solve so im assuming thats the way to do it
but
the way she gave the questio is wrong
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Can someone help me please
denominator should have an (n+1) in there but otherwise fine
Oh okay
I see the denominator is technically has a higher power than the numerator so the lim goes to zero?
Also don't quite understand part a
part a is precisely what you've just done
Why should it start at 0?
Idk the reason why I just know it does
Ahh okay. How would I change my work to reflect that? as far as the sum of the following series?
Well if u shift downwards u must change the exponent to make up for it
So if we go down from 1 to 0
U would get (3/11)^n+1
Ohh I could probably use the ratio test instead of this hmm?
No u can still use geometric thingy
This is equal to 3/11 * (3/11)^n
Oh wait
It seems ur work already accounted for that
Maybe I messed up on the arithmetic somewhere
Thank you
My bad for adding extra complications I didnโt see ur work already accounted for it ๐ญ
All good
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#help-29 message
Something like that
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.reopen
โ
there are hypotheses to such "local limitedness theorem"?
such as the type of function f is?
because if I set f(x) = 1/x if x not equal to 0 and f(0) = 0, good luck
What theorem are you even referring to?
I think he's talking about "that one theorem some random person on the internet was talking about"
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Ik sum is equal to 10 and that we need to use the numbers 1 and 4
Just lost
Translated: a region is bounded by the x-axis, the lines x = 1 and x = 4 and the straight line y = kx where k > 0
determine the direction coefficient k algebraically so that the area of the region is exactly 10 area units
do you know integration or are you doing it geometrically
no intergration
alright, you need the y values at 1 and 4
then you can find the area as a trapezium or a rectangle and triangle in terms of k
i think y = x so x = 1 y = 1 and so on with 4
why is it 4 times k
because y=kx?
i told you
i mean, you can find that quite easily
think about it
isnt the height going 3k?
ohh okej
imma solve it
got it thank you
but im so confused on this part particulary
i know y = kx in and out
yet im still confused on why it becomes 3k is 3 the x? or wha is it y = 3k im just confused on that part espcesially
@icy lance
because the base of the triangle lies at y=k and the top is at y=4k so the height of it is 4k-k=3k
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I dont see what I did wrong
u = 3x-2
du = 3 dx
Umm
Youre giving me a hint but im not getting it ๐
Youโre forgetting a dx 
Ahh yeyeye
fixed?
Its been a while since I did these hehe
But oke
(u+2)/3 = x
So sub all that into the original
(u+2)(u^6)/3
Is it wrong? ๐
It IS wrong or thumbs up cause im not wrong? ๐
Im confusedddd ๐ญ
Yea was gonna say that you need the integral at some point (in case you were getting to it) 
So its all (u+2)(u^6)/9 ?
Yep (but remember youโre integrating that wrt u as well)
Ahh yeyeye
I think I can solve it now tho hehe
Thank you so much everyone!!
โค๏ธ
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I have to find the flux of a sphere with a very ugly vector field and was wondering if there is short cut to find the Jacobian instead of trying to solve it by hand
There's divergence theorem 
oh my gosh you're right
actually the other part of the question is there is another surface in it and I'm not quite sure how to approach that with the divergence theorm
oh do i just adjust my domain
actually I can't do that wither becuase I've defined one surface in cylindrical coordinates and the other in spherical
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Hi
whats ur question?
!dontasktoask
!da2a
No need to ask โCan I askโฆ?โ or โDoes anyone know aboutโฆ?โโitโs faster for everyone if you just ask your question! See https://dontasktoask.com/
yay
Hi
@ruby kestrel Has your question been resolved?
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I just need a quick clarification on dominated convergence theorem
00100000
and if so, is it fair to say that if DCT implies to a series of r.v. $X_n$, $Y_n$ converge to $X$ and $Y$ respectively, then $E{X_n}+E{Y_n}\rightarrow E{X}+E{Y}$?
oops
00100000
or like, some form of using absolute value to shuffle it around?
i studied this theorem for the lebesgue convergence of a sequence in which case the convergence is pointwise, so i assume that also in this case the convergence is pointwise
but this notion of convergence is weaker than pointwise
the notion of convergence for the random variables
so I'm just not entirely sure
oh wait
I don't know what lebesgue convergence is
so I'm not sure if that's a strictly weaker or equally strong criterion
every probability resource just says that it converges
and not pointwise/in probability/a.e.
so I'm just confused :(
basically, it converges pointwise for not all x's in the domain, so is a little weaker than a normal pointwise convergence
so, then is it fine for me to just add the convergence of the expectations?
i.e. $E{X_n}+E{Y_n}\rightarrow E{X}+E{Y}$
oops
00100000
I honestly totally forgot if this is a property of pointwise convergence ๐
the E(X_n) are just numbers right, there's not a zillion ways for sequences of real numbers to converge
yes
oh also, sorry to bother you so much ๐ , but to apply DCT to a r.v. $X_n$ that already is shown to converge to $X$, I can just say that $|X_n|\leq |X|+1$ a.s. because otherwise there are an infinite number of terms for which it's a certain distance away from the convergence point, so it wouldn't converge, right?
00100000
you just need to find a variable that "dominates" over you X_n, it can be anything, now i don't specifically know which proprieties can have a r.v. but for reference, in the lebesgue case, the function that dominates it's defined only on positive numbers
a random variable is real-valued
is that enough information to tell if it's dominated by $|X|+1$? ๐
00100000
however, if you define $Z_n = X_n + Y_n$, for which i know that $|X_n| \leq X and |Y_n| \leq Y, then |Z_n| \leq X + Y$ that we call $Z$. So i think that $E{X_n}+E{Y_n}\rightarrow E{X}+E{Y}$(?)
mercidy
hmmm....
This is valid because of the linearity of the expected value?
I'm trying to justify the thing i'm not totally sure about it ahahah
I'm not sure what this is meant to show tbh
the connection between $Z$ and the expectations is unclear to me
00100000
it's probably just me being bad tho
are we trying to understand if this is possible right?
yes absolutely
dw i went insane for this theorem about a week ago ๐
lmaooo
oh okai
but im pretty sure if you're right abt the convergence being pointwise, it's true
take https://math.stackexchange.com/questions/1214225/my-proof-that-sum-of-convergent-sequences-converges-to-sum-of-limits for instance
the convergence here is pointwise
@faint coral Has your question been resolved?
okai, sorry if i'm late, i searched what a.e. means xD
I'm sure that the almost everywhere convergence implies the pointwise convergence
you are basically saying that it converge pointwise for every point that is not in the set of measure zero
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Iโm confused and the answer sheet gave a different answer than a scan app and I got a diff answer.
Iโm also new to this
what did the answer sheet say?
i guess you're asking, are the solutions to (x+10)(x+5) = 0
-5 and -10
yes they are, you can see by plugging in those values for x
Let me send another pick of a different problem
to see it from the equation, just recognize that if the product of two numbers is zero, then one of the numbers has to be zero
That gave a weird answer
ok,any thoughts?
But the answer sheet says 2 and -7
answer sheet is wrong
I also just talked to someone who already pointed out a typo in my book
But I wasnโt sure which way is actually right because this is my first time doing this
Okay thanks. I just wasnโt sure if the answer was the opposite or not cause this book is backwards.
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Hello, I want help with a concept, if I have a sphere and I slice it in two, each half contains half the surface area of the sphere. By the way Im not counting the new surface area created by cutting the sphere, it's not relevant to my stuff, only focused on the outer curved bit.
Ok so if I cut the sphere at 33% of it's diameter, would the smaller 33% chunk's surface area be 33% of the surface area of the sphere, and the larger chunk be 66%? That's how I assume it works, but is there some weird shenanigans due to it being curved?
Does it exponentially becomes less surface area as you go farther out or is it just linear?
@silk talon Has your question been resolved?
<@&286206848099549185>
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Hi
I was wondering if anyone could explain limits in two variables in brief
I have an exam on it today
Thanks!
<@&286206848099549185>
In the section weโll take a quick look at evaluating limits of functions of several variables. We will also see a fairly quick method that can be used, on occasion, for showing that some limits do not exist.
@rancid sierra Has your question been resolved?
I want theory bro
Idk what it really means
That's what I'm tryna understand
That isn't explained here
Like in normal limits they explain stuff using graphs right?
How does that work for two variables
I don't understand it
They do do it
But I kinda need help
You want someone to draw pictures for you?
This is a good tool
https://www.desmos.com/3d
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I dont really know how to get things to cancel out here
u = sqrt(x) + 1, du = 1/2sqrt(x) dx
How do I get rid of the x in the du?
<@&286206848099549185>
well this is just the wrong u sub
Oh yeah oops
consider u = sqrt(x)
Ok...
you couldโve done $dx = 2(u-1)du$ if you wanted to though
knief
$\int \frac{2u-2}{u^4} du$
knief
Its inside the brackets
no lol i meant like
as an answer
you said you didnโt know how to proceed
oh iโm blind
๐ญ๐ญ
nevermind
before i zoomed in i thought you typed 1
Oooooh hahahaha
But oke I thiiiiiink I know how to do it now
Thank you so much for your help!!
โค๏ธ
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youโre welcome
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If a series contains a $\bar z$ term, can it converge to an analytic function? Moreover, if a power series contains a $\bar z$ term, can it also converge to an analytic function?
Kakaka
series of functions that is
@unborn wigeon Has your question been resolved?
Wdym a $\overline{z}$?
SWR
complex conjugate
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which of the of the expressions in the square can be written as the following.
I need help with understanding how to use double angle to solve them
state the double angle identity
for sinus its sin2x = 2 sinxcosx
nope
well you see its 2x inside sin and cos
yes
what if you put x = 2x in the identity
2sin(2x)cos(2x)?
2sin4x?
a
so you got the sin(2x)cos(2x) down
but you got a 4 in the front
how do you get a 2
idk
whats the relationship between 2 and 4
half
so 4 = 2*2
yes
2sin4x so twice
sin4x
2sin(2x)cos(2x) = sin(4x)
yes
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how do i evaluate this integral as a power series
@jaunty steeple Has your question been resolved?
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so like sin(2x)=1/2 * 2 * sinx aka sin(2x)=sinx is it solvable or does it require more information?
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The nth statement in a list of 100 statements is โExactly
n of the statements in this list are false.โ
a) What conclusions can you draw from these state-
ments?
b) Answer part (a) if the nth statement is โAt least n of
the statements in this list are false.โ
c) Answer part (b) assuming that the list contains 99
statements.
//
I am stuck on this proposition question. Cannot get through it. I need help.
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which part?
b part
b) Answer part (a) if the nth statement is โAt least n of
the statements in this list are false.โ
the binary property always help, what if this statement is correct, what if it is not
sry is boolean lol
so, that means atmost 100-n are correct?
assume k are correct
so that means 100-k are correct?
100-k are false
yes
and how many statements are true if 100-k statements are false?
statement 1,2,3,4,...,100-k are correct, right?
I didnโt get that. Like when i say in statement 1: at least 1 statement is false.
Statement 2: at least 2 are false.
.
.
.
In 99 : at least 99 are false.
In 100: at least 100 are false. Which isnโt possible because if 100th is true then 100 statement can't be false.
Then how do i determine which is true.
so if 100-k statements are false
let us say k = 40 for sake of simplicity
than atleast 1 statement is fasle
atleast 2 satemnts are false
atleast 3 statements are false
...
atleast 100-40=60 satements are false
so thes statements are trye
so 100-k statements are true
Sorry i donโt have much time. I have to go. Thanks for trying to help me. I really appreciate it.
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Does set of exponential functions over R form a ring?
Yea, + and *
what are your thoughts
Idk what axioms it may hold or not to be a ring or not
Wait
No?
As in, there is no 0
In set of the exponential functions
yes, that is one of the problems
you could fix that by allowing all functions of the form f(x)=c*e^(ax)
does that make it a ring?
the same as before
some parameter
some real number
if you allow c=0 then you would at least have a zero element in your set
so then its closer to a ring
Yup
for example e^x + e^(2x) is not again in the set
Thus?
Why?
Shouldnt the set of ce^x (+,*) be a ring?
Yea you are right
Why won't ce^ax(+,*) be a ring?
.
Why it aint
its a bit ugly to show
not sure what the nicest way is
you can pick three points, eg x=0,1,2 and then show that no function c e^ax goes through the relevant points
or another option is to differentiate and see that the derivative is not the a multiple of the original function
thats actually not that bad
So closure under addition isn't satisfied?
yes
But e^x+e^2x is convergent and the new function is also an exponential one
what does convergence have to do with this
what do you even mean with the function being convergent
convergent to what and in what sense
do you mean continuous?
e^x + e^2x is not of the form c e^ax
and those were the functions we allowed
Wait
Acc. To this yea, e^x + e^2x isn't the form of f(x)
But it's an exponential function still ain't it?
c(e^x+e^2x)
I.e., Set of exponential functions of the form ce^ax form a ring
Yo?
no
e^x+e^2x does not have the form c*e^ax
two terms are not one term
just because it still has exponentials in it does not mean it has the form c e^ax
I get what you mean
For it to satisfy the closure under addition,
e^x+e^2x have to return element of form ce^ax?
for the set to be closed under addition the sum of two elements has to again be in the set
but the only things in the set are functions of the form c e^ax
so the sum again needs to have that form
@lusty hornet Has your question been resolved?
I fully understand your argument, but I'm confused over the fact that any exponential function of the form ce^ax can be mapped to a number in R, and so can be the sum of such functions.
How do we establish that the axiom doesn't hold
what does that have to do with it
what do you mean with "can be mapped to a number in R"
As of the function has a number as it's image,
do you mean that the set of functions of the form c e^ax has the same cardinality as R?
a function has a set as its image
No, as of that image belongs to set R
and for a function of the form c e^ax the image is always one of (-infty,0) or {0} or (0,infty)
depending on c<0, c=0 or c>0
doesnt change anything
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Is it true that $(\mathbb{Z}{10}, +) \cong (\mathbb{Z}{11}^*, \cdot )$?
๐ธdฯn๐ฒยฒs
So that makes them isomorphic?
I wrote down the group tables and was asked what I could notice
And I thought they should be isomorphic
prereq: prove that there is only one cyclic group of size n, up to isomorphism
often writen Cn
the hard part is showing the second group is cyclic
There's a theorem saying Zp* is always a cyclic group, but you don't know that, so you just need to find a generator (try it by hand, there's no great method)
Looking at my table I noticed the generator should be 2 so Z_11* = <2> which would make it cyclic
So since both groups are cyclic and have the same cardinality that makes the isomorphic
1 -> 2 -> 4 -> 8 -> 5 -> 10 -> 9 -> 7 -> 3 -> 6 -> 1 is indeed a cycle of length 10
hopefully you've proven that before
Otherwise I recommend you make sure that's obvious
cause you didn't seem to
i am not even going to try to understand ๐โจ
The task was just about writing down both tables and then write down what I could notice about both groups
It seemed to me conclusive that it's about them being isomorphic since that's also something new we recently studied
The generator of Z_10 being 1 is obvious, and for Z_11 * I wrote down the remainder of 2^n mod 11
what does isomorphic mean
step 1: study intro group theory
In my understanding, imagine you had a big cube from a set A and 4 small cubes from another set B, that together resemble the big cube.
Even though one is just the big cube and the other "big cube" is made up from the 4 smaller cubes, they are still the same, since they both represent that big cube. So the big cube is isomorphic to the 4 small cubes.
They basically have the same structure
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(The solution on the book)
Did i do smth wrong or is the books solution just missing a piece?
@earnest rain Has your question been resolved?
hmmm welps
Wdym?
can't read your image since it's rotated
and can't use the bot since it only rotates the most recently sent image
@plucky elk there
yea unclear what the question is
It asks to calculate the job of the vector field
With that vector field in the curve written on the 2nd line
-y,x
The job, the question of the edercise which is integral of F(r(t))r'(t)
Rรธcosรธ Rรธsinรธ
L = job?
,w int 0 to 4pi of x [-sin(x) + cos(x)] + x^2 dx
yea maybe there's a part of the question you're missing
that cancels the 4pi R^2 part
It just asks the job
Of the spiral p=Rรธ
And that vector field
What can I be missing?
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@twin owl based on the size of this video, it seems that I will need to upload it here.
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What are you looking for?
Itโs a statement
which is why the question confused me
W isnโt guaranteed equal to Z, because XW and YZ isnโt parallel
if we remove the A would these two be equal?
so the ones furthest to the left and right have to be parallel?
Hereโs an exaggerated example
i see, that makes sense
how could I apply that rule in general?
as in how do I know which lines have to remain parallel
The one on the furthest left and the one on the furthest right
no but like if it's in a different scenario / different orientation
Can you demonstrate it?
hmm cant find a tricky one rn
@magic junco for this one could u pls show how they would be equal
like by drawing the lines
@tired python Has your question been resolved?
If AB is parallel to BC then the angles marked in red are equal and the angles marked in blue are equal.
The fact that, in your problem, โ XWQ=โ QYZ is only true because the problem statement said so.
can you draw it on this image, i still don't get it
you wanted was โ XWQ=โ QZY but this is not nessecarilty true, what SkyAndNight was trying to show with that image is that they are visibly not equal hence why they said an "exaggerated" example
so ฮฑโ ฮฒ
is this why they are equal?
they are not equal
wait why
the vertical lines you drew are not parallel
in this example they are parallel, no?
and they are not parallel in the problem either
if we assumed they were parallel
would this be a correct way to deduce the anglews
if we assume they are parallel then yes, ฮฑ=ฮฒ
kk yeah I got it, ty
i'm just so used to these types of questions always being parallel
the parallel problems are very common, but your original problem doesn't have the lines parallel, you have to find another method
btw if the lines (to the most left and right ) are parallel, then the angles on that the lines are always the same right
yes, it's the same rule but with a different common line
Thank you
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am i right with C here?
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if the sequence decreases with each successive term how is the ratio 3?
@patent musk Has your question been resolved?
oh yeahh the common ratio must be less than 1 not greater. so it has to describe a decreasing sequence? in that case its B right
nope
you just guessed
check that it actually goes through one of the points
like let n = 0 or something
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,rotate
,rotate
,rotate
i need help with 1
The problem is a little tricky because you will need the perpendicular height of the triangles and parallelogram, but they are not given and there is no way to calculate them
However, if you recall the properties of ratios in similar triangles, that may help you
let the area of ABC be a variable and simmilar triangles bo brrt
brrt?
like you use it alot
two sets of parallel lines
yeah do those lines have anyhing in common?
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am i right with B here?
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Calculate the weighted mean inverse square root of all perfect numbers between (10^{15}) and (10^{18}), multiplied by (\pi^{e^{\pi}})
Tazculator

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can smb help with #1? i know it's easy but i can't like.. grasp the concept of it
so i need to find w, 1 & 2?
because isn't there supposed to be 3 interior angles inside of each triangle? or is that entire thing counted as one?
every triangle adds up to 180 right
yeah
<2 and S
wdym
in the triangle
wdym
what is it
uhh
angle 1 and angle 3 are given
60 deg. and 30 deg.
i actually don't know, our teacher didn't explain that
those are right angles basically
so whats angle 2 equal to
90
why isn't it


