#help-0
1 messages · Page 271 of 1
right but since the OG equation uses x1,x2,x3,x4,x5
do i have to go through that process for all of the problems
ok so basically
within the vector set w
we have cx1,x2,x3,x4,x5
wait hold on
right here we mean v + u is within w correct?
right so we just set them equal to each other
let me explain it and then you can confirm if you understand
we have a set W
which has elements of the form (x1,x2,...,x5)
and satisfying those conditions above
for example
the element (0,0,0,0,0) is in the set
right
because it satisfies the conditions above
what part b is asking of us
is to show that
if u and v are both in W
meaning if u and v satisfy the conditions to be in W
then u + v is in W
meaning
u + v satisfies the conditions to be in W
forget i said w = u + v
we're going to call it something different
say x = u + v
let me know if you understood that or not
before we do that
can you confirm you understood everything past this
right
right
right and we factors
right
so
w3 = 2(u1 + v1) - 3(u4 + v4) = 2w1 - 3w4
lets cut out the middle man rq and you get w3 = 2w1-3w4
is it because we were able to get back to our condition
we proved that u + v vector are within w
?
i see
we need to prove all conditions are satisfied by u + v
right so we need to check the rest of the conditions
right so let me see if i can start us on this one
would we start with x2=3x1+4x5
then sub it out with u2 = 3u1 + 4u5
then same process for v
yup looks fine
ideally you'd include some comments on why each of those steps work
but yes
divide both sides by 7
or
maybe don't even do that
let's start with x = u + v
right
then x5 = u5 + v5, right?
yep
so 7x5 = 7u5 + 7v5
right
7u5 = 2u3 +6u4
yup
yup
yes
ok cool so by this crazy insane logic right
does that mean for part c, it would be x = uv
where u vector would be u = {u1,u2,u3,u4,u5}
and v vector would be u = {v1,v2,v3,v4,v5}
no
awe
vector multiplication is not defined
i was feeling super slick
we want scalar multiplication
oh wait youre right
so its just r as any numbre multiplied by u
where u = {u1,u2,u3,u4,u5}
so we have r which is any value
and u which is that massive value right
r is any real number
u is a vector satisfying the conditions to be in W
we want to show ru = <r * u1, r * u2, ..., r * u5> is in W
meaning ru satisfies the conditions to be in W
right
so can we start with
w = r * u(vector)
that would be an alright first step ye?
yes
yes
this part?
do you know how to multiply a vector like
<1,2,-2> and a scalar like 5:
5 * <1,2,-2> = ...
yes
scalar multiplication is multiplication component by component
so when i wrote
r * u = <r * u1, r * u2, r * u3, r * u4, r * u5>
i was saying this stuff
.
then what
ok cool
then we go back to our conditions
find x3
sub out x3 for u
wait hold on i might have lost myself
lmao i was feeling really confident for a second
was i right up to this point
honestly dont know what you're saying
do you just want to walk through it together
let's review the statement
we are assuming r is in R
and u is in W
we want to show
r * u is in W
let's call v = r * u
now what is v3?
v3 = r * (u3)
and since u is in W
we know that u3 = 2u1 - 3u4
so we can say
v3 = r * (2u1 - 3u4)
= r * 2u1 - r * 3u4
= 2 * (r * u1) - 3 * (r * u4)
sorry but the variables are kind of messing me up
Am I somewhat close with this statement?
i would prefer if you pointed out what confuses you
so i can explain
you are essentially writing a lot of statements which i don't know if you will actually understand
Right here is where I’m getting lost
Right
and u is in the set W
Mhm
mhmright
so u must satisfy
u3 = 2u1 - 3u4
so the next step would be x3 = r (2u1-3u4)
?
yes
though i recommend you stick to one letter
either v or x
gotcha
uhhh i have x written on my paper so ill use x
but i know x and v are interchangeable
so from this point
i distribute the r
i want to make sure you understand that this isn't just a
assumption
step
step
step
step
answer
thing
why we are doing the steps should be clear to you
(to the point where we shouldn't be discussing each single step)
if it's not clear that's fine
theyre clear for me nwo where if im understanding this properly
but why we do stuff is more important than actually doing it
this is really all just algebra
associativity, distributivity, commutativity
etc
right
which is why im suggesting you read carefully and understand the algebra
and then analyze why we did what we did
mhm, understood
.
which now i can say i confidently understand after analyzing all the steps
i understand how b and c work now
my only question is
the next step after this would be to use associative property and sub out values to get x3 = 2(x1) - 3(x4)
but why does this prove that u * scalar satisfies the description provided
"the description provided" is the conditions to be in W
ah ok
so because they are able to be subbed in and out of each other, they satisfy the conidion
condition*
i dont understand your question
Show that if ~u satisfies the description of W and r ∈ R, then r · ~u does as well
this is what the question asks
the process of proving that its the same is the same as part 2b
correct?
like what?
how do i prove closure under scalar multiplication?
i take an arbitrary scalar r and arbitrary vector u in W, and show r * u is in W
this is the process
and how do you prove closure under vector addition?
you take two arbitrary vectors u,v in W
and show u + v is in W
ah i see
the specifics of this example are symbol pushing
you'll be doing it a lot probably
but that's the "whatever" part
the important part is understanding closure
so instead of thinking of this as a 1 by 1 process, i should be memorizing the justifications of each step because in a wider picture
right
you should understand how to prove:
- inclusion of the additive identity (0)
- closure under vector addition
- closure under scalar multiplication
right and i do understand how to prove these now
but part d asks for the basis
so how would i find the basis of these properties?
rref
yeah, we are able to use a calc for this part
which im super grateful for
would step 1 be to put all the conditions as a matrix
and then calculate the rref
cool!
give me one minute
your good!
[
\begin{bmatrix} x_1\x_2\x_3\x_4\x_5\end{bmatrix} = \begin{bmatrix} x_1\3x_1 + 4x_5\2x_1 - 3x_4\x_4\\frac{2x_3+6x_4}{7}\end{bmatrix}
]
maximo
[
\begin{bmatrix} x_1\3x_1 + 4x_5\2x_1 - 3x_4\x_4\\frac{2x_3+6x_4}{7}\end{bmatrix} = x_1\begin{bmatrix} 1\3\2\0\0\end{bmatrix} + x_3 \begin{bmatrix} 0\0\0\0\\frac{2}{7}\end{bmatrix} + x_4\begin{bmatrix} 0\0\-3\1\\frac{6}{7}\end{bmatrix} + x_5\begin{bmatrix} 0\4\0\0\0\end{bmatrix}
]
maximo
so we get the following matrix
[
\begin{bmatrix}
1 & 0&0&0&0\
3&0&0&0&4\
2&0&0&-3&0\
0&0&0&1&0\
0&0&\frac{2}{7}&\frac{6}{7}&0
\end{bmatrix}
]
maximo
do you see how we got here?
uhhh
why did we skip x2?
ohhhh
os its there
but since its a 0 vector
we dont put it in
ok
yes
i get everything so far
then you can reduce this to rref
and the pivot columns correspond to the columns which are basis vectors
in this original matrix
right using the calculator
you may run into an "issue" where you don't have integer values in the basis vectors
but you can just multiply each row by a scalar that will give you an integer
first lets discuss what you got
do you know what the pivot columns are
in that matrix
no
uhhh then no i do not
lets talk about what a leading 1 is
a leading 1 is a "1" that appears at the left-most position on its row
you'll notice there's 4 leading 1s there
if your column has a leading 1, it's a pivot column
so the pivot columns are
c1
c3
c4
c5
so in our original matrix
mhm
the basis vectors correspond to columns 1, 3, 4, and 5
but columns 3 and 4
don't have integer values in every component
can you elaborate on this
is 2/7 an integer
ohhhh ok
so in regards to our og column
we know that c1 c3 c4 c5 all have a leading one in them so they are the pivots
which we use to relate back to the OG matrix
yes
yes, but we want them to all have integer entries
like
look at c3
we want every value to be an integer
right
so the entries in c3 are {0,0,0,0,2/7}
no matter what we multiply by, the first four entries will always be 0
yes
so why would be multiply that column by some scalar
.
yes
and the same thing with c4
yes
right
those are the basis vectors
only ones that were pivots
you shouldnt be including the c1, 7c3, etc
you should just be writing these as vectors
like
[\begin{bmatrix} 1\3\2\0\0\end{bmatrix}]
maximo
and ideally put them all in a set
just like that?
these are basis vectors
your basis is a set of vectors
so
{<1,3,2,0,0>,<0,0,0,0,2>,...}
right
i got it!
so finally last but not least
the dimensions
if i remember correctly
every matrix is A sub(mxn)
yes
yes
I also do concur
I agree with the OP that the dim(w) is just 4
Do you agree that the dim(w) is equivalently 4 maximo?
i believe i do
now this may come as a bit of a shock of a question
but austin
do you agree the dimension of the subspace is 4?
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this one is occupied
does dimension have anything to do with nullity?
sort of
dimension no, rank yes
cuz i know the dimension theorem talks a lot about how dimension of col and dimesnion of row space
ah thats the word
rank
mhm
every subspace of a fintie dimensional vector space is the image of a linear transformation
so the dimension is always the rank of some transformation
so there is a connection between dimension and nullity
right
ok
everything makes sense and i feel a lot better now
thanks so much for your help!
no problem
your welcome
i really appreciate you taking the itme to help me!
anytime
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we suck
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do you have a question
"yeah i want someone to hand me the answer"
this is just number crunching, compute AB and AC and verify that they're the same
verify it

@balmy vector you there?
oh yeah
ok so what's troubling you with the problem
yeah thanks i got it!
go ahead and (.close) then
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\begin{align*}
\lim_{x \to 1} \frac{\sin(x-1)}{-(x-1)}
\end{align*}
casiofx991exz
Guys how do I use the lim x to 0 of sint/t = 1 here
can I say
Let t = x - 1
t -> 0 <=> x -> 1
?
can I say that?
something like that
yes
x->1 implies t->0
nice
it’s not really proper
that specific arrow is not really used in this kind of case
so I should just do this?
Yes
thanks
I got another question
When proving limits don't exist in multivariable calculus, do I really have to check all the time if the thing I'm substituting has the point we're approaching
all the time?
Do I have to say something like, y = x passes through (0,0)
all the time?
just an example
What does Sin stand for
I will @ mods
@true sandal Has your question been resolved?
are you talking about that second step? where you found that as x approaches 1, t approaches 0?
nah
1 sec
\begin{align*}
\lim_{(x,y) \to (0,0)} \frac{5xy^3}{x^2+2y^6}
\end{align*}
casiofx991exz
this for example
let's say I do
Limit along x = 0
Do I always have to point out if x has (0,0)
Because writing sentences take tiem
I am slow at that
assuming you do a substitution like z=xy+1, then you would plug in (0,0) and say: as (x,y) -> 0, z -> 1
and then z -> 1 would go under the limit of your new equation
sorry i meant to put 1's in the example. i changed it
yeah
You can often come up with a family of paths such that the limit changes for different members of the family. For example, x = ky^3, to show the limit doesn't exist.
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how do you do ii).
Im guessing i have to construct a differential equation but not sure how
@safe tartan Has your question been resolved?
but its repescts time
yes so differentiate wrt time
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I need some help with this, I know that triangles ABC, CEB and BDE are similar, and triangle BDC is similar to CEA. Im not sure how to continue from here tho
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Can you explain the second last line to the last line of the solution
@remote flint Has your question been resolved?
<@&286206848099549185>
<@&286206848099549185>
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(√12+2)(√12-2)-(√3-2)^2=
1-4√3 <- is that answer i got
but i was wrong andi t said 1+4√3 is correct
why?
i was doing (√12+2)(√12-2)-(√3-2)^2=
then i got 1-4√3
cuz (√12+2)(√12-2) can be solved by the x^2-a^2 equation
and (√3-2)^2 can be solved by the x^2-2ax+a^2 equation
which makes (√12)^2-2^2-(3-4√3+4)
then thats 12-4-7-4√3 cuz (3-4√3+4) is the same thing as 3+4-4√3
but then i was wrong and it said the answer is 1+4√3
why?
then thats 12-4-7-4√3 cuz (3-4√3+4) is the same thing as 3+4-4√3
Bracket
Inside the bracket it's negative
which makes (√12)^2-2^2-(3-4√3+4)
then thats 12-4-7-4√3 cuz (3-4√3+4) is the same thing as 3+4-4√3
You forget to distribute the negative to -4sqrt(3)
wait let me process it
OHHH
so the -(√3-2)^2's first minus also affects the -4√3
i forgot about that
ty!!!!
ty @ornate ginkgo @wary stream
i understand what i got wrong now
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10001016114
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how to show that when $V$ and $W$ are vector spaces with respect to the field $F$ that the tensor product is equal to the span of all elementary tensors so: $V \otimes_F W = span{v \otimes w | v \in V, w \in W }$ by only using the universal property of the tensor product. I know how to show that both sets are isomorphic, since they have the same universal property, but I don’t know how to show that they are the same set.
10001016114
They are not the same set in general, the tensor product is only defined up to (unique) isomorphism
Yeah I see rn that I wrote the set wrong I mean the span of the elementary tensors is equal to the tensor product. How can I show this to be true
I know you meant span, and my message still holds
I know that the universal property is defined up to unique isomorphism, but my prof said that one could also proof this fact by using the universal property
If you've already shown that the span of elementary tensors is a tensor product then there's nothing else to do
But is this enough to conclude that it’s the same set as $V \otimes W$?
10001016114
I know that it’s a tensor product, but why exactly this one
No, and it doesn't have to be the same set
There are many tensor products, they are all isomorphic and not the same sets
ah that’s what you mean
The notation of being the same is being isomorphic for tensor products
But they also are the same set, because we can form a basis of these (atleast one can prove that)
So one should be able to prove that they are the same set or not?
A tensor product is just anything satisfying the universal property
This need not be the set of the span of elementary tensors
But it will be isomorphic to it
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is there a lhopitals rule for multivariable limits
No, it only goes for single-variable limits only
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how am I supposed to find the asymptotes if i dont have h(x)?
how else would i identify them
a goes up to y=2 and b only goes up to y=0
Yesss, for A, f(0)=2 and for B, f(0)=0
One of them cannot be possible
Look at your numerator!
how can I test the value without the denominator though
what if its negative or something
would b not be possible because of dividing by 0
B is saying f(0)=0
And to have a rational function = 0
The numerator must be = 0
Our numerator at x=0 is not 0
So, f(0) is not equal to 0
f(0)=0 for all of them
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Good Afternoon mathematical ppl. In the photo, I didn't understand this until now. They didn't express 3 hm then 6 dam, they took 364 meters. Because it is on a scale or the metric system
Like 1 m 67 cm is = 167 cm
ALL is right??
whats 2 dam 5m and 7dm in meters
anyone need help?
no
ok
The creator of this table was on some drugs
It took me 1 minute of pure staring to understand what was going on
???
itz toooooo easy
I have never seen a table like that before
this is never an appropriate thing to say
anyway so it looks like each row in this table is a single length measurement but given in this maximally broken down form
Go check out other channels if you don't have a job
but... @wispy ice can you repeat what your issue is with this problem?
So 1m 67 cm is basically 1m + 67 cm.
the understanding of what thy wanted me to express because the numbers are broken up
But thank you all for your help and this community
you got 25,7 m for second one?
Convert it to the "whole" form rather than the "split" form would make it easier for you to understand.
For instance 1m 67cm = 1m + 67cm = 100cm + 67cm = 167cm
25.7m
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Why have I been given a function with one line while every other YouTube video I find about Fourier series showing two lines of the function
your function is correct :
x² in the interval -3/2 to 3/2 , it is 3 length
then in the second line, you have 3-period
so its good
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Is that all that's given?
Nothing about differentiability and such?
By hit and trial f(x)=x² comes out to be one such function..
Sorry for late reply! Thank you for explaining
There's others as well, guessing will only get us so far.
Besides something like f(x) = 0 works as well, nothing sophisticated to think about.
Yeah.
@daring totem Has your question been resolved?
both f(x) = 0 and f(x) = x^2 satisfy the functional equation, idk about differentiability
Nothing too rigurous
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does anyone know how to tell if function is continous?
hi,
hey
you check on the bounds of the interval
so in x= 0 and in x= 2
no ned moiren because 2+t is continous on R, 2-t too
in x = 0 in first interval you calculate f(0)
I don't really know what those meant
and you compare to f(0) in the second interval
I haven't done ned moiren
so f is continous in x = 0
so by continous it means that they connect?
on a graph, it means they connect yes
but why does -2 and 2 matter then
you can draw the curve of f without lifting the pencil from your paper
now you check in x = 2 : the bound between the second intervall and the 3rd interval
yes
but that doesn't show they conenct
yes it is continuous
because for x = 2 : before the 2 and after the 2 they connect in image 0
for x = -2 it is the same
image 0?
draw the cruve you will understand better
i have drawn it
but those two points do not connect back to each other
they are the outer bounds
This doesn’t make sense can someone explain
Show your drawing, maybe there's something wrong in it
oh ok i sorta get how its continous
the 0 goes on forever
but what if it doesnt have 0
for otherwise
Then it would be continuous only at x = 0
so if i wanted to say the function was continous at t
it would just be if the bounds of each function connect
What puzzles you in particular??
A and b on the picture I sent
when the function is defined by intervals, you look for continuity at the bounds of the intervals
They didn’t really do any math but just got an answer
Not mathem. rigorous, but that's the idea yeah
But where precisely?
A)
Where is x² - 4 ≥ 0?
Yes
I mean, solve that inequality 😅
if i wanted to prove the function was continous for my maths exam, how would i write it btw?
With limits
since you said it was not mathematically rigourous tho
btw the exercice you had is not rigourous
they put t = 0 in both intervall, it is a fault
yeah but i just want to know the correct thing to say in my exam
Here ( https://en.wikipedia.org/wiki/Continuous_function ) you can find it, I'm not able to write the formulas in a good looking manner
In mathematics, a continuous function is a function such that a continuous variation (that is a change without jump) of the argument induces a continuous variation of the value of the function. This means that there are no abrupt changes in value, known as discontinuities. More precisely, a function is continuous if arbitrarily small changes in ...
you first say that t --> 0 and t --> 2+t and t --> 2-t are continuous on R so they are contin ous on each intervall
then
you said you will check the bound of each intervall
yeah but in notation
for t = -2 : you calculate f(-2) = 2 + (-2) = 0
and you calculate
lim( t --> -2 , 0 ) = 0
then f is continous in t = - 2
lim f(t-) t->0 = lim f(t+) t-> 0
definition is :
f is continuous in a
<==>
lim (t-->a , f(t) ) = f(a)
ok i think i get it then
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Not sure where to start with u substitution for this problem
Could someone point me in the direction?
when in doubt just u-sub the annoying part and see what you get
well I would argue the sum inside the sqrt is the annoying part
@mortal river Has your question been resolved?
You’re saying sub out the entire radical? Or just the 1+x term?
doc gave you the sub
dopediscorduser
Or could you do this?
how did you get rid of the sqrt?
[\int\frac{u-1}{u} du]
[\int \frac{u}{u}\frac{-1}{u} du]
dopediscorduser
I figured
[\int\frac{u-1}{\sqrt{u}} du]
[\int\frac{u-1}{\sqrt{u}} * \frac{\sqrt{u}}{\sqrt{u}} du]
[\int\frac{u \sqrt{u} - \sqrt{u}}{u} du]
dopediscorduser
Maybe something like this?
Pull apart like this?
Ah gotcha
Could you subtract the exponents of the u/sqrt u term?
Like 1-(-1/2)?
[\frac{u}{\sqrt{u}} - \frac{1}{\sqrt{u}}]
[u^1 * u^{-1/2} - u^{-1/2}]
[u^{-1/2} - u^{-1/2}]
dopediscorduser
Would this be correct? Just in terms of simplifying?
$1 - 1/2 \neq -1/2$
compusomnia
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You mean how $\frac{2/3}{\sqrt{5}/3}$ is related to $\frac{2\sqrt{5}}{5}$?
math_is_fun
Yes
First multiply the numer. and denomin. by 3
Do you know how to rationalize fractions?
Apparently I have forgotten
math_is_fun
In this case, c=5 and d=0
I will have to look into this again. I don’t really remember learning that
Maybe you haven't
I’m in precalc learning about trig right now so that’s what all of this is
In your question you can just multiply the numer. and denomin. by sqrt(5)
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Chi(z) is the function takes value 1 if |z| <= R, 0 otherwise
How to estimate the heat flux at |z| = R?
reference about taylor series of average around Ball or on the shell
d is the dimension, here d = 3
The relative estimate I got is depending on 1/R which is very large. But it should be a percentage which should be very small
My answer didn't depend on f(t) which is impossible, I must make it too large
the initial condition is T(r,0) = 0
which is initial flat
The second image is my progress
this?
right, its quite compact hah
I am trying to get a better bound or estimation
I didn't even make it an upper bound
@main lantern what r you studing for
right
It is an engineering problem
thats thermodynamics
thought so
the heat flux of a point on an obvect a point in time
So in the space, there is a sphere with one material and the surronding is another
There is a thing called interfacial thermal resistance that is proportional to the heat flux at the contacting boundary
I am trying to estimate the resistance by estimating the heat flux
yeah, the layer between the two materials
so using the taylor series to determine the function between the point of contact?
sorry if my english doesnt make sense, its not my first language
That is what I am doing
that's too broad though, no?
it is too inacurrate
the problem starts from estimate this integral where T is the solution of the heat equation
I claim that it is bigger than 4/3 pi R^3 min Delta T
But that makes the magnitude so big
well yeah, but i dont see another way you can do it
Do you think my estimation of Delta T(0,t) is good or bad
i would do it like that
i think the problem is with the taylor series
shouldt you use the chebyshev approximation to get a more accurate result?
since you're using polynomials to determine a function
which chebyshev
thats the approximation of delta T?
i think i see the error
if its that well
youre going to feel stupid when you figure it out
Hmmmm i still didnt see it
oh nvm didnt see that
and the problem youre having is that the answer is too broad?
2/RG is going to blow up to infinity if R to 0
yeah
that is kind of impossible
Or maybe I am right
But that is percentage
The temperature drop cannot go down to negative
if 2/RG is > 1, then the outside will be negative
This equation is modeling there is a heat source at the ball
it is heating up the surronding
if the heat flux is getting "absorbed" by a material with a better heat conduction coefficient
or am i reading into it wrong
I am thinking my answer is wrong
It is not realistic
because there exists materials that G is relative small compare to 1/R
yeah
yeah, thats too loose
what engineering program are you in?
oh?
I think a lot of professor in ECE are just doing convex optimization
or machine learning
well, isnt that hardware issue going to resolve itself with quantum computing?
I know nothing about it
Well another confusion is I think I should use f(t) which is the heat source somehow
but I didnt use it at all
Which is weird
well, how would you use it
I dont know, but intuitively they should be related
Q= dKA(T 1 −T 2 )
Maybe I should post this to stack exchange
Or maybe I should post it in ode and pde channel
i have a rough idea of what you're doing but i dont know the specifics of it, sorry
.close
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How do you know what angles to use as points on the x axis
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Not sure the answer to this question.
what did you try
Adding 3 to both sides then seeing the slope. And the question is looking for a line that is not parallel to that line so I was looking for something without the same slope but it was kinda hard to even put those answer in a form that I could properly see the slope.
so what's something that we know about parallel lines? What do they all share in common?
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My discord was bugging so I had to
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