#help-33
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It's sort of bending the rules
I think this example works
Except that it doesn't
It says it is oscillating too much at 0 for it's to be continuous there, but for that to happen the function needs to overlap so much that it is not a function and not defined there, but earlier it said that the original function is defined at x=0
And it said it's differentiable
It seems like if the third statement is false it creates a contradiction for the first 2
So all three must be true
But common sense says pick choice B
Hehe
This is a weird question
@past estuary
Could you ask it to graph the original fc?
The first one oscillates too
So its not continuous either
Idt continuity is dependent on oscillation
But ik finding the limits is
I could be wrong tho
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is number 8 still a function if it doesn't cross the verical line, and one number 7 to find range does one only count the points or is it the lowest and higest point of the line and is it the same for domain
Yes it is
As long as there is only one value of the function for every x,it is a function
That came out wrong
so it is a fuction even if it doesn't cross the line??
Yes
but what if there is more that one line
Do it this way
Inorder form a curve to represent a function
There should be only a single value of y for an x
Like
This can't be a function
Because
yea but what if the lines aren't connected
There are two values of y for a single x
What lines ?
Do you mean the coordinate axis?
like this
Oh
would that still be function
Yep
This is the only condition for a curve to be a function
so if two of the line were to cross over the verical line would it still be fuction if they weren't connected
You mean this ?
yea
Well ,what do you think ?
.
???
What do you think,
Does this represent a function or not?
i guess???
Now, what did I say the only condition was for a curve to represent a function?
for the same line not to cross over twice??
Now check it,
Is there a line which crosses the curve twice ?
there can't be more that one y value
Mhm
no it doesn't there is only one y value and two x vaule per line
so it would be function
one*???
lol
I can just keep on drawing the line
What do you conclude from this ?
i was thinking about the end of the line but it was still be considered one vaule
End of the line ?
where it started and ends
wait what line segment
And I don't think you get the reason why are are drawing a line
We are*
Say we have a function f(x)
Okay?
ok
now it's graph looks like this
When we draw a vertical line
Say at x= 0
I.e the y axis
The point where the line intersects the curve,is the value of the function
In other words
f(0)= point of intersection of curve and vertical line passing through x=0
Understood?
as for what im understanding it would be considered function as long as the same like doesn't cross over the verical line twice
I'm explaining why we are doing this
.
im sorry i don't understand the f(0) what does that mean
does it mean it starts at 0
kind of understand it
Try this
What is f(0) ?
f(x) is the same as x sqared
Yep,kinda kinda
so 0^
so f(0)= 0
Yes
ok
The graph of f(x) looks like this
Now, here draw a vertical line passing through x=0
Where does it intersect the graph?
Imagine the curve touches the origin
the origin being the verical line
That statement is so wrong
or where the the y and x cross??
Origin is a point where the x and y axis meet
Yes
ok so it starts at 0
A line has no start nor an end
yea what i mean it that it cursve is touching 0
Yes
By 0, you mean origin
yea where the x and y meet
me too
Ah
Do you understand this now?
Note that this curve represents a different function
i think
Kinda kinda ?
Anyways
So let's see what happens if a vertical line crosses the curve twice ?
it wouldn't be a function
it wouldn't pass the verical line test
Bro ,
You know the vertical line test ?!
yea i have been trying to explain
it was that if there is two different lines and they both cross over the verical line how would i put it
if the two lines overlap would i put it in different () or would i just take the started of one and the end of the other line becuase they overlap
I lost you here
This is what you are talking about
wait let me draw it
Okay
Inorder to define the domain,
You have to first check whether it's a function or not
Is this a function?
Does it satisfy the vertical line test?
yes becuase the same line doesn't pass over twice
🤨
no
You sure ?
You circled it yourself
The region where the line passes the curve twice
so it doesn't matter if the lines are connected or not as long as there is two likes crossing over the verical line it wouldn't be function
Yes
lines* crossing over
Try watching a video on why we are doing this
I tried to explain but failed miserably
so that problem wouldn't be able to be solved
By problem you mean finding the domain,no
not at all i'm thankfull for your time and patience
sorry to interrupt, it's been an interesting conversation and you both are great! 👍
One thing though, even if it's not a function (but if it's a relation) it has domain and range too
no worries!
so i would be using Uinion
Can you continue @lofty gyro
I have a class to attend soon
oh sure, i can, i have around 1.5 hours before i have to go to work
Thank you!
I am very thankfull for you trying to help me you are so kind no need to be sorry
have a good day and thank you sooo much
You too!
hello there! @atomic quest
can you repost the question, it's been a very long talk and it's hard to scroll all the way back up
how would i put this
how would i find the domaind and range on a question like this
to see, using vertical line test, we can see it is not a function
but if you got a question like this asking for domain and range, you'll have to check the valid x-values (domain) and outcomes y-values (range)
it doesn't matter if its overlapping or not, as along as the graph shows x-values that has their corresponding y-values, the x will be in the domain
for the range i think i just i would use U to show the difference
but what sould i do it it would laps for domain
would*
ok
so we wouldn't add the overlapping like this (-2,3)
i would still use U
to show that there is more than one line
well, if you wanna split into 2 curves, we still have
[-4,-1]U[-2,2] which is just equal to [-4,2]
so both are the same
yep
ohhh ok i understand
but that probably won't appear in the exams lol
so i just worried for nothing....
for for range with there is a gap i would have to put it in different ( ) and use U in the middle of the parentheses
yes
but sometimes it's again having overlapping y-values
and we don't need to double them in the intervals
so i would do the same and put it in one parentheses
so it would be (-infinity, infinity)
for the range and domain
ok i understand now thank you soo much
cheers!
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I have come across an interesting calculus puzzle: Can anyone give an example of a function whose derivative is defined at a point yet the derivative is noncontinuous.
take a noncontinous function and find its antiderivative
Basically, an example of this would be: f'(x) = 5 (A derivative exists), however, the derivative of f is not continuous at x = 2.
that antiderivative will be what you are looking for
well you have to be careful. you have to pick a noncontinuous function without a jump discontinuity
$$f(x)=\begin{cases}
x^2\sin\left(\frac1{x}\right)&\text{ when }x\ne 0\
0&\text{ when }x=0\end{cases}$$
ugh how do I align it properly
&
kheerii
true
Is it usually a piecewise?
there
or can you get a plain function
I mean..
well this one is barely piecewise
yeah the extra branch here is just to make it continuous
at a single value
this is the classic example that i remembered but you can create arbitrarily many examples
you have to do some trickery with "dividing by 0" or absolute values or something somewhere
otherwise if you only use all the usual functions then the derivative will also be built from all those usual functions and therefore be continuous again
Does this still involve the 'antiderivative' some guy mentioned earlier?
no
this is an antiderivative of some function at all values of x, that's why it is differentiable
particularly it is the antiderivative of $$f'(x)=\begin{cases}
2x\sin\left(\frac1{x}\right)-\cos\left(\frac1{x}\right)&\text{ when }x\ne 0\
0&\text{ when }x=0\end{cases}$$
kheerii
I lack too much knowledge for this
Thanks for the input
Ill try to figure out what all this sorcery means
well for f'(0) you have to put in quite a bit more work
you actually have to compute the limit
and squeeze
well, yeah
he did that in his head trivially
well I am just saying this sounds like if you took the pieces on their own and differentiated them as usual. which you cant do for the second piece
well the derivative is continuous here
Would you agree with this claim?
makes sense.
@sinful ruin Has your question been resolved?
I think I got it finally
$$f'(x)=\begin{cases}
x^{2}+3x\
5x-5\
x^{2}+3x+\left(x-2\right)^{3}$$
Artificial Stupidity
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cooked
f(x) =\begin{cases}
x^{2} + 3x & \text{for } x < 2, \
5x - 5 & \text{for } x = 2, \
x^{2} + 3x + (x - 2)^{3} & \text{for } x > 2.
\end{cases}
thats not how derivatives of piecewise functions work
you cant just differentiate each piece individually
thats what I was talking about earlier
derivatives cant have jumps. if they do then at the point of the jump the original function is not differentiable
Isnt the discontinuity in my function a removable discontinuity?
Since the left and right approaches the same value, but the value is something else.
Artificial Stupidity
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YES
I am just saying that if you get a jump then you need to have made a mistake cause derivatives cant have jumps
note that if I just replaced the 5x-5 by for example 7x-7, then suddenly you would claim that the derivative at 2 was 7
even tho the function didnt actually change
Oh I see
that should tell you that you cant just write down some formula for a single point and then differentiate that formula at that point
and the fact that the derivative need to be discontinuous while having no jumps should also tell you that you are looking for some weird thing
cause jumps are what we usually think of for discontinuities
well thats rip but nothing I can do about that. I would still suggest to try to understand the example mentioned earlier
there is the reason its the go-to example
Apparently, oscillations dont count
wdym dont count
I proposed that exact function
and he mentioned something about it being continuous still
it could be that I misunderstood
but he is a man who got accepted to Harvard and denied it
so I wouldnt jump into such conclusion
All I am sure about is that periodical functions do not count.
the function from earlier is not periodical
oh
Using the example, something like this then:
$$f(x)=\begin{cases}
x^2\sin\left(\frac1{x-2}\right)&\text{ for }x\ne 2, \
5x & \text{for }x=2.
\end{cases}$$
Artificial Stupidity
ah ok
but that example isnt differentiable
even if I change it to 10?
have you checked for the original example why it is differentiable?
with the limit def?
uhh
I am not sure you are talking about the correct limits
this sounds more like you checked for continuity
this
given that I just pulled it from the internet
ok good
there is no actual reason to separate left and right limit here
you never used that h is positive
but ok whatever
now try that same approach with the other function you had
alright
I just realized
I mistyped the function
$$f(x)=\begin{cases}
\left(x-2\right)^2\sin\left(\frac1{x-2}\right)+5&\text{ for }x\ne 2, \
5 & \text{for }x=2.
\end{cases}$$
make it 5 instead of 5x. otherwise its not continuous
Artificial Stupidity
if I understood correctly now, the antiderivative is simply the derivative of a function?
which means, there is a way to reverse engineer the derivative back into the original function
is that correct?
antiderivative means "undoing the derivative"
Im trying to get f'(2) = 5
wouldn't that turn f'(2) into 0?
oh wait
right, limits
hold uon
isnt sin(1/x) undefined at x = 0?
oh but xsin(1/x) is 0
makes sense
thats why we do the whole piecewise thing
we never get sin(1/0)
0*undefined isnt 0
I still dont really understand why
x^2 sin(1/x) behaves pretty much like xsin(1/x)
Cant you just use the Squeeze Theorem for that
which means the lim = 0, as x -> 0 either way
aaaaa, but right, plain x plugin is undefined
I keep forgetting
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Brother this is a headache
I learned the basics of this function
But this is not what I needed
the derivative is still continuous
The goal is to find a function whose derivative is defined at a point, to which said derivative is noncontinuous.
at 0
apparently, it is though https://math.stackexchange.com/questions/232672/show-that-the-function-gx-x2-sin-frac1x-g0-0-is-everywhere
and?
that shows that g'(0) = 0?
g'(0) exists and is zero, sure
Thats what Im wondering
but it doesnt show that lim x->0 g'(x)=g'(0)
yes
this is what the derivative looks like for other values of x
But how does that make the graph discontinuous?
there are no jumps or breaks
so it is continuous
although it doesn't fit our usual idea of 'a function is discontinuous if it jumps from a to b'
it's still discontinuous
thats...not the definition of continuous
what is the definition of continuous?
I am truly a confused man now
A continuous function, as its name suggests, is a function whose graph is continuous without any breaks or jumps. i.e., if we are able to draw the curve (graph) of a function without even lifting the pencil, then we say that the function is continuous.
the limit $\lim_{x\to 0} g'(x)$ does not exist
Denascite
yes, the limit does not exist
no thats the intuitive def. that wont bring you far
ok so that's like an intuitive definition
but the intuitive definition fails for cases like these
^
I think thats what my evil teacher was using when he gave us this challenge
a function $f$ is continuous at a point $c$ iff $\lim_{x\to c} f(x)=f(c)$
Denascite
oh interesting
or we can also do the eps delta def but you will like that even less. and its less suitable here
so you also have to be able to determine the limit.
yh
was this seriously the definition ur teacher gave lol?
yea
bruh
but then I think he was trolling me
because I recall him telling us the 'calculus' definition
and you in fact have to check the limits aswell
thank you guys
I think that finally concludes my journey
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nw!
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can i get an example?
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(x-2)^3
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how do I even approach this
this is what I found:
P_300 = k * e^(-0.5/K_b*300)
P_310 = k * e^(-0.5/K_b*310)
then taking their difference
so basically taking their difference i get
(1-e^-10)*P_300
ohh
lol
i dont know this sorry
i have only done first law of thermodynamics rn
yea
nope, we can assume its constnat
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i do not understand these truth values. i need someone to help explaining it to me
Let $ P $ and $ Q $ be continuous and have continuous first partial derivatives in a region $ \mathcal{R} $. Let $ C $ be any simple closed curve in $ \mathcal{R} $ and suppose that for any such curve $\int_C Pdx + Qdy = 0,$
$(a)$ Prove that there exists an analytic function $ f(z) $ such that $$ \text{Re}{ f(z)dz } = Pdx + Qdy $$ is an exact differential.
$(b)$ Determine $ p $ and $ q $ in terms of $ P $ and $ Q $ such that $\text{Im}{ f(z)dz } = pdx + qdy $ and verify that
$$
\int_C pdx + qdy = 0.
$$
$(c)$ Discuss the connection between (a) and (b) and Cauchy's theorem.
Franklin244
Let $ P $ and $ Q $ be continuous and have continuous first partial derivatives in a region $ \mathcal{R} $. Let $ C $ be any simple closed curve in $ \mathcal{R} $ and suppose that for any such curve $\int_C Pdx + Qdy = 0,$
$(a)$ Prove that there exists an analytic function $ f(z) $ such that $$ \text{Re}\{ f(z)dz \} = Pdx + Qdy $$ is an exact differential.
$(b)$ Determine $ p $ and $ q $ in terms of $ P $ and $ Q $ such that $\text{Im}\{ f(z)dz \} = pdx + qdy $ and verify that
$$
\int_C pdx + qdy = 0.
$$
$(c)$ Discuss the connection between (a) and (b) and Cauchy's theorem.
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find the derivative of the integral?
yeah
well you could but the integral and derivatives are opposites
so 'a derivative cancels out an integral'
you have to do a bit more work here because we hvae x^2 rather than x
uhh no
i think i saw u posted a question here about integral and derivative cancelling each other out, did that ever get resolved?
nope id be happy to go back to it
yeah i think it's best to start with understanding this first before u try to tackle problems
right so the statement of the theorem has a lot of jargon
you have all ur conditions etc. etc. etc.
don't worry about those for now
let's just say our function f is a 'nice' function
as in it's one of those functions u'll encounter in the wild, not some monstrosity that technically exists
well we can define a function g(x) by
$g(x) = \int_0^x f(t) dt$
i.e. the signed area below the curve
LY
so g(2) would be the area between x=0 and x=2
g(5) would be the area between x=0 and x=5
now let's say we wanted to differentiate this function g
now i have no idea what g(x) is, it's some weird function that tells me the area under a curve between 0 and x
but this theorem states that if i differentiate this function g
i end up with my original function f
this formalises what it means for 'the integral and derivative to be opposites'
and your original function f is x^2 here right
well in the example image i gave, yeah
but the point is it doesn't matter what function f is
it could be f(x) = e^cosx ln(x) + arctan(x) or whatever
i have no idea what g(x) equals!
but i know that it's derivative is f(x)
there's an intuitive reason why it works out like this
like we're given the answer now we have to find the question
so let's say we're at a and we wanna find the rate of change of g(x) at a
then the area effectively changes by f(a) as i've shown in this diagram
(the green bit)
hope that cleared some things up
a is the red line on the right?
yeah forgot to label it
so the area we're looking for is between a, a+delta
and we want a function to represent that area between a,a+delta?
as in loosely speaking, that's 'the rate of change' of g
(well we really should divide by delta x etc.)
so loosely speaking, the function changes at a rate of f(a) there
so the rate that f(t) under a curve grows is described by that curve
i think i found a good definition to help
i think i understand whats going on here
first you evaluate the integral at [a,x]
then take the derivative of that
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first off
its best that i should do
2.54 lb to g?
then get the volumee
by v=m/d
yes convert
ok thnxs
If you have that many questions to ask you can ask in one channel, you have closed and opened a lot of channels for each question
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Hi guys I'm new
yeah have any questions?
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do you know distance formula
just minus smaller from larger?
and some worked examples here:
https://www.mathsisfun.com/algebra/distance-2-points.html
btw
in the answers
it just says the mid point
so are they the same or did they just not say
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GIYS
Help
Post your problem
Well, when you throw it, time = 0
Yes
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@woeful root Hello, I was reading through the messages and I think @sinful ruin may have found an answer, I think we were using the wrong definition of continuous also
Original Question:
Final Point
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idk why symbol looks confusing
But
Ik that it will be element F right
like im looking at the other symbols
what is that 2- and that 3+
like ik 109 is mass number
52 is proton
Charge
Typically not
ah
this aint maths?
charge is protons-electrons
how to find charge
oh
perfect ok
so it wil always be 0 ??
da heck
oh in neutrals
ok
got it
thxn
that's for neutral yeah
charge isn't something that's 'inherent' to an atom
an atom is neutrally charged
and then you can have different ions of that atom when you add/remove electrons
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This might be physics heavy, maybe someone is familiar? lol. Sooo..
Bungee Jumper has a mass of 50kg. And will jump from a platform 30m above the ground. The bungee cord is 6.0m long when no forces is applied to it, and has a spring constant of 150N/m.
a) How far below the platform is the speed greatest?
(Actual answer: 9.3m)
b) How far below the platform does the jumper get before she is pulled up again?
(Actual answer: 16m)
c) What is the acceleration of the jumper? (Use the max displacement from question b)
(Actual answer: 21m/s^2)
I finished a and b. I'm stuck at c. I need to find the acceleration of the object at its maximum displacement from the platform.
Equilibrium position: 9.27m below platform.
Total Energy in the system at 9.27m = 3210.32J
Maximum displacement from equilbrium position: 6.5425m.
So max displacement down is 15.8125m below platform.
What to do.
At 15.8125m, I tried to to plug in "ma=kx" into "Ep=0.5*kx^2" to get 0.5max, but a=19.6275ms^-2, not 21.. badbad.
I tried a=kx/m, got 19.63ms^-2 too.
I tried (kx+mg)/m, this one I got 29.44ms^-2 on,
I'm stuck
and for "x", i used "6.5425" bcuz thats max displacement
im actually stuck, need to sleep. but plz try if u are familiar with physics.
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Need help working through this problem
OK. I think if the max displacement is 16m and the equilibrium is 9m, the jumper is 7m below the equilibrium. Hope that helps. if you need something more, feel free to post again. Also a = (kx)/m looks right. Just make sure you're using the right values.
Hi Egg
Hi
all of it lol
OK. Looks like you have a line in $\mathbb{R}^2$ parameterized as a vector equation.
Stefano
How familiar are you with vectors in the real plane?
very little
Do you know how to graph $\vec{c}$?
Stefano
its just a vector going through 1,3 right
It might be better to think of it as going to (1,3)
gotcha
What do you think of when you think of a vector in the real plane?
(I just want to clear some things up so we can make sure you're able to answer questions like this in the future.)
a line with direction and magnitude
Sure. So, it doesn't have to end at (1,3), but by convention we start at the origin.
Does that give you enough information to try to graph c?
Cool, a vector in space can be thought of as a relative position. Let's say you're playing a video game, like a first person shooter and your team mate is in front of you and a little to your right. If the two of you keep that formation as you look around, you can describe their position with the same vector
They're always 1m to the right and 3m forward from you
Even if you move around
Even better. The same vector.
the same vector in two places at once?
No.
Your teammate is 1m to the right and 3m forward from you and you're on the second floor of a building. (Maybe looking for zombies, gold, enemies, whatever!)
Then you two go outside, but keep the same formation. Where are they relative to you?
1,3?
Of course. You're well trained and keep a tight formation. That relative position from you and to your team mate is a vector
It's the same vector as long as you don't break formation
OK. Now, where's the one place neither you nor your teammate should aim your guns? (Sorry if you're not into shooting games)
towards eachother
Exactly
And if you have a third teammate who's another metre to the right of the second one and 3 metres farther to the front of the second one, are they still in that direction you don't want to aim?
yes
You could have a fourth, fifth, sixth... etc you could have teammates all along that same line of fire
That's a vector equation for a line
We start with your coordinates and then we say whoever is in this direction ahead or behind is on the same line of fire
thats vector form?
Exactly! In our example, we might say your position is (5,2) and your teammate one's relative position is (1,3) ahead of you. Teammate two is (1,3) ahead of teammate one.
I see
Do you know what the vector from you to teammate two is?
No
First teammate is 1 metre to the right and 3 metres ahead, second teammate is another one metre to the right and another 3 metres ahead for a total of?
2,6 meters?
Perfect! 2 metres to the right and 6 metres ahead
yes
Notice that 2*(1,3) = (2,6)
yes
If there was a teammate a metre to your left and 3 metres behind you, they'd be at (-1,-3) relative to you
right
If there was another teammate ahead of the _third) and they were also spaced (1,3) from the second, they'd be at 3*(1,3) relative to you (3,9)
yes
So, starting at your position we could say anyone from your position plus or minus any fraction of (1,3) is on the firing line
yes
$L = t \begin{bmatrix} 1 \ 3 \ \end{bmatrix} + \begin{bmatrix} 5 \ 2 \ \end{bmatrix}$
Stefano
OK. So that's the firing line. Starting at (5,2) and going any multiple of (1,3) away from there.
Exactly! In our example, we might say your position is (5,2) and your teammate one's relative position is (1,3) ahead of you. Teammate two is (1,3) ahead of teammate one.
I just made up that example
And technically, it's a starting point
But let's look at the example $\vec{x}$
gotcha
Stefano
that makes sense
Can you identify the starting point? Can you identify the vector that defines the line?
(brb)
for the problem I posted?
Yes
It would be 1,0
There are two questions there. Can you try to answer both? And be specific about which answers go to which.
the 1,2 defines the direction and the 1,0 defines the starting point
yes
sure
Do you have any thoughts about what $\text{proj}_{\mathbf{k}}\vec{c}$ might mean?
Stefano
OK. It's read as the vector projection of 'c' onto 'k'
Remember how we were talking about the vector from you to your teammate being the same (if you maintain formation) regardless of where you are?
yes
And you were able to draw the vector c, right?
yes
Nice! So "move" c (you can draw it again) so it's on the line K
Good point.
We want c to start at any point on k
Recall, we used the convention of starting c at the origin, but that's not how we define the vector. Just like you and your teammate moving around. (In fact any teammates where one is 1m to the R and 3m in front have the same vector as you!)
ok so how do we start c on any point of k
- Pick any point on K
- Pretend that point is the origin and count out x and y coordinates of c
- Draw an arrow from the point on K you picked to that endpoint you found
so when sketching projkc I just draw any line with c direction starting anywhere on k?
That's the first part. We're finding the projection; we haven't drawn it yet
But yes. The vector C is always the vector C
Just like 1m to the right and 3m ahead doesn't change if you start in Sydney, Australia or Lagos, Nigeria
gotcha
How many units to the right or left of that point on K and how many units up or down from that point on K will you go to find the endpoint of C?
-2,-2
Why?
I chose the point 2,2 on K
and had to go down and left 2 to reach the origin for c
No
oh
1,3?
Right
Hold on
If you're teammate is 1m to the right and 3m ahead. And that vector always stays the same regardless of where in the universe it is, how far to the right is your teammate and how far ahead?
1,3
OK, but what if you stay in formation and go to Tokyo?
still 1,3?
OK, but what about in London?
same
What about New Mexico?
same
So you're telling me that we define the vector by its relative coordinates regardless of where it is?
yes
OK, just lemme make sure. What about if you stay in formation but go to Sao Paulo?
OK, so an ant walking from your feet could walk 1m to the right and 3m ahead to get to your teammate, any where in any possible universe or multiverse as long as you stayed in formation?
yes
Even if you were standing on line K?
yes
That vector from you to your teammate is (1,3) right?
yes
And C is (1,3) right?
yes
So if you're on line K, say at (2,2), where does the ant go to get from you to your teammate?
3,5?
yes
yes
Imagine the sun is shining right above K. What shadow would C make on K?
(To be precise, when I say above, I mean as if the sun's rays make an upside down T when the hit K)
a 1,3 shadow?
Not quite
Notice that the shadow might not be the same length as the original vector
i see
In the last image in particular, can you see that the shadow (in grey) is shorter than the vector (in yellow)
(the line in blue would correspond to K)
it looks the same length as the yellow vector
It's a little shorter. If you use a compass, it might be easier to see
Hold on
Can you see the other yellow vectors now? They're all the same length
yes i see them
Do you see that they are longer than the grey one?
yes
Here's another with the vectors and lines labelled
yes
I didn't sketch it, but I suppose someone did
i mean thats it conceptually though right?
That's literally the projection
gotcha
The vector projection is that vector, in this case that grey arrow, but the grey arrow is really defined by a start and end that stay in formation.
You could move it wherever
The scalar projection is the length of that grey arrow
right
If the yellow vector, in the above example pointed towards the centre of the circle, the grey vector would reverse as well
That's pretty good. Remember that K is that line of fire we were talking about. It goes on forever in both directions
right
And you should be able to draw a perpendicular line from your vector c to the tip of the projection on k
(a line perpendicular to K)
Hold on, just want to check with you
ok
Just a quick check. Which projection is correct?
doesnt that depend on the direction
The direction of what in this picture?
both k and v
yes
How do you define its direction?
x and y
More precisely, how would you use x and y?
for example 1,2 is the direction of k in the form x,y
Hmm. I see.
Not quite
Let's say that in this photo, K is flat along the x axis, ok?
yep
infinitely in both directions
yes
More precisely, does it have only one direction?
no
That's it
No
despite being infinite?
but then why was k in the problem make k 1,2
There is no "from" with (this type) of infinity
but then why was k in the problem make k 1,2
To position the line
but isnt that the direction in the vector form we were given?
No the line "goes in both directions". Unlike a vector, it does not have (only) a single direction.
but its described as xvector=[1,2]+[1,0}
In fact, from your teammate's perspective (-1,-2) is the vector used to describe the line
t[1,2]
that t could be negative
To your teammate you are behind (negative ahead) and to the left (negative right)
Literally the opposite direction, but the same line
right but
why is it described like this then?
So if we go back to the first person shooter example:
Your teammate is 1m to your right and 3m ahead (then you are -1m to the right and -3m ahead of your teammate)
But
Your opponents are also in formation their formation is one is -2m to the right and 5m ahead of the other. They will be on a different line.
Both lines go on infinitely. They are not the same lines
Each line is parallel to a vector (1,3) in your case and (-2,5) in your opponent's case
So the vectors have specific directions. They are oriented with from and to. We can define them with a start and a stop (regardless of where we put them)
The line has no start or stop
But those lines are still defined right?
I am lost now
Forget all the math and just picture 4 soldiers (we do have to imagine that bullets go on forever), two are in a certain formation along a line, two are in another formation along another line
I just dont understand why we are stating this now after we just described and sketched the line k with a direction
I realize this may seem overly precise, but we're differentiating between one direction:
And two directions
If I tell you to go in one direction, you know where to go, right?
yes
If I tell you to go in two directions, where do you go?
two directions
You can do that?
isnt that what you've been telling me?
I am confused.
how so
You can get up, maybe divide your body in two, and walk to the left and to the right at the same time?
Ah. I think I see the confusion
You mean, I can travel, for example, both north and west, right?
(northwest)
whats confusing me is that we used 1,2 to draw the line k but you said its not the direction of the line
yes but in the context of the line north and south makes more sense
yes
Good. That's what a line is like, it's like a highway that runs along the north south directions (and again, note in the interest of precision, it's "directions" plural, not "direction" singular). You can go one direction or another on the highway, but not both at the same time. You can do that because you start somewhere
The highway has no start.
that doesnt make the vector form irrelevant tho
Please, go ahead....
is that we are talking semantics like what we did was wrong
because you can solve it by describing the line by the vector form in the direction 1,2 and just extend in both directions right?
Yes
ok so thats all we really need to know right?
sorry if that comes off as rude I enjoy the theory but
Yes. In a sense you're completely right. Your instincts are spot on
gotcha
It's OK. Semantics can really help hone those instincts
again not trying to be rude just Ive been working on this first part of the first problem for the past 4 hours lol
and this is due tomorrow
Your drawing had an inccorect angle


