#help-23
1 messages Ā· Page 433 of 1
Then my bad
Ohh for tan that was a mistake
Oh ok
But its still wrong
How can I make it that form
You irrationalise it
How
1/2sqrt2 is actually a bad format, write in sqrt2/4 is better
Can u use latex pls
1 sec
Ok
$\frac{1}{2\sqrt{2}}$ is a bad formatting, since you have the square root in the denominator, $\frac{\sqrt{2}}{4}$ is better
Nefer
Yes but how would ik if im right or wrong if I don't have the book answer
tan^-1, in calculator
.
And what am I supposed to get
$\frac{1}{2\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}}$
Ik whats that
flynger
You can always check if your answer matches in a case like this by rationalizing fractions (removing the radicals in the denominator)
Multiply the top and bottom by the radical and simplify
since you are multiplying by 1 it is equal
There is no radical in tye denominator
Whats a radical
Idk
I assumed its a sqrt number
yes its a number under a root, usually square root
$\frac{1}{2\sqrt{2}} \cdot \frac{\sqrt{2}}{\sqrt{2}} = \frac{\sqrt{2}}{2\cdot 2}=\frac{\sqrt{2}}{4}$
flynger
for the question asker
Then add 180 to move it to the second quadrant
if you want to remove the $\sqrt{2}$ from the denominator, we know multiplying by itself will get rid of the radical (root). So if you multiply both the top and bottom, you can get rid of it, while keeping the value of the fraction the same
flynger
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this book is riddled with errors, what the hell is this pfd
It does appear to be correct
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eh you know what they say, get good at calculus to fail at algebra
what
welcome back
long time no see
heyo
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Not sure if control theory/dynamic systems are applicable here, but i will try my shot:
\medskip
Im working with a linear dynamic system in $\vb R^2$ governed by the two ODES:
\e{align*}{
\dot x_1(t) &= -x_1(t) +2u(t) \
\dot x_2(t) &=2x_2(t) + 3u(t)
}
where $u(t)$ is a scalar control input. We care about $y(t) = x_1(t) - x_2(t)$.
\medskip
Assume the system starts at rest where $x_1(0) = x_2(0) = 0$. I want to design some sort of feedback control function $u(t) = k(x_1, x_2)$ that drives the output to a strictly positive constant $y^* > 0$ but with $u(t) \in [-1,1]$
$u(t)=k(x_1(t),x_2(t))$ ?
flynger
If you analyse the gain of the system you get[
\4{Y(s)}{U(s)} = \4{1-s}{(s+1)(s+2)}
]
but the issue thats giving me a headache is the zero in the numerator. Any controller designed to push $y(t)$ toward a positive value will guarantee that $y(t)$ moves in the negative direction, at least initially
yeah
but then if you try to aggressively overcome this wrong movement you need to demand a huge spike in u(t)
which violates the [-1. 1] boundary
basically: i want help figuring out how to handle the initial reponse without saturating the controller
i also asked in #dynamical-systems fwiw
@opaque fern Has your question been resolved?
@opaque fern Has your question been resolved?
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Yes š
The points you've been given are written in polar forms
oh..
(as the Ļ is suggesting)
bruh
my reading comprehension skill strike again
welp
rip
anyways, thanks a lot
appreciate it
Happens, don't worry š¤
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can someone help me on these problems please?
!show
Show your work, and if possible, explain where you are stuck.
im just confused on where to start
do i start with factoring the trinomials or do i multiply first?
So for the steps is determining the theorems that you can use.
What problem first?
For Q23 You can use a/b * c/d = (ac)/(bd)
You need also make use of equivalent fractions. i.e. (ka)/(kb) = a/b
oh i donāt need help on 23
i need help on 24 and 25
sorry i didnāt clarify that
How about we start from 24
yes
Golden rule: factor if you see a mess on fractions like 24
mhm
I mean onyl the 2nd one looks factorable
i canāt factor the first trinomial?
These guys have to be factorizable right?
No, due to -6
Hm
No that's possible
wouldnāt it js be (x + 2) (x - 3)
Yeah
Fuh ig
k i thought so
so if i factor both of them it would be
(x + 2) (x - 3)/4x^3 *
2x^2 + 2x/(x + 2) (x + 3) ??
Yea
ok so what now
I mean the numerator in the second one can be factored further into 2x(x+1)
Multiply both together then simplify i guess
Now that its factored it would be easier to multiply
my final is next class period
uh huh
i need help w that too
that made me more confused
I mean read this i guess https://www.mathsisfun.com/fractions_multiplication.html
Note: instead of numbers you can also multiply algebraic expressions involving variables roo
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Help with trig study guide
!da2a
Asking the actual question right away is more likely to get responses.
Asking "Can I ask...?" or "Does anyone know about...?" doesn't give people enough information to decide whether they can help, and answering can feel like a promise to help with the actual question, which they might find themselves unable to.
I need help solving a few trig questions on a study guide
?
"Dont ask to ask"
Ok so does this work or would I still need to rephrase it
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ā Original question: #help-23 message
Help with trig study guide
@fleet frost Has your question been resolved?
Do you have a specific question you are stuck on?
What it is there are a few groups of questions that ask about the same thing that i am stuck on those pictures so those questions and the ones that I have already done
In total there were about 22 that I havenāt answered because I didnāt know how to
Do you not know the ASTC rule
No
If you knew you can solve 7 8 questions
All Silver Tea Cups.
Ohhh I know what you are talking about now my teacher calls it all students take classes but how would I use it in those questions
So for sin <0 , it needs to be negative
Check where it is negetive
and tan <0 is only in quadrant 2 and 4
for sin <0 it's only in quadrant 3 and 4
so for both to be negative, what do you think is the answer
So it would be quadrant 4
That's right
@fleet frost uk that cscx=1/sinx
Ya itās starting to click I little bit again
Then answer of 10 should be clear
The values should be reciprocals of each other
And doesnāt that mean the same
So
Quadratic 1: All are positive
Quadrant 2 : Silver - Sin and cosec (since cosec is inverse of sin)
Quadrant 3 : Tea - tan and cot (tan is inverse of cot)
Quadrant 4 : Cups - cos and sec (since cos is inverse of sec)
Hence all silver tea cups or ASTC is the code word
Ok ok I understand it quit a bit better now
Yeah so in what world 0.2 and -0.2 reciprocals of eachother
They arenāt so then that would be itās impossible
Correct
Thank you that helps me understand that a lot better it just wasnāt clicking in my head for a bit
Are you able to help me with a few more or not if not thatās ok
So the next ones are 11, 12, 13, 16, and 17 those are the ones on the next page
I feel like 11 is easy I just am missing something
Did you find the coterminal angles? If what are they
Or do you know what are co terminal angles?
No i couldnāt even think of the right way to start it and I canāt think of what those are off the top of my head right now
Uk how we measure the angle from the x axis they are telling you to measure the given angles starting from 115
Ohhhhh ok I think I got what you are saying
So there are two types of co terminal angles
- Positive co terminal
- Negative co terminal
For positive co terminal you add +360° to the give angle which is 115 here
For negative co terminal , you subtract 360° to the given angle which is 115 here
Ok ok I got that now so why are there two things with the same numbers but different pictures
And you might ask , then what will be the answer A or B?
Or basically rotate in clockwise direction for -ve angles
you know why?
No not really
So 115° in figure A shows the correct slanting of the arc whereas in option B , the arc angle is less than 90°
so which is the correct answer?
It would be A then
that's right
Ok I understand now how to choice the right picture
So how would you do 12 and 13 then I have never been good with those ones
Huh
Are you familiar with the unit circle
Ya some what
I'll let @zenith maple answer cuz I believe I'm intruding šsorry my guy
Your all good more help the better
Ok what you do is plot the point
Join it to the origin
And drop a perpendicular onto the x axis
Ok ok I got that
im not interrupting, watch this and I'll tell you a trick my teacher taught back when I was in school https://youtu.be/PUB0TaZ7bhA?si=KWzGm3aCCCRBgEKk
This math video tutorial provides a basic introduction into trigonometry. It covers trigonometric ratios such as sine, cosine, and tangent. It explains how to evaluate it using right triangle trigonometry and SOHCAHTOA. In addition, it explains how to solve the missing sides of triangles and how to find the missing angles using inverse trig f...
Ok I will lyk when I am done watching it
You get a right triangle so use trig ratio concept
Ok ok sorry for the confusion what I am seeing now isnāt that I donāt know what to do on this problem itās that I donāt really know what itās asking for I have a hard time with word problems like this I am better with just numbers and no words
See they are asking for a trig func of an angle corresponding to that point
So there basically just asking for it to be one of the functions things but only from the point they pick
Wdym?
What I mean is that after you make the triangle they just want you to put it in like sin, cos, tan like those type of things from the part of the triangle they pick
Yeah exactly
Ok so for 16 I know that the evaluate is you make it either like a 1 or 2 either pos or neg but how do I know which number and if itās pos or neg
I just have the sohcahtoa thing in my head I always just write it down on my paper but thanks for a different way to think about it
so that is what we use in the 12th question
Ok I understand it now just totally forgot how to do it just like all the ones I have questions on
Been a long semester
Wdym? It is just (cot90)²
But for it the answers are 0, 1 , -1 , 2
Yeah put the value of cot90 like how you did with sec180
Btw cot90=0
About that I had no idea what to do on that I looked through some of my notes and saw it turn into a one but donāt know how it did or what do to to do that
You get 0²-(-1) which is 1
Ya so how do those turn into a 0 and a 1 I donāt understand that part
See sec(180) is just 1/cos(180) and cot90 is cos90/sin90
So why is the 180 a 1 how did you get that and same with the other one I understand like the changing it to sin and cos I just donāt understand the getting it to 1 and 0 part
See you need to use the unit circle
I understand most of it but not all of it because we got thought a different way that we didnāt really use the picture
And the fact that if there an odd multiple of 90 the function changes into it's cofunction
Ok then wait a minute
What
Then are you familiar with these
No what my teacher did was she used the circle thing but only in parts so we had to memorize only parts of it at a time but not the whole thing so by the end we new it but we never used the whole picture if that helps explain it at all if anything we can skip this problem and I can ask my teacher in the morning I have some time in the morning to work on this but just not a lot and if anything we can always come back to it
Sorry for the confusion
A trigonometry introduction, overview and review including trig functions, cartesian quadrants, angle measurement in degrees and radians, the Unit Circle and the Pythagorean Theorem.
2026 update: This was my first video and I thought I could do a better job now, so here is a "better" version: https://youtu.be/y4MiAOm5quk
Also: I have posted a ...
I hope this helps you visualise @fleet frost
It most likely will I will take a look at it after we get a few more problems done if thatās ok and this is really been a big help
Ok once you understand the unit circle you wouldn't need to remember all those formulae nor all the values
Ok I think I get what you are saying that I need to just remember the numbers and not the formulas and I have that most of the way done I remember like the sin 30 is 1/2 like that stuff and the pie stuff too itās just the 1ās are throwing me for a loop but I kind of what to just skip 16 for now if thatās ok so we can get a few more problems done if thatās ok with you instead of being stuck on one
I mean you need to remember only values till 90
And for 17 just reciprocate
and rationalize
Ok so i would flip it right then do you mean by rationalize like make it (2ratcal7/2)right or am i thinking of that wrong
I'm sorry but wdym 2ratcal7
This but with a 2 at the bottom
Why would you get 2 at the bottom?
Good question I donāt know
I mean to multiply by ā7 to both numerator and denominator
So what do you get?
Answer A
And I am realizing now I called it the wrong thing to itās a square root sign not a ratcal sign
Yup
Ohh so you meant a radical sign
Both work
Ya
And for 40 use the formula thetaĆr²/2
Ok ok So the next questions are 23,24 I have the answer and work to 23 because it gives the answer but I only have the first step to the work and I donāt know how to solve it
If you want I can start sending a better pic of the questions and new ones so you donāt have to scroll back as far
Yes please
It's ok np
Ok
For 23 you use the same logic as 16
Ok ok that is what I was just realizing
Ok and for 24 I know you just put it in the calculator but I donāt remember how to do it for csc
Sorry but I don't work with calculators only by hand
Ok your all good I can just ask my teacher tomorrow
Man I was so close I new it was something like that I put in like 3 or 4 different things like that but just not that
I have done that a few times now
And here is 41 and again I canāt thank you enough for all this help
And counting this one I got 7 left
You did it correctly for 41
Are you sure bc I'm pretty sure that the answer is A
The answer sheet on the back says it c for some reason
Maybe it is printed wrong or we are missing something
Maybe
But let's not waste time on that
Wait what do you mean I understand the function just not what to do with it
what do you know about cos in quadrant one
They pos
so can you remove 2 answers?
They have given you tanx value and you need to find the secx
Use that relation
So would you then treat it like a squared +b squared = c squared types thing so you just move the 3/4 over by dividing the 1 by it then square root it
ohh it wants u to use fundamental identities š
? U get sec²x - (3/4)² = 1
Ya thatās what I ment
Ok ok
For 44 remember if cos(ax) is given it's period is 2Ļ/|a|
Same for sinx
And both their reciprocals
But for tan and cot replace 2Ļ with Ļ
This is explained by the graphs of them
@fleet frost do u get it
No not really I donāt really understand what you are talking about with this problem and the voltage thing is the thing the is confusing me the most
I have absolutely no idea what itās asking me to find
Like I get it wants the period but how do I find that with this problem set up
Just forget the voltage they just mean to find the period of that func
Use the formula I gave you
I am starting to understand I bit
See if you do f(ax) for any function it gets compressed along the x axis by a factor of a
Same logic applies here
Give me one sec I think there might be a few examples in my notes that might help I will lyk if I find any
I'd love to stick around but it's getting late for me
I have to go
Bye
Your all good thanks for the help I should have enough time to get the rest done tomorrow
don't forget to watch that video on unit circle
Ok I wonāt
K bye
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Uh, I think Iām asking right
Hey, if someone would be so kind to help me on this problem? I think my bounds are right but I am unsure on which to go at first. If I go after Ļ first that leaves me with the Ļ^3* e^ Ļ^2 , I am lost a little. This is me looking back on my exam, we have no key for it and what not
You can just use a u substitution for rho^2 = u, it should be a straight forward calculation
If u = Ļ^2 then du = 2Ļ or 1/2du= Ļ then do I use integration by parts to resolve?
yes
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some important features of a trig graph:
- the amplitude
- the period
- the phase shift
- the
"translation up"y-intercept - and with all of these features, you literally don't even need the equation anymore!!! but the equation is useful for checking your answer as a final step.
now, let's get into each one
- the amplitude is the vertical distance from the bottom to the top of the curve, or in this situation, from the bottom to the top of the motion right?
so we need to figure out the lowest and highest points.
oh that's genius ty
this is related to the y-intercept too, except the y-intercept gives us an indication of where the motion starts (at t = 0) and then the amplitude is by how much we move up and down in the motion
okay personally I am not calling it the y-intercept from here because I'm thinking of a different y-value that's more relevant
I'm just going to call it the middle axis I think it was something like that
Right, so:
- the middle axis is the line that splits the curve in half. The curve oscillates up and down about this axis, with an amplitude
- to find the axis, we take the average of the lowest and highest values;
- to take the amplitude we take half the total change in vertical distance of the graph / distance from middle axis to the top, or bottom, of the graph
part 2: period and phase shift,
- period is the time taken for a full cycle from bottom -> bottom or top -> top
- phase shift is indicated a bit by the y-intercept; it's the first time at which the middle/highest value is seen for a sin/cos function respectively
yeah that's it! if i catch u online ill help u thru the specific question but i honestly have to go now i hope the detailed content dump helps
This is all very helpful but I still have no idea how to determine the equation
i did forget that bit that's mybad
Like what do a, b, c, and d correspond to is what Iām confused about
Middle value? You mean the peak of the wave?
no, the average of the highest and lowest values
it's this
Oh ok
c can be a lil complex. you can use the phase shift, but there are 2 different situations
- inside the cos function you have (bt-c)
- or inside the cos function you have b(t-c)
personally I've always used the equation at this step because once you have 3 variables you can find the last. just choose a coordinate from your graph and substitute it
now
is half the difference in highest & lowest
highest is 80, lowest is 4 (i should highlight it's not immediately that the highest is 80 because it's the highest in the table. ill explain why that's not always true after)
amplitude = (80-4)/2 = 38
did u find that?
Why is it halved?
that's just how we define amplitude, as the distance from middle to top, or middle to bottom
But not top to bottom
Ok
the axis is the average of the top & bottom values
= (4 + 80)/2
= 42
the axis has equation y = 42; and we also get d = 42
Ok now how do I solve for c
First we do b
I got b
the period is between t = 0 and t = 9, so period = 9 minutes
as?
4Ļ/9
^^
It's 2Ļ/9
Shit
Full period is from one point to the same point again
Ok
@lavish dagger i think you want this?
correct i think
um
hold leme elaborate
ok see how the amplitude says 3 KEEP THAT IN MIND
ill be a lil busy getting ready for school U two so might respond slower
(the top graph) where tf does it say 3 anywhere so where did they get 3 from
oki
so you're clear that the amplitude is 3?
it's 3 bc you can count 3 units/boxes from middle axis to top
They don't give us any values you're right
šµ
Ok so 4=38cos((2Ļ/9)(9-c))+42 is the equation I got how do I isolate c
We take each square on a grid as 1 thou
Okay so
Subtract d, 42, from both sides
-38 = 38cos((2Ļ/9)(9-c))
Then divide by the amplitude in front, 38
-1 = cos((2Ļ/9)(9-c))
Clear?
Yeah
Dyk the cos^-1 function?
If not just think "when does cos(x) = -1?" and you'll get x = Ļ
so Ļ = (2Ļ/9)(9-c)
divide both sides by 2Ļ/9
9/2 = 9-c
and finally c = 9/2.
I'll tell you now that there are actually an infinite number of possibilities for c
We uuuuusually want the smallest (which we happened to get!)
but to check if your c is as small as possible, just make sure it's less than the period ( = 9)
if it isn't, just keep subtracting 9 from your answer till it's small enough
e.g. if we got 27/2 = 13.5 i'd subtract 9 to get 4.5
sound good?
I gotta go goodluck š¤š¾
Wouldnāt c = 27/2 then?
.
Wtf happens to the 9??
subtract 9/2 both sides
add c both sides
see what you get
I donāt get it how can 9/2 = 9-c and c??
did u get this eqn?
Yeah
okay, so you did get pi = (2pi/9) (9-c)?
Yes I got that
Yeah I did that
so then you managed to get 9/2 = (9-c)?
Yes
Oh I fucked up on like the last couple steps
Iām a fucking moron
Sorry for wasting your time
dw happens to best of us gngš
All good!
Thought I had to add 9 to both sides instead of c š
Brainfart
So youāre telling me all this time c was just half of the period?
Or is that just a coincidence
.
@full ridge Has your question been resolved?
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yo, quick question about infinite limits, with this rule, on the case I have
(2-3x)/(1+x²), I have to look for the term that has X and the biggest exponent, right?
correct. essentially you want to determine the degrees of the numerator and denominator polynomials.
If I follow this, by the 2nd rule it's zero, and if I solve it by dividing everything /x² it also gives me zero
nice ty, just wanted to confirm
chatgpt was very sus
i appreciate it!
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I donāt undedtahd this problem at all. I donāt understand how to fit the wind into this one triangle. We never learned any equations for speed so idk how we know the speed . And I thought we already knew the speed 325mph. And I donāt undedtahd what it means to find a direction. We already know its direction
hint: consider that wind (or water currents, or any moving medium in which an object is itself moving through) affects the velocity of the object as seen from a stationary point of view.
I dont know where to put it on the picture tho
I just donāt even know where to start
consider drawing the movements of the airplane and wind separately first. but get their angles right.
,rccw
this is the movement for what?
Wind
so I presume the slanted arrow on the right is true north.
I donāt really know what Iām doing I tried looking at the answer key but kn it even mroe confused
not a very convenient direction to point north in, but sure.
It said it was pointing west to north
I know.
but normally we draw north directly up. you made your north arrow slanted.
but I digress.
now then, draw another north arrow, and draw in the velocity of the airplane.
also, don't forget to label the actual velocities of the wind and plane.
(with the numbers.)
I was just trying to make it look like forty degrees
I never said that was wrong.
my whole point is about the direction the north arrow is pointing in.
I never said a single thing about the size of the angle or the direction of the velocity of the wind because both of them are okay.
ok
What about the competent form of the velocity it never gave us the velocity so idk what it is referring to
the component form of the velocity of an object is the velocity, broken down into the vertical and horizontal components.
Yea but how do we know which side to use for velocity which side to use for speed , etc
example: if the black arrow is the velocity of some object, then its component form is the blue and red arrows.
velocity is speed with direction.
I thought that was the speed tho
there's no side to use for speed.
speed is a scalar. you don't usually draw vector diagrams with speed.
I thought speed was like this I put v but I would not know which letter it is
well yeah, speed is the magnitude of the velocity vector.
Iām sorry Iām completely lost š
I just canāt keep tract of which variables belong to which part of the triangle
then I'll step back, since I saw another helper potentially trying to help.
So is velocity always the diagonal side or smth
But some of the problems have multiple of those so idk
I donāt understand the answer key for this. Because they said the current is between s and west. But in this photo it is between north and west
Well what is the ship's velocity vector?
I donāt know how to know that
I thought the velocity vector was also the speed vector but on the next problem they switch so idk what to think now
Ship is heading North for 12mph.
And I thought the velocity vector is the magnitude vector
Does it have to be north to be a vector?
Well, what do you define a vector?
Magnitude and direction but Iām confused because I thought the speed was determined by the vector but on other problems it changes so not sure how to know when it changes
and also for 5 we have no magnitude or direction
I thought
A vector is a line with direction.
Ehh that's why they invented the arrow :))
this line has no direction. (sorry for stepping back in just to make this comment.)
-# No problem there -.-
Well, from Chiaki's illustration, it have no direction, since no arrow is indicating the direction it is going to.
Iām just confused because the vector line keeps changing on every problem it feels like. Like I know they are going to be different but sometimes the vector represents speeds and sometimes it doesnāt
But then there are multiple ?
Multiple?
That line there, suppose it have 2 endpoints A and B, we do not know if we are going from A to B, or B to A.
How would we go from
Sorry I know this is off topic itās the same problem Iām just trying to figure it out because I think Iām confusing them
What are you writing there? I can't read...
Is that better?
That is a vector transforming into it's magnitude, or norm.
ok but then for this one I lost track of what I was orginally asking. I donāt understand where I went wrong with my drawing
And for the next one I have the same issue. I donāt know if I start the next line on the side with the arrow or the side witho it the arrow
Suppose you have a compass... Then from the centre you would have 4 different arrows pointing toward West, South, North, East.
We are given several informations for the current flows and ship's velocity, since they are having direction and magnitude, it is sufficient to transform them into vectors.
Start with the ship, it is heading North, then it is moving up on the y-axis (a.k.a. positive side), then it would have positive magnitude, etc.
a "positive magnitude" doesn't really make sense here since the magnitude of any vector is always non-negative, you may be referring to the sign of the y-component of the vector
That's what I am mentioning, you can re-read the conversation to understand which scenario I'm I referring to.
Better to use the correct terminology then to avoid confusion
@soft lava Has your question been resolved?
The magnitude of any 2D vector is the square root of the sum of the x component squared and y component squared
$$
|\vec{v}| = \sqrt{ v_{x}^{2}+v_{y}^{2} }
$$
proxy_warfare
assuming you're familiar with component form of vectors
$$\vec{v} = \begin{pmatrix}
v_{x} \
v_{y}
\end{pmatrix}$$
proxy_warfare
You can takeover the channel then, thank you.
No problem
@soft lava if you can tell me what you are confused with specifically I can help you better
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Bro this is the second self solve already
embarassing atp
Fr
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im so worried this should be easy
i forgot how to do this though
because i ended up doing IBP twice which is obviously overcomplicating
theres no way in hell they would ask me to do IBP twice like that
isnt it the integral of y from 0 to 1?
idk what you mean by "IBP" but just integrate it
seems like that to me
I think IBP is required. But you can use that one DI method that makes it easy
IBP is integration by parts
@formal wolf Has your question been resolved?
so yes
but it's the integral of x^2(e^-3x)
which is annoying because it's if the only way to do it is IBP it's long and easy to make mistakes on
and if i make a mistake well i lose my place at my university because in the uk i have to perform flawlessly to meet the conditions of my offer
so yeah
you mean dv/dx = e^-3x
Integration by parts by using the DI method! This is the easiest set up to do integration by parts for your calculus 2 integrals. We will also do 3 integrals to illustrate the 3 stops of the DI method.
Dear calculus teachers, please let students use the DI Method (& why it is really the same as integration by parts) š https://youtu.be/8xPfNu...
Take a look at this
oh wait actually yeah i remember a table for this
It makes integration by parts very easy
Its a very useful trick. I think a couple of books have it too. Not sure if they teach it in school
I've never heard of it
Its very useful
Its a pretty common shortcut
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Are there any errors in my solution?
i feel like the integral in part a might be a bit too hard
your solution for a should be correct even if it looks tedious however in part b, there is an error in your setup for this part cuz you forgot to square the function when you substituted $r = \theta$ into the integral
reze ā”
yep shouldve been theta squared
thanks a lot, appreciate it.
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nah its fine no worries lol
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Consider the potential $V(x) = ax^{-7} - bx^{-3}$, where $a$ and $b$ are positive constants. A particle of mass $m$ is initially located at the minimum $x_M$ of the potential. No other forces are acting on the particle.
\[10pt]
Sketch the potential. Where is its absolute minimum $x_M$ located?
\[10pt]
The system is evidently conservative; that is, the total mechanical energy $E_{kin} + V$ is conserved. Graphically determine the allowed values āāof $x$ as a function of the kinetic energy $E_{kin}(x_M)$ that the particle possesses at the potential minimum $x_M$. Hint: You must distinguish between the cases where the sum $V(x_M) + E_{kin}(x_M)$ is positive and negative.
Regarding the last part of this:
I found out what x_M is
Now how do we approach that? What x are allowed?
wym what x are allowed? @strong nexus
"allowed values of x ..."
I need to graphically determine those
Im not given a, b
I can just take a = b = 1 as an example and plot it with GeoGebra
so ur just gonna simulate things?
graphically means they must give u something to be based on i guess
Nothing is given, no
no
it is variant
well if u can solve Ex^7 +bx^4 -a=0
sure
u can find the turning points hahaha
I did, to get x_M
but for total energy E = 0? u already got a turning point x = (a/b)^(1/4)
no u only found the minimum
Yeah, I did not plug back
yes so V(x_M) is only the minimum value for V(x)
so since the system is conservative
E = E_kinectic + V(x) = E_kin(x_m) + V(x_m)
you need to study 0 = E- V(x)
@strong nexus they gave u E_kin(x_m)?
Right
No
then try simulation use python
use whatever u want
So, we want E_kin >= bx^(-3) - ax^(-7)
@strong nexus Has your question been resolved?
Ok, got it. Now assume that the kinetic energy is relatively small, such that for all $x$ permitted, $|x - x_M| = \delta \ll x_M$. Expand the potential around the minimum up to the first non-vanishing order in $\delta$.
So that means we need to Taylor expand, right?
i think so because the minimum is a stationary point, the first derivative vanishes, so you Taylor expand in the small displacement but the second one doesnt
Is there a neat way to do this?
Do we actually need to compute the Taylor expansions of 1/x^7 and 1/x^3?
yes
So i got V(x) ~ a * (1/x_M^7 - 7/x_M^8(x - x_M)) - b * (1/x_M^3 - 3/x_M^4(x - x_M))
Now >Set up the equation of motion for small \delta, using the result from the expansion. What do you notice?
How do we set up the equation of motion?
try using (1+x)^n for small x
@strong nexus Has your question been resolved?
How does that help?
We need an equation in terms of x, dont we?
I think so
@strong nexus Has your question been resolved?
better off asking in the physics server. see #network
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Can someone explain the Functions defined by branches and module functions, like the picture?
Get a new channel please
how?
Send this in #help-20 (or any available help channel)
ok
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how is g, i and k incorrect?
Me when {1,2,5} is a subset
it is a subset?
Itās a collection of elements of A (1,2,5)
So itās a subset
But because {1,2,5} isnāt among the elements of A, g is false
epsilon means contained in {1,2,5} isnt an element of A
nor is the empty set
oh my god
The elements of A are 1, 2, {3,4}, 5
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purge this chat
lol
itll be documented for the ages
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Can anyone verify if I did this right? Itās been a while so I want to mke sure I didnāt mess up anywhere. Thank you!
method looks right
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just missing the 1/2 on the semicircle in the beginning
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ā Original question: #help-23 message
you added that later so it's fine
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Okay this is what I remember being taught but this definitely canāt be the answer, right? Please help, ty!
Yeah - you can probably see that <BDC looks larger than <BAC just by inspection.
The trick to this question is to use inscribed angle thereom of a circle. Does this sound familiar?
Yeah, it sounds familiar but I donāt remember how to do that for some reason
bac is 29
Basically, inscribed angle theorem says that the inscribed angle (the angle at the circle) is double the angle at the center.
Refer to the top two theorems :)
Oh! Itās been briefly mentioned but Iāve never seen this before. I guess itās somewhat an introduction to something new I havenāt seen yet.
Now I remember, it taught be about the central angle but not the inscribed angle.
Tysm! Iāll keep this in mind now! Itās definitely super useful.
No problemo š
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How to show that for compact spaces the pointed gromov Hausdorff convergence implies the ordinary gromov Hausdorff convergence?
@tropic hatch Has your question been resolved?
!status
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
@tropic hatch Has your question been resolved?
1
Begin here. Read this and see if it helps.
And if neither of those help then I'm sorry, I can't help you. I don't know this.
Are you still stuck op
u cant tell me these words arent made up
It isnt
Gromov and Hausdorff are real mathematicians
@tropic hatch Has your question been resolved?
Thank u very much šš»
Its okay
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how do I express it in Cartesian form
I suspect it could be referring to (f_x(t), f_y(t), f_z(t))
@fringe drift Has your question been resolved?
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@fringe drift Has your question been resolved?
Is this A level mathematics?
but u already got the right answers
hy but I don't understand why
so u just copied it?
no this was provided
ah okay
so ur struggling with (ii)?
u can try plotting f(x) = exp(-x) and g(x) = -y , x = 0, x = 2
,w plot exp(-x) , -x , x=0, x=2
but I won't have a graphic calc
ofc u dont u wont need it, because they asked for a slight sketch not smth rigorous
exp(-x) & a linear function are easily plotted generally
so after u do that, the area is basically the integral of the difference between those two functions
how would I know which function is which though
s in which one to minus the other one from
you dont know properties of exp function?
I do
tell what do u know
yea
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Ok so (if we presume our Function is always continious and integralable)
such as if "ā« f(x) = A" is true, "ā« f(2x) = A/2" is also true
Ok great But why i cannot do this if there is x in multiplication? Such as
if "ā« xf(x) dx = A" is true, "ā« f(2x) dx = A/2" is false
And is there a way to solve this withOUT doing substution?
(Such as)
if "ā« f(x) dx = A" is true "ā« x^n f(x) dx = uA" is true too (n and u are reel numbers I guess)
We can try a simple f(x) to see why it isn't true.
For example, let f(x) = 1:
⫠xf(x) = ⫠x = 1/2 x²
ā« f(2x) = ā« 1 = x
Well, is it possibke to solve that
There's no A that works
So, I must do substution?
Some integrals need ipb or substitution. Are you struggling with u-sub?
Well, not really
But lets say despite it works, I try to avoid it as much as I can do
It feels like I might miss somethig (even a simple co efficient) while doing it
Like for example, a basic one
ā« (2āx + 3)ā“/āx
I do x = u², dx = 2u du
than i find the answer 2/5(2u+3)āµ du, but the answer is supposed to be 1/5(2u+3)āµ du
Hello?
Ok uhhh i wont get an answer I guess
.clode
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uhm do notice that the coefficient of u after substitution is 2 and not 1, I guess thats where you made the mistake
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ā Original question: #help-23 message
Ok so uh
Does that mean I always have to subside the final resulr with coefficient
technically cause after the substitution you again have to make another sub say z=2u so du=dz/2
I hope you get it
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11th Problem. I could only make this much progress that, b is odd definitely.
hint; the digit on the right must be divisible by 5, what can multiples of 5 end in?
Oooh
0,5
only
So b=5
Damn
whats the bar over ab mean
why is there a bar over it does it not mean anything else
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$e^x = \sum_{n=0}^{\infty} \frac{x^n}{n!}$
ā« (larp larp) dx
This is my working srry
Im just a bit stuck
jokes aside asking that question feels irrelevant to the problem at hand, maybe try asking "how to make my answer fit that form" or something like that
Sorry I thought I sent my working but I didnāt press the send button
š
hm
hi so
Can someone help
do you remember that we can write A as $e^{\ln A}$
Itsuki
as $A=e^{\log_e A}$
Itsuki
||@barren fjord||
-# did you just spoiler a ping?
-# puts bucket on your head and sneaks past
oop, i gtg urgent work can you take over please?
soz might be too drained atm
You've suggested what I'd suggest as well tho so
so far anyways
Yeah
<@&286206848099549185>
which part are you on?
how do u do tht text
I showed my working
-# this is so cool lol
-# cool
-# lmao
-# š
š
WOA
š š š š š š
we're doin everything except the problem š
-# we're doin everything except solving the problem š
-# tsk tsk
yea
why 9B?
whts the problem
Oh yh I made that mistake but my values for ABC r right
I just wrote down the wrong thing
[problem](#help-23 message) [working](#help-23 message)
woaaa
how'd u do tht
Omg focus
sry
q9 right?
Yes
No ii
alr
I showed my working
was tht sarcasm
No
A must be all the constants
Yh
gosh i remember studyin this havent done calculus since a long time
@patent citrus @stone shale
try this
I'm in 10th hrade
right click message
click copy message link
type out 'problem'
paste the link in the parentheses
.close
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im in 10th grade
š gng
wowwww
ur smart
is ur query resolved?
Whats the point in having the helper role
If ur js gonna waste time
Like actually lock in or js go
mb mb
srry
.reopen
ā Original question: #help-23 message
but i serously pinged them cuz they know calculus
Clearly not
they're faking it, they both know calculus....but anyways lets focus on the problem
I SWEAR IM IN 10TH GRADE
Just shush pls
you couldnt solve it?
ā¦
uhm


