#help-0
1 messages · Page 538 of 1
No no, you assume it's true for each k = m and then you prove it's true for k = m + 1.
Oh ok, I'm a bit stuck on that part though
Let's see
So, firstly we assume this is true for some positive integers n and k
aka inductive step
Then we'll show it holds also for k = k + 1 (or m+1, doesn't matter if k is m)
yep
Modus
Yes
Recall that in this sequence every term is the sum of the two previous terms
In other words:
Modus
How do you think we can use this statement?
substitute Fn+k with what we assumed ?
Might be, but I think it'll be better to use this later, but who knows
You can try it
My suggestion is to write down (based on the assumption) what is F_(n+k-1)
Then we'll add them i.e. F_(n+k) and F_(n+k-1) and then we'll be able to use the above fact
How do you find F(n+k-1)?
you should write down the definition of Fn in the first place, will help you think
@marble knot Has your question been resolved?
@marble knot what course is this for
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is it just me or are the bases of these switched?
a) Write the mapping matrix of A*B (* being compositum) in standard basis of R^3.
also, don't use asterisk, that means lots of other things, use A o B
if outside of latex
\circ in LaTeX
ignore the slovenian, its mostly just explanation
ik
dollar signs
$\circ$
#latex-testing to play around
N1cK
mb
is it just me or are the bases of these switched?
not sure which way you think it is suppsoed to be but
matrix multiplies on vectors from the left
if that helps
we had to find the matrix of the composition in the basis (1,1,1),(1,0,1),(0,1,1), what would the mapping graph look like then?
ok, what if we had to find the matrix of the composition in the basis pi=((1,1,1),(1,0,1),(0,1,1)), what would the mapping graph look like then?
lets call the base pi, then we would go from pi --S--> standard base --B--> standard base --A--> standard base --S^(-1)--> pi?
you can ignore the part about rings and modules and just trea tthis as vector spaces over fields, regular linear algebra
the notation here is
$\mathbf M_{f, \mathcal B, \mathcal A}$ in the notation of this website means
gfauxpas
this is too advanced for me
matrix for the function f, assuming the codomain is written with respect to the basis B, assuming the domain is written with respect to the basis A
I'll traqnslate for you
wait before you do, am I right about this?
Let R be a scalar field
Let M, N be vector spaces over R, finite dimensional.
Let A, B be ordered bases of M, N respectively.
Let f: M to N be a linear transformation.
im not sure what you mean when you ask about a matrix without giving me THREE Ingredients
the mapping, the basis for the codomain, the basis for the domain
there you go, now it's in English
the mapping from my original task
everything from the original task, the only things that are changed are written here
I dunno can you ask your question without referring to the picture please? or just crop oiut just the part of the picture relevant? lots of stuff going on
and its hard for me to read the small print
ok, gimme a sec
Assignment: Write the mapping matrix of A*B (* being compositum here and not multiplication) in the basis pi = ((1,1,1),(1,0,1),(0,1,1))
Would the mapping graph (in the style of the one in the second screenshot) be the following:
pi --(S)--> standard base --(B)--> standard base --(A)--> standard base --(S^(-1))--> pi?
im just writing up the theorem in linear algebra language because i have to go soon
can I tag some other helper?
I guess so, <@&286206848099549185>
of course, i just want to leave you with something before I leave
happy birthday
oh, thought you were writing somethins outside of this
now with more bullet points
yea this is just too much for me to currently understand since I'm focusing just on the practical part of linear algebra, sorry
plus I only have 1 more day until my exam
bombaclat
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k im profreading it for errors
theres a lot of places where i could have made a mistake so... hopefully ig o t it right
reopen?
the question is a bit lost since there is a lot that happened in between, thats why I openeda new help channel
also 31h of vsc is crazy
0_0
gotta grind
(not fr tho lol, it just stays open as long as the laptop is open)
cant do 31h of code
youre pre uni and youre coding and doing linear algebra? thats crazy
It's not anything extra lol what i talk about here is just whatever was taught to me
the coding too is just from school
i mean i learned it in school
and then started stuff myself
nice

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alright
The working is right there
Don't threaten suicide.
ayo chill
👍
24/3, 21/3, what do you get?
also there is no way you are undergrad in math, youre pre grad
helping me would be a lost case 4 you
wdym
You're the one who asked for help.
damnnnnn
,tex.alg manip
Executor (ask on server b4 DM)
Read this once.
so you can write it as 8*3/7*3, cancel out the threes and you get 8/7
Won't work for you nick
Need to have the preamble uploaded
Come to #latex-help can walk you through it if you want
@alpine sable Has your question been resolved?
@alpine sable Has your question been resolved?
Just clicking the cross doesnt help.
Tell us whats troubling you.
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How could I simplify this expression? I know that sin^2 + cos^2 = 1 but I don’t know how to separate it from e^x.
It is also possible that it can't be simplified, there are no instructions stating otherwise.
i dont see how anything nice can happen here 
you might be able to reduce the number of terms a small amount but i dont think any magical cancellations happen
i could be wrong though
alright, thank you
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Why did we get the following matrix for b) and not the transposed version of it?
first column of matrix is the coordinates of F(a) in the basis (a,b,c), second column is coordinates of F(b) etc
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any help would be greatly appreciated 🙏 i dont know where to go from this
Replace √x with another variable
aweh
Such as u = √x
But first write down that x must be ≥ 0 for the sqrt to exist
Otherwise you might forget it later
wati what
south
no worries
how did you know to do this ?
then it becomes this ?
practice
you'll find you get a hidden quadratic
indeed!
what matters isn't the exact name but knowing the technique
the problem-solving approach
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thanks for the advice
np!
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any advices for when i should use 2^n, (n r), n^r and n! / m!
A bit more thorough and has examples:
https://www.mathsisfun.com/combinatorics/combinations-permutations.html
that's really helpful, thanks
it looks like my teachers learned from this lol, because they told that you should rethink the problem to another similar, like "balls" like the website
but well, thanks
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i do not know how to do this
,w 13/8 - 3/5
Good luck
what are the steps for you to get that answer
That’s not even the answer
Wait @velvet finch are you allowed a calculator
What calculator is it
,w 3/10 - 13/8
Use the fact that $\sin\left(\frac{\pi}{2} - \alpha\right) = \cos(\alpha)$ or, if you prefer, $\cos\left(\frac{\pi}{2} - \alpha\right) = \sin(\alpha)$
but you gotta show steps for the question to get marks ykwim
actually no, this is doable?
Alberto Z.
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https://youtu.be/NJdhrS0SLG8?si=trl9stpQhO3fhOud
Could anyone fact check this video if it's true? I doubt that the 1.5th root of 4 is 3
.........
I know i know
The 1.5th root of 4 is not 3
Then tf is this video saying then
💀 💀 💀
-# didnt watch the vid yet
Ah
idk
But 1.5th root of 4 is 3 is equivalent to saying that
what?
$4^{\frac{2}{3}} = 3$
Carbonite
that is kinda bullshit
It's obviously irrational what number wouldn't become irrational after that torture of 1.5√
!occupied
Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).
ok np @lunar saddle
So like
and welcome to mathcord @quiet hemlock @umbral mountain
but you understand why the vid is wrong right
proving it is irrational is a fun next excercise
Is this actually inaccurate
It says 1.5√1 is 1.5
WAIT
It's actually 1.5 x √1
Not 1.5√1
!solved
!solve
solved
well $4^{\frac{2}{3}} = 2^{\frac{4}{3}} = \sqrt[3]{2}^4$
Carbonite
@quiet hemlock this is clearly not 3
According to the vid 1.5√8 ≈ 4.1
It's either 4 or 4.24
What is this kid smoking
And 1.5√7 is EXACTLY 4
,w 1.5*sqrt(7)
...
Radaca where are you getting these measurements from
That block is shorter than that one
It IS 3.96
Radaca isn't dumb
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Hello 👋 could someone verify this question ? The answer key says it’s B) but isn’t A) also false?
yeah a is obviously false
So both A & B are false right?
yes
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Ik this is a silly doubt but i need help, in this question pulley is moving with acceleration a so wouldn't the blocks also move with the same acceleration a both of them in the upward direction and in relative acceleration it will just cancel out and we will be left with acceleration of block with mass m as g/3
You're working in a non-inertial frame so the laws don't work normally
Please help 😭
,rotate
Im getting acceleration of block as g/3 if there was no acceleration in pulley
Do you understand fictitious or pseudo forces?
Yes
I understand that there would a force in the negative x direction equal to (mass of block)(acceleration of pulley)
yep
But i don't understand the theoretical part if pulley is moving with some acceleration so block should have that acceleration also and in relative acceleration shouldn't they cancel out ??
The pulley isn't affected by gravity (assumed massless) so there is an imbalance here
Ohh tysm i get it now
@indigo tapir Has your question been resolved?
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I am trying to solve for the length of EF, I am guessing it is 14 because I just extended the EF line segment towards points D and B then found out CBF/ADE were a multiple of the 3-4-5 triangle. Which then allowed me to also see that triangle DBC is also a multiple of the 3-4-5 triangle.
But what I am struggling to understand is why is it that I am able to extend EF to points B and D? I feel like it is illegal, like the EF line segment if to be extended could end up either in-between BC/AD or AB/CD...
it is illegal. I don't think it is generally the case that DBEF will be on the same line, but the length they gave is nice so it might just so happen to work out.
I am a teacher at a school in a top gov school of Bangkok (I am a CS teacher. But I am trying to help my math teachers who are also stuck)..I feel like this is some kind of complicated gifted question.
So I can't assume that watsoever even tho it "works" or maybe the answer choices contain red herrings.
I have been stuck on this question pondering trying so many different things for 1+ hours now
dont do that, this task purely for Pythagorean theorem
simply draw rectangle EFCK, and use diagonal of ABCD for calculations
,calc sqrt(40^2+30^2)-2*sqrt(30^2-24^2)
Result:
14
yeah you can't assume it
try and use vinton's method
This is a question for 8th graders learning Pythagorean theorem for the first time (this is a question at the end of the unit).
I am trying this now
I just computed it, in this case it doesn't even work out.
Let me try it
So, how does one (my students and myself) get good at this stuff? How am I just supposed to see things like how you all helped me?
I'd say just by doing exercices, it comes with some practice, like almost everything
My students haven't learned about congruence yet. So using only Pythagorean theorem would be the only approach.
👍
Yeah, then just consider CFB instead of EFC
Btw how do I explain to the students + my math teachers that it is illegal, when it feels like it is plausible? What rule am I violating? I am guessing "it is the assumption that the extension connects directly at points B/D"?
by drawing a graph to scale
lemme do one
I recommend you not to change the drawing given in any way, you can connect some vertices e.g. point E with point D and point F with point B, but you musn't change the length of EF. It's illegal because this way you change the constraints given
I am struggling with this as well
Would they still be 90° angles at AEF and CFE?
yes ofc
1st step:
2nd is to find BD (or AC) then subtract
This is what I did initially to get my answer of 14
tell us how you get right angle then
But it is illegal to assume that E to F to B is a straight line, no?
right, that would require showing that E and F lie on the diagonal
here
That's why I was so confused and so unsure about that approach I had initially to get the answer of 14 (which ended up being the correct answer anyways 😭) poor kids
and that they're collinear, so it's actually better to follow the previous solution
So this would be the only way in terms of this unit being the Pythagorean theorem, right?
it is also possible to construct E' and F' as the points on BD such that E'A is perpendicular to DB and F'C is perpendiculat to DB
and then show that E'=E and F'=F
but this assumes that you already know that DEFB are on the same line
but the proof would not be flawed
Which in this problem's case DEFB are on the same line, but we cannot assume they are from the get go since the problem did not give us any indication of it being an assumption that we could make.
yeah that's why I said that one way to proof this is you could assume E',F' are on the same line, and show that E'=E and F'=F
also there is another way to draw the diagram satisfying the rules:
AE = CF is wtill 24
but in this case, it is clear that DEFB are not on the same line
E' and F' are just translated points of E F right?
wdym
Sorry, could I get clarification on what E' and F' are?
perpendiculars on BD from A and from C
^here
Ohhh got it makes sense now
Btw, would you consider this as a gifted question? (8th grade math)
idk much in that area, but i feel like these types of stuff anyone can pick up and learn in a reasonably fast pace if they are interested
Nice haha, can you point me to any like resource or question bank/book to do more questions like this?
If you or anyone here knows
(I plan to be a math teacher in the future, I know this is probably not setting a good example 😅)
there is a bunch of high school math contests where you can find the test bank of, like amc and stuff like that
AMC and just search for math contest questions?
there is a list on aops
high school contests
iirc
Is it ok to show u my work for another problem to confirm my work?
wmi, amo, sasmo have alot of problems like these
show it
Yeah correct
Pls ignore problem 12, currently working on it and I found some logical mistakes lol
looks fine
AEF has base EF height AD, EFC has base EF height DB
Man, completely forgot about the ways to calculate area of obtuse triangles, thank you 🙏
looks fine
🙏 thank you!
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.reopen
just to clearify the answer is
1.For an inconsistent system of linear equations in two variables, the lines representing the equations intersect at no point.
2.In a dependent system of linear equations in two variables, the lines representing the equations intersect at infinitely many points.
3.In an independent system of linear equations in two variables, the lines representing the equations intersect at one point.
right ?
and dont i need to make a slope or soemthing for this ?
Seems right
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There's something wrong with my answer for this question of finding the rank for the matrix A.
Here's the solution, which stated that the r(A)=3, while my answer is r(A)=4. https://www.scribd.com/document/323700526/2-1Problems-on-Rank-of-Matrix
The document discusses the rank of matrices and provides examples of solving problems to determine the rank of matrices. Specifically:
- It provides an example of row reducing a 4x5 matrix and showing that its rank is 3.
- Examples are given of determining the values of a parameter P for which a given 4x4 matrix would have a rank of 1, 2, or 3...
!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
4, 5.
Oh, right. Let me correct that real quick
Yup, I got the solution. Thanks for helping me.
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Can anyone explain why Ln(2/0)= +infinity
While Ln(0/-2) is -infinity?
!xy
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
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Please help
only solvable with trig
So how do I do it?
can you calculate FB?
solution is quite ugly btw
Do you know the solution?
yes
do this first
4-2sqrt3?
yeah
can you tell me the answer first so I can first see if its correct
then explain to me
exact answer is sqrt(4+2sqrt(3))
its wrong....
@crystal token Has your question been resolved?
@crystal token I'm probably gonna show you the solution directly
wdym directly
so FB = sqrt(2)
angle FBA = EBA - EBF = 60° - 15°= 45°
angle FBC = FBA + ABC = 15° + 90° = 105°
using cosine theorem:
FC^2 = BF^2 + BC^2 - 2.BF.BC.cos(FBC)
@crystal token got it to this part?
I think so
so we have FC^2 = (sqrt(2))^2 + 2^2 - 2.sqrt(2).2.cos(105°)
= 2 + 4 - 4.sqrt(2).((-sqrt(6)+sqrt(2))/4)
@crystal token you can just evaluate this
I really don't know where you got it wrong
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Can someone help me
hey @trim lava
Yo
you have 2 variables right
Yh
Yes it is D, because 5 * (8a - 2b) = 40a - 10b. Remove the brackets by multiplying everything inside with 5.
No! 40a MINUS 10b!
Ty
what they are asking you to do is somehow get the constants in one place in front of the variables with mutliplying
IT MUST BE C
now the best you can do would be 10(4a - b) right
think about it in peace. When you really did that, ask again.
I agree
that can also be simplified by taking out 2 leaving us with 5*2(4a-b)=10(4a-b)
This is not the question. Read the problem again.
just take common 10 from that equation
then it would be 10 * (4a - b)
you'll get 4a-b
and c says 10 * (4a + b)
C option yea
ohh i get it now
no!
ah
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can someone help me with these two questions i need to know why before exams
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
step 3
3
- I got an answer but I was told that it's wrong.
I got an answer but I was told that it's wrong.
wait am i supposed to respond to the bot
No lol
I dont know why the first question's answer is 6% though
Well... you're supposed to answer, but the bot won't talk to you. It's just for people helping
Oh
,w (1.005)^12
This question is worded strangely
I know
the second question is even worse though i didnt even know where to start with this one except using the one equation with the negative power in it
I'm not super happy with this as an answer
Because I'm not sure I'm reading this correctly
What did you put for the first one btw?
I got 6%, but the answer key said 5%
Did it have any explanation?
Not really, thats why I'm asking
I'm not sure how to get 5% tbh
I'm leaning towards it being wrong, but I'll see if anyone else can explain it first
If each monthly factor is r = 1.005 the monthly rate is 0.5 percent. Multiply by 12 months to get a nominal annual rate of 6 percent so pick d).
After the 150 dollar down payment 1 894 − 150 = 1 744 dollars is financed. Eighteen end of month payments of 113 dollars satisfy 113 = 1 744*i / (1 − (1+i)^(-18)) Solving gives i = 0.0167 per month so the nominal annual rate is 0.0167*12 = 20.06 percent,matching choice c
thank you very much
i never thought of switching around 1744 with 113 in question 13, thats a great help
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i did this integral by doing derivative (when u change variables). then i did parital differentation. but chat gpt says that it's really hard integral. have i done it right?
What's your result?
x * e^arctgx - e^arctgx
Have you tried differentiating your result to double-check?
Also, don't trust AI assistants for this kind of stuff, they are often wrong
no i didnt. cause im not that good at it
How did you find your antiderivative? Did you recognize a familiar pattern?
guys i need help in math for igcse
,w d\dx (x * e^arctgx - e^arctgx)
Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).
Can you show us your work?
Are you sure this is the correct exercise? Is it not this one you're willing to compute?
$$\int\frac{1}{x^2+1}e^{\arctan(x)}\mathrm{d}x$$
import matplotlib.pyplot as plt
What's wrong here is that you firstly stated that u is arctan(x) and then that u is x
You can do it with the above one too (with x/(x^2+1) e^arctanx)
By parts first
Then u sub
how i should solve it then
this is not working by sub
It isn't a valid integral.
Answer this.
This substitution doesn't lead to anything nice, because x = tan(u) and the integral tan(u) * e^u isn't elementary I guess
should i leave it then without doing anything to it
Besides, if you do a substitution, the integral after the substitution should only have the new variable in it.
my problem is this
No, show us the original question.
This is how it works in general
this is the one which im solving and when u et to the pouint where u need to get answer for u
im getting this integral which sent to u
You are, or gpt is?
Yea, it seems you indeed gonna obtain such an integral from the integrating factor
no
this is
differentatial equatoon
which im solving
and when u get to the point where u need to know answer for (u) im getting this complicated integral
and now im asking maybe i can leave it without solving it?
Is that the entire question?
this is apparently would be an answer
yeah
Yes, it would
but should i just leave integral
If you're just asked to solve the DE, then yes
Wait 2 secs lemme just check one
v= e^ -arctgx
Ok yeah that is what you are getting
Remember to take the IF to RHS
im saying about DE
Whys your e^arctgx in the numerator
my y would be this if im not solvin my integral
is this y correct?
are u here(((
How would your y be that
It would be this multiplied by 1/IF
u mean this would be an answer but i should multiply it by e^arctgx. right>
?
1/e^arctanx
This question is still weird. Are you 100% sure that is the complete question?
You cannot
yeah
one sec dude i ll come back
actually not
Yeah
oh yeah i get it
,w solve (1+x^2)y'+y=x
but what i should do then
oh shittt
Yeah gotta leave the integral of e^arctan in there
but this is would be on my exam paper
I mean it has solutions, but not ones that you can express easily
It's wrong
Is setting f to be an antiderivative of something and expressing the solutions in terms of f a satisfactory solution?
Without saying explicitly who f is?
Answer the question first 
u mena this one
u actually dont have that deeep knowledge in these theories
That's not a deep knowledge question
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Can someone please explain why the the boxed statement is true?? I alr asked for help yesterday but i dont quite understand
Because you already had (g(a+b)^2 – g(a)^2 – g(b)^2)^2 = 4 g(a)^2 g(b)^2 taking the square root gives g(a+b)^2 – g(a)^2 – g(b)^2 = ± 2 g(a) g(b); rearrange to g(a+b)^2 = (g(a) ± g(b))^2 and since every g(·) ≥ 0 we can drop the outer squares leaving g(a+b) = ± g(a) ± g(b)
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Find the volume of the solid of revolution obtained by rotating the region bounded by the curves y =x^2 and y = 2-x^2 about the y axis
i have a question but when ur rotating about the y axis, u use DY essentially so u flip your equations with x as the subject, so sqrt(y) and sqrt(2-y) then your integral is pi integral bounded by 2 and 0 sqrt (2-y)^2 - sqrt(y)^2 DY
the solution says its pi u^3 but im not getting that
I just worked out what you wrote before you edited it and it was a lot more difficult than that 😭
sorry lol
We first find where the curves meet by solving x^2 = 2 - x^2 which gives x = ±1 so the region in the first quadrant runs from x = 0 to x = 1. Using the shell method take a thin vertical shell at position x: its radius is x (distance to the y axis) and its height is the upper curve minus the lower curve (2 - x^2) - x^2 = 2 - 2x^2. The volume of one shell is 2*pi*(radius)*(height)*dx so the total volume is 2*pi times the integral from 0 to 1 of x*(2 - 2x^2) dx. Expanding inside gives 2x - 2x^3; an antiderivative is x^2 - 0.5x^4. Evaluating this from 0 to 1 gives (1^2 - 0.5*1^4) - 0 = 1 - 0.5 = 0.5. Multiplying by 2*pi yields V = 2*pi*0.5 = pi. Therefore the solid of revolution has volume pi cubic units
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Okay so my problem was to solve the differential equation and I just wanna confirm if all of the work I did in red is right or if not, where i made mistakes
Wait I don't think I did the integral of e^(y+t^2) correctly
Oof
I just noticed that I assumed t was a constant
Wait but the integral on the left side is with respect to y
Hmmm
Write dy/dt = (e^{-y}/y)*e^{-t^2} Multiply both sides by y*e^{y} to get y*e^{y} dy/dt = e^{-t^2} Separate: (y*e^{y}) dy = e^{-t^2} dt Integrate to obtain e^{y}(y - 1) = 0.5*sqrt(pi)*erf(t) + C Your result e^{y+t^2}(y - 1) = t + C is wrong because the e^{t^2} factor belongs on the right not inside the left exponent
Okay I get that process but I don't understand why mine is wrong
Your step kept the factor e^{t^2} inside the y integral so you ended up with e^{y+t^2}(y-1) on the left. but t is independent of y so e^{t^2} is a constant during that integration and should be pulled outside before integrating. once you do that the left side integrates to e^{y}(y-1) and the e^{t^2} factor stays on the right, giving e^{y}(y-1) = e^{t^2}(…)+C; dividing by the constant puts the correct form e^{y}(y-1) = 0.5*sqrt(pi)*erf(t)+C
If that's just a constant wouldn't that still work though
I mean if you don't pull out the e^(t^2)
Because separation demands every y dependent term stay with dy and every t dependent term stay with dt the factor e^{t^2} (which depends on t) must be moved to the t side before integrating giving (y*e^{y}) dy = e^{-t^2} dt whose antiderivative introduces the error function erf(t) = (2/sqrt(pi))*int_0^t e^{-s^2} ds
Oh wait I see now
I completely failed to separate correctly which I probably should have seen but whatever ig
Tyty
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For this triple integral problem I'm having trouble understanding why the bounds for theta would be from 0 to pi, instead of from -pi/2 to pi/2 since the cylinder sits in the first and 4th quadrant.
sing cylindrical coords you can do it two equivalent ways: integrate once over the right half-plane (theta = –pi/2 .. pi/2) or integrate over just the upper half plane (theta = 0 .. pi) and then multiply by 2 to mirror the volume below the x axis which is what the worked solution does
But when im integrating it im getting different solutions.
also I thought the 2 comes from the sqrt(36-r^2) since z = += sqrt(36-r^2)
also if you were just integrating over upper half why would it be from 0 to pi/2 then multiplied by 2
this is an example in the textbook and the bounds are 0 to pi and this makes more sense to me since the cylinder would be in the upper quadrants
Since (x-3)^2 + y^2 = 9 gives r = 6 cos(theta) we need cos(theta) >= 0 so theta runs from –pi/2 to pi/2; writing it 0->pi just lets r flip sign and still traces the same circle. the front “2” merely doubles the upper hemisphere volume (z >= 0) to include the lower half; it is not coming from sqrt(36 - r^2)
im calculating the integrals using symbolab and its giving two different solutions though.
Symbolab’s first set up (theta from –pi/2 to pi/2) is correct because r = 6 cos theta is non negative there so the integrand stays valid and it returns 72 pi
Thee second set up runs theta 0->pi and just multiplies by 2; over theta in (pi/2, pi) the cosine is negative which makes r negative and flips the integrand’s sign so Symbolab spits out a nonsense negative volume
both volumes are positive tho
ok I think the textbook might be wrong. The answer its giving in the example problem doesn't match the integral given
no, the volume in the 2nd setup for theta in (pi/2, pi) becomes negative, which shouldn't happen
evaluating the top integral doesnt give the bottom solution
yeah I think the solution forgot that that could happen to cos
I was scratching my head at what was going on too
but ash has pointed out everything really neatly, in ways which I couldn't do myself
I think the solution and the textbook is wrong in this case.
thanks for the help. imma close it now
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Question 5. Let the universe for the variables in the following statements consist of all real numbers.
In each case negate and simplify the given statement.
a) ∀x∀y[(x > y) → ∃z(x−y >z)]
b) ∀x∃y[(x < y) → ∃z(x < z <y)]
c) ∀x∀y[(|x| = |y|) → ∃z(y = ±x∧z = −1)]
I just want to check my answers, because chatgpt is not helping much
@gloomy peak Has your question been resolved?
(a)why did the inside variable turn into x
Looks good, just a couple small nitpicks for a:
For the second to last step it should be ~∃z instead of ∃z~ on that last term.
And for the last step you accidentally wrote ∀x instead of ∀z
oh oops
Element118
whcihc rule is that?
Its called "syntactic sugar" in Python
Wait does python let you write conditionals like that?
hmm how do i explain it, without knowing the rule
Yeah
Dang never knew that, python has so much random syntax lol
How do you understand x<z<y?
I understand why its equivalent to that, but im just wondering why the way i wrote it isnt good. since wouldnt it be x>=z and z>=y ?
How do you negate a conjunction
it becomes a disjunction and the statements are negations
~∃z and ∃z~ the same? and should it be ∀z~? or just ∀z
It's not the same, since the inverse of an existential is the universal of the inverse.
therefore it should be ∀z~?
Yes, although I would recommend adding ~∃ before that step so you can show every step
like this!/
Yes, except you actually wait to perform the negation of what's inside the parentheses until the next step, since your negation would cancel out with what's inside to go back to how it was before but with a universal, which isn't correct.
Yep perfect
thank you!
np
where can i find all those extra rules? theyre not in our current lectures
"syntactic sugar" is a computer science phrase to mean syntax that makes it easier to write certain things. So here a < b < c doesn't do anything special beyond just being a cleaner way to write a < b & b < c. So it's not really a "rule" as much as just notation.
Yep it would be or
alright
one last question
Question 6.) If p,q are primitive statements, use duality theorem to prove that
(p →q)∧(q∧p∨True) ≡ (p∧q)
this is what i have so far
I know ~p or p is p, but then theres still the "and" false. But im trying to get p from (p and p) or (p or p) or aP ∨False ⇔ P
P ∧True ⇔P
I'm not sure what the duality theorem is, could you paste the theorem here?
Hmm it seems like the goal is to get "p or q <-> something" so we can use duality theorem. But I'm not too sure how to get there tbh
I have to get going but hopefully someone else can help you finish up!
ok thank you
@gloomy peak Has your question been resolved?
@gloomy peak Has your question been resolved?
@gloomy peak Has your question been resolved?
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did you cancel the h at the denominator because it's a 0 or did you do smth else?
$\frac{2hx+h^2}{h} \neq 2hx + h$. you fumbled the fraction cancellation
Ann
idk why the channel's not opening in any of our names
bot down ig
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bot still struggling apparently
oh yes i did cancel it out
i cant do that?
you can do it when the numerator is h * (something)
but like generally $\frac{ab+c}{b} \neq a+c$ yknow
Ann
why not?
can u texit it what you mean
i can give you an example with numbers where it very clearly doesn't work
if you want
or i could tell you what the correct cancellation is
take your pick
this
is that because if the h gets canceled on the denomiator, it would be 0? or 1?
$\frac{2hx+h^2}{h} = \frac{h \cdot (2x+h)}{h} = 2x+h$
Ann
oh yes i have the answer to that now but im just wondering why we cant do this?
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ok yknow what @coarse crag i think we should move to #precalculus or something
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this bit lmao
There's so much :(
ightt
This is so sad
what is so much ?
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Or is this not a queue
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just. dm me the bot is down atm
Thank uu
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Yes
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.reopen
.this is open already
Hey, i need help for my Math presentation. The subject is : ‘How did the Weierstrass’ monstrosity function revolutionize the esthetics side of maths and the analysis side of maths’(Im french so i had to do my best to translate the subject im going to talk about). Right now, besides talking about the history of the function and talk about how the function is formed, i dont have much else to say.
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Why do we care about the function? What does this tell us about functions in general?
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.reopen
✅
hey its like the subject i chose for my presentation
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to avoid falling down which direction should the man move?
The floor is smooth yeah?
yeah
What do you think it is
Is that really a maths question?
maths=physics
There's loads of physics questions asked on a daily basis
It's fine
to right
Well, sure, a physics question might be answered here, but does the question posed as is warrant maths?
But if there are people who know how to solve it, why not let them help them
Why?
then the trolly will move opposite?
And why is that?
idk

thatwhat i want to know
Do you know about something called center of mass
Well in a lot of cases center of gravity = center of mass
So they're almost the same
ok then?
So you know it or not?
know
Ok then look at center of mass of man and trolly system
Since friction between man and trolly is internal, we don't include it while drawing fbd
Can you tell me what horizontal forces act on the center of mass of the system
the center of mass must constant?
We're getting to that
Let's progress a bit slowly
man+trolly weight
Is it horizontal though?
sorryy
Np
friction?
Where's the friction?
from foot
Yeah but thats internal right?
ahh ok
Because we're now looking at man and trolly system as a whole
then what?
Not just man
ok
Well since you mentioned that the floor is smooth, then there's no friction between trolly wheels and ground
So basically
No horizontal force on the system
ok
Hence Fnet(horizontal) = 0
No no
Position of Center of mass will always remain constant
The man and trolley however, will move
This is because no horizontal force acts on the system
Note that this is only true for HORIZONTAL direction
but when move a force is excert by the foot?a push while move?
Ahh but we're looking at man and trolley as a whole yeah?
Look at it this way
hehe
The man exerts a force on the trolley
ok
And trolley exerts an equal but opposite force on the man
So net it cancels out when looking at the system
okok
So center of mass is conserved along x direction
So if man moves to the right, the trolley would have to move to the left, thus saving you from eternal misery
didnt getit
.
Center of mass of system is fixed yeah?
yeas
(Moves the center of mass to the right as well)
ahh
So the trolley, moves to the left, to balance the change in center of mass' position
so trolley move same to cancel it
ok
But yeah
Yes
is there a relation with momentum
Yeah
If Fnet = 0, then pnet = constant since Fnet = d(pnet)/dt
So delta (pnet) = 0
So momentum is always conserved if sum of all external forces is 0
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Even symbolab gave up idk how to proceed
looks ugly af, where did you get this
Please don't ask 💔
Tried 1+√tanx = u
But it gets kind of even more confusing to isolate x
Then it becomes integral of ( (arctan( u² +1 -2u) )/u² ) du and I have no idea how to proceed from here
why do you think there's an answer then
,w integrate x sec^2 x / (2 (1 + sqrt(tan x))^2 * sqrt(tan x))
u = sqrt(tanx)
du = sec²x/(2sqrt(tanx))
seems easy from here
LOL
oh nvm, there's an x I didn't account for
no limits?
Like just stop saying "hardest integral pls" to gpt
no
Brochacho if u don't wanna help that's alright
whats wrong..
yep i don't have any idea how to proceed further even if I take a substitution
gotta do IBP ig 🌚
Im gonna leave that up to you
tbh, it looks more like a "normal" or "standard" question without the x
intuition
IBP leads to integral of 1/(1+sqrt(tanx))
yea use this and FTC
Which is still pretty hard to do, but doable
You have to suffer to solve it and that's all
Waig i think I caught on


