#help-26
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Yea….
Can you give any suggestions for finding that angle? Cuz I don’t know calculus and don’t really wanna solve it by coordinate geo….
@dry oxide Has your question been resolved?
You don't need any of that
This probably I think it's mildly hard and I have no idea how to help you get to the solution editor straightout telling you the solution
Do you want a hint?
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Hello
At first I did row operations to get a row in each matrix with zeros, but I don't think that's correct. After I tried calculating what the determinant is, but I don't know how to show that X x Y is perpendicular to x and y with that information
If the determinant = 0, does that mean that X x Y is perpendicular to x and y?
note that $x\cdot(x\cross y)$ is a scalar triple product, which is also equal to $det([x|x|y])$
Mosh
and det([x|x|y])=0 by alternating
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hello i am doing ap calc homework and for the question below I have given my question, the steps ive taken, the answer i got, and what it should be. thanks for the help
f(x) = 3x-2
lim Δx -> 0 [f(x+Δx)-f(x)]/Δx
to begin the solution i subbed in f(x) into the equation
lim Δx -> 0 [3x-2+Δx)-(3x-2)]/Δx
i then cancelled out the 3x and combined -2
lim Δx -> 0 [Δx+4)]/Δx
after inserting 0 for Δx i get the answer 4, yet the book says i should get 3
im wondering if i did the algebra of the equation wrong
you didn't simplify f(x+Δx)
properly
you didn't expand -(3x-2)
properly either
which looks like the exact same type of mistake
$a(b+c) \red{\neq} ab + c$
ℝamonov
you still need to
simplify f(x+Δx)
properly
how would I do that, this part of the lesson i didnt really understand
do i just put the f(x) in for x?
this is basic function notation
alright let me take a step back (3x-2+Δx) is not correct right for when I implement the function?
f(x) = 3x-2
to get f(x+Δx),
replace the x in 3x-2 with (x+Δx)
(inserting parentheses as needed)
im replacing x with 3x-2
that doesn't look like what you're doing
it looks like you're just adding Δx to 3x-2
im replacing x with 3x-2
you shouldn't be doing that either
in all honesty i dont know what else I would do i didn't understnad this part
starting with
f(x) = 3x-2
replacexwith(x + Δx)
(and do nothing else)
3x+3Δx-2
not quite what i wanted, you went ahead and skipped steps but yes
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What digit will be at the end if n is a natural number
@quick lynx What does the grey box mean?
OK, does natural number include zero?
yes
OK, then 4n + 1 goes: 4(0) + 1, 4(1) + 1, 4(2) + 1, ⋯. This is 1, 5, 9, ⋯.
So, basically, you start with 3¹ and then repeatedly multiply it by 3⁴.
3¹, 3⁵, 3⁹, ⋯
3¹, 3¹ · 3⁴, 3¹ · 3⁴ · 3⁴, ⋯
Well, it's the same sort of process.
You have 3², 3² · 3⁴, 3² · 3⁴ · 3⁴, ⋯, which is 3², 3² · 1, 3² · 1 · 1, ⋯.
so it's 9
Yes.
thanks i guess it was easy 
Yes, you can see why it works either with modular arithmetic knowledge or with the old method for multiplying on paper.
When you multiply on paper, the digits in places other than the ones place can never affect the ones place.
So, you can look only at the ones place and forget the rest to see what the result's ones place will be.
okay i will ask if i will have questions thank you for help
You're welcome.
.close
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help in graph theory
@fiery current Has your question been resolved?
@fiery current Has your question been resolved?
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So <K = 87 and <T = 42. But when I try to get value of k (the side), i get 26 while the textbook says its 36 can i get some help
Do you have your work
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Hello, I would just like clarification on whether I'm doing this right or not.l
I think the answer is all real numbers greater than 0?
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doing a truth table but this feels wrong
my logic was that the left most NOT would invert all the others but now im getting everything as false which isnt great
because i have:
(p or not s) and (s then (t and not p)) but of course there are no situations where thats satisfied and it doesnt feel correct
i also tried solving by applying the leftmost NOT only at the end and I got this, which is a tiny bit better but not really
<@&286206848099549185>
u can reduce the given propositional logic to a shorter equivalent propositional logic
I tried reducing it, and I'm getting (p^~s)
yeah i thought of doing that but i wasnt personally sure how to
also whats the ~? is that supposed to be NOT
do I send u the pic of the steps?
sure
where does the T go?
is this one of the equivalence rules? im not too familiar with them
t^0 = 0
Yeah
U can do without reducing it also, bt then u need keep track of so many truth values and then combine them at the end
Yep
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just verifying my work again, like I said, I'm not too proficient at equivalance rules
Yep, all seems correct to me
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I need to create 1 function with all those requirements. Can’t do it ): so can anyone please help me? <@&286206848099549185>
@viral flax Has your question been resolved?
@viral flax Has your question been resolved?
do 1 requirement at a time
Did the first one. But then it becomes complicated since you have to meet the 2nd requirement while keeping the first met
so only change something at (5,10]?
that keeps the 1st condition met
I don’t I understand
The function I got was X^2 - x. I believe
Average rate of change =5 for t in [1,5]. So if you just do your function so that is met then do something so average rate of change is =-20 for t in [1,10] by only changing something in (5,10]
you need a piece-wise function
Yes
so why can't you do what I said?
I don’t understand how you got the (5,10) interval
you just said idk how to do 2nd one while still keeping 1st condition, yes?
Yes sir
I told you to only do something with your function in (5,10] then
that has nothing to do with 1st condition then
so 1st condition will still be met
(doing 3rd one before 2nd one might be smarter)
Wait a minute, I think I understand what you meant by [5,10]
(Would recommend doing 4), 5), 1), 3) then 2) in that order tbh)
this avoids you having to redo/rethink your function
np
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Ok, so I feel embarrased asking this but can anyone help me solve this problem? It is an economics problem but it requires math.
Here is the problem: In Country "Faraway," cigarettes are forbidden, so people trade cigarettes in a black market.
The cigarette demand is Qd = 12 − P , and the cigarette supply is Qs = 2P. Find the equilibrium price and quantity in the black market (the equilibrium price and quantity is where Qd: Quantity demanded and Qs: Quantity supplied, equal each other).
Can anyone help?
@visual merlin Has your question been resolved?
let the equilibrium price be $P_e$
Ken G
then we know that at $P_e$, $Q_d = 12 - P_e$ and $Q_s = 2P_e$
Ken G
And also, $Q_d = Q_s$
Ken G
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So I know how to do the substitution in general, but can someone explain how to isolate one of the variables to get the substitution staryed in the first place?
add one to both sides on the bottom equation
that's one example
you're isolating a variable like any other
right, but then what order do I put them in
so like when I add one does it become x=1+4y or something else?
ahh, ok. I wasn't quite sure because there are some things where when you move it into a different order it becomes negative, etc.
wdym
Like, I forget exactly rn, but in some things when a number is one one side of the equation/inequality, when you reorder it to the other side it becomes negative/positive depending on what it was before
i think i remember it mostly in graphs and stuff
oh, ok
i guess that just confused me, so i would end up getting some problems wrong because of it
but i think i get it more now
thank you
wait, one more thing: so if I just had x+y=11, for example, and I wanted to isolate x I would add y to both sides. So could I make that x=y-11?
or would it have to be x=11-y?
idk if it matters but just checking
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I don't follow how they got to the second step
$\sum_{i=0}^{n-2}3^i = 3^0+3^1+3^2+3^3\dots +3^{n-4}+3^{n-3}+3^{n-2} \ 3^{n-1}+\sum_{i=0}^{n-2}3^i = 3^0+3^1+3^2+3^3\dots +3^{n-4}+3^{n-3}+3^{n-2}+3^{n-1} = \sum_{i=0}^{n-1}3^i$
quantum
@mortal zealot
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i need help
a) Estimate the width of your index finger (in centimeters AND in inches).
b) Determine the number of times that you can place your index finger alongside the other to cover the width of a standard piece of letter paper.
c) Estimate the width of the paper by multiplying the estimated width of your finger with the value obtained in (b), in both centimeters AND inches.
is this a real homework lol?
ya
ok
@strange pendant Has your question been resolved?
no I actual need help
what a homework
yes Its due in 20 min so I need the awsers now
dude
just
write numbers
it's not like they're gonna walk up to you
pull a ruler outta their bum
and measure your finger
lol wtf
just make an estimate
ok
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To check if a system x(t) oscillates, is it enough to check if x(t) = 0 for some t?
What is a system
A function x(t)
Shuri2060
you may also have an oscillation while the system never intersects 0
I'm talking about functions that can oscillate, like some general solution of a ode
such as $y = cos(x) + 2$
Khazali
Hm, in this cases what do you think is a good way to check if a function oscillates?
Shuri2060
does an oscillatory system have to be infinite? or can we include systems that decay over time
Oh, I had forgot it existed, thank you!
It can be either one, but I guess that answer is enough for now. I'll see if I can solve the problem if it, if not I come back
not sure how i'd define this version?
if you allow decay
if we define sin(x) to be oscillatory, then we must also specify its domain, since:
indeed
yh im not sure how u'd define that
?
sure.
oh sorry i don't know how to use the bot yet
Only way I can think of for decay
is you have f(x)g(x)
f(x) decays, g(x) oscillates
But might not encompass all cases
i'm sure it's got some e^-k term
damped sine wave
don't know the general equation but that's what it's called
there you go
i think it is something along these lines:
$f(x) * e^(-kx) : k is some real number$
messed that one up too
my bad
Khazali
$f(x) * e^{-k} : \text{k is some real number}$
dldh06
yeah that's better, but i also forgot to multiply the k by x
$f(x) * e^{-kx} : \text{k is some real number}$
Khazali
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i did question 1, but i'm .03 off. and I am not fully sure how to do part b.
show method?
show us 🙏
the first two branches are bag 1 and bag 2. then off those two points i have red and blue with their probability
6 red 10 blue
7 red 3 blue
Ok and what do you get
what are you adding/multiplying
for part a, i got .42
but the answer is .45
i was multiplying numbers, then adding their products
uhhh
I don't understand why you're putting all of that stuff on the bottom
$$\left(\frac{6}{16}\right)\left(\frac{7}{10}\right) + \left(\frac{10}{16}\right)\left(\frac{3}{10}\right)$$
Shuri2060
The final answer should just be the top you've written
Sorry, I'm a bit lost with where the bottom comes from
idek, i wrote it like a week ago
,w 6/167/10+3/106/16+10/167/10+10/163/10
@prime hollow Well the bottom is meant to be 1
You probably calculated/inputted it correctly
maybe ur misreading 0's for 6's
you write them similarly
Because the sum of all possible events = 1
dividing by 1 isnt needed
We have 2 independent events
Lets call it A
and B
A' = not A
B' = not B
of course, makes sense
is the tree right?
well im not sure about drawing a tree
for this
yeah i dont think thats the right tree
Your first branches should represent the 1st bag
right?
im not sure
let me try draw it
i wasn't sure how to make it
i think that would make more sense in terms of order of events
I should change my diagram
the R and B should go where the numbers are
and the probabilities should go where R and B are
Then you multiply along the tree to check the event
I want to check 'Tails then Heads' I do 0.5 * 0.5
I want to check 'Both same' I do 0.5 * 0.5 + 0.5 * 0.5
If that makes sense?
Thats probably better (random tree I found)
Then if I need 'same outcome' I do P(B, B) + P(W, W) = 9/64 + 25/64
hmmm, how do these relate to the original problem?
you replace the probabilities
with the right ones
and 'B, W'
hmm
alright
i got it
I also had a question about another question that I've been trying
?
hmm
I would draw a tree first
Can you show me after u do that? or would u not be sure how
👌
You can. But you can also use your tree
Well tbh I would prefer formula (in the end u kinda have to use it)
i was confused about what you put in the denominator
ok so
do you get what the conditional probability is after?
like in terms of what it means
i just know, its the the probability of A &B happening over the probability of what B is. Or it is also the probability of A given that B happens.
Given you have an umbrella
means you consider only the branches where the umbrella exists
As 'the things that can happen'
So thats the 1st and 3rd branch
Then you are interested in the chance the 1st branch (rain) occurs in that 'universe'
$$\frac{\textnormal{1st branch}}{\textnormal{1st branch}+\textnormal{3rd branch}}$$
Shuri2060
Kindof like this vaguely 🤔
makes sense, imma try it
$$\frac{\mbb{P}(\textnormal{1st branch})}{\mbb{P}(\textnormal{1st branch})+\mbb{P}(\textnormal{3rd branch})}$$
I think the formula will tell you to do that
Shuri2060
is it not the same 🤔
it got .79 repeating
👌
I can but as far as I can see the approach is similar for all
lets see
yes, again you can do a tree here
i tried
but
if u leave the umbrella at store one, then the probability for to leave it at the second store is 0. thus how does the tree work without only getting zeros?
That branch does not exist
you cut off the tree there
because they cant leave the umbrella again
so what would the tree look like?
its the same as a normal tree
that says 4/5
the bottom aprt is just missing
If you work along the branches the sum should still be 1.
1/5 + (4/5)(1/5) + (4/5)(4/5) = 1
i get that it all needs to add to one
but doen't that show its more likely to not loose the umbrella at the first store?
so yes?
the chance he doesn't lose the umbrella after 2 stores is 16/25
which is more than 0.5
So after 2 stores they probably still have it
oh, i just assumed he lost the umbrella
do u multiply U and L
?
idk
i still dont get it
U and L arent numbers
are u asking about your question?
Do you get what 1, 2, 3
represent
individually
@prime hollow
Like what is (1)
yep
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hey
i am not a amazing at this kind of thing, but my guess would be c
Don't give answers
Also, you need to wait at least 15 minutes before pinging helpers
sorry
You can try and eliminate the wrong answers
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It's because the purpose of the server is to teach people, not give out answers
.close
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Like I said, the purpose is to teach, not give answers. You want answers, go somewhere else
if it's shitty, why are you still here?
Well, if you recently joined, then you should have read #❓how-to-get-help
And one of the rules
I highly doubt you depleted all the options for help.
@neon iron If you don't want to use the server's resources properly, just leave. No one is forcing you stay here and make a fool of yourself.
<@&268886789983436800>
lol
lol
lol
🇷🇸
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how will i work this out
i made it to y = mx + c
so i got y = 3x-20 over 5
what do i do next
is the answer 3x?
you dont need 3 channels.
sorry man ... im always left hanging mid way through my help and no one helps me out so therefore im left unnoticed
yeah, you still only should have 1 channel.
i dont know how to close them
.close
.close
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get it into the form y=mx+b
Yes
Now you can write the fraction separately but you don’t have to
Now identify the gradient
the gradient is 3 over 5 right?
Yes
👍
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I need help, can you help me?
@mossy hazel Has your question been resolved?
i believe you can use residues
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Hiya, could I get some extra clarification on what this is actually doing, slightly confused by what the map does.
My understanding is an action on a group takes elements of the group and maps each of them to a permutation in the set omega, is that correct?
@topaz egret Has your question been resolved?
I think the 2nd defn is more intuitive
The first has me 🤔
Ok I see (for the 1st), but not sure how to explain
@topaz egret Has your question been resolved?
Yes.
The set of permutations, of elements in omega
I guess it is easier to visualize if you think about how the actions combine.
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✅
@topaz egret one should see motivating examples of group actions before the formal definition
a group action encodes a certain way in which the members of a group permute a set of states
an example is the group D_8 of the symmetries of a square acting on the set of configuations of the square (the rule is defined by how we expect every combination of flips/rotations to affect a square)
so the result of a flip acting on a square is what we expect, the same square but vertices flipped
now the product rule in the definition just formally states how we expect compositions of flips/rotations to affect a square
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ik how to find tangent line but how to find horizontal?
what's the slope of a horizontal line?
parabola?
??
o wait
parabola isn't a number
yes, and where does a slope of 0 occur on a graph?
at the highest or lowest point of parabola
yes
o and then i plug in that value to find y and then thats the tangent line?
yes, y=that value would the be the eqn of the tangent line
but that's not what you're asked for
you're just asked for x=5/2
yes
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hello my problem is as follows, Solve 5cos(7x)cos(3x)+5sin(7x)sin(3x)=0 for 0≤x≤2π. I started by seeing it was a sum identity and i wrote is as 5cos(7x-3x) = 0which is 5cos(4x) = 0. I was wondering if the next step would be to divide by 5 on both sides but Im not sure if you are allowed to do that
Of course you can divide by 5
Yes
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The lengths of the sides of a triangle are 13, 14 and 15. A circle touches two shorter sides and
its center is on the longest side of the triangle. Calculate the radius of that circle.
could somebody help?
have you drawn a diagram?
which lengths/angles can you calculate?
also 13-14-15 triangles are quite nice that they decompose into 2 right triangles
a diagram?
yeah, of course, sketch a diagram to help you visualise
by diagram do you mean a sketch?
yeah that
what can you say about the angles alpha and beta
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Do you know how to set this problem up?
Do you have some working out that you could show me? (Just to get an idea of what you need help with exactly)
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The command went through earlier, I just replied late X)
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Oh ok cool thank you very much
What about this one?
What makes that aaabba? Lol
This one got me I have no idea at all
Please don't occupy multiple help channels.
please don't occupy multiple help channels for the same question
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I’m confused on how I would factor with only x. Question is “solve by factoring x^2 - x - 42”
find a and b in (x+a)(x+b). you have a+b=-1 and ab=-42.
(you can confirm that this method works by just expanding (x+a)(x+b))
oh hi yottachad
1, 2, 21,42
and what are the factors of 21?
....that's not all
Those are the ones off the top of my head
there's more
yep!
Thank you!
(also it's actually 6 and -7, since the sum needs to be -1) (you probably already know this, but just in case....)
Awesome, thanks!
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Hello, could somebody please help me why what I did was wrong?
The question asks to find f^-1(f(x))
For the equation given
Now it’s all completely wrong and makes no sense with the graph either but I don’t understand why especially since in a question before the solution was found by the exact same method?
little trick here for f^-1(f(x)) would be to use the symmetry of the parabola
Yes that is what made me understand that what I did was totally wrong but I’d like to know why because I don’t only work with parabolas
I don’t understand really understand the method we were taught for determining f^-1(f(x)) in the second picture. Well I thought I did but I messed up totally for the first screenshot so I don’t understand
Sorry I don’t follow
set y = f(x). Suppose x' is such that f(x') = y. Use quadratic formula to find x'. This usually gives 2 values, which are the 2 elements of the set
you end up with a condition on y. That does not look like an x value
y is held constant. You have a formula for delta, use it to compute x' such that f(x') = y
Okay I see
Still get them a bit confused
Um as for finding f(R)
So we determined f(R) in the second screenshot as a condition of y
But it is totally wrong for screenshot 1, why?
I am just trying to understand when we use the method on the y condition and why we use it
$f(\mathbb{R}) = {y \in \mathbb{R} | \exists x \in \mathbb{R}, y = f(x)}$
themateo713
Hence reasoning on y values is natural, you're deducing for which y values there is such an x, and determining that is finding f(R)
it is however not the only way, sometimes there is simpler. For instance, exp(R) = R+* because an exponential is strictly positive and can reach any positive number.
In the case of a parabola, you can look at its convexity and extremum to determine which interval of values it hits
that interval (for a parabola) being precisely [f(-b/a), sgn(a) inf)
That makes sense
Although
I swear I did everything right and got all values between the range of -7 and 9 only
Even though the real answer is ]-infinity, -3]
I know this because the maximum of the parabola is -3 BUT why did I then find ]-7,9[
this goes wrong when you write delta =
that is absolutely not the discriminant
I wrote >= 0
For the delta
Ah right I wrote delta equals
Please walk me through it I really don’t understand what you mean :( I’m sorry
it's just the wrong formula. You look at whether delta >= 0 to see whether there are solutions (so to find f(R)). When looking for the solution to f(x') = f(x), you look at the solution, not at whether delta >= 0, you already know delta >= 0 because x is solution
you want the full walkthrough for f^-1(f(x)) ?
But you say here that you look at f(R)
I looked at delta >= 0 to find f(R)
Except my f(R) with that equation is ]-7,9[
ok, it sounded like that sreenshot was for f^-1(f(x))
don't try to do 2 questions at once
“ direct image”
especially since you need to write them separately too
😭😭😭 you’re right
So let’s pretend I was doing the first screenshot for f(R)
I did the condition on y
you tried
what's the formula for delta
b^2 - 4ac
it made me think you got confused between just delta and the full quadratic formula (where you did also not divide by 2)
I was trying to follow example from second equation and I think I was trying too hard for that
To follow it
You’re right thank you a lot
I understand the difference now
Between fR and the f-1
if you struggle with that, do review the definitions
and also, I think we don't throw that around for no reason "faut maîtriser les maths de lycée avant d'essayer les maths du supérieur"

I had maths for only 2 years before I went to uni so really not enough time to master everything
😭😭😭
Trying
tout un chapitre en première et des utilisations répétées pour l'oublier en L1 (je suppose), c'est quand même dommage
Okay I’m trying to write in French but it keeps autocorrecting since I didn’t install French keyboard
It is dommage
ok lol
Yea i am l1 then
I heard the prépa system in France is better than first year of uni sometimes due to competition or something
Don’t really know
Impressive that you’re in prépa
Thank you for the help
the top students go to prépa (usually), the weaker students to uni. So you naturally have a higher level where students do in 2 years what they do in 3 (with a different focus). Personellenement je suis en MPSI à Louis Le Grand, donc on peut dire que je m'en sors très bien (si tu connais pas, c'est une des 3 meilleurs prépas de France sur le plan scientifique)
That’s very cool, I didn’t know
Always cool to know how they do it in other cities. I have family in France so it’s definitely an option
you think of studying in France ?
I do
not to feel harsh but I do
Yeaaa it’s tough
la rentrée est en février non ?
what are you doing right now then ?
Studying for my retake exams because they were last week but I tested positive with Covid lol
The retakes are in march so
I’m actually surprisingly passing the year so far which is shocking
covid friend. Me too so instead of doing my homework I'm here on discord doing math anyways
But it’s the moyenne of two exams
*mean/average
Well it’s good practice I guess
I’m pretty strong in geometry and also got really great grades in computer science
But analyse?
On oublie
https://cahier-de-prepa.fr/mpsi2-llg/docs?rep=16, si tu veux t'entrainer, voici le site de notre prof. Il met tous ses pdf en ligne. Comme ça tu peux prendre de l'avance si tu veux, ou travailler des exos de TD (il serait normal que tu peine sur du niveau 1, et passe 1h ou 2 sur du niveau 2)
calculer des dérivées c'est algorithmique
l'analyse entière est très algorithmique
Thanks a lot that’s very nice of you
Yea I’m not very good at structure
But I’m trying

faut juste être bon en calcul
et se souvenir des méthodes oui
ok bonne chance
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frere
Please don't occupy multiple help channels.
@small cradle Has your question been resolved?
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4
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@neon iron Has your question been resolved?
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anyone know what sign the answer should be at?
@wary solaruse this formula when you get to the part when you're supposed to square the equation
👍
@wary solar Has your question been resolved?
its the Pythagorean theorem (a^2 + b^2 = c^2) try that and i think u will be good 👍
replace a with x, b with y, and c being 20 or 1/20
ok thanks
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hi can someone please help me
what's f(pi)..?
just repeat what was said per the last time you asked this style of question.
why are finding f(pi)?
so would i set cosx=pi?
no, f(pi) = cos(pi).
that had nothing to do with trig, it was just function notation
but yes, cos(pi)=-1
i mean yea function notation
so g(f(pi))=g(-1).
yes.
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Is my solution right?
It is how I solved.
So I got that same rank but not that RREF that you got
You messed up some algebra somewhere
could you tell where the problem is?
If you did C3 - C1, you don't get all zeros
@rapid terrace Has your question been resolved?
please share the solution
I don't understand the final answer.
When you did operation 4, you canceled out the 1s, they never fully cancel and become 0
Correct now?
@rapid terrace Has your question been resolved?
Yes, because the matrix after operation 4 is the same as the calculator you used
Okay, thanks a lot 🙂
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How to find the product of,
cos(x) cos(x/2) cos(x/4) ... cos(x/2ⁿ)?
So you're looking for a simplified version of $\prod_{k=0}^{n}\cos\left(\frac{x}{2^{k}}\right)$?
Chixen
Basically I need to find the product of cos(x) cos(x/2) cos(x/4) .... Upto infinity. Is it possible to do?
Chixen
