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i have a conceptual doubt related to conic section
in conic section we have a directrix, so is it a random line or the line along which we cut the cone?
what exactly does the directrix define?
the cone is cut with a plane
not a line
directrix lies on that plane (since it must lie in the same plane as the conic section)
so basically it can be any line in the plane?
is the directrix just there to define eccentricity?
not really, im trying to find the graph to demonstrate it...
there is a pretty interesting connection
press the set alpha = beta for parabola button
oh wait they are missing the cone
ill edit it
okay now this should work
so we have a plane that cuts the cone parallel to the cones slope
that results in a parabola
now the neat thing is that when we put a ball into the cone, such that it touches the sides of cone and the plane (i.e. is tangent to all of them), it touches the plane exactly at the focus of the parabola
ok so that's how the focus if found...
then what happens is, those red lines are equal because they are both tangent to the sphere
its kinda like this in 2D, the red lines here are equal
and it can also be proved that the blue line equals the red line
hence why its the directrix
ill show this in few mins, gtg now, ill be back soon
so can i say that the directrix is the line perpendicular to the point of intersection of the two tangents of sphere which also happens to intersect the plane along which the cone is cut?
u still here?
tick the additional constructions box in the graph
yes
ok
yes i ca see planes
this directrix lies in the horizontal plane at which the ball touches the cone
now we will prove that the parabola property indeed holds, i.e. that these 2 lines are equal in length
youve already seen that this red line is same as the other red line (because they are both tangents to the sphere)
so it suffices to show that the other red line is equal to the blue line
we can first move the other red line like this to the back of the cone. That doesnt change its length
like vector shifting?
now that blue line is same as this orange line (its actually drawn as blue in the graph)
we're only moving it along the cone. We dont change its length
ohh right mb
these are the intermediate steps of the move
so by moving it like that, the length stays the same
after that, we can again shift it from the back of the cone back to the front
and finally, these 2 blue lines are the same length
so we've proved that the red line = the blue line
i.e. the directrix property works
it doesnt have a name, it's there only as a part of the proof
it's the one that was shifted from the back of the cone
because as it turns out, it works. It's called a "dandelin sphere"
it works for ellipses and hyperbolas too
I too wonder how it was discovered
i guess we will never know
Dandelin spheres, conic sections, and a view of genius in math.
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Thoughts on the recent change to be sp...
pretty cool vid on similar topic btw, just ellipses
it too uses the sphere
what about circle? it is too part of conic section
circle has a very boring dandelin sphere, it touches it at its center
but for ellipses and hyperbolas, the dandelin spheres touch it at the focus points
and so we can say the same for pair of intersecting lines too then.. from this one earlier
this fact is unrelated to conic sections, it's just used a lot in the proofs
that fact has more to do with symmetry / congruent triangles
isnt intersecting lines also part of conic section?
like if we cut the cone straight down.. we have 2 lines?
yeah, thats true
there actually is a connection between that picture and hyperbola
but its too deep to be uncovered in discord chat
hmmm
A really cool book which includes a very interesting section on conic section is Measurement by Paul Lockhart
probably my favorite math book
if u wanna learn more about this and perhaps geometry in general, that book is really great
well thanks a lot, ive always preferred calculus over geometry
but this one was actutally really really cool and intresting to learn about.
thank, sure will try that out now
this has a section on calculus too btw
it does?
yeah
and it probably offers one of the best takes on calculus ive ever seen
it makes it look incredibly easy
btw this is actually really cool.. mind blowing
then i need to definitely check that out
You wont regret it if you enjoy math and getting your mind blown
could you just tell me just a bit more about this?
sure
well, the main difference between that book and standard textbooks is that the book doesnt care about rigor. It only offers intuition. And instead of writting stuff like d / dx x^3 = 3x^2, it writes it like d(x^3) = 3x^2 dx
and it has couple of advantages
in general, d(f(x)) ~ f(x+dx) - f(x)
here is a super quick derivation of the product rule:
d(xy) = (x+dx)(y+dy) - xy = (xy + xdy + ydx + dy dx) - xy = xdy + ydx + dy dx ~ xdy + ydx
its literally just algebra. Unlike the standard way where you have to randomly add +f'(x)g(x) - f'(x)g(x) or sth like that
and chain rule with this setup is literally so easy you dont even notice you are applying it
yeah, this is quite better than the standard proof and quite amazingly it is following all the properties too
d(u^2) = 2u du
d(u^3) = 3u^2 du
d((x^3)^2) = 2(x^3) d(x^3) = 2(x^3) * 3(x^2) dx = 6x^5 dx
I just applied chain rule (actually, i just did normal algebra with the d-operator)
It's so good it makes me wonder why its not taught like this in schools
if it was taught like this, maybe students would actually understand what theyre doing
i am thinking the same damn thing, this could save so much time in competitive exams too.
and the fact it is always vaild too, almost feels illegal now
it actually only works on nice enough functions (but so does normal calculus)
pretty much every rule of calculus breaks if applied on ugly enough function
np, have a great day :)
yeah, u can use .close
.close
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My answer doesn't match even with options
,rccw
Shouldnt answer be cos(beta)
Yet it was told wrong
I mean it can be an answer but it's not in options so it should be one of the option that I can't derive
,rotate 30
Just doodled writing whole giving exam to solve
ok, so it's meaningless. got it.
from my perspective, it looks like there's no correct answer...
Will hit and trial work?
That's meaningless ig
Is this a live exam?
ah wait no
yeah, ok, you have to go through 2(alpha+beta).
turns out the question was not wrong
but it is quite evil
,rccw
I mean it's npi/2
(2n+1)pi/2?
npi/2 allows for n=38 which gives 19pi and cot(19pi) is undefined not 0, so your disappointment will be immeasurable and your day ruined
I have another doubt question no 60 wait it's on path
It's evil
60
No idea where to begin
,rccw
this reads less evil and more laborious unless you know dirty trickery
I hate laborious questions
unfortunately i am not a JEE nut and so do not know the right trickery.
JEE is freakingly asking for tricks
Meanwhile Olympiad 💕 which I haven't prep for
<@&286206848099549185>
so you have no idea?
try to use sin^2(x)+cos^2(x)=1 to simplify the first and second equation
There's an a and b multiplied too
yea so its (a-b)(sin^2(x)+cos^2(x))=a-b
U r right but b-a or a-b?
@weak kestrel the answer at the back of the book turns out to be ||b||?
i solved it rn
Book?
Oh solution
Lemme check
Idk
!nosols
The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.
i knew this will happen
!nosols
As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.
Not noans
mb sir was conforming
Bro just don't use anything anywhere
Why was it made?
Paste it there, for what was it made
if more help is needed on how we deduced the answer by helpee then i am free enough to give it without hesitation
no issue there
oh yea mb
dms
No need now
Tho if u wanna confirm or verify answer then dm me
.close
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hello, here i suffice to model the ODE. but i have no idea of what even to start from, since the weight would oscillate right?
it would oscillate indeed
the oscillation is a consequence of how the ODE is set up though, all you need to do for the set up is use Newton's second law
By y do you mean x
include the oscillation factor
Newton's second law is $\sum F = ma$
κλαουντ ☁ (cloud)
no, g is not the acceleration here
mg is the force of gravity
in general though the acceleration is always the second derivative of position
Resultant force = mass * x’’(t)
wait im a bit confused here because why wouldnt we just put mg, since the only force acting on the cube downward is gravity
there are two forces, gravity and spring
yes
so a = g is a consequence of F = ma in the specific case when there is only one force, gravity. then you have ma = mg therefore a = g
but that logic is untrue whenever you add any other forces
yes, so uh..in this case it would be right to take newtons second force ma and make it mg right?
i thought earlier you were against me using mg instead of ma here
We want to find the total force right now
so we have newton's second law is
[ \sum F = ma ]
the gravitational force $F_g = mg$ should appear on the left side as one of the forces being summed, it should not appear on the right side replacing the mass*acceleration term
κλαουντ ☁ (cloud)
okay so what youre trying to say is that i shouldnt replace ma with mg
both should be included
yes
ah sorry i misunderstood earlier
uh
okay so
what force would ma even be
if the only force here are the spring and mg
ma isn't a force
Newton's second law says that the sum of the forces on an object = that object's mass * its acceleration
it relates cause (forces, on left) with effect (acceleration, on right)
okay yes i see, so uh yes
okay im just a bit lost because
i see what you mean but i fail to see the connection to the overall problem here
like i cant make the link in my head yet
well there are two parts to setting up a newton's second law problem:
- find which forces are acting on an object
- find the formula for each force
- add them up (this is the ΣF part)
- find the acceleration (from definition) and put that in the ma part
- set them equal and you're done
- there is the force of gravity, opposin the force of the spring's resistance 2. -kx and mg, okay yeah this is where im stuck, because i dont see where ma comes into play
ma doesn't come into play until step 4
okay then 3. -kx = mg 4.
for step 3 you should only be adding them, not setting them equal. this forms the left side (the ΣF part) of the ΣF = ma equation
ah okay so overall force F net would be mg - kx? im not too sure whether it should be mg + kx or mg - kx because they do exert their force in opposite directions
Minus although I only know that knowing the answer
well we know that mg should be positive because downward is the positive direction
and the spring force should be upward (in the negative direction) when x > 0
okay yeah so my logic is that Fnet = mg -kx because when the spring exerts force F net towards the positive direction would be less
okay so here ma = mg-kx
indeed
What is a in terms of x and t
second order
x
over dt
oh yeah thing is
im not too sure how i can incldue the oscillation here
Then solve the differential equation
Oscillation comes out of it
As the solution
the oscillation comes completely free from the solution of the ode you set up
it doesn't need to be included explicitly in the setup
okay uh just a slight problem here so
in the solution they gave here
they kinda just disregarded g?
was it another way they did or
oh you can do that by a change of coordinates
change of coodinates?
so given F_spring = kx, at what coordinate x would the sum of the spring force and gravity be 0?
exactly at x=0
-k(0) + mg = 0?
i think so yes
oh wait jno
uh
okay you see how for them
x= 0 is when the spring is at natural
like balanced
yes so we set up the problem in a coordinate system where x = 0 is the position of the unstretched spring, whereas they set up the problem where x = 0 is the position where spring force and gravity force cancel
so let's revise our forces to match that coordinate system
so we know that spring force = -k * (distance from unstretched position). using their coordinate system, what is that distance in therms of x?
it would be k * ( -x) until when it surpasses the equilibrium point where it then would be k*x
no, because x is not the distance from the unstretched length point
we know that s is the distance between the unstretched length and the equilibrium position, and that x is the displacement from the equilibrium position
so in total, what is the total displacement of the mass from the unstretched point?
ah so x = k+s
k isn't a length
but if you plugged in x = 0 would you get (elongation of spring) = s ?
imagine the mass started out in the unstretched position and then moved to x = 0. then it would travel distance s. it then moved to some position x, which is the additional distance it travels beyond s
it would make sense if abs (s)
yes, so the spring force = -k*elongation
that's the only thing that really depended on where we place x = 0 in our ode
yeah i was calculating smt else i got confused
okay so
i basically replace my x before by x+s
in the spring force specfically, yes
so now im at the step where i have ma = mg-k(x+s)
and i ahve to make it in terms of displacement x over t
so plug in the definition of acceleration
as in i put everything to second order?
wdym?
yes
it would just be d^2(x) / (dt)^2 = (mg-k(x+s))/m
it should be just dt^2 on the denominator but yes
because it's meant to be read as (dt)^2 rather than d(t^2)
you can simplify the right side
using the fact that the sum of forces is 0 when x = 0
d^2(x) / (dt)^2 = (mg-k(x+s))/m im not too sure how to simplify from this
just looking at the sum of forces mg - k(x+s)
we know that when x = 0, this should be 0
okay lets put x=0, aka at equilibrium then (mg-k(x+s)) = 0, it just turns a = g
which uhh
where did the a = g come from
also you didn't actually plug in x = 0 to the equation here
like assume this is a case where x = 0, so (mg-k(x+s)) = 0 then we are left with a = 0/m okay wait uh
i think i got confused somehwere
so i only plug x=0
actually this makes sense cos acceleration would just be 0
if x is 0
we aren't plugging in x = 0 to our entire equation $\sum F = ma$, we are making a separate equation $\sum F(x = 0) = 0$
κλαουντ ☁ (cloud)
and this seperate equation
we assume it to be
at equilibrium
and not moving?
since Fnet =0
it's at the equilibrium position. it may or may not be moving since it says nothing about velocity
if the velocity is 0 then it would stay there forever. if velocity is not zero then it just passes through and swings to the other side
okay uh well
if its at eq
then mg -ks = 0
thing is
im not too sure wehre im supposed to reach
ok so we know that mg = ks. this information can be used to simplfy your ODE
okay if i determine a condition, or like simplify an equation from equilibrium, can i plug this equation back into my original equation where it is not in equilibrium
yeah i dont usually get sHM questions haha
Basically, think about the restoring force when you nudge the block slightly by x from its mean position (it'll oscillate). Then think about the equilibrium condition.
Rest is just Math, honestly.
this is waht im not sure about
cos if i can just take an equation from equilibrium
and plug it back into my original eqaution
i can just easily simplify it
but idk if i can
you can do that, it's completely valid
remember that mg and ks are constant, they don't depend on position at all
d^2(x) / (dt)^2 = (mg-k(x+s))/m
okay then
yeah its just that
i just didnt know i could substitution an equation from eq into one that isnt at eq
it feels kinda counter intuitive
okay tytyty
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when they ask instantaneous velocity, is it acceleration?
@royal sky Has your question been resolved?
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i need help with this because it is about WRITING EQUATIONS WITH VARIABLES ON BOTH SIDES
Well, what would be the equation for Jaycie?
Yes
wait what
No, okay tell me
how much would it cost Jaycie to watch a movie after buying a membership, like collectively
Dude no
Like imagine Jaycie's a rich gal
ok
So she brought the theatre membership
It cost her $27
Now to celebrate this, she decides to watch a movie, which costs her $6
So how much did she spend collectively on that theatre?
like 6.00m + 27
Well, alright then, you've found your equation I see
Now, what would be the equation for Claire?
like 8.25m because i cant seem to find another number or value to make like another mx + b
Yes, because there is no starting value
ohh
Now you're asked when is 8.25m = 6m + 27, so just evaluate them, find the value of m, and that's your answer
(Or just pop LHS and RHS on Desmos and the point where they intersect is your answer)
whats LHS and RHS on desmos?
like input y = 8.25x
and y = 6x + 27
The x value of the point where they intersect is your answer
wait so what does evaluate mean
wait show me a math example of what that looks like
Alright, 6.25m = 5m + 5
(Subtracting 5m from both sides)
1.25m = 5
m = 5/1.25
m = 4
Like that
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65
what's the original question? please take a screenshot with the instructions too
which question are you doing
65
sorry I misread
do you know derivatives?
i alr did that part
that doesn't see quite right
its quotien trule
i did d/dx = to the slope
you do not need qoutient rule here
= k(1/x)
oh ig u can do that way aswell
quotient rule applies to when you have something like:
f(x)/g(x)
in this case k is just a scalar(number) so you can do it as greaterthan wrote it
and even then it's just product rule in a slightly different form
does quotient rule still like work
yeah but its just more work for no reason
you can do (x)(1/(x^2)) if you really really wanted to i guess
ok
You can do quotient rule, but you'll find out a lot it cancels out to give k((d/dx)1/x))
ok let me do the d/dx one more time to get the right answer
Since f(x)=k has f'(x)=0
use Power rule 👍
You’re c-cheating on me @delicate topaz!? who is this man?
why
what is bro doing🗿
then you can solve for k because -k/(x^2) = -3/4
why is k/x =y?
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How was this simplified
$V = \frac{4\pi}{3} \cdot \frac{(\sqrt{S})^3}{(\sqrt{4\pi})^3}$
Ann
would you like further elaboration or do you think you can continue the simplification yourself from here
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Guy help with this one
Yo like can we see the original question
Cuz like I can't read the handwriting man
Aight thanks
I tried substituting, but the end answer was not satisfying at all
What did you sub?
X +4 = t
If you're doing it this way, you should split the fraction into 2
I got this in end
Yes, I did that
Bruh the ans didn’t match
You could also try subbing t=√(x+4)
Maybe mistakes in your calculations
Yeah, and then use the chain rule, while differentiating
I don’t think that I made any mistake in calculation. Can you see the actual answer? Wait, let me send it.
See 11
Guys?
So is my answer wrong?
You're not far off
I think you just made a mistake in subbing
Just look through your workings carefully again
After that you should be able to simplify to the answer in the answer key
Wait, let me send my work to you
Alright
Oh yea that's correct now
You were missing the ^1/2 in your first answer
@fallow wharf
Oo
Although in exam I don't think they'd reject this form
But just to see how they're equivalent
Factorise 2/3√(x+4) out of the expression
That let’s do a cubic expansion
$(x+4)^{\frac{3}{2}}=(x+4)\cdot(x+4)^{\frac{1}{2}}$
denzio321
@fallow wharf
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Hello, I'm kind of unsure what to do next. So far I have found length BC (arc length) to be 6pi. Could I get some hints on what to do next and how I should be using area?
find the radius of the small arc
call OA=r
express the areas of sectors OAD and OBC in terms of r, then take their difference and equate it to 209pi/5
thank you very much 🙏
.close
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For Q1, how do I plug x into the original equation
do I need to make it in exponent form then sub it in?
what x's did you find
but idts, question is asking to put it into original equaion
5,6
same as answer key
yeah replace "x" in the original equation with "5"
and see if it still makes sense
$\log_a(5^2 + 30) = \log_a(11\cdot 5)$
artemetra
theres no "a" in my calculator
simplify what's inside the log
but the question is saying sub it
not simplify
the whole point of this exercise is for you to check that after you solve the equation, you don't get something like log(-5) which is undefined
well yeah you subbed it in
and now you simplify to verify it
I didnt sub it in
would you know how to plug x in if there weren't any logs?
@chilly walrus I just plug it in without the logs,, corect?
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Is this correct?
Which one?
Both…. Sorry I keep asking I don’t have an answer key for this
I think it may be the same one I did last night I forget tho
Why are you being sorry?
Yes, its the same
I would check my paper from last night but it’s at home and I’m at school
think I've seen these questions before
We did it 8 hours ago
I’m est time zone so I went to bed and now I am at school and have a free
Cool, btw we checked and it was correct if im not wrong
,rccw
gdi
?
look at your first image
Yea
did you list two domains for f^-1
No we only need to find the range
But I’m confused why google says the range is zero to infinity but I think it is 1.7 to infinity
so you want to find the range of f^-1
Oh wait
Domain of f^-1(x) is the range of f(x)
if this is the case neither range makes sense, because f^-1(0) = (0^2 - 8)/5 = (0-8) / 5 = -8/5
X^2 makes any number positive, so we're js going from 0 to inf
Since there's no real number that makes the function undefined
Yea but my teacher told us to use the tables to find range and my table says 1.7 so I’m confused on a test how I would know which to do
that's why I'm asking if you're finding the range of f^-1 or f
this is the graph of f, not f^-1
Lool
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In space, given 2 lines $l_1$ and $l_2$ with equations $l_1:\frac{x-3}{1}=\frac{y}{2}=\frac{z+1}{3}$ and $l_2:\frac{x+3}{3}=\frac{y-1}{1}=\frac{z+2}{2}$. Determine a plane equation (P) contain $l_1$ and maximize angle between that plane and $l_2$
Alexis_Fx
This's the original question, after doing a bunch of thing now I have to maximize $\frac{3a+b+2c}{\sqrt{14(a^2+b^2+c^2)}}=\cos(\theta)$
Alexis_Fx
$a+2b+3c=0$
Alexis_Fx
this's the condition and also a,b,c can't all be 0 at the same time
Well I tried Cauchy-Schwarz but equality hold when a=b=c=0 which can't be true so
Should I just sub a=-2b-3c? that seems lengthy
and also 2 variables
maybe I could use AM-GM after I sub?
idk
Im guessing theta is the angle between the plane and l2 right?
between normal of the plane and l2 yes
oh wait I can't use AM-GM cuz a,b,c can be negative bruhhh
hmm sounds very TSA-ey
Đề Chuyên ĐHKHTN Huế câu nào thì em ko bt thấy họ ghi nguồn mỗi v( ko cần rep đâu để kênh này tiếng anh đi )
bruhh, $(a^2+b^2+c^2)(3^2+1^2+2^2) \geq (3a+b+2c)^2$
Alexis_Fx
This's what you meant right?
Then it cancel out the numerator
But in this case equality hold when a=b=c=0 which can't be true
Have you tried converting it in vector form?
I actually converted it from vector form to that thing
Vector is difficult to work with
With vector, applying cauchy schwarz might be easy
we have to follow this condition, not sure how we could do that with cauchy schwarz
I’ll try to solve myself and send the solution if you wont get any help
Im currently out rn
btw vector equation of that plane look disgusting
Gotta dig up the cauchy schwarz conditions
actually imagine this
I'm listening
your 2 lines I1 and I2 are seperated now right?
yeah
Imagine there's a line parallel to I2 and intersects I1
now when does the angle reaches the maximum?
you can try to visualize this with 2 pencils on your hand
okay...
have you imagined how it'd look like
đc r
thế thì e có đồng ý là lúc đấy vector pháp tuyến n, vector chỉ phương u1, u2 nằm trên cùng mặt phẳng ko
cs
nên ra công thức n = [u1, [u1, u2]]
bấm máy tính, xong
trường chuyên dạy xịn v
Hiểu
;-; Em nghĩ đến việc nếu 2 đường thẳng đó cắt nhau thì tìm hình góc như a
Nhma tính ra ko cắt nhau nên bỏ luôn ý tường, vl
má sách ngu
Xong còn nhìn gợi ý nx tr ơi
đốt sách đi
có quyển nào hay ko
anh
Cho e bt phát
I'm the better book
lol, a có rảnh để em hỏi 24/7 ko
sáng thì ko đc hehe
e thật sự rất cần quyển nào hay về Oxyz bruh
a ko phải cái phao để e dùng đâu
Trường thường có dạy mấy cái này đâu tr🥀
Rip
à mà
chụp cho a xem cái cách trong sách
okay em chụp lời giải luôn, có lời giải nhma e ko đọc xd
bruhh, em ko có ,này em lấy file thg bn em ra in
In mấy câu nhìn căng căng vs đáp án thôi
ok chúng ta sẽ cùng check body cho quyển sách
còn 1 khúc nx mà chắc a ko cần đọc

Em ra giúng họ đó
Có mỗi k bt tính max
thế này quyển sách phải lọ 36 phát mới ra cái lời giải điên khùng này
tính max à e?
thì max là góc giữa u1 và u2?
yeah
hold on
Em cần 1-2p để load
Thông cảm, đang ốm
a cx hơi ốm
em đang chảy nước mũi đây
same
Um okay mọi thứ vẫn v
bão chó
chắc ko cần
hồi đó anh ôn sách j
ko có sách j
aw
Làm quen ms tư duy đc
Đề trường chuyên nó khác....
Đề em đi tính max min MA^2+MB^2+MC^2
vcl
lol
thế này thua
Làm riết chán
chịu rồi, trường em ntn chứ bt sao
trường biến HS thành gà công nghiệp
Yeah, mé em cần quyển nào có đề hay để luyện quá tr
yeah cái đó ms là cái e cần....
tsu có thì cx hiếm lắm
Làm bài mà nó ntn thì....
hmmm, oke luôn
Hay ngồi luyện đề Trường Sở nhẻ
Căng quá k
Hợp lý phết kk
Cảm ơn a nhá, em ốm nên đi ngủ trc đây
ok e
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How do I solve absolute value functions?
,tex .abs def
riemann
use ^
do you have a specific example in mind?
do you see the right side and its signs?
Yes
can you be more specific then?
How do you know what direction to go?
,tex .transformation rules
riemann
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Hello guys does anyone know comp sci servers that help with java
so
let x < 60
day 1: x for $12 each, making $k total
day 2: 2x for $9 each, making $k + 342 total
so day 1 he made $12x and day 2 $(18x + 342)?
leaving him with < 80 spruggles (stock)
can u find x using this
Day 2 is 12x +342 and its also 2x×9
wonderful gng
12x + 342 = 12x + 342
bruh

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what😭
what u sent me is correct but it js didnt help much w/ the ques
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only day 2 was needed to form the simultaneous equation
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this is the most trippy question
why is it so hard to visualize
i would have to draw it out but the problem is i'm bad at drawing
I mean i can visualize it quite well
The answer should be 5
Oh wiat
Ye im dumb my bad
it's A - 1
it's like you have to look at it straight on, rotate it, visualize what numbers are behind what and which side is going to be touching the board
Ye damn this is hard
Its pretty easy to visualize if you consider whats the number on top instead of the bottom
From the start point: you have 5 at the bottom, 4 on top
You move to P, 3 ends up tops, so 6 is on the bottom.
and mind you, the triangles on top and bottom have opposing directions
so Q would have 5 on bottom?
the only way to get 6 touching P would be to flip the dice upside down (to fit into the triangle outline on the board)
then if you would push that forward, it would fall onto 5?
You get 3 tops in P, so moving to Q, you have 2 opposed, so ends up with 2 on top, 7 bottoms.
if im not going dumb
imma hardly try to draw this in paint
wish me luck for a sec
no yeah, theres no chance that i draw this and it makes sense
idk, you can kinda see how by rotating it from Start to P, the one side facing to you its the 2, per se, the opposing face.
Once you roll to Q, since you are rotating perpendicular to the 2, it has to end up tops.
And by determining tops, you can know the result in bottom
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Hello.
How does this make ANY SENSE
b* means anti-parallel
no?
matter of fact on the right side he is writing b // b* which means b is parallel to b*
I've never seen this notation honestly
well he said it means anti parallel
Oh ok
by negating the arguments (with multiplying -1)
Exactly, that's the meaning of antiparallel
Dude this is my first day ever at uni and its already confusing
But I don't understand your doubt
why did he say b = 2* b*
maybe he meant to write b = -2b* and write b* = (-1, 1)
well thats what I thought but doesnt b* also miss a 2
b* = 2 (-1,1)
well idk your notation so idk if b* is meant to be any antiparallel vector or specifically -b
Indeed, that's what confuses me as well
well even tho its german its readable, anti parallel vector it says
and he drew a and a* parallel even tho they are anti parallel
The only thing you have to know regarding this photo is that two vectors u and v are parallel if and only if u = k v (for some number k)
@blazing umbra
Yeah the issue isn't the language, just the notation
Wait, anti-parallel doesn't mean NOT parallel
If two vectors are anti-parallel, they are parallel as well
it means opposite directions
Anti-parallel means parallel with negative value of k
So they're still parallel 😅
how are they parallel if they are going away from eachother
That's what you need to know @blazing umbra
just because of this definition or what
Huh?
Sure
one vector going down right and the anti parallel going up left
but I get it doesnt matter
if thats the definition
the b = 2 b* is still stupid
hoping he just missed the -1
I think that's probably a typo or something
Yeah I think so too
Yes correct
even tho its AI sounds true, no?
my teacher said anti parallel means negating by -1 which would mean magnitude is equal
so I was lowk confused
but alright gotta blame myself
Yes, this is correct
dude I should really start asking questions
I was already suspicious mid class ngl
Im just showing the stuff he wrote down meanwhile
whatever thanks alberto
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If P(x) is a monic biquadratic polynomial with P(1) = 10, P(2) = 20 and P(3) = 30, find the value of (f(12) + f(-8))/10
ok one moment
what's f
P
and also when you say biquadratic, do you just mean degree 4? or do you also mean no odd-power terms
Note: f(x) = P(x) is true.
Not x^4 + bx^2 + c but ax^4 + bx^3 + cx^2 + dx + e
linear term known absent?
We also call it a quartic, yes.
4 unknowns and only 3 equations damn thats crazy
maybe the variable parts cancel while calculating the sum f(12) + f(-8)
that what will happen
Yes, this apparently has a unique solution
First of all, you said monic, so remove that leading coefficient
Then take the three points, make a system of three equations and four variables, and solve it
You'll have a free variable, it's fine just keep it and calculate the answer
f(x)-10x has roots 1, 2, 3 and another unknown one. does that help us at all or no?
factor theorem should help
f(x) - 10x is a quartic, right?
a monic one, even
i mean yes but is the lack of knowledge of the 4th root an impediment
this is where i assume we'll get stuff cancelling
f(x) = 10x + (x-1)(x-2)(x-3)(x-r)
f(12) = 120+11×10×9×(12-r)
f(-8) = -80+(-9)×(-10)×(-11)×(-8-r)
yeah the r parts will cancel 
yeah
@dusky ridge you can continue from here yourself, can't you?
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