#help-10
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equations have equal signs
Idk its just so weird
(And inequality signs as well)
Let me see if I can find something that's similar to the question

My laptop died
I will return w this question tmrw lol it takes forever to charge
But tysm for your help guys!
Also one question
seems like what you want is expanding and distributive property
Ohhh maybe
I mightve skipped that section
But that does seem to make so much sense
i'd recommend avoiding stuff that mention foil
Got it
I wanted to ask do u guys have like a review channel? Like to review the server or something? You've been helping me sm I'd like to give u 5 stars somehow

no
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Hey, so I'm following the formula used for the theorem, but its making no sense when I combine them.
Ik the formula is (EC)(DC)=(AC)(BC), but combining the terms are confusing me
can you show your working?
The only reason why i got it right was because i guess
but
ill show u what i have
Oh wait oh, i got mixed up, I understand now 😭
.close
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Why did they just not perform EROs to row reduce this normally to end up with an upper triangular form.
That way we can just see the diagonal as the product of 3 numbers and determine what value(s) K can be?
Won't that work too?
As A is invertible iff the det(A) is not equal to 0
have you heard of cofactor expansion?
Yes
if you put 0s as they did on the first column, the determinant becomes easy to compute
Yes but doesn't my way work as well?
yes
For some reason my way isn't giving the same answer
I did r3 -> 1/2(r3)
to get
[3 5 7
6 k 14
1 2 3]
then I did
r3 swap r1
[1 2 3
6 k 14
3 5 7]
This leaves me with -2det([1 2 3
6 k 14
3 5 7])
Now I perform addition eros
I do r2 -> -6r1 + r2
to get
-2det([1 2 3
0 k-12 -4
3 5 7])
Then I did r3 -> -3r1 + r3 to get:
did you take into account how you row operations affect the determinant?
-2det([1 2 3
0 k-12 -4
0 -1 -2])
yes
this is where I have gotten
I need the -1 in the third row to become 0
idk how to do that
Yeah so this method is not possible here then?
looking closer it might not be
i mean, the method does "work"
as in, it should produce the right answer
but getting it to upper triangular form may not be with the k hanging around
damn
why is linear algebra so painful bro
I really gotta put it into a form to use expansion 
How did they know what these eros would be the best ones?
To allow for expansion in the second row
Or do we just try and see how we can easily add zeros or a column and row and then work from there?
not really
you could expand right away
and just simplify
it doesn't matter
you just want zeroes along a row or column
but then again
you could just have taken the determinant of the original matrix
it's just a little more work to do so
Yeah true
Alright well, ty.
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Help
idk how to do it
tan x = -1/sqrt(3)
use arctan and u will get ur answer
@cunning tulip do you know what arctan is?
i wish to give you solution directly but
!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.
What’s arctan
tan inverse
inverse tan
wont he be getting two ansswrs?
yes
ok
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Where can I learn more about this?
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Isn't this Bézout's Identity for polynomials?
What do you want to learn about?
This specific case of if they're coprime they also satisfy being equal to h(x)
Honestly our teacher hasn't taught us this yet but gave us homework that included this so I just wanna learn in advance
Not sure I have any ressources on hand except just looking up things related to the identity online, sry
Ah okay, thanks
Maybe you could find someone more specialized in the Abstract Algebra channel too
Might have more insight and ressources
Ah alright, thanks for the suggestion!
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@gloomy trellis Has your question been resolved?
y = x and y = -x are not the same line
Which is actually logically incorrect as we have infinite path to approach the point
so to check existance of limit we have to discuss limit of the function about every path.
yep
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what do i need to study multivariable calculus?????????
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Based on the data from the picture, calculate the area of the figure that consists of a triangle, a trapezoid and a right triangle.
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Why is my answer slightly off from answr key?
seems to me like you're right and the key is wrong
Uhhh
Are you sure?
Could we get a 2nd opinion on this guys?
Similar thing happening with the problem before that
what is the original question?
Original questions underlined in green
The one on top is 4b)
One on bottom is 4a)
Answer key for reference
so the answer key and what you got are the same thing
yes
That is a stupid way to write it
exactly
the way you wrote is the correct way
So I did do it right
yes
Cool thanks
but the answer key is also right
If it weren’t for you this book would have thrown me off
it's the same thing
yeah... when you take the variable out, you can put it anywhere you want and they chose to put it after the radical which makes it look confusing
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Solving for values of p that hold this inequality
can someone help me finish this problem I think it’s quadratic formula, I’m just a bit out of practice
goddamn
what’s up
I should also preface I’m solving for values of p that keeps this inequality
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@river kindle Has your question been resolved?
@river kindle you have two unknowns, n would need to be in terms of p, and the probability of actually solving this seems very low without a computer. You could also set n to different values, but again… There are many solutions and most are extremely ugly. Did someone actually give you this problem?
Here are the solutions that solve the inequality: https://www.wolframalpha.com/input?i2d=true&i=8np+-+8Power[p%2C2]n+%2B+4p+-+n+<+0
Obviously I don’t think anyone is going to be able to help you do this by hand
Also note that some of those solutions aren’t possible
For example, your n can never be 0
It also can’t be +/- 2
Do you see why?
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I have no idea on how to even proceed
Like sure you can write that the addition of all elements in set is not equal to 0
But what then
<@&286206848099549185>
Yea
Hello
So any idea?
!15m
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I know
Usually vectors have a certain form
Read #❓how-to-get-help
What
Wth
True
But x^n e^ax is a weird form
Hm. Yea
Unless for all scalars being equal to 0
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can someone help me recheck
what's your reasoning behind your choice
that's one way to justify it
yep
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What have u tried
i have done the Q and have gotten the answer but my friend is tellin me its wrong
Can u send ur work for it?
i have taken peri of smaller semicircle (30.84) and then the peri of large semicircle(92.54). Then i have subtracted the small semicircle twice and added it back once for the peri of whole shape.. i have gotten the perimeter of whole shape = 61.7
Hmm
Do u have this working on paper?
I feel like it would be a bit clearer to understand
,rotate
For the smaller semi circle circumference, how are u getting the pi * r +d
I’m not seeing where the 2r is coming from
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'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
what
We are literally working on the problem
Phantom notice that
This has the same perimeter
Hey this is his friend
currently its fast time
and we about to break fast
you know ramdan for the muslims anyway he'll prob be back in a few mins
Oh ok
Notice that to find the perimeter of the figure, u can use this
So it’d be (circumference of big semicircle) - (diameter of big semicircle) + (3 circumference of small semi circle)
Idk if that’s what u were getting at, but I gtg now, hopefully u can understand it
@reef hatch Has your question been resolved?
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Could someone help guide me intuitively for why dividing by an integral by another integral gives the average? How does the bottom integral become "volume."
It all seems so strange to me.
This is the understanding I'm trying to reason with.
We're summing up all the values of dx here, multiplied by an f. In 1-D, this would give us an weighted area?
Then we divide by the sum of all our small distances?
the integral of 1 over a 3d region represents the volume of that region
Why is that?
it’s akin to how the integral of 1 over some interval is the length of that interval
Hm, but why does the function f disappear in the bottom integral?
in general, you can think as the integral of 1 over an n-dimensional space as the n-dimensional volume of that space
how did it disappear?
b-a is exactly the integral of 1 from a to b
Well, there's no integrand.
the integrand is 1
I see.
And why do we divide by volume to find the average?
That also doesn't make sense to me.
How is the top function like "total mass"?
think about the average of a function over an interval
you sum up all the values of the function (the integral), and divide by the length of the integral
f defines the mass at some point
so the integral over the whole space is the total sum of the mass at all points
hence the total mass of the space
I see.
And if we follow this analogy (physics), then average is density?
Because mass/volume is density.
yeah
So if I divided the bottom function, by the top one, I'd get the density of the cube.
Hm.
yes
Interesting.
I still don't completely get why, but I do understand it more. Thank you!
a few examples may help it sink in
👍🏻
I just find it crazy how length is also "volume"
Because in single variable calculus, I remember doing questions that asked about volume of a disk or etc.
they’re using volume loosely
volume here refers to some arbitrary n-dimensional measure of size
length, surface area, volume, etc.
this is just another way to compute volume
what interval
b-a
this is literal volume
Hm?
b - a is a length
Right.
you’re not taking the integral of 1 here
so you should expect the length of the interval necessarily
I guess these are just two different definitions of volume.
read what i sent above
they are using volume to refer to n-dimensional measure of size
in this conversation about the last picture you sent, we’re using volume as the usual 3d volume
I see.
that’s why they said “total volume”
Then a lot of things can be volume.
you shouldn’t focus on the verbiage
they are just saying the bottom thing is the size
of the space
I see.
the “total mass” and “total volume” are meant to help you visualize, they are not literally mass and volume always
Got it.
don’t think of it as a rigorous definition of what’s going on
The physics definitions always trips me up.
I don't like how physical properties are applied to more abstract concepts when they don't always match everywhere. But, your explanation helped! Thanks again.
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I need help with finding the perimeter.
not given
36/3
i have taken peri of smaller semicircle (30.84) and then the peri of large semicircle(92.54). Then i have subtracted the small semicircle twice and added it back once for the peri of whole shape.. i have gotten the perimeter of whole shape = 61.7 i have done this much but my friend is arguing with me sooo i need some help :p
what
have i done this right?
because the whole shape doesnt include the two top small semicircles as they are cut out it just includes one small one
yea that is the shape
the large semi is 92.54?
yea
but isnt the formula pi*r+2r?
the 2r doesn't matter in this equation
Oh
yea i took that for the first perimeter.... because i can remove the two smaller semicircles from this in the end like i did
the weird squiggly bits are 3 semicircles
solve for the diameter of the semicircles
uhh so bascially
then use the formula you'd normally use to calculate the perimeter of a circle
but divide it by 2
i have taken the whole top semicirlce as one
and taken the perimeter
then i have taken the peri of smaller semicircles which are all equal
then i have subtracted the peri of smaller semicircles with the peri of top one.... in the end i have then added 1 more peri of the small semcircles for the bottom one
why did you subtract the peri
@reef hatch Has your question been resolved?
.close
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1.8/(2x-4) = 0.9/(x-2)
easier to apply chain rule,
but doesn't matter whether you convert that
i integrated ln(2x-4)
so i got 2/2x-4
integral is incorrect
still no
Yes but you want it to be 1.8/2x-4
It must be 0.9*ln|2x-4|
If you differentiate 0.9*ln|2x-4| you would have 0.9 x 2 x 1/2x-4 and that is 1.8/2x-4
you can view/do things in a slightly different order
valid actions will lead to the same end result

The second ln is also wrongly integrated

Try to differentiate 0.9*ln|2x-4| than you will see that you get 1.8/2x-4
yhyh
()
And the other one should be -2.4*ln|x+3|
So your integral should be 0.9 x ln|2x-4| - 2.4 x ln|x+3|
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I don't know where to begin
can you show the figure or the question?
You have a rectangle and cut out 4 quarters of a circle
So we need the area of a quarter of the circle and subtract it 4 times
But notice that the circle quarters are all equal, so we pretty much do area of rectangle minus area of circle
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unsure if angles are pos or negative. any hints
say for theta5 is inversecos of -0.5
<@&286206848099549185>
i have 60,120, 30 for all 3 angles
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hello guys
.close
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Hey, how would I prove this?
start with the more complicated side
lhs here
first thing that pops out to me is that we have a difference of squares
that's a big hint, see where that takes you!
I think this is what I am looking for, is this correct? @upbeat island
ye
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how to do this but for third order odes
more specifically in matlab
like i can wrap my head around and code a first order
this was my code for 1st order ODE
[y,t]=RK4(0.5,1,3,@(t,y)(y^2)/(1+t),-1/log(2))
function [y,t]=RK4(h,a,b,d,y0)
t=a:h:b;
y(1)=y0;
for i = 1:length(t)-1
k1=d(t(i),y(i));
k2=d(t(i)+h/2,y(i)+hk1/2);
k3=d(t(i)+h/2,y(i)+hk2/2);
k4=d(t(i)+h,y(i)+hk3);
y(i+1)=y(i) + h(k1 + 2k2 + 2k3 + k4)/6;
end
end
% d=@(t,y)(y^2)/(1+t)
% h=0.5
% a=1
% b=3
% y(1) = -1/log(2)
but im stuck at the starting point for 3rd order
% BOUT TO GO into depression
% v''' - vv'' + (v')^2 = 0, with initial conditions V(y=0)=0, -(V'(y=0))=1, V''(y=0)=-1.
% 0 < y < 10
% so let v'= w, v''= x, v'''= x'
% so now we have x' = vx - (w^2) = 0 = f(t,v,x,w)
% so v0 = 0 w0 = -1 x0 = 1
f= @(t,v,x,w) (vx-(w^2))
h=0.5
a=0,b=10
t=a:h:b
I can't say I have experience with the a third order, but i've implemented a second order, and setup was referenced from https://www.youtube.com/watch?v=nJ_f1h49jfM and https://www.youtube.com/watch?v=TjZgQa2kec0. It mostly is the same idea just a couple extra steps, I can imagine it extends into third order.
This video covers the two body assumptions, Newton's universal law of gravitation, Newton's 1st law, and Kepler's first law, to explain the two body problem of orbital motion.
Instagram and TikTok: @spaceengineeringpodcast
https://www.instagram.com/spaceengineeringpodcast/
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The two body problem a...
In this video we apply RK4 to the solution of a 2nd order ODE and compare it to the exact solution.
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also asking around the physics discord might help as they might be familiar with numerical integration for your application
i see thanks
also ,
def updateBodiesRungeKutta(bodies) : # * Working as intended , much better accuracy.
Y = []
dt = TIMESKIP
t = 0
NElements = 3
for i,body in enumerate(bodies) :
Y.append(body.position)
Y.append(body.velocity)
Y.append(body.mass)
Y = np.array(Y,dtype=object)
k1 = dt * f(t,Y)
k2 = dt * f(t+dt/2 , Y + k1/2)
k3 = dt * f(t+dt/2 , Y + k2/2)
k4 = dt * f(t+dt , Y + k3)
yout = Y + 1/6 * (k1 + 2*k2 + 2*k3 + k4)
for i,body in enumerate(bodies) :
body.position = yout[i*NElements]
body.orbit_points.append((body.position[0],body.position[1]))
body.velocity = yout[i*NElements+1]
def f(t,Y) :
Yout = []
NBodies = int(len(Y)/3)
NElements = 3
for i in range(NBodies) :
tempv = Y[i * NElements + 1]
tempa = 0
for j in range(NBodies) :
if i == j :
continue
else :
tempa = tempa + (_acceleration(Y[i * NElements + 0],Y[j * NElements + 0],Y[j * NElements + 2]))
Yout.append(tempv)
Yout.append(tempa)
Yout.append(0)
return np.array(Yout,dtype=object)
this is the (very unoptimized barebone) implementation for the second order in python
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does second moment of area change depending on axis shift
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Does anyone know what the theta(x) function could be here?
This is from the second table in the "Connections within the group of rounding and congruence functions and with other function groups" section on https://functions.wolfram.com/IntegerFunctions/FractionalPart/introductions/FloorRelated/ShowAll.html
Or maybe it is defined somewhere else, and I overlooked it
@maiden garnet Has your question been resolved?
The Heaviside step function, or the unit step function, usually denoted by H or θ (but sometimes u, 1 or 𝟙), is a step function, named after Oliver Heaviside (1850–1925), the value of which is zero for negative arguments and one for positive arguments. It is an example of the general class of step functions, all of which can be represented as li...
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how do you do this i am completely clueless
what is the question ?
U wanna make a right triangle
What is the exact value
Use those side lengths to make the lengths of the right triangle
Notice that it’s equal to $\frac {1}{\cos {[\arcsin {\frac {\sqrt 2}{3}}]}}$
sorry i dont understand that
Stephen
arcsin?
Np
3rad7/7 right
Yep
Ah lol
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Help
Ok so what have u tried
8 is not correct
Show how u expanded the denominator
1/b --> b^-1 ...
Expand the 7^(2+t)
Stephen
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How would I set this up?
ok i think i have something
first two lines say
A B = I
and
[ 1 1 1 ]* = B [ a b c]*
asterisks transpose so i don't have to type column vectors lol
i think if you right-multiply by [ a b c ]* things reduce nicely
A B [ a b c ]* = I [ a b c ]*
A [ 1 1 1 ]* = I [ a b c ]*
Thats fine lol
What did you get?
what did you get lol
the second line here should basically be it. does it make sense?
^
yep!
Can you check these 4 problems if they right
you can post them and i'll try. my linalg is kinda weak though
Thats fine
Im pretty sure all of them are right
Besides the theory question
On the invertible matrix theory
first two are good
for IMT check here again: https://mathworld.wolfram.com/InvertibleMatrixTheorem.html
last one breaks my brain gimme a sec haha
Last one is right I js need help with that theory one it messes me up
number 12. on that link matches
i'm not so hot at proving that
def get a helper if you want more details on that. it's prob worth it. IMT and all the equivalences are pretty important
i had to at once point 😭
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Is this right?
Ye
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What would the image of this map be?
My intuition is to say that it’s just the span of x_1?
since u can write the map as something like
0 0
1 0
0 0
And then the column space is just span(1 0)
?
Do you mean span (0 1 0)^T?
Then it should be right 
(Remember that x_1 is a scalar rather than a vector of R^3 of course)
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.choose
I feel like the notation of (x1, x2)^T instead of just writing it as a column vector is lawful evil
Threw me off for a second when I first saw the text
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yo how do I round to a penny again
nearest 0.01 s
so 72.29? since 86 rounds up to 100
,calc 68.52 + (68.52*0.055)
Result:
72.2886
yep
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How do I get started with this one?
@timid silo Has your question been resolved?
What's F'(x^3)
x^3cot(x^3)?
yes
No. Read the problem again
oh, i see. but how do i integrate? substition with u = F'x or something?
you can see
this is chain rule
@timid silo
like how sin(x^4) becomes 4x^3cos(x^4)
if you want, you can try use u = F(x^3)
huh, but it's integral not derivative
im saying that
this is reverse
chain rule
if you see 4x^3cos(x^4)
you can immediately tell
that the integral is
sin(x^4)
wait, but if u = F(x^3) , du = F'(x^3)3x^2 dx
=1/3∫du
yh
does that work with no u?
doctor99268
what do you think the answer is
oh, =1/3u
yh
and you just sub in F(x^3) back into that
when youre dealing with reverse chain rule
there are two ways
first way is called integration by inspection
which is just looking at it
and seeing it
like, how i saw that it was immediately gonna be 1/3 F(x^3)
second way is substitution
which is just the more mathsy way
if you cant immediately see what the answer is
i see, do i just leave it as 1/3F(x^3) or do I need to go further?
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Express as a trigonometric function of one angle.
cos 17° cos 53° − sin 17° sin 53°
im not sure how to even attempt this and i also cant find any videos that explain how too
do you know angle sum identities?
not sure i do
sin(17 + 53)= sin(70)
cos(17+53)= cos(70)
cos(70) - sin(70)=?
is this what you mean?
no this is not what i mean
forget about your problem for a moment
i'm trying to see how much you do/don't know
wdym sin=y and cos=x?
as in a unit circle or a point
no again that is not what i am referring to.
bad wording
$\sin(a+b) = \sin(a)\cos(b) + \cos(a)\sin(b)$
Ann
do you know this identity yes or no
no
okay then you will have to learn about angle sum formulas or compound angle identities
(those are both searchable words)
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So, i need to check convergence by using the root test
but, because its the absolute value of the limit, can i just ignore the -1^n-1 here?
Same diff
These tests don't operate on alternating series, you start by ignoring the (-1)ⁿ
ok so i can just ignore, cool
so i worked it out, and i got 3/2 * lim(n^3/(n+1)^3
and the limit diverges, so this just diverges as well?
That limit goes to 1
Ignoring the 3/2 out front
I mean - your total answer will be 3/2
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can anyone please explain how the two are equal?
!show
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Why don't you evaluate it yourself?
ahh it's because one produces positive value while the other gives negative and when squared, it's equal
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Stuck on this Ellipse question to do with transformation of the ellipse
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A robot is equipped with a sensor to determine if a door is
open.
Sensor performance:
p(z=open | open) = 0.6
p(z=open | not open) = 0.3
Initial condition:
p(open) = p(not open) = 0.5
Using Bayes Rule calculate the probability of the door being
open after one measurement suggesting that the door was
open.
how do i find p(z=open) as thats my denomiantor in bayes rule
you can find that with p(z = open and door is open) + p(z = open and door is not open)
so 0.9?
ans says 0.45
P(z=open) = P(z=open | open) * P(open) + P(z=open | not open) * P(not open)
total law of probabaility
it's asking for p(open | z = open), is it not?
so what did you get for p(z = open)?
hows dominator that
how's the denominator what?
P(A | B) = P(B | A) * P(A) / P(B)
thats bayes rule
so i can see top matches but bottom doesnt
i dont see how P(z=open) = P(z|open)(p(open) +P(z|cllosed)p(closed)
do you agree
that p(z = open) = p(z = open and door is open) + p(z = open and door is not open)?
contemplate the equation carefully
think about what it means
do you not see why it's true?
yh
so you don't actually know why it's true?
yh unsure
In summary, the probability of the event Z = Open can be found using the law of total probability by considering the probabilities of the event happening under the conditions that the door is open (D) and the door is not open (D').
thats what i thought
yh
good to know that you can't be honest about it
so what does z=open mean
is it probability sensor thinks door is open
which then u check when door is open and door is closed then sum
@frosty spoke
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Hello guys! Just a quick one!
What should be the sign right there in the box
< or >
And if it would be log 0.5 then it would change right?
@dawn escarp Has your question been resolved?
yes
because $\log_a(b)=\frac{\log(b)}{\log(a)}$
Toby
Ohk thanks Toby!
yw :D
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I got 1 as an answer not sure if that’s right.
Show your work, and if possible, explain where you are stuck.
not correct
I substituted t for 20 and P(t) for 1.23, and got that.
0.005* 20 is what
0.1
calculation error
show your working
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what does inverting projection matrix mean
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<@&286206848099549185>
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I'm trying to find such a and b that the limit is finite but I don't even know how to begin this one
@clever spoke Has your question been resolved?
What's tg?
Tangent, I guess
Well guessing isn't good tho
Fair point
Are you allowed to use l'hospital?
check if there is in-determinant form
There r often ways to not use l'hospital and still determine the limit using quite adhoc seeming trig identities. It annoys the shit out of me cuz then they're just making u do trig under the illusion that u're doing calc.
So the first question to ask is if using l'hospital is allowed or not. If it is, things are much easier. If it isn't, things can go very south very fast.
fair point
that is indeed infuriating
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Surely OA+OB=AB, wouldn’t it have to be OB-OA? Same for 4b
OA+OB=AB?
resultant means sum of two vectors, so resultant doesn't mean AB
<edited>
I see, alright
Isn’t that what the resultant of two vectors is?
Like the line joining them together
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if the question is asking me for the maximum value of this function, how do I format my answer. is the maximum value 11 or is it (3π/2, 11)
just eleven, 3pi/2 is the x coordinate where the value of the function is 11
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calc 2 differential equations
Here is what I tried:
mm maybe they want something like y = ...
you should simplify the expression
$\frac1{e^{-x}} = e^x$
kheerii
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