#help-42
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can someone help me understand how the top one makes the bottom one?
I know you have to "expand" n! so its n(n-1)(n-2)! so the (n-2)! cancel out but what about the 2!
it doesn't, the top thing equals n(n-1)/2
need more context!
link video and timestamp.
well fuck
well i can't really see what's being done in the vid
oh uh
so they rewrote the expansion to equal 1-3x +4x^2 ....
then they expanded (1+kx)^n to that
and now equating coefficients
this is the other bit and then the tutor just simplifies that expression for binomial into n(n-1)
somehow
@barren nymph ah but he multiplied both sides by 2 as well.
ah, because 2! is just 2 right?
yes
ah I see
just one more quick question about this
I noticed they neglected the first term, why is that?
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When i plug the integral into my calculator with the limits i get math error whys that?
And when i plug it into integralcalculator.com it also gives me a different value
remember to change the bounds of integration if you haven't already
if you're plugging in 0 and 4 into logs, that'll give math errors
Wdym
What am i meant to change it to
Im given the bounds no?
when you do a variable substitution you need to change the bounds to be in terms of the new variable
u is sqrt(x), and the original integral is from x=0 to x=4, so your new bounds should be u=0 to u=2
Ah ic
Nah but that still doesn’t change what i get tho
After doing the u sub i get the 1/3 on 5
Ln*
But if i try this way its wrong
But y would this not work? What’s wrong with this?
what's the original function f exactly?
because your working on paper uses 1/(9-x)sqrt(x)
but you've put in 2/(9-x) into the website
O
Bruh mb
Plugged it in wrong
Aight ye ur right it works now
Thanks
after i get rid of the sqrt x why can i not then integrate it with ln tho?
what do you mean by integrating it with ln
When i have 2 / 9 -x cant i move 2 outside the integration then do
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could someone explain what in the world they are doing ??
for which step?
uh sorry, I realised didn't specify, I'm asking for when they rewrite the geometric series and write in that wacky fraction form
also soz for late reply
$\sum_{k=0}^n r^k = \frac{1-r^{n+1}}{1-r}$
Steakanator
this doesn't look familiar?
it's used to find the value of the series as a whole
in your question r = 1+x
and 1 is the first term
wait this is the thing were using right?
this is just a general term, not related to anything
but then what is that long line of n+1 c 1 and such
Binomial expansion
that long line is only happening because the context is binomial right
if it were anything else it would just stay as (x+1)^(n+1)
@barren nymph Has your question been resolved?
yes, sorry for late reply
ping me when you reply
Yes
Its very confusing to me a bit 😅
Because the bottom doesnt look like the tip but I assume its om for some reason
And idk how that is the coefficient of x^r
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@eager acorn Has your question been resolved?
@eager acorn Has your question been resolved?
@eager acorn Has your question been resolved?
I would rewrite tan^2(u) as sin^2(u) / (1 - sin^2(u)) and then try to make it into a quadratic equation.
(a quadratic equation of sin(u))
I guess the question is wrong because when we put π/8 it doesn't give -1
yo can u help me from the 2nd last step
I tried the same tbh
but the fact is solving for sin(x) is unreal in terms of b^2 -4ac on the quadratic equation
@eager acorn
did u not understand the condition?
i did not
i dont understand anything from the 2nd last step
we get a new quadratic equation
and as per the conditions given
we want all real values
@meager moat
the thing that i dont understand in this quetions is why did the (m-4)(m-6) =< 0
resulted into 4=< m =< 6
can we talk in dms
ya
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hi i need help with naive bayes assignment
Predict using Naive Bayes classifier for the following input attributes. Clearly show your computations and the classifier'sprediction. (i)x1 = 1, x2= 1, x3= 0
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How am I getting to the wrong answer here?
I get a = 2 and b = -8 when a is right b is wrong
x = -5/4
10 = a(4(-5/4) + 5) + b(-5/4)
10 = a(-5 + 5) + b(-5/4)
10 = -5/4b
this is what i do to try and get b
what a and b dude
to get rid of -5/4b would u not multiply 4/5 * 40/4?
partial fractions just
a/3x + b/4x + 5
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i have to find the points (if any) at which the graph has a horizontal tangent line, i dont know how to start
set the derivative equal to 0 and solve for x
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how does one go about doing part c?
see its understandable
but for the injective one i dont get why you equate the x and y
surely calling them x and y implies theyre different
god youre right
screw functions 😢
my brain no understandy the funny symbol
🤓
lol jkjk
ty for the help
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where is the additional sin(x) coming from. The final form i have before intergrating is
$1-2u^2+u^4$
Flamester7 Tv
@lone kiln Has your question been resolved?
<@&286206848099549185>
1 becomes x
calculus is fun
after getting the answer in terms of u use u=sinx so that you have it in terms of x
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Hey, I have a question
!just ask
My task says to show that these two operations
are well-defined binary operations
but what does that mean?
you can ask a helper
no hate to you dude
but you came, acted passive aggressive, and left
i am asking helpers
thats why im in the help channel
it means that the result of an operation is a unique value i.e. unambiguous
hmm okay
and do u know what the line above the ordered pairs means?
because if it's important then i'm unsure of the notation
and if not then tysm anyway
i think it's the congruence class
okay i googled it and i know what that means but it is definitely not what the question is sking
asking*
yeah i see
seeing the full question might be useful
not sure what either S nor ~ are
got it, this clears things up
i'm just a little unsure how to start thinking about this
i've done part i)
showing reflexivity, symmetry + transitivity was very simple
honestly
for ii) though im just
i have no clue what the overbar means
yeugh
ive read thru the lecture notes
and they do not feature
any kind of overbar notation
wait no they do
i missed a page
oh thats so annoying
im sorry for wasting your time lmaoooo
$\overbar{x}$
just means
george clooney real account
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
ah lmao
$\overline{x}$
artemetra
i also always write overbar lmao
ive been trying to write my working on pen+paper and then all my theorems in obsidian using latex
and im still trash at latex
thanks for the help
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can someone tell me how 2.6672 was obtained?
Because I've plugged in 1 into k and I didnt get that
a better question would be is what did they plug in for k in this example?
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Having trouble setting this integral up, kinda got a understanding of what the graph looks like and that its only a portion of the whole given x,y > 0 but cant seem to get the setup
kinda got a lil mess sketched out
I dont think what I wrote is correct for the bounds
@severe geode Has your question been resolved?
<@&286206848099549185>
wondering about the above, how I can set up the integral for question d
I see that z is from 2 to 9 but cant quite understand how to get bounds for y and x
When discord lags super hard:
Can you please show an example
@severe geode
By providing more information
It depends
this was my question
Oh okay
Cylindrical coordinates should be easier I think
I assumed but I have no idea how to do those in 3 planes yet
they went over it breifly havent done many problems with it yet only like 1
Oh bet time to practice it then 
I suppose
So first off, $dV$ with cylindrical coordinates is equal to $r dz dr d\theta$
992qqoloy
next, cylindrical coordinates is p much just polar with an added z value
$x^2 + y^2 = r^2$ in particular
992qqoloy
So we have $z = r^2$
992qqoloy
so theta would be 0 to pi/2 in this case since its a quarter circle
992qqoloy
radius from sqrt(2) to 3 and z from 2 to 9? I believe idk I think I may understand how to do this with cylindrical coords now
yeah
^
yup
If I run into more problems I will reference the book but htank you
np
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for part b) i got 3.3166666667
but it says its incorrect
cant get c either
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Tried solving the highlighted above 3 equations simultaneously but I’ve made a mistake somewhere and I can’t seem to find it
Yep, made a mistake when solving the equations simultaneously and I can't seem to find it
Nvm found it finally lol
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need help with number 16
helo
@remote mural Has your question been resolved?
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@remote mural
i found it very difficult
with this question
are you at first year uni?
the solution is x=3 and y=2sqrt 5
@remote mural
you need to find x+iy such as x+iy=sqrt(11+12sqrt(5))
this means (x+iy)^2=11+12sqrt(5)
develop (x+iy)^2 and then put imaginary equal imaginary and real number equal real number then solve the system
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What would the interval [3pi/2 ; 2pi] look like on a trigonometric circle?
do you know where 3pi/2 and 2pi are?
it refers to the same direction as 0
it means "go all the way around the circle exactly once"
4th quadrant
and then you end up pointed the same way as when you started
Ahh I see
not helpful
[3pi/2, 2pi] is all the points between those angles
I'll send the exercise I'm trying to figure out XD
ok
Knowing x is part of the interval [3pi/2 ; 2pi] and sin x = -2/5.
Find cos x
ok i see
well to work out what part of the circle is [3pi/2, 2pi], i can suggest the following:
I'm having trouble if I should find cos x and -cos x at the same time ;-;
suppose you begin at angle 0 and then you start traveling around the circle counterclockwise (increasing angle)
suppose you have a paintbrush or something
as soon as you reach angle 3pi/2, let your paintbrush touch the circle
then when you reach 2pi, lift the paintbrush
everything you painted is [3pi/2, 2pi]
Wait so is 2pi 0?
yes it refers to the same point
So is would be like a quarter of the circle right?
namely the point x=1, y=0
Ahhh...
but you wouldn't write [3pi/2, 0]
Oh-, jeez these mathematicians
because intervals like that should have a smaller number first, then a larger number
Ahhh
Yeah make sense...
but yea it means, start at 3pi/2 and then everything is included up to 2pi which is the same as the point called 0
so can you describe which part of the circle this is?
Um the part on the bottom right?
Yaaay
Ahh so that's what he was talking about
yea
but it's more helpful to guide you to the answer instead of just telling you
and we're not supposed to just give answers anyway haha
True true, I definitely liked the paint brush 🖌️:)
cool
Thanks again :)
sure, cheers
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I have to solve that limit using the definition but I got stuck there
you could also notice that n²+3n+2 = (n+1)(n+2) and 6n+6 = 6(n+1), so you get 6|1/(n+2)| < epsilon
it was easier from there, bc then you have n > 6/epsilon - 2
so you can take N = rounding up of 6/eps - 2
@astral dune Has your question been resolved?
Oh that makes a lot more sense
How can I notice easily that n²+3n+2 = (n+1)(n+2) ?
Well, in this case I'll probably just remember it but what if it's (n+3)(n+2), (n-1)(n+2)... ?
the way I think is that, if it didn't simplify nicely, your teacher wouldn't say to find an epsilon proof
and the more obvious case where polynomials simplify nicely is when they share a common factor
6(n+1) has only n+1
and then, n²+3n+2, bc of viete formula, has -3 as the sum of its roots and 2 as their product
so I immediately now that it's (n+1)(n+2) and that the (n+1) will cancel out
and if it wasn't the case, well, it would be a pain
you would still need to do the long division ig, so that you can bound the thing in terms of n
What's viete formula?
or you use some camel's trick (I think it's called like that in English) where you add and remove the same thing at the same time on the numerator
it's in fact, several formulas, that express some things about roots of a polynomial in terms of the coefficients of the polynomial
if you don't know them you can just factor the way you usually do
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Okay thank you so much, I'll look that up
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**The displacement from O of a particle moving along a straight line is given by
x=t^2−4t
The distance that the particle has travelled after 4 seconds is ???**
Please don't occupy multiple help channels.
how do i convter the displacement to distance?
@icy pumice Has your question been resolved?
you can just sub in t = 4 into the displacement function
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displacement function?
uhhh area under the graph is the distance?
it's moving on a straight line so the distance is the same as the displacement in this case
i think
thanks
wait
is average velocity and acceleration the same?
whats the difference?
oh im guessing
that you find the average of the numbers?
Test
huh?
@icy pumice Has your question been resolved?
@icy pumice Has your question been resolved?
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Which one is correct? Top or bottom? I think it's bottom but I'm not sure
you're right it is the bottom
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im so confused on how to even set this up
Seperation of variables
say S(t) is the amount of substance 1 at time t
S is consumed at a rate (prolly some derivative thing going on here) proportional to S(t)^2, that's what the question says
@harsh kelp
Okay
so we have dS/dt = something involving S(t)^2 pretty much
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got it ? @harsh kelp
yes thanks
aight
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I need to find the inverse of this function, but after swapping the x to y, i get two y's in seperate functions.. how do i solve for y?
i can do either arccos or arctan to get the y out, but tthen there's 1 y left in either function
and my domain was [0,pi/2]
Express tan(y) in terms of cos(y), then solve for cos(y) in your inverse function
You do not need to find the inverse function.
Use the inverse derivative property
Otherwise, this would be your inverse function
It absolutely is
thanks! i have one more question
which is
don't mind the dutch, but i have to prove this inequality by using the mean value theorem. i only got so far
i'm not sure how i'll get any further given that 2/pi is equal to cos(c)
i mean i'll have to talk in terms of sin in the end
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Hi, I need help bc I am not a maths person 
context: I am trying to model bacterial growth to make it so that bacteria can grow, reach a plateau and then die bc of nutrient depletion.
I just have 2 components, "sty" which is the bacteria and "nut" which is the nutrients, and I have the following code
reaction_network <- function(t, y, p) {
dsty <- p[1]*y[1] -p[2]*y[2]*y[1]
dnut <- p[2]*y[2]
list(c(dsty,dnut))
}
y0 <- c(sty = 0.1, nut = 1)
p <- c(1, -0.5)
times <- seq(0, 100, by = 0.1)
out <- ode(y = y0, times = times, func = reaction_network, parms = p)
now, "out" is the output and I can make it so that "nut" decreases, the problem is that it goes to negative numbers and I need it to not go lower than 0... any idea how I can do that?
forgot to mention that "y0" is the initial conditions (low bacteria and some nutrients)
and "p" are the parameter of the kinetic constants (how it changes)
nice pseudo you got there ^^
i got 2 questions
- what's the differential equation that describes your system ? maybe you typo'd idk
- does
nutbecome hugely negative, or is it very small ?
@honest trellis
idk how the system is described as an ODE, I don't even know how to make them (I am just a biologist scared of math)
and nut becomes hugely negative (like 1*10^-200 or something like that)
10^(-200) is ultra small
@honest trellis
like pretty much 0
and 1*10^(-200) is still a positive number
just very very tiny
isnt what you need basically a logistic map?
this is what I get
ah yeah ok this is problematic
floating point numbers in computers can completely screw up like that sometimes, I'm just throwing explanations around
what does the curve look like for small times ?
care to explain your code?
what are those variables?
like t is time i guess but p and y
ok so, I am trying to copy this code and logic into bacteria
I tried to do the same but it didn't work apparently
so yeah this is the logistic map if you have only one population that starves
we'll do a sequence instead of a function so its easier
unless you want to get fancy
its a problem that you are using a predator prey model but with just one population at first
and second, the fact that you are doing that tells me you are lost about the maths you are doing
always tbh
ok so I am gonna do more research sinceI am having trouble with basics
none
okay so dont try to do what they are doing
my degree just got up to derivatives and integrals
are you at ease with coding ?
okay so you want to code something along those lines
let P_t be the population at time t
$P_t = r P_{t-1} * (1-P_{t-\tau})$ with P inside $[0,1]$ representing the percentage of the max population and $\tau$ representing the time bacteries take to die roughly, r is an adjustable parameter that you can fiddle with
Benjamin
and you compute for integer values of time t
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can you translate, is that...I'm gonna guess Hungarian?
damn wasn't even close 
Here's a hint: $\cot\theta=\frac{\cos\theta}{\sin\theta}$
wait
what is this question asking exactly?
like just evaluate cot^2+cos^2?
PajamaMamaLlama
$\cot^2\theta+\cos^2\theta=\left(\frac{\cos\theta}{\sin\theta}\right)^2+\cos^2\theta$
idk why it's giving me an error
PajamaMamaLlama
I think I understand. I need to equalize the denominator.
so the cos need to be positive
because of its between 0 and 90
For this, a unit circle needs to be drawn
.
@main marlin
@final dock Has your question been resolved?
i resolved
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!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
Please send the whole question
33?
x+1
How I can solve it
with th square root over it
both of them or one by one
both
it will be 25-x^2 and x+a
x+1*
idk the app
which app u are talking about
can you show me on paper is it possible f+g ?
why are you squaring the whole thing?
you have no need to square it
it will stay same but I will plug them
sorry f+g
what about times and divide
f*g and f/g
same idea, but multiply or divide instead of add
I confused a little bit `cause I expect that is not easy
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f(g(h(x)))
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in 51?
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word
The answer is m + 14 but I’m not sure how to get that
4m+ 20-3m-6
u have -3xm -3x2
U distribute the - also
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I am trying to calculate the odds of getting at least one unique dice when rolling 5 dice. By unique I basically mean a die that is alone in it's set.
For instance
[1, 3, 4, 4, 3] has one unique die: 1.
[3, 5, 4, 2, 4] has three unique dices: 3, 5 and 2.
So I am looking for the probability that there exists a unique die in a set of 5, if that makes sense.
My intuition tells me that if we fixate 1 die and 1 number, we can calculate the probability as
(1/6)*(5/6)^4.
Let's say we fixate "die 1" and a number 5, then could this be called the probability of rolling 5 on "die 1", and anything-but 5 on the remaining 4 dices?
Then in order to account for all the dices and all possible numbers we multiply by 5C1 and 6C1 respectively
(1/6)*(5/6)^4*5C1*6C1 = 2.4112654321
Which obviously isn't correct, but rather the average number of unique dices per 5-throw.
How can I go about solving this correctly?```
Also, I know that the answer is very close to 96%, according to my Java simulation which appears to be working correctly.
you can notice that there's only 2 ways it doesn't happen: 3+2 or all 5 are the same
,calc ((6)(5)(10) + 6) / 6^5
Result:
0.039351851851852
i'm curious if there's some cool general way too
Oh okay, yeah makes sense
Would it be possible to calculate this with generating functions some how?
Would you mind explaining this? How the exclusion works I mean
I understand that the denominator is the total number of cases
But how did you come up with the numerator?
There are 6 ways to have all 5's, I understood that one
and there are 5*6 ways to pick two numbers for 2+3, but where does the 10 come from
then 2+3 you get by choosing a value that appears twice and then a value that appears 3 times, and 5c2 counts the order
i was lazy to write out 5c2 with factorials
i think we can calculate it with a table, just like stirling #2, but without creating singles
unfamiliar with the concept
Like stars and bars sort of?
stars and bars would only count the different amounts that would add up to 7
for each shape of 6 rolls we can extend it to 7 by using an existing group
ABABCD → ABABCDA
ABABCD → ABABCDB
ABABCD → ABABCDC
ABABCD → ABABCDD
so we multiply 65 by 4
and also for each shape that has 3 groups we can add D, so we add 90 times 1
the order of letters is not interchangeable, there's no 4!
it just to make thwe numebrs smaller
so i tihnk if do this and just not add 90
This is beyond what I can comprehend
But would stirling be covered by an advanced statistics course?
i don't know sorry
Well, thank you very much for the help. I'll leave this open for a few more minutes if someone has a general/alternative solution
ok it kinda doesn't work
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hi
closed other from long tim eago
Wat i do wrong for this plz 😭 the answer is there and my work is here
@halcyon ore Has your question been resolved?
@halcyon ore Has your question been resolved?
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y = -f(1/3x)
how do i find the two points? given 6,5 im confused atm
i got (18.2,-5) but it's wrong and im not sure what to do or change
What two points
vertex
this is basically doing transformations
.close
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Hi
Pedestrians approach a crossing from the left and right sides following independent Poisson processes with
average arrival rates of λ_L = 5 and λR = 1 arrivals per minute. Each pedestrian then waits until a light
is flashed, at which time all waiting pedestrians must cross to the opposite side (either from left to right or
from right to left). Assume that the left and right arrival processes are independent, that the light flashes
every T = 2 minutes, and that crossing takes zero time – it is instantaneous.
What is the probability that in a particular crossing, there are total 10 pedestrian and they are all
crossing from left to right?
wtf
really
just bc u said hi
okay .close
.close
sorry my dude they beat you here, it's first come first serve
@frank gullin one metric yes and in another no. i asked a question first technically
but it's fine i got another channel
How am I supposed to solve this, and what am I doing wrong ?
This is the formula
Don't you need to use the y coord of the focus?
,w plot y =(1/8)(x + 4)^2
Oh wait
alr
I just dont get which part of it is wrong ?
<@&286206848099549185>
Isn't p the distance from the directrix to vertex or focus to vertex?
Not from the directrix to focus?
Yes
Is it 1 ?
So if the overall distance between the two is 2, and the vertex is halfway, then p is half that distance
Yeah, I believe so
Yeah but the final answer is wrong
I wasn't referring to the k part anymore
Yes
Do I write it with 0 ?
You can but it's not needed
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The volume V and the surface area S of a sphere of radius r are given by the formulas V= 4/3 πr^3 and S= 4πr^2. Express V as a function of S
I just dont understand how to get the r^2 to r^3, because theyre very similar equations, but I just don't know where to start
solve for r
so would i be solving for r in the surface one? and then just plug in that into the r^3 of the volume one?
.close
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I need to find the relative minima for this graph
I believe the relative minima to be (-3, 3) although I am unsure if endpoints are relative minima or if there are any more.
@next tangle Has your question been resolved?
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@next tangle Has your question been resolved?
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can someone tell me what i did/thought wrong in the red squared area? and how to avoid that in the future?
@winter jacinth Has your question been resolved?
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answer i was given was on the right side
left side would be an acceptable answer too?
They're the same answer
both are the same
multiply by -1/-1 to either to obtain identical solutions
oh and hmmm. if i wrote the answer from the left on a test i should get that right though or is there some formatting convention that i should be aware of that makes the right side answer more correct?
It would be correct on a test
there is no preferred formatting
in this case
personally I like to have as few negatives signs as possible but that's just for aesthetics
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Am I just supposed to differentiate this?
Plugging in m1 and m2
Im left with
F = G * 36/r^2
I think you should just take the derivative
yeah just plug in the two masses and then take dF/dr
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pleaze help
take common denominator
that’s your job 👀
since youre going to tell me stuff i slready did
ill show you my work
and you tell me the error
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that's how things are supposed to be done here anyway lol
what is
(x+2)(x+8)(x+1)
just multiplying it changes the equation
so what u have is not equivelant to what they have
so
whqt the cd
whats
im so confused
for common denominator youre just multiplying by 1, cuz anything multiplied by 1 is the same. you need to rewrite 1 so that when multiplied it gives the same thing
whats the common denominator
if its not ehat i had
what
what is it
please tell
a/b + c/d for example
simplest way to get cd is the multiple of denominatiors, which is bd.
for b to become bd, you need to multiply by d. for d to become bd, you need to multiply by b.
so you multiply a/b by d/d, and c/d by b/b. then both fractions have the denominator bd. if its difficult to factor out you can also multiply both denominators by bd/bd (the multiple of the denominators)
(reposting so i could rotate it)
this isnt chegg
how do we ask for help-?
the point is to help you figure out how to do these on your own
sorry for the bother
!help
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take your own channel
ohh tyy
its midnight i want to sleep but im bot sleeping until i figure this out
not
i had work until 9 and ive been doing math since i vot hone
home
@rustic blaze
simplest cd us the product of denominators
then multiply by cd/cd (cd = comon denominator)
you want me to myltiply all three denominatore
only 2
you’re trying to prove LHS = RHS
consider LHS on its own and manipulate it to equal RHS
ok ill do it
does it matter which two i multiple
multiply
come back
@hollow mural
ok
you’re only considering one side of the eq at a time
either consider left and make it equal to right, or the opposite
in this case, since the right is a single fraction, it’s easier to consider the left
so consider the left side alone
and simplify it into a single fraction by taking cd
is the cd 2(x+8)(x+1)
yes
^
? you don’t. you take common denominator and then simplify into a single fraction
youre trying to prove the right side, which has a denomiator
what would the 5/x+2 turn into
5/2x+2
?
multiply by cd in the top and bottom
is that y?
if you just multiply by 2(x+8)(x+1), the function changes. you can only multiply by 1. so multiply by 2(x+8)(x+1)/2(x+8)(x+1)
basically multiply top and bottom by cd
otherwise the function changes
can you pls solve it on paper
ive done every other problem
i dont have paper
this is correct. multiply the top and bottom of each fraction by this
2(x+8)(x+1)/1
yes
thsts just mutiplying the top
and changes the expression
you can only multiply by 1
^
multiply the top AND bottom
by the same thing
thsts the same as multiplying by 1, so you doing change the expression
otherwise what you do is wrong
but
whyve the other problems been rivht
whats different about this one thwt makes me have to multiple both
show the other problems and your work
this goes for any problem
ignore everything about 13


