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We've started learning about differential equations I was wondering if anyone had a good website or links to math videos for introduction to differential equations.
Khan academy
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I’m trying to do this Lagrange problem, but it seems to complicated is there something I’m missing?
@crimson sedge Has your question been resolved?
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Need help with proving
"Claim: For any integers a,b,c,d,p∈Z, if a≡b(modp) and c≡d(modp), then ac≡bd(modp)."
if someone knows how you could manipulate this into something
refer back to the definition of x ≡y(modp)
(for example p|(x-y))
then your job is writing ac - bd as a multiple of p
(hint: -bc +bc)
I don't quite understand.
how does p relate to that
?
how would we define p that we could figure out to put it back into this equation
a - b and c-d are multiples of p
use that info
right and I want to prove that ac-bd = p*(some number)
so then I can set it equal to itself, how do I use - bc + bc
I mean what relation could they have
c is some remainder and b is some value that p divides
ah wait do we divide by c and b to get isolated terms we can define?
like
(ac-bc) + (bc - bd)
and then
(a-b)/c + (c - d)/b
then we'd have isolated terms that are multiples of p, so we could replace them with
like p*(n), for n in Z
so
(p(n))/c + (p(n))/b
I don't know how that helps me
<@&286206848099549185>
sure sorry so then factoring out c and b
oh
yeah yeah I see it now
wow that's dumb thanks
pnc + pnb
so ac-bd = pnc + pxb
yeah, be careful it's not necessarily the same "n"
I see, that's true
$pn_1c + pn_2b$
rafilou is not not born in 2003
Ayu beem
I see, and since the term we have multiplying p is an integer because the terms in it are integers, we have that ac-bd = p(...) some integer
it doesn't matter than c and b are variables we already had or anthing like that
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Here is my working out
I believe the y is right
But everything after I suspect somewhere a mistake occurred
I'd like help spotting the mistake
It's reduction order question**
<@&286206848099549185>
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I am currently in theorems and proofs in geometry. I am having a hard time trying to figure out how to start out.
Its just I don't get it, it does not say if it is getting triseced, or anything
Trisected*
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hey
linear functions are functions that essentially only have one degree
y = 2x + 4
it represents constant change it's the same every time
rise/run
number 3 is linear because it is a straight line
i'd recommend learning your parent functions
all the others are non linear because they curve
ofc
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my initial idea to solve this was to write the polynomial as:
x^100 = q(x) (x+1) + R
all i know is that x^100 / (x+1) = (-1)^100 = 1
remainder theorem
i dont know how to proceed though
you have your R as 1 from here
reminder theorem
substituting it into the equation
we get
x^100 = q(x)(x+1) + 1
now do you see how we can find q(-1)
?
would that not be 0/0
:O
i dunno 😓
we are supposed to simpligy (x^100 -1) / (x+1) so that we get a polynomial
how to factor x^100 -1
hmmm
basically
excuse the bad hand writing
but the reason we cant solve this because we have (x+1) and x is -1
so what we need to do is find a way to remove the x+1 from the denominator
can you think of something ?
uhmm
i was thinking since x^100-1 is a difference of two squares it could be written as (x^50+1)(x^25+1)(x^25-1)
but idk if thats useful
yes!
why did you stop
since we have to eliminate x+1 from the denominator, we need it in the numerator
simply keep repeating this until you get x+1
couldn't you just do polynomial long division from the start?
then just ignore the remainder
as in
at this step?
oh but x^25 isnt a perfect square is it
uh
at x^100/(x+1) on the original question
a pattern will emerge really quickly
can you show what you mean, i am dumb today
i mean like
you cant simplify the numerator further i think?
not sure
(x^5-1)(x^5+1)
isnt that equal to (x^10 - 1)
uhh
x^99 - x^98 + x^97.. right?
yea
oh yeah, alright time to sleep then
my bad
all good!! dw
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np!
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hi guys, so I have a physics screening test today and this is their past paper
im stuck on question 2, I’ve thought about using pyth theorem + 1.1km but it seems wrong
ive also tried searching online but no videos seem to have a map similar to this, they usually have a guard
does anyone know how to solve this question? thank youu
specifically how
sorry for the wobbly lines
the "legs" of the triangle are going to be the blue and green lines
you can calculate blue by adding together 800m and the vertical component of the 1.1km
and the green by adding together 1.5km and the horizontal component of the 1.1km
do i get that by using sin cos tan?
you'd have to use two of the trig ratios in order to get the vertical/horizontal component of the 1.1km vector, yes 
you can calculate the angle
well, the angle you drew is unnecessary 
oops
it's extraneous information, even if it is correct
your goal is to get red
and you get it via getting green and blue, and then using Pythagoras
green = all horizontal vectors on the path going from A to B added up
blue = all vertical vectors on the path going from A to B added up
yup ok
and you can use this to get the angle b/w A and B too
using Pythagoras?
well, that would get you the hypotenuse
to get the angle, you can reexamine the green and blue lines
let me try to draw
okok thank youu 😭😭
maybe a little complicated, but I can try to explain
inside the orange circle is what we need to find: theta
that angle is the angle between A and B
but you can clearly see that the small dotted triangle inside the orange circle looks exactly like the bigger one with red hypotenuse and dotted green and blue edges
so to calculate theta, we can just use the bigger triangle
note that tan(theta) = opp/adj = blue/green
so theta = arctan(blue/green)
but you already calculated blue and green, from part a)!
so it turns out there's very little work you need to do to get your theta 
does that make any sense? 


oops
you mixed the two up 
one sec
you can find the vector from a to the 30 degree angle and add that vector to the 1.1km vectro
the angles don't match, so you can't
it will not be a straight line
that won't be the minimum distance
not just adding the 2 lines
which is what we need
yes
sure, but to do this in practice requires you to decompose both vectors into their components
and at that point, you may as well decompose all 3 of them right from the get go
should r be 2800 or 2024
unfortunately, I have to go to bed now 
so I'm not going to be able to help you finish this one
but I have given you all the pieces you need already
thank you!
good night 😭
good luck with the problem, and I wish you a wonderful day or night! 
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i have no idea
partial fractions
rewrite y as a generalised summation, and use partial fractions on it
1+n^2+n^4 has a very nice factorization
so like 1/(x^2+x+1)(x^2-x+1)?
thats just factorizing the denominator
yea
partial fractions are 1/factor - 1/factor
can you write this, and simplify the addition?
youd see the numerator appear in some form or the other
oops typo
just write a/factor1 + b/factor2 and go at it
do we need to find like the a and b furthermore?
alright ill try to continue it, i gtg now
thanks for the idea and hint
i get it now
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im not sure how to do (b)
@lethal canopy Has your question been resolved?
<@&286206848099549185> 🙏
Not probability theory 😭
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$\begin{aligned} y^2+25&=x \\
10y&=x \end{aligned}$
Urara4ya
If
(x,y) is a solution to the system of equations shown, which of the following is an
x-coordinate of the solution?
oh
doesnt the first part refers to the property of the residuals in a simple linear regression model??
yeah i did that part already
umm
oh then which part do u want help with?
specify it
make a channel
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bruh
what
i think you guys were discussing previous question so just not to intervene
i was helping them in this question
in the second part u plug X into the estimated regression line equation
like
ik but i have to show the proof
substitute X(-), the mean of X value into the equation duh
not really how that works
:?
The resulting Y> will be the mean of the Y values
does this show work :d @lethal canopy
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i guess so
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why is a not a lower bound of {d, f}, I am guessing I am reading the hasse diagram wrong, but i know that it is read from bottom to top but in question it is given horizontally
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hi is this projection onto subspace correct?
@oblique lynx Has your question been resolved?
it feels sus
proj W(x) = proj W1 (x) + ... + proj Wn (x), how do you know that is true here ?
@oblique lynx
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Why is it that $E(E((X|Y)^2)= E(E(X^2|Y)) = \sum_{k,j} j^2\frac{p_{x,y}{j,k}}{k}$ , where X and Y are random variables?
Pen
I don't understand why the first equality holds, why is it not E(E(X^2|Y^2))?
i need help , i don't remember how to find x and y
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@cosmic marten Has your question been resolved?
<@&286206848099549185>
The only reason that I can think of is a notation issue
Since, per definition
$E((X|Y)^2) $ should be $E(X^2|Y)$ otherwise you'd end up with $\sum_{j} j^2p_{X|Y}(j|k)^2$
Pen
bump
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anyone?
@cosmic marten Has your question been resolved?
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Guys, how am i supposed to do this if i don’t know the total number of households in the whole Arka?
i don't think it matters, it's a big number
(this is a binomial question - how many houses there are in total doesn't matter)
Ooooohh
Okayyy thank you so much
Thank you so muchh!
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i found found the derivative of f(x) which i got as -8cos(2x) and then set that equal to zero and got pi/2 and 3pi/2 and im not sure why it’s wrong! please help if u can
Show your equations
Cause you don’t get pi/2 and 3pi/2 solving that equation
@sleek gale
NVM I GOT IT I WAS SETTING COS X= 0 when it was COS 2X=0 so 2X is equal to pi/2 and 3pi/2
THANK YOU THO
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There are 3 solutions between pi/2 and 2pi
And pi/4 is not one of them
i got 3pi/4,5pi/4, and 7pi/4! does that sound right?
Yeah
That is correct
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Please help to me find out the correct limits, i just can't figure out how this limit work
wich one ?
is this a test or graded assignment?
We have to check which one is correct
It's a quiz with 22 questions and this is one of them
is it graded though?
yep
It requires us to finish in 50 minutes and other 21 questions just beyond my knowledge
Isn't this cheating then..?
i submitted it yesterday but i still dont know how to do this question
i wish i wasn't asian
I'm asian too
So in the first limit
sinx/x will go to 0
can you see why
yes
Substitute 0 in that equation
Sinx/x i mean
It's 0/0 approaching
He asked for zero, right?
no?
My bad
np
Okay I got it
In 1 st one sinx/x will 1, right?
I am solving the limit after 1 yr lol, but it was easy, not that difficult
no, its 1 when x approaches ZERO but here its approaching INFINITY
,w limit sinx/x as x approaches infinity
i think that -1/x< sinx/x < 1/x and when x approach inf, lim of -1/x and 1/x will be 0 and so sinx/x will approach 0 as well
You know L'Hopital?
yea
another way you can think is that
-1< sinx < 1
yep
Ohh ok
yea so you can use that on the second term in the first question
$$ \frac{ a + 6^x}{3- 9^x} $$
TheBlueMoonVampire257
in this I mean
oh so when x approach inf of like (a)^x with 0<a<1 then it will approach 0 as well
but we don't have a^x here
we have 6^x
and 9^x
which are >1
so it's (6/9)^x and 6/9 <1
so they blow up to infinity
ohh you mean like tht
I see
yea you could do that
since a<<<<6^x
and same for the denominator
(so neglect the finite terms)
so the prob becomes (6/9)^x as xgoes to inf
and we get 0
ok and how about the 2nd one
to evaluate we write it as e^( log ( lim ..... ) )
then
e^( lim( log(.....) ) )
since log is continuous
??
bro you here?
yeah but i dont get it
do you know that $$ x = e^{lnx} $$
TheBlueMoonVampire257
?
yep
oh i get it
after that we use L'HOSPITAL and the function will approach -1 so it will approach e^-1 right ?
yea
Idk if it will be -1
you should evaluate tht
the next two problem also use this
sorry I can't walk you through it, I'm working on another problem
You can ping me though
ok thank you for this helpful method, i have already sovled other questions with it <333
Have you done all of them?
yea
!done
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@vagrant surge Has your question been resolved?
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Circle the letters of the statements that are true for the implicit form of curve representation.
A. In many cases, the conversion to the explicit form is not possible.
B. Conversion to the explicit form is always possible.
C. Describe by so-called coordinate functions. ´
D. we make the function in y = f(x) form.
E. A closed shape can be created
yep, that looks all correct
I'm not sure what they mean by "coordinate functions"
but yeah, implicit equations are in the form $f(x, y) = k$ for some $k \in \mathbb R$
or $f(r, \theta) = k$, you get the idea
south's secret twin brother
uhum
i think about coordinante functions
they meant this
that we have (x, y) given
"given"
anyway
thanks for the help
yeah I'd say it's true
implicit functions can be described in terms of x and y
they are not always described in x and y though, for instance, r and theta
the wording of option C has a slight issue
so it's ambiguous
if you justify your reasoning well enough a good teacher should give you credit
I'm hoping me and your teacher are on the same brainwave
lol
I mean actually r and theta can be also coordinate functions, in polar coordinates
I don't see the issue then
can this mean anything else, that would make this false?
it's just maths terminology
coordinates can be any system, not just Cartesian
if we say the coordinate axes though, we mean Cartesian coordinates
implicit curves can be described by coordinate-functions
yep that's correct
or are described is more accurate
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This is transform methods
I dont understand exactly but i think we know that a0 = 1 and rest of a = 0 right, considering the input signal?
Are u talking about the sequence in the picture?
yes
why do u have 0 in third position ?
isnt a1 = 0?
ok but then shouldnt 5th also be 1 then?
yes
actually they are all 1
but important
we agree that (an) = (a0, a1, a2, ...) right ?
mm
mm= yes ?
oh my bad
i didnt read well
i thought they added the terms of An till A0
so it is because, when A0 doesnt appear anymore, the value will always be 0 since A0 was the only terms wich was not equal to 0
I understand why 1th, 2th and 4th are 1 because a0 is there but i dont understand 3th where there is only a1?
why though? shouldnt then for example a2 equalt 1 (the 5th index)?
if u agree with this, then A2 = 0
u see ?
isnt this the output when the entry is (an) ?
here i talked about the 3rd term in the output
and sorry i have to leave
ill not be back soon too
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why arent my lambdas cancelling out??
lambdas *?
yeah my fsult
🤓
determinants?
yeah
.
That would give you a -8x
I am trying to say that
To open the determinants
We take a11 * smaller det - a12 * smaller det + a13 * smaller det
So the -(-4) = +4
thats why you are doing
(5-x)(-6-x) - (5)(-6)
is everything after that - (5)(-6) also -
ill rewrite it out
in one line
and see
at the bottom i still dont understand where the 4 becomes positive
im reading this
see they mul -1 to b1
yeah now it all makes sense
i didnt know that was a thing at all
do they just take that into account when they do the sum?
e.g
horrible quality
in this example, different question
so they just dont show that?
its how its defined
Determinants are the scalar quantity obtained by the addition of products of the elements of a square matrix according to a prescribed rule.
have a read here maybe
yeah i get it now
these examples confused me since they never mention that at all
when i write it out, should i do it like the example i sent or factor in the fact im doing -a2
right here shouldnt the second red arrow be a +?
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@regal hollow Has your question been resolved?
Yeah it should lol
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Here, there is something wrong, and I don’t know what it is. If I replace -4 at the beginning of the inequality...
Here are the conditions that the root inequality must meet to avoid being negative (working in the real numbers)
There are no real solutions to the first inequality
I can’t see how to prove that conclusion
Break your first line into two cases, x>0 and x<0.
You already kinda arrived at a contradiction with the x>0 case.
this one?
If x>0, this work arrives at x<0 at the last line, a contradiction
If x<0, you'll arrive at a contradiction sooner with much fewer steps
thank you 😇
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not too sure how u do this
sister sage?
how is s5 going?
do you know about tree diagrams?
as it is randomly selected im gonna assume its 50-50 that its first-class or second-class
what is s5
yes i do
refernce to a series lol
use that maybe
^
how will that help to draw it tho
you can start with 2 branches
each having 1/2 chance
sorry for late reply
@obtuse orbit
i dont think the question is right
if u work backwards you realise its not 50-50
its 60-40, but the only way of knowing that is from the answer
@obtuse orbit Has your question been resolved?
im not sure how to start the tree diagram
^
But this time one has 6/10 whole other is 4/10
@obtuse orbit Has your question been resolved?
ohh i see
yea i should be able to do it now
ty
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Good afternoon, I'm writing a paper for IEEE and I'm having trouble for writing a sum notation. I have v_d and h={-5, +7, -11, +13} and I want to write v_d as the sumation of v_h in such interval, hopefully it can be understood
do you want (-5) + (+7) + (-11) + (+13) but in sum notation?
v_d=sumation of v_h in the interval h={-5, +7, -11, +13}
i want v_-5 + v_+7 + v_-11 + v_+13 in sum notation
rbit
okay, seems good
so instead of providing a range for i, you specify it as all the elements of a set instead
thanks!
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Hi ! I need help with this exercise. I’ve spent time on it but I still don’t see how to start.
I tried, unsuccessfully, to find an upper bound for (a_n), and I also tried using the following relation:
[
a_{n+1} = a_n \cdot \left(\frac{u_{n + 1}}{u_n(1 + u_{n+1})}\right)
]
Let ((u_n)) be a sequence of positive terms. For ( n \in \mathbb{N} ), we set:
[
a_n = \frac{u_n}{(1 + u_0) \cdot (1 + u_1) \cdot \ldots \cdot (1 + u_n)}
]
Show that the series ( \sum a_n ) converges and that:
[
\sum a_n \leq 1
]
@reef slate Has your question been resolved?
<@&286206848099549185> 
Yea
👋 Hi !
Tell me the problem
Can we talk in dms
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Can you have a basis of nullA [0 0 0] ?
Please don't occupy multiple help channels.
Or is [0 0 0] dependant, therefore not in a basis so its basically emptyset
@green scarab Has your question been resolved?
The zero vector never forms a basis
Are you guys not contradicting eachother rn? @mental trail @south tundra
Not sure
Anyway, {0} is not linearly independent since 1*0 = 0 and 1 =/= 0, so you can't have that as a basis
Okay then let say im finding the basis of a nullspace
I get the trivial solution with no free variabeles, x1 = x2 = x3 = 0
Will my basis be emptyset
Yeah
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✅
The empty set
What is this then
Does this say empty set
I'd assume they meant the empty set by empty basis
Which is weird since they stated the opposite before
Do i need to write the o with a line between it
Anyway the basis of {0} is {}
$\emptyset$ is the basis, yes
A Loner Bean
A Loner Bean
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I am confused by these steps
Were trying to write A as LU
so for the second one
they did R_3-2R_2
that means for the L matrix we'd do the inverse
we'd add 2 times row 2 to row 3
but why is entry (3,1) = 1?
shouldnt that be 5
2*2 + 1 = 5
how come they didn't apply the operation to that column?
got this but it’s wrong
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How do I find the derivative of xabs(x)?
hint: $|x| = \sqrt{x^2}$
Astar777
So, f(x) is now equal to x^2?
Should I now apply the power rule?
how
what, no
ekaborate pls
$\sqrt{x^2} \ne x$
Astar777
oh yes, because its the principal root meaning it must be 0 or greater
what you have now is $f(x) = x\cdot\sqrt{x^2}$
I'm assuming from here apply product rule?
Astar777
differentiate this (product rule)
x/2sqrt(x) + sqrt(x)?
no
how x
because the derivative of sqrt(x^2) is 1
said who
what is it then
$f'(x) = \sqrt{x^2} + x \cdot \frac{1}{2\sqrt{x^2}} \cdot 2x$
Wait, does this derivative of sqrt(x^2) require the chain rule?
Astar777
I havent learned that yet lol
you havent learned chain rule?
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How do I do this?
plugging in 1 for x works, so start by factoring out (x-1)
Factor
Why would I just randomly plug in 1, tho?
Isn’t there a different way of doing it?
How?
rational root theorem
Figure out what two numbers add to -3 and multiply to 2
with a cubic there's either 1 real root and 2 imaginaries or 3 real roots
Isn’t there also a way to do this using Pascal’s triangle?
Or am I thinking of smth else?
This is the easiest
TIL Fibonacci's first and middle name
is his name even fibonacci?
iirc its a made up name (short for filius bonacci)
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Hello I need some help with sketching rational functions
My main problem is the sign chart
And the type of asymptote.
But it would be really helpful if someone could confirm my answers
For the sign chart I know im supposed to factor the rational functions but I'm really bad at it.
Factor it to get the numbers for the bottom of the sign chart
y = 2 is a horizontal asymptote
so the points to test are the horizontal asymptote, x = -2, and the root at x = 2
you want to test one point from each region:
- x < -2
- -2 < x < 2
- 2 < x
so testing the signs of x = -3, 0, 3 for example will work
also your asymptote form is wrong
$y = \frac{2x + 4 - 8}{x + 2} = 2 - \frac{8}{x + 2}$
south's secret twin brother
Did i do the synthetic division wrong? Where do I get that?
so yep, bring the 2 down
then 2 * -2 = -4
add that to the -4 on the top row and you get -8
so the quotient is 2 and the remainder is -8, hence it's this
I'm confused on the sign chart. The sign chart my professor wants us to use is usually a line containing multiple signs (+ or -) showing if they flip at certain points. I can give an example of what one looks like
I know what it looks like
read this again: where are you stuck?
I'm stuck because I don't know where you are getting the -2 and 2s from and inequalities. I never had to use them when splving
those are what the question asks when they say "test point(s)"
the sign of the function changes at the roots, by definition of what a root is
the sign can also change before and after a vertical asymptote
But what about the sign chart itself? Like what numbers to I write there and the sign changes?
They usually look like this
Just to confirm we have the same idea
My professors way (which i have to do) i have to factor the original linear function and use the numbers to put on the bottom of the sign chart. I'm confused on how to factor that problem and how to create the sign chart. Idk if there's supposed to be numbers on the top too
well, so you're talking about the roots then
to find the roots of a polynomial, you have to factor it
the issue here is that this is a rational function and not a polynomial
so the process of finding the roots is to set the numerator equal to 0
2x - 4 = 0, x = 2 like you did
sometimes the numerator can be a polynomial, like a quadratic or even cubic, so yes you would have to factor the numerator in that case
here is a sign diagram for another rational function
this shows how you need to consider the asymptote as well
in addition to all the roots
I don't know why what I said isn't entering your brain
roots: x = 2
asymptotes: x = -2
white circles on the sign chart: -2 and 2
Sorry I'm a little slow. What about the signs themselves? Do they change from positive to negative or what do they start as or end?
that's why you have to test values in each region to know
you want to test one point from each region:
- x < -2
- -2 < x < 2
- 2 < x
so testing the signs of x = -3, 0, 3 for example will work
What do you mean by test them?
Do it substitute those values for x?
I still don't understand the inequality signs because those aren't used on the sign chart
yes
so what I mean by 'regions' are the parts between the white dots, and also like away from them as well
imagine that -infinity exists
so between -infinity and -2 for example
so in the region x < -2, they have tested x = -4
Ohhh so I test a point between each
yessss
So i tested -10 and got 3 which is positive so it starts positive im assuming
yes that's correct
So is this what it's supposed to look like?
And how do I know if open or closed circles?
open circles just mean the function doesn't exist at x = -2 and x = 2
Ah ok
yeah, your sign diagram is now correct!
you could have saved yourself some trouble actually
Tysm!
cause you don't need to test the region -2 < x < 2 twice
yeah so your graph is correct then
it's easy to see the shape for (ax + b)/(cx + d)
when you have anything harder then you really need the sign diagram
Mm ok
np!
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Am i doing problem number 45 correctly? Something seems off
just to be clear for that third line is product rule
but i had to move it doen since i didnt have enough space
am sorry
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@dire radish seems fine to me
or maybe you can just break the ln[(x^2+2)^2(x^4+4)^4] using
$\ln(ab)=\ln(a)+\ln(b)$
yajat
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Is my answers correct?
the domain is just $(-\infty, -9/2) \cup (-9/2, \infty)$
south's secret twin brother
that's a fancy way of saying $x \ne -9/2$
south's secret twin brother
np!
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for c, d, and f conditions in the image. I don't know how these are graphable? if there are two f(f(x)) as x approaches -1 how does it approach from both sides to -inifnity and infinity. For the f what should i even do to address this?
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what to do next
<@&286206848099549185>
Next, you need to solve for $k$ by factoring or completing the square for the equation $k²+k+2$.
JustYourAverageDude
@compact gulch
Okay but then how does that help us?
,w k^2 + k+2
If $k^2 + k + 2 \neq 0$, the matrix has a non-zero determinant, meaning it's non-singular (invertible).
JustYourAverageDude
true but like how do I show that its not = 0
using discriminant
Use the discriminant: $\Delta = b^2 - 4ac$. For $k^2 + k + 2$, $\Delta = 1^2 - 4(1)(2) = 1 - 8 = -7$. Since the discriminant is negative, there are no real solutions, so $k^2 + k + 2 \neq 0$ for all real $k$. Thus, the matrix is non-singular.
JustYourAverageDude
np
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How do I factorize this and solve for the value of x? With the extra variable x on the farthest right, I don't know how to solve this.
