#help-39
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Ok one sec
Given these functions and limits, I've shaded the area I'm looking for, how do I determine what k is and how do I know if I need to use it
I'm following
The volume of this washer is π(outer radius - inner radius)²(thickness)
Ok so since it is going around the x-axis, k is 0?
Hold on gimme a sec I think I'm fucking up the volume
π((outer radius)² - (inner radius)²)(thickness)
If the axis of revolution is not on an axis, you want to subtract the axis of revolution from the equation that determines each radius.
Do you agree that that's the volume of a washer?
Yes it is(given an integral from a to b is in there)
Well, we're just looking at a single infinitely thin washer
So we're not integrating rn
Ok
Using the graph for help, what's the outer radius of a general washer?
And what's the inner radius?
The outer radius be the function furthest from the axis of revolution, so 2x+1, and the inner radius would be x+1
Yep
And since the thickness is dx, you can find the volume of a general washer
Then you can add them all up, which is equivalent to integrating
Right, but my question was when to use k and how to determine it, granted my example has k as 0 so my bad
Well, just follow the basic principle of finding the outer and inner radii of a washer using geometry
If the axis of rotation isn't on a coordinate axis, then the equation for the radii will be different as well
Ok, I think @leaden wadi explained it well. So if the axis of revolution was x=-1, I would subtract -1 from both functions right?
Making it (2x+2)^2-(x+2)^2, yes?
If the axis of rotation was x = -1, then each of the radii would be increased by 1, which is equivalent to subtracting -1, yes
Ok thanks. And sorry about earlier legit thought I was in an unoccupied channel.
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I'm not a fan of the whole "just remember you should subtract k from the radii." I much prefer the intuitive geometric interpretation. Whatever works for you though
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Use implicit differentiation to find y’. I’ve tried using product rule and chain but I keep getting stuck. Thanks
@inland thicket Has your question been resolved?
<@&286206848099549185>
Show your work @inland thicket
,rotate
The RHS is correct
But you should be multiplying sec²(xy) by the derivative of xy, not just y
Wouldn’t the derivative of xy just be 1 and then put (dy/dx)?
1(y)+(x)(dy/dx)?
Yes
?
sec²(xy) is multiplying the entirety of y + xy', not just the first part
Also, the y just disappeared between steps 1 and 2
So sec^2xy(y+xy’)
Yes
Then how do you get the y’ out from the sec?
It's not in the sec
You have sec²(xy)(y + xy')
The y + xy' is not in the sec
It's just being multiplied by sec²xy
Sorry. I meant to ask how do you get the y’s on one side?
Start by distributing, probably
The secant to the y and xy’?
Got it. Thank you. Do you mind helping with one more please?
Maybe. Depends on the question
Find the points at which the graph x^2 +2y^2 -4y-6=0 has a horizontal tangent line
What have you tried
I found the derivative which I believe is (-2x)/(4y-4)
Then I set it to zero to find the horizontal and wasn’t sure how to go from there
Rotate
,rotate
Well, if a/b = 0, what does that tell you about a or b
It’s 0. But how did you know that from the function?
What's 0?
A or b
a=0
-2x=0 so x=0
Yep
And you can use the original equation to find y
And then you have the point(s)
So 4y-4=0? So y=1? So (0,1) is the point?
Where'd the 2y² go
plug 0 into the original function?
For x, yes
Why not the derivative?
Let's say you're given f(x) and you want to find the point where x = 2
To find y, you find f(2), right?
You don't calculate f'(2)
That just tells you the slope
We don't want the slope, we already know it's 0
We want the y value at the point
Ok. Gotcha. I got y=0 and 2
2(y+1)(y-3)=0. Is this what you get?
Yep
Am I just being dumb? 1 and 6?
No
If 2(y + 1)(y - 3) is 0, what does that tell you
Remember that if ab = 0, then either a = 0 or b = 0
Y=-1,3?
(0,-1),(0,3)
Yep
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how is rank[A|b] and rank[A] different?
one is the rank of an augmented matrix, the other is the rank of a coefficient matrix?
i mean, why can they be different
because [A|b] has an extra column
if A is a 3x3 matrix, then [A|b] is a 3x4 matrix
consistent only apply with augumented matrix, right?
yes
consistent refers to the original system of linear equations you're trying to solve
so it only makes sense in the context of having the system
every matrix can be thought of as an augmented matrix
but
without a system of equations you're trying to solve
there's no concept of consistency
Why is the augumented matrix's rank =3 ?
oh, does the b column also count towards the rank
an augmented matrix is just a matrix
you can ignore the bar
so yes your conclusion is correct
for any matrix (augmented or not) the rank is equal to the pivots in the reduced row echelon form
although personally i reckon that's the worst way to think about rank
but why is the augumented matrix rank = 3?
if we do r3 - 2r2, wouldnt r3 be 0 0 0 ?
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Okay so I've been having issues with something. I can't seem to figure it out.
A venn diagram type question
The question goes as follows: 50 people were asked whether they can paint or sew, 13 of them said they could paint and 14 said they could sew. 6 of them said they could do both
How many of them cannot paint or sew.
Now I've tried multiple ways by placing the remaining people as the answers but can't figure it out.
33, I tried that method yet it kept saying it was incorrect.
Okay, i forgot it was a venn diagram
Yea i didnt read the last party of the question, sry lads
So 17? Apparently they're asking for the number of people who cannot either sew or paint.
Out of the 50.
Yea, i bet 17
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✅
Okay so new issue-
It asks that 40 people if they can knit or sew.
11 of them said they could knit and 14 said they could sew. 9 of the people who CAN KNIT said they could also sew.
How many people can neither knit nor sew.
since this is a venn diagram, it's a harder issue.
Being the 9 is removed from the 11.
@queen ember Has your question been resolved?
<@&286206848099549185> I was told to ping and all. Sorry for the ping!
I tried multiple methods but couldn't solve it.
@queen ember Has your question been resolved?
have you tried using the inclusion exclusion principle
I have, the one to include and remove from one or the one they added to have the number for both.
I just dunno how to answer it.
just subtract the cardinality of the union of both sets from the cardinality of the finite universal set (40). if S is the set ofd people who can sew and K of people who can knit, then the question can just be rephrased as
|(K∪S)`|= |K' ∩ S'| ( De morgans law)
= |U-K ∩ U-S| ( Removing the complement)
= |U-(K∪S)| (Distributive property)
= |U| - |K∪S| (K∪S is a subset of U)
= 40 - |K∪S|
should be correct rite
hmm
probably
the answer is 24 right?
It it, holy hell it was more complicated than I thought-
Thank you so much.
Rather, more simply K∪S = People who can EITHER sew or knit so |K∪S| is the number of people who can either sew or knit. the total number of people is 40
so people who can do NEITHER = total - people who can do EITHER = 40 -|K∪S|
lol no problem
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I'm supposed to find (f^-1)'(1) and i have been trying to get the inverse, i've tried online calculators but they dont make sense and i don't really know what the (1) means and how i would use it, the book i have only confuses me more, basically how do i find the inverse in this case and what is (f^-1)'(1)?
I’ve never seen that notation, I’m guessing it can mean 1 of 2 things, multiply the function by 1, which seems pointless, or find the inverse of 1 which sounds more likely, so I’d guess it’s that
@ocean cobalt Has your question been resolved?
this is the only thing i've found in the book thats similar
<@&286206848099549185>
@ocean cobalt Has your question been resolved?
@ocean cobalt Has your question been resolved?
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Would someone mind looking this over?
.close
?
See #❓how-to-get-help 🙂
@dawn ermine Has your question been resolved?
Helloooooooo? 🙂
@dawn ermine Has your question been resolved?
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okay whats your calculation?
How is -1 wrong
Cuz
q’x= f’g-g’f
q(5)= -1(3)-0(6)/3^2
wait
Oh i used the /3 from last time instead of 9
Nevermind
It would be -1/3
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why did the sum start at 1
we needed to make the general power (n + s - 1)
so made n= n - 1
some of those look like m's but it's hard for me to read
this is an n?
yeah
what are we trying to do here with the sums
lol ok
i think there arent any ms
just long tailed ns
if you shift the index
you gotta shift everything
including the a_n
so this is frobenius method
yeah okay
the a_n hasnt been shifted properly
the way you can think about it is
just think about the first term in the sum
yeah i forgot the n-1
so when n starts from n=0
the first term is a_0 x^s right
so then if you want to keep the same sum but reindex
yeah
and n starts from n=1
then you gotta have a_(1-1) x^(1 + s - 1)
for the first term
anyway if you want to know why we do the reindexing
its so that you can put the same powers of x together
and that means you can combine the coefficients across the different sums
what do you mean
wait
since we changed n to n-1
A becomes a_n-1
to make a be a_0
the sum index n=1 ?
okay i think i get it
the starting term will tell you everything
so yes originally n=0 so a_n = a_0
now n=1 so we need a_(n-1) = a_0
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where do i start for a problem like this
do you know when a function is continuous at some point?
not sure how to find that just with a set of equations
it's not set of equations, just piecewise definition of the function
Can you examine sided limits at x = 0?
I mean
am i supposed to plug in x as 0 for them?
$$\lim_{x \to 0^+} f(x)$$
$$\lim_{x \to 0^-} f(x)$$
Modus
basically, but you need to take a suitable formula
ok so should i be using x as it approaches from the left for the top
ye
so the answer would be the lim=5 for the top right
good
and then for the bottom its 0
so it shows its discontinuous bc the limits are different?
yeah
ok that makes sense
nope, since f(0) isn't 0 (it's not equal to the limit from the right)
should i be using the top or bottom equation to derive that f(0) isnt 0
top, because it tells x is less or equal 0
when the another says x is only greater than 0
so in that scenario always use the one that has an equal part to the inequality sign?
Modus
Hence function is continuous from the left
ok so we know that its not continuous at 0 and at 5 right
or am i wrong about the 5 part
why it's not continuous at 5
because the lim for the top part =5 but not for the bottom at f(0) or is that wrong
the neighborhood of the point x = 5 is included in formula at the bottom
we don't need to analyze top part
or even we can't
ok so then we only know its discontious at 0
yep
remember that it's continuous from the left at x = 0
@jaunty needle Has your question been resolved?
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For each $a, b, c \in \mathbb{R}$, prove that:
$a^3 + b^3 + c^3 - 3abc = (a + b + c) * (a^2 + b^2 + c^2 - ab - bc - ca).$
how ?
I had to solve a similar problem a few hours ago. Due to the help of somebody here, I figured out that I gotta bring terms together in order to form structures like x^3 - y^3 or x^3 + y^3 etc, which can be further simplified. But in this problem, I have really no idea how to group terms together.
do you know how to multiply polynomials
Multiplying Polynomials
Practice this lesson yourself on KhanAcademy.org right now:
https://www.khanacademy.org/math/algebra2/polynomial_and_rational/polynomial_tutorial/e/multiplying_polynomials?utm_source=YT&utm_medium=Desc&utm_campaign=AlgebraII
Watch the next lesson: https://www.khanacademy.org/math/algebra2/polynomial_and_rational/polyno...
Yes.
But if I multiply the right-hand-side of the equal sign, I'd have 18 different terms.
That's why I try to find another way of solving it.
fair enough
@midnight haven Has your question been resolved?
@midnight haven Has your question been resolved?
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Why is this not being accepted?
not quite the answer
what is 4 - 1/2?
wait I'm ture
*tired
have you tried submitting it as $-2y^{\frac{7}{2}}$?
MellowDramaLlama
maybe they want it in that form
it says entire radical it should be correct tbh
cant submit it as this since its asking for an entire radical
try
$-\sqrt{4y^7}$
imagine
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gg
i need help understanding venn diagrams if someone could help me that would be great
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is it possible to find the n+1's complement of a number of base n
for example the 11's complement of a base 10 number
I found my answer sorry for disturbing
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F(x) = x + cosx, find (f^-1)'(1)
let's see your work dawg
I'm just baffled at how to even start ngl
I just need 1 example, and I can probably figure it out from there
I'm currently also trying to find a yt video to help
@wicked yacht Has your question been resolved?
This is called the inverse function theorem
Basically, doing this:
Let g(x) be the inverse of x + cos(x). We want the derivative of g(x).
f(x) = x + cos(x)
x = g(x + cos(x))
Take the derivative of both sides, remembering to use chain rule on the right:
1 = g'(x + cos(x)) • (1 - sin(x))
Sub some value of x that gives a g'(1), then solve for it
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Help
What is happening
<@&286206848099549185>
Nobody
It’s crazy how 3 questions take hours to get help for In this server
<@&286206848099549185>
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do you know the formula for the defintion of a derivative
1/sqrt(x)+h
oh
u have to replace the x with x+h
yeah
ok
try it with that?
let me try doing now
could wait around for a sec
ill just try rq
ok am at sqrt(x) - sqrt(x+h)/h * sqrt(x+h)*sqrt(x) not sure how to continue
writing math stuff on discord is a pain lmao
honestly lmaoo
can you send me ur working to how you got there
just click a picture
it would probably be easier
ok
im on computer
so photo booth
😄
half of it is from the past
@jaunty oar ya still there
yeah 1 sec im tryna simplify it
k
how did u get h in the numerator im confused
how did u get h in the numerator
thinking
1s
yea not sure
teacher does it that way
like that type of way
in those circumstances
wherer
ohh
my bad
ok then 1 sec 😭
lemme try to solve it from the start
ok
end of book answers says f'(1/4)=-4
just wanna know how to get to there
like get the derivetive
lets go bro i was on this problem for an hour
yeah i got it
klemme send pic
i didnt write lim everywhere but u get it
@wary dragon
u had to rationalize
sorry fr taking so long 💀
send graph f
i dont have no graph
ill just post this again
Does it mean the limit definition?
$\lim_{h \to 0} \frac{\frac{1}{\sqrt{x + h}} - \frac{1}{\sqrt{x}}}{h}$
Olly
this is correct
with the thing i found
@wary dragon
it works with the derivative we found wdym
wdym otherway
yeah
alright
alr
$\frac{\frac{\sqrt{x}-\sqrt{x+h}}{\sqrt{x}\sqrt{x+h}}}{h}:=:\frac{\sqrt{x}-\sqrt{x+h}}{h\sqrt{x}\sqrt{x+h}}$
imagine
did you get it or should i explain
yea i got
alr cool
it will
in the denominator
kk
oh right
plug in a value for x and u will find the slop at that point
yeah
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does this type of cone always have a radius of 1 ?
Cones can have different lengths of radii
mhm, so basically if you get this function, it is a cone shape but you don't know how long the distance from the centre to the outer point is?
I guess?
I mean it's true regardless of the height
All it would really affect it height and slant height
what is true regardless of the height? and sorry this question is really out of context
i can send you the question i am applying it to if you want but i think what you have said is helpful
thats ok i appreciate the help!
I mean you don't have a range for the values, so it's just a never ending cone
yeah thats what i was thinking but i wasn't sure
You're right
A cone is just a lot of circles with increasing radii put on top of each other
Not sure if this helps, just another way to look at it
tysm no that is really helpful
i might send my questions for reference
but they are a huge mess tbh
2 and 3 are the issues for me
i think i have the info i need tbh. tysm
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Hey
Ohh @junior pawn sorry but the channel got taken by few seconds
Ok
So I’m doing precalc and we have a f(x) equation that goes like this g(x)=(x-3)/(x+2)
And the x to put in is (x+h)
I am currently on e
So you put (x+h) in place of x in g(x)
Yeah I did that for the normal numbers
So you get $g(x)=\frac {x+h-3}{x+h+2}$
Deep.
I’m on my last check for this problem but I want to make sure it’s a normal X and not x^2
Yeah you were right
Thanks
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No problem 
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Im having trouble finding these 2
Is it asking for an exact value?
no. also I figured out the first question. I only need help wiht 7
the answers should be fractions
@echo flint annything?
im sorry my man i havent done this stuff in a long time im not a helper
alright
ping them theyll be able to help u better
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why do u say that
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In Rudin's book there is statement that segment (a,b) is not open if we regard it as subset of R^2 but it is open subset of R^1... can someone explain why it is not open in R^2
open means the tiny neighborhood around every point is still in the set
in R2 the neighborhood is a tiny circle that goes above and below the 1d line segment
it looks the same, just a line, like {all the points (x,0) for 0<x<3}
here's the picture
okie okie
now I understand
i have another question also
is phi (empty set) a point of Z.
?
not sure what phi means in rudin
empty set
in R? sure
in R^2
still closed yea
how?
closed set is if every limit point of E is point of E
but Z has no limit point so
in math that counts as true
since there's no limits points that break the rule it counts as closed
okieee
i remeber a time when for me just [a,b] was closed set.. i had never thought that Z is also closed ..why it is so complicated now🥲🥲
it's like [a,a] U [b,b] U [c,c] U ... 😛
this makes it so easy to understand.. why don't they write this in books
🫠
but a union of infinitely many closed sets doesn't have to be closed
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What am I doing wrong here?
so what's the original expression?
4 1/4 * 4/6
is x a variable or a multiplication symbol?
multiplication
ok so
first of al
there is one thing you can get simple very easily
look at the first part
the
what could easily be done here?
yes yes
Multiple 4x4+1?
nno, not plus
its a fraction
is 4 multiplied by 1 divided by 4
so first remember, that as it happens with additions and substractions the division is the opposite of the multiplication
so basically divisions undo multiplications to say it one way
I didnt do that with any of the other questions?
"Multiply and express improper fractions as mixed numbers"
but dont you have to multiply those fractions to get a result?
yeah, but that's incorrect
you cant do that because there is no plus symbol
there is only multiplications and divisions
hmm i see, but that's not what you did up there
Thats an example
because there it's not adding the 3 to the one or to the two for example
yes i know
2*3+1 is 7
so ok let's proceed with that technique
shows 7/2
I can show you more
Also in this video, https://www.youtube.com/watch?v=5tv4vRNQqHk&ab_channel=TheOrganicChemistryTutor
This math video tutorial explains how to multiply mixed numbers and fractions.
Subscribe:
https://www.youtube.com/channel/UCEWpbFLzoYGPfuWUMFPSaoA?sub_confirmation=1
Adding Mixed Numbers:
https://www.youtube.com/watch?v=EvYgX0wz0xY
Subtracting Mixed Numbers:
https://www.youtube.com/watch?v=CFAKElDnws8
Multiplying Mixed Numbers:
https://www.y...
But this one question is playing with me lol
ok so
umm
your sheet is not well expressed
because for that to be true it should be this:
while it's showing this
I understand, but why would it show in my pdf, and a video?
That's how hes solving it xD
well idk, but that syntax is not correct for what they are doing
they are doing a different thing than what they are expressing
ok, so let's assume that what's written in the sheet is correct
then following that, this would be correct
indeed
but
i don't really get why you are doing a square root
ah its a division
I can show you another question
ok go ahead
But the one I solved before isnt simplified enough
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7 couples are sitting in a circle, Each Partner must sit exactly across from each other in the circle. John Cannot sit with Mary. How many sequences can this be done?
Im not sure if I am doing it right but I drew a circle and set John as the reference point
then theres 12 options for whoever sits next to John because it cant be mary or his partner and 11 on his other side
then just fill in the rest of the number
Heres what I got
12x11x11x10x9x8x1^7
1^7 is because half are partners which only has 1 spot for them since they have to be sitting exact opposite
can anyone tell me if I got this question right or if theres anything Im missing
This is Data Management class btw and its permutation unit
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why it cant be mary's partner i dont get it
oh John's not Mary's
you can say that there's 11 options for John's left but you can't tell how many is left for his right, it could be 9 or 10
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Hi
So Basically
Uhm I'm having a bit of difficult with some things
what kinda of graoh has 2 vertical asymptotes
Please ping when u respond
Generally, you get a vertical asymptote from division with zero
1/x has a vertical asymptote at x=0
1/(x+1) has an asymptote at x = -1
Sometimes you can have more than one way to make zero in the denominator
These functions might have 2 or more vertical asymptotes
E.g.
1/(x^2 + 3x - 4)
The denominator can be factored into
(x-4)*(x+1)
This expression equals zero when x = 4 or -1
So this function ends up with vertical asymptotes at x = 4 and x = -1
That should give a pretty decent hint at what kind of strategy you can follow
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Anybody using professor Leonard’s diamond method for factoring?
That's a very common method to factor
It's just a difference variation of it
Like I stated, it's a very common factoring method, it's just a variation of it
Who taught you this method? Just curious
I haven’t heard about it before.. wouldn’t say it’s a very common factoring method imo
only heard of box and cross method
It's common
There are many different names to it
X box method, AC factoring method, etc
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yo
what do u think it is
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help
help this man
@grand birch wouldnt it be the opposite of points?
since it's inverse
i think u'd just flip the points, ex. (-6, 0) would be (0,-6) as an inverse
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What is the purpose of the absolute value around z? Why couldn’t it just be z^2?
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hello is this the correct answer here?
somebody told me it was wrong and i'm not sure why
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am i doing it right? it says to square the expression
what are the exact instructions
word for word,
only the first 4 are expressions,
and if you were indeed asked to just square the expression, you shouldn't be setting those to 0
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Hello can someone help me with this factorisation
(2b+3)(-12b+5)+12(2b+3)=(2b+3)(...)
And tell me the way please thank you
have u tried anything?
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shouldnt we take the square root to get r?
since r^2 = 2rcostheta
so wouldnt r be the square root of the RHS expression instead?
u can divide both sides by r
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some explain
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.reopen
eh
✅
don’t close and open
ok
also what do you not understand
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can someone help me solve this?
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Hello! Is it possible to create "digital" functions? For example, a function that equals 1 when the variable x has a decimal point and 0 when it does not, etc. And if yes, could you provide an example?
indicator functions are functions that are equal to 1 when the input is in a certain set and 0 when they aren't
so you could have an indicator function for the set of non-integers
do you know how to construct piecewise functions?
No, i dont. Im relatively new to math
something like this
you can also put an "if" after the comma, maybe that makes it more clear
the top line basically just says that its a real function (you can plug in any real number) and that it outputs either 1 or 0
And what does the \ do?
you know R and Z yeah?
I know Z
Z is set of all integers and R is set of all real numbers
and R\Z is the set of all real numbers excluding all integers, so it only contains all the numbers with a decimal point
sometimes its also written as R-Z (as in, "minus", to show the exclusion)
And whats the difference between piecewise functions and indicator functions?
maybe this is easier
hmm for that one you might want to be a bit more familiar with set theory
basically the indicator function for a set A gives back the number 1 if x is in A and 0 if x is not in A
it is a piecewise function
the term piecewise function is a bit more general
this is a piecewise function too
its just splitting up a function into two or more cases
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How does one rewrite this
Do you remember slope intercept form?
So we're given a function that's all mixed up here, but we can change parts of it to resemble that y=mx+b form
Namely, we isolate the y variable from the rest
Mhm
I just have never been gave this type of function so I would like help with steps on how to get it to y=mx+b form
Here, let's start by moving things to the other side of the = sign to get y on its own
If we subtract 18 from both sides of the equation, we can move it to the other side
$-8x + 10y = -18$
lexitorius
And then you would divide 10?
Not quite
You could, but that wouldn't get you much closer
We still have to move the -8x term
How would we get rid of -8x and move it to the other side?
Add 8x?
Almost; the x can move with the -8 too
or 1x
lexitorius
Think of 8 and x being stuck together, if you move them with addition and subtraction then they move together
Oh ok so now you divide 10 both sides?
Exactly
y=4/5x-9/5?
$y = \frac{4}{5}x - \frac{9}{5}$
lexitorius
That's exactly what I got 👍
Just remember that when you have terms that have a number and a variable, addition and subtraction will move them around together
You'd need to use division to split them apart
Otherwise it seems like you know what you're doing, just had to get it started for you
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just asking a generalized question, but how do you know when to use u-subsution or to use uv-∫vdu
