#help-27
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hi
I dont understand something in this example
NotDyatlov
we can say that this is equal to
,tex $\lim_{x\to2}{\cos({\frac{x+2}{2}\pi})}$
and this is equal to
,tex $\cos({\frac{2+2}{2}\pi})$
there reason that we are allowed to do this is because cos(x) is continuous on its domain
but in the original functin 2 is not in the domain at all
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am i supposed to use this 2nd formula here?
yes, the second formula is the definition of the derivative f'(c)
so after i find the secant line i plug 2 in?
oh, the derivative at a specific point is not a secant but a tangent
so it is asking for the tangent when x=2?
im guessing your class just introduced the derivative, so you didnt do $f'(x)=nx^{n-1}$ if $f(x)=x^n$ yet ?
ImToxiiq
yeah we did, but im allowed to use chain rule even thought we haven't learned ityet
it's a few units down but somebody asked if we can use it and the professor said yes
wait is that chain rule
no, its not
my bad. it looked similar
you can solve the derivative of h(x) with the rule above or with the definition of the derivative. both are valid
its called power rule btw
i mean to do the derivative without the definition you need the sum rule too. i would advise against it for now if you havent covered all of that in class yet
ok
i'll try to set it up with the definition lmk if i do this right
and then i solve?
ImToxiiq
h(x) is a function that takes some x, which can be anything (in this case (c+h)) and does something to it (cubing it) then it multiplys by 1 and adds seven
wait ill make an example to show you
ok
example $g(x)=x^2$, then the derivative is $g'(c)=\frac{(c+h)^2-c^2}{h}$ because plugging $(c+h)$ into $g(x)$ gives you $(c+h)^2$
ImToxiiq
,rotate
two key points:
1.you only replace all x with (c+h),not the whole term has to be cubed
2. you cannot plug in any specific number, like 2, yet. this is only allowed at the very end, if the derivative has been calculated
in my example above, if $g(x)=x^2+1$, you would have to plug in c+h again and would get $\frac{(c+h)^2+1-(c^2+1)}{h}$
ImToxiiq
Ignore top
right, now you just have an extra +h in the middle that you dont need, and you forgot the minus sign before the second 4
i thought the 4 would be positive since it is originally -4x^3
i see the extra h error though
ok
i got h^2+14
After doing what exactly ?
Oh, please dont forget that $(a+b)^2=a^2+b^2+2ab$
ImToxiiq
oh my god
im gonna go eat im to braindead to do math rn
sorry brother i dn't wanna waste anymore of your time
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How do i start this?
do you know how to calculate the distance of r from origin?
do you know how to calculate the distance of r from (0,0,0)?
@plucky drift Has your question been resolved?
let t = lambda
r = (7 + 2t, -1 - t, 2 + 3t)
is it that?
this is a vector
not a positive real
the distances squared is $x_1^2+x_2^2+x_3^2$ where the vector is $(x_1,x_2,x_3)$
everg
now just find the minimum of the function distance(r)
it's just $sqrt(2^2+1^2+3^2)$
ether
this is the distance of (2,1,3 ) not (7 + 2t, -1 - t, 2 + 3t)
depend on what you mean for solve...
this function has no zeros ... so you have to find his minimum
i would use the derivative maybe
,w expand sqrt((7+2t)^2+(-1-t)^2+(2+3t)^2)
i just said that this function has no zeros.....
apologies
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I have to find the highest and lowest value of the function in given domain
I'm very lost when it comes to graphing the derivative of the function
I will send my "solution"
does your teacher make you find the max and min by graphing?
Nah
ok good lol
ok show ur work lemme see lolz
in (0,1) are both incrising function ... so have the min in x=0
Lemme write it on the whiteboard for better clarity
in (-3,0) are both incrising function ...so the product is incrising right? so have the min in x=-3
everg go to the available channels!!
like literally the section "available channels" sorry that sounded rude
I'm too new to use latex in here
lol
slapppoo ... i just answered to the question of this channel ...
i didn't ask any new question
I accept your apology
I could explain what steps I take
oh sorry everg
So basically from what I remember from class
We first calculate f(-3) and f(1) (not sure why even)
ok let's stop there
the reason you do that is in the case the endpoints of your interval are actually the lowest or highest part in the function
otherwise, as you know, they'll be at critical numbers
ok keep going
because an incrising function f in the domain [a,b] has the maximum and minimum in a and b
Then we get the f'(x)
I'd distribute the x first btw easier to derive
If I did it right it would be f'(x) = 32 + 4x^3
yes
now your function its everywhere increasing
So I got 0 and x^2 = -8 which is (idk the english word but not right)
you were close
Oh shit
RIGHT
It's fine then lmfao
So we have x=0 v x=-8
Then we draw the function on a graph
not quite
aw gl!!
ok
So I have something like this
The dots marking that the domain is closed on both ends
Now the -2 and 0 are in the domain so the graph will be a parabola
Going through -2 and 0
Upwards
And after that I have no clue what the fuck is going on
have you done 2nd derivatives/concavity
Apparently the function stops at the extreme points
that's how we do it
I think this might just be a language thing but I don't get your thought process with your graphing
but keep going
Yeah that's where it ends for me 😂
Maybe we had done 2nd derivates something in class but I just don't know without seeing
have you done increasing/decreasing using 1st derivative
Math language barrier much 🤣
ikr
Where are you from btw
what is your native language
Polish
But I use it very rarely
Aight back to the question
What do you mean by increasing/decreasing using 1st derivative
Oh
dne is does not exist or undefined
Yea yea
so you can actually set up intervals using your critical numbers
like
in your case
(-3, -2) (-2, 1)
and then you pick two x values to test in those intervals
Oh wait is it related to this
With like a table
probably!!
Yeah then we did I think
that's super useful when you have to graph a function
It's like <-3, -2>. -2, <-2, 1> right?
It would be an open thing no?
so have you done concavity?
with second derivatives?
I don't see how you avoided that one lmao
googles images
Oh
I think so?
We usually draw arrows
On the graph
Pointing if the graph is decreasing or increasing
that's not with second derivatives
do you need help with those topics or are they like
just the same thing but with different names
the absolute or relative?
what
you're doing absolute then
We call it local I think 😂
local means relative
b r u h
The smiley face stops at -3 and 1
Is there like a proper math vocabulary book in english
So I can actually talk wiht people
hmm
If you have a spare minute could you draw the graph properly
are you comfortable just calling, I'll admit this is pretty visual so screenshare might be nice
Sure
ok give me 2 seconds I gotta hop on my ipad
Take your time
@oblique gale Has your question been resolved?
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For part a, I found theta, but how do i find r?
@sage kernel Has your question been resolved?
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is this right?
what do i need to fix?\
going from y=g(x) to y=g(x/2) is a stretch by 2
in the horizontal direction obviously
also the peak should have the same height as it did pre transformation, which rn it doesnt
so like this?
you don’t half your y values
i just leave it right?
so the new graph should have the same height
but be narrower
for example, your highest point should be (1,4) not (1,2)
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. @jade sleet you still got it wrong -- you compressed the graph by 2 when you should have stretched it
oh
wait i was told to make it more narrow
right here
so who is right
me.
Nah im on crack
try graphing something like sin(x) vs. sin(x/2) in desmos
you will see sin(x/2) is stretched
i dont understand
so this is the final then
your 3rd point is not stretched enough either
how
(4,0) does not transform into (6,0)
oh its 8 my b
2*4 isn't 6
Looks good
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my bad for forgetting algebra 2 concepts lol
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I watched a video of him proving this theorem and had a question about it
so it is only linear independent if c1 to ck = 0
well, what does orthogonal mean?
linearly independent means that sum c_i v_i = 0 implies c_i=0
so is 0 vector orthogonal to 0 vector?
but he also said c1 to ck had to be 0
no
?
right?
well yes he proved that
it says "nonzero" vectors
yes it is
but where is the part he proved that c1 to ck except ci = 0?
he took sum c_iv_i=0
where
and then multiplied both sides of that by v_j
on the left only c_j v_j*v_j is left
on the right 0 is left
im confused now on what your question is
v_j*v_j is nonzero because v_j is nonzero
why are you talking about 0 vectors when the statement clearly says nonzero vectors
you are talking about 0 vectors
a set that contains the 0 vector, even a set of a single 0 vector is not linearly independent
well you do the same for all of them
or is i 1 to k?
but isn't i just 1 particular number?
well for each number you can do it separately
yes
I think I then understand it
that part of the proof which i think you are showing is just setting a linear combination of vectors equal to the 0 vector and showing that if you dot product that with each sides v_i must automatically be the 0 vector
ye and vi times vi can't be zero
so ci has to be zero
and the i of ci implies 1 to k so all c are zero
aha
so yeah to answer your original question, the set is linearly independent if and only if the only representation of the zero vector is the trivial one (all c's = 0)
i think i was confused and misread at first, i thought you were asking if the v's were equal to 0, my bad
I was also wondering about this one
he is talking about standard basis vectors
does he mean vectors with only a 1 and 0 everywhere else?
so [1, 0 ,0 ]
[0,1,0] etc
well yes thats for R3 specifically, but this is a more general statement on Rn
ah but in other dimensions
so (1,0,0...,0), (0, 1, 0...,0) ... (0,0,0...,1) etc
yes thats what is meant by standard basis
ah okay thx
any other basis which are not the standard one are called just basis right?
do u by any chance know how he got this?
do I put in in a matirx?
ye I see it it I put in matrix then row reduce it
ah
@mystic musk Has your question been resolved?
can someone explains how the matrix becomes like that
so why is it q1 * q1
so acutally why is q1^T the same as q1
do u know this too?
I think this is because it is a vector therefore the transpose is itself
but now I am wondering it says it counts for all m x n matrix but then the they won't be a vector and therefore the transpose is not itself
<@&286206848099549185>
@mystic musk Has your question been resolved?
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hey im not sure how to do this question: (the answer is (0,6))
find the tangent line equation at x = -1, 1
no just the tangent line at -1
ya but using derivative would give you slope of 8
f(-1) = -2
8(x-(-1)) + (-2)
oh wait im so stupid
-8(x-(1)) + (-2)
im dividing*
and then intersect them
Yo
@hushed hinge Has your question been resolved?
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idk what I did wrong for e)? Does anyone see where I went wrong?
@violet matrix Has your question been resolved?
that is a nightmare to go through
just ask an integral calculator
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just wanna make sure my answer is correct?
the second equation has me messed up
if x = 0 y = 4
but no line goes thru (0,4)
it’s kinda confusing
oops lol
@forest hound Look at the second segment on the graph of C
What x-value does it start at?
hmmm
Yeah
Now that I look at these, B is the only graph that's even a function lol
It's the only one that passes the vertical line test everywhere
😂i thought so
From your equation too, we can see it's supposed to switch rules at x=-2 and x=2
which B does
no problem 👍
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If there’s a - like in d and h
Like -3(pi)/4 for example
Does that mean the answer will always be negative?
cosine is negative if and only if the angle terminates in Q2 or Q3
Ok so it still depends on where it is
Right?
Ofc
@lavish canopy Has your question been resolved?
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@torpid roost Has your question been resolved?
Someone please help
@torpid roost Has your question been resolved?
@torpid roost Has your question been resolved?
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i solved it and found $\frac{1}{2}$ \
But the answer is wrong.
,w 17/36+1/2+2/8+13/18+9/27
how do you calculate median ?
wait shit
why you add all numbers ?
i did
.205, .303, .5, .702, 2.10107
.5 should be median right ?
w, calculate median of 17/36, 1/2, 2/8, 13/18. 9/27
$\frac{17}{36} , \frac{18}{36} , \frac{9}{36} , \frac{26}{36}, \frac{12}{36}$
bettim
its $\frac{17}{36}$ no?
bettim
yes but why ?
yes
you have arrange them first in ascending order then find the middle most elemnt
but i did arrange them, convert all the fractions to decimals and then arranged them from low to high
no need to convert to decimal
what then ?
...
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In the given circle, DC is a cord and BF is perp to EF and AE is perp to EF
Prove that EF || DC
Any idea how to do it??
often I think it's helpful to have a list of things you know
and maybe also a list of things that you want to find out
So we can start with AE || BF
<EBF = <AEB by alt. interior angles
hmm
@odd elbow Has your question been resolved?
Drawing out some less symmetric examples gives a bit of insight
Calling the unnamed intersection point M, we see that AMB and CMD are similar
AME and FMB also similar
From there try to prove EMF and DMC are similar
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Are the calculations circled in red correct?
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hi
half angle identity on sin^2(x) might help some
...or maybe not, on second thought
triple angle identity has a better chance
I have already tried that but lemme check again
do you just look at it?
Rare triple angle identities sighting
no way the 2 in front of cos is the same absolute value as -2 on the right is a coincidence
I tried that as well, I moved it to the rhs and then rewrite it as -2cos^2(3x/2)
by this i mean, find an x value in the cos(3x) that gives the correct sign according to the -2 on the rhs. then what happens when you plug that x value into sin(x)?
I did not get it.
btw the actual question asks for the number of answers between -pi and pi
when is 2cos(3x) = -2?
in this range for x
yeah
well x =pi/3
keep going
keep listing all the x
is it too hard to solve?
first divide by 2 on both sides
then substitute y=3x so you get cos(y) = -1
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why isn't it good enough?
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✅
I was looking for a trigonometrical way
I mean something like this: cosx=cos a or sinx = sina
is this not trig?
there's a cos
does it not get you all the answers?
but by just plugin the numbers, I didnot find any answer
either it does not have any asnwer or I have understood something wrong
that's cuz you gave up?
and didn't do this?
I did this but wherever cos3x = -1 , sinx is never equal to 0
you didn't find all the x in [-pi, pi] then
exepct for 6pi/3
2kpi /3 are all of them but only at 6kpi/3, sin is equal to 0
you missed this one
@somber shore Has your question been resolved?
I am really really sorry but could explain once again? I think I did not get it right
I did not get what should I do after pi/3
after finding all y where this is true, solve for x using y=3x
because cos(y) = cos(3x)
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Only partly correct
That's why this list is incomplete
oh because x is between -pi and pi
y can be between -3pi and 3pi
so x=-pi, -pi/3, pi/3 and pi
got it
I am just stupid ty
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why is my answer incorrect
<@&286206848099549185>
here is how they did it for a similar problem
I followed similar steps and my answer came out wrong
<@&286206848099549185>
You used a decimal and not fractions
Definitely the first issue I notice
If you’re confident that your method is correct I’ll bet it’s just that, since the question specified that you need to give your answer with integers and fractions
I’d highly Recommend solving this type of question by hand
It will give you a much better intuition than just using a formula and plugging it into a calculator
so i got the right answer but i need to type ln2*(1/3) for k? the exponent? to get an exact value?
they never said to round to 4 decimals so i wasnt sure
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when i try to solve this i keep getting the wrong answer
do i solve this by taking the <∂z/∂x, ∂z/∂y> * u ?
and then plugging in the points
no you have to use the limit definition
This is from wikipedia
f(x) is given in your problem statement
and v in this definition correspond to u in your problem
oh man i have to take the limit for this ??
so just plug everythjing in and solve that limit
yeah thats what the question says
if you need help with using this definition i can try to help
so would the limit just go to 0/0?
i havent done any work, so would you show me yours
if it is 0/0 you could use lhopital rule tho
i forgot how to do limits
so would i plug in f(x,y) + u for (f(x + hv)
or would u == 0 since h -> 0
no, just lemme show you, gimme 5
ok
I think you might have been misunderstanding the formula
you gotta remember that $f(\vec{x})=f(x,y)$
llspacebarll
its a function that takes a vector as input so you have to put the different components in the right spots like i did
for $f(\vec{x}+h\vec{v})$, recall that $\vec{x}+h\vec{v}$ is a vector in itself: in your case $\vec{x}+h\vec{v}=(3+h\cos(\pi/4),4+h\sin(\pi/4))$
llspacebarll
so then you plug those components into the function f like i did
once you get where i got, you just need to expand the squares and and try to simplify as much as you can, ideally the h's will eventually cancel out somehow and you can take the limit easily
ok im getting it now
i should be able to solve from here
thank you so much for your help
nw friend
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How would I find the domain and range from these functions
@restive river
@balmy bloom Has your question been resolved?
<@&286206848099549185>
@balmy bloom the domain of question 16 will be all real number. Because nothing can stop it
As for range
Conver f(x) into f(y) then find the domain of it. It would be the range of f(x)
Similar with question 1
y=2(x+5)²-1
It's domain will be all real numbers
For its range convert f(x) into f(y).
Thus. x=(√(y-1)/2) - 5
Now finds its domain
It will be the range of f(x)
@balmy bloom Has your question been resolved?
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hi, i need help with this problem; it was on my test today and i memorized it and wrote it down to solve later. i just didn’t really know where to start with it
and no the area was not given
can anyone help me with this?
you're given sufficient info to determine the area
i dont really know since i dont know the height
use pythagoras
what type of image should i upload?
wym hint
okay
also this channel is occupied
wdym wym hint
rotate the page a bit
label all the sides you know
until the side with 36 appears to be the base
neither is true
ohyeah
wdym by "it"
yep
and the height would be 24
dude omg
so just 36 by 24 for area
tysm i was clueless
what did you mean by use Pythagoras though
how would i use that?
im curious now
@nova idol
I realise that it was unnecessary, ramonov’s answer was much better
thanks alright
also
rq
is there like a place where i can find good formulas
like a lot of them
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Just want to check, is this correct?
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abuse of notation
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How do I identify the sides of the square or an angle, when I dont have a parallel line to reference to?
It says they're perpendicular to the x axis
The other other thing on the XY plane that's perpendicular to the x axis would be anything parallel to the y axis
I'm not sure what you mean by this?
It says that "the indicated cross sections [are] taken perpendicular to the x-axis"
So they gotta be parallel to the y axis
Well technically parallel to the y and z axis but I wouldn't worry about the technicality
If the cross sections are parallel to the y axis, then each cross section's length is gonna be the vertical distance of the region at any given instant
That is, upper function - lower function
oh its like the washer method
What if it was a rectangle?
How do I find the width
Width is just the distance. Are you talking about height?
Like its height parallel to the z axis?
No the x axis
Are you sure its just the distance?
hm
ok right
its the distance
but how do I assume the distance?
I mean sorry, find the distance?
Is it a default 1?
yes
It's basically 0, but not quite
0?
The cross section lives only on planes parallel to the YZ plane
If you add all those cross sections on those planes, you get the volume
Yeah no if you cared about volume cross sections, you're accidentally finding the 4D volume lol
lol
But those planes have nothing to do with the x axis
Other than they're "perpendicular" to the x axis
You'll learn more about this if you take multivariable calc
But in this question, why did he say that the "width" of the rectangle is 1
I get that
but why 1?
OHHH
1 is parallel to the z axis
aha
I just got what you said to me lol
ChatGPT is fucking terrifying, this mf solved it all with details
fuck it made a mistake
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how would I solve for a?
oh
f(0) = 3
f(3) = 3 + 3 + 3(3)^2 - 3^3
f(3) = 6 + 27 - 27
f(3) = 6
for secant I use y - y1 = m(x-x1)?
yup
OK so i find m using point slope form for a
how about for b?
find all points x = c (if any) on the interval (0,3) such that f'(c) = m
differentiate f, then set it equal to m found in (a)
you will have a quadratic that you can check if it has roots or not, if it does then those are your solutions
you are finding any x such that f'(x)= the gradient of the secant line in (a)
if it does (have roots) then those are your solutions
yeah, because those will be the x values where f'(x)=m
the quadratic you are solving will be f'(x)-m=0
oh and it just so happens using zero product property the solutions fall on the x-axis
so that will tell us the slope wherever y = 0
depending if there are roots are not
if there are no roots, no solutions?
and only between (but not including) x = 0 and x = 3
interval
the gist is if f'(x)-m=0 has any solution on [0,3] then yeah those will be your 'c' values
(0,3)
true
youre finding any points where f'(x)=m, if there are any
oh
what a strange question to ask.. i wonder if we would ever use it in life..
but i guess math is not about practicality, it's about logical thinking and puzzle solving
It’s def used in life
well, not all questions have to be directly applicable to life; they might identify gaps in your understanding
and understanding calculus is definitely used in life
some forms of math, maybe, but certainly not calculus
example where i need to use this in life? find all points x = c (if any) on the interval (0,3) such that f'(c) = m
For optimisation for example
the very fact that you cannot figure it out immediately by yourself shows one useful application in life -- reinforcing your knowledge of calculus
I mean learning calc is important for learning calc
,w mean value theorem
But I think that’s not really an application
but uh yeah the mean value theorem is actually used in life
well, it's intuitive, but still used in life
wait this is mean value theorem? find all points x = c (if any) on the interval (0,3) such that f'(c) = m
it literally is MVT
i thought it looked familiar..
imagine caring about applications of math 
interval and roots
it's not exactly the mean value theorem, because you're asked to exhibit the point
but the existence of the point is because of the mean value theorem
one of the funniest moments this month for me was one of my friends telling me that they were never going to need piecewise functions in their life
and then also telling me they spent money on a paid tax preparer
solid 20 minute roast session
taxes are different tho, you need to know what forms to fill, maybe there are things you don't know
extra refunds
i don't see how it relates to piecewise functions lol
is not really gonna help at the tax office
the amount of tax you pay against your taxable income is a piecewise function
lol sure, but it's not quite that simple
actually it is
no, there are other forms you can fill out
income, working from home, spouse, etc. etc.
it matters not much in the sense that you have to know how to evaluate a piecewise function, but in your decisionmaking with regards to tax avoidance
yeah that's why I said taxable income
i guess it depends on how you look at it. piecewise function (math) or "tax bracket"
no it doesn't
i mean you don't need to know this math is what I am saying
you need to know how it works
yes you do, if you're going to make certain decisions before the tax year is over to minimize your tax liability over time
for example, if you have a bunch of unrealized losses, there is a mathematical way to understand how much of those losses you should realize per year
uh no you can't
yo avid is up late
no person on planet Earth can imagine what a tax bracket is without first visualizing this piecewise math function using mathematical notation of left curly bracket { to declare each piecewise function declaration?
the mathematical notation is very easy to learn, but the underlying intuition about it is not
12:17am here, hbu?
and chances are if you can't see how piecewise functions apply to taxes in a very relevant way, you don't also get it
a different time 
i suppose you can just look at your bracket, if your income falls within it, follow that, ignore the rest
this feels a bit philosophical, how everybody must think, is a hard notion to force on the world
are you sure you even know what a tax bracket is?
tell me how much tax someone with $60000 in taxable income would pay
single filer
not enough 
60% lol
high earners get taxed a lot, believe me
so I'm not even referring to the calculation of your tax liability, because you could conceivably outsource that
but you need to know how to do that at the bare minimum to actually make decisions to reduce it
Why reduce it 
meh, most people just take it to tax firm, or use tax software. all of this math is done for them.
yeah the tax firm won't tell you what to do to reduce your liability before the tax year ends
it'll just calculate an amount you have to pay
and you pay that
lol how is this related to piecewise functions and a 20 minute roasting session?
not to mention you pay an exorbitant amount
Tbh I didn’t even know people could reduce their liability
because if you need to understand piecewise functions and the math behind them to optimally reduce your tax liability
At least in the us
only for returns that are sorta simple
for example, if you have $200,000 in unrealized capital losses, and you make $150,000 in capital gains in year 1 and $100,000 in capital gains in year 2, as well as $50,000 in ordinary income in year 1 and year 2
What do you consider “sorta simple”
ones that don't involve certain partnerships, random capital gains, possibly AMT
What percentage of normal people have that stuff
I'm saying that most people can outsource the calculation of their tax liability
but they can't outsource the decisions that they make before the tax year is over to reduce it
there are reasons, for example, to sell your loser stocks before the end of the tax year to reduce the amount you pay
it's all in SVB and FTX anyways. Easy! $0.