#help-0
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Did you calculate T2, T3, T4?
You can obtain its Generate function though, not sure what to do next cause I don’t study combinatorics
$T_{n}(x)=\sum_{m}a_{n,m}x^m$.then you obtain that $a_{n+2,m+1}=2a_{n+1,m}-a_{n,m+1}$, multiply $x^{n+2}y^{m+1}$ both side you will have the expression of $f(x,y)=\sum_{n,m}a_{n,m}x^{n}y^{m}$
I checked, All you need is $a_{n,0}$ $a_{0,m}$ and $a_{1,m}$ those can be directly calculated
Not sure I understand hmm..
I also don't know anything about combinatorics, I've studied up to calculus and linear algebra so I assume those are all that is needed to derive the explicit expression
Anyway I got $f(x,y)=\frac{1-xy}{1-2xy+x^2}$
I am not sure what it’s called, cause I didn’t learn this in English. Generate function? Generating function?
Anyway something in combinatorics
so apparently this called Chebysshev polynomial:
https://en.wikipedia.org/wiki/Chebyshev_polynomials
and they have an explicit expression there
Not sure how they got to that explicit expression
Cogwheels of the mind
Funny, I almost got the same thing
It says 1-tx but I got 1+t-2xt
I must have calculated it wrong
I don't get how the generating function is related to the explicit expression though
But the approach is correct
I only know how to obtain that generating function, not sure what to do next. Maybe you need someone know combinatorics to proceed or you read combinatorics yourself
I got the same thing now
Anyway I got $f(x,y)=\frac{1-xy}{1-2xy+x^2}$
Cogwheels of the mind
I'll probably have to find a different way of doing it, but thank you. It doesn't seem like I'll have to dip into advanced topics unless the professor is being very unfair lol
You sure you professor asked you to find expression?
Maybe he didn’t ask for that, maybe he only asked to prove some simple things like T_0,T_1,…, is a basis of space of polynomials
Yeah the question says to
derive an explicit expression for $T_n(x)$
Ezra
😂 I see. He really wants you to learn combinatorics 😂
Well I'm looking through notes and I found something similar to deriving an expression for fibonacci
using linear algebra
right
yes, and that is what is throwing me off! haha
https://mathoverflow.net/questions/286626/is-there-an-explicit-expression-for-chebyshev-polynomials-modulo-xr-1 found something here
not sure what modulo means in this context though
but the matrix representation from one of the answers looks somewhat familiar
Oh that makes sense
That matrix is diagonalizable , with eigenvalues x+/-sqrt(x^2-1)
Seems like a good approach
😓
Good luck with that
yeah classic "you took a semester of linear algebra so its fair game" type of professor
When x doesn’t equal 1 then it’s diagonalizable , when x=1 the Jordan normal form is
(1 1
0 1)
Whose power of n =
(1 n
0 1)
I believe your problem will be solved, just very complicated to calculate the final result. And you need to add conjugate parts to obtain a real expression when |x|<1 so when the eigenvalues are complex numbers
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hey, calc newbie here
we just started calc 1, and its only the second week and we are already doing derivatives limits and chain rule. I thought a typical calc1 focused primarily on limits and derivatives
if we are already doing this, this early in, whats the rest of the semester usually bound to look like?
i've been doing a large amount of derivative problems to really make sure i can take derivatives easily, but i am wondering what is next, is it worth to keep practicing my derivative skills? or should i move on
doesn't your course have a syllabus?
well it may depend on the course, but usually you do various topics related to derivatives
I definitely don't feel like i have 'mastered' taking derivatives yet, but would you say its worth it to just keep doing derivatives?
sum and product and quotient rules, chain rule
or should i try to learn new concepts
maxima and minima of functions
or just get to the point where i can do derivatives in my sleep?
no. derivatives are not hard, it's just applying chain, product, sum rules over and over
so you are suggesting i look into those theorems?
what should i do with my time? I am motivated to get an A in this class
well they should be covered in the course, if not already then they will be
and with those theorems you'll know how to take derivatives of just about everything
oh and presumably they'll spend some time on particular functions like sin, cos, exp
log
and apply derivatives to those right?
yep
im doing practice problems involving sin cos exp log
etc
taking derivatives
do you have any other suggestion for a calc1 class? like what i should do in my free time
is being comfortable in derivatives the single most important thing for calc1?
maybe brush on trig?
hard to give specific advice without knowing what the course will cover, but more practice problems for anything you're rusty on
sure, trig will be helpful
how much more complex do derivatives get?
i solved all of them and got a couple wrong but reviewed em
and im out of problems so im just on google finding many worksheets with answer keys
you can also buy a calculus book that has answers in the back (maybe for odd numbered problems or whatever) and they usually have tons of problems
if it's not a required textbook you can get older editions for dirt cheap usually
and calculus hasn't changed, so old editions are fine for problems
okay, but nonetheless practicing as much as possible with different derivatives problems
is useful right?
for calc1
sure, as long as you don't do so many that you get bored or burned out
more practice can't hurt
okay, no i wont. i promised myself i am getting an A in this class. i got a C and am retaking
playing catchup with math
fair enough
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@remote pendant Has your question been resolved?
hi
tbh i feel like the question is kinda ambiguous 
its not very clear whether they care about the order in which the rides go
@remote pendant Has your question been resolved?
@remote pendant Has your question been resolved?
5 DIFFERENT horses, 3 IDENTICAL chairs total is 5
if i had 5 cups and you had to pick 3, which 3 would you pick,
5C3 = 10 I think
it’s quite vague but I think they meant chairs go on horses,
I thought it had to do with combinations,
permutations would suggest the order matters, combinations suggests the order doesn’t
if the order does matter as suggested by @proud ibex
it would be 5P3 which is 20 if i’m not wrong
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which one is larger and how to prove
the number inside the cbrt is less than 1
so the number with cbrt will also be less than 1
you can prove which is smaller from there
This is how I would think of it
1 - cbrt 0.999
vs
-1 + cbrt 1.001
Multiplying both expressions by 10 will net you the same comparison needed to do
10 - cbrt 999
vs
-10 + cbrt 1001
notice 10 = cbrt 1000
I think this might be enough of a hint
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"An approximate answer to the right problem is worth a good deal more than an exact answer to an approximate problem or Far better an approximate answer to the right question, which is often vague, than an exact answer to the wrong question, which can always be made precise", what does this means? what does approximate problem means ? . I could not understand this
I understand that we should try to find the exact answer to a real problem, and if we could not do it for many reasons like time or cost, the best action is to use approximate answer to the real problem, and we should never try to find solution or exact answer to the fake problem or to the wrong question, but I know this is wrong, so I want someone who can understand English to explain this to me please because I found it confusing
it could be that by approximate problem they are referring to a problem close or similar to the initial problem but simpler than the original problem.
🙂
@alpine sable Has your question been resolved?
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hi! is there a way to solve this limit without using l'hopital's? thanks!
and then? how do i proceed given that it still becomes indeterminate? sorry
?
You don’t know Cauchy MVT?
Then it equals cos(t)/3 for some t between π/6 and x
Cos is continuous
how do i determine which value of t to use?
You don’t need to
You don’t know continuous function? Like any ε>0, there exists δ>0,|cos(y)-cos(π/6)|<ε for |y-π/6|<δ
ohhhh yeah i recall that limit definition, but how do i use that to arrive at a limit for the expression? sorry
alright thank you!
Nice with Cauchy mean value theorem
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Hi
It’s the same
12C7=12C5
Oh
12 terms you choose 5 bx, other 7 are a
For those 12
So C(12,5)
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xgiven kcer explain why f(x)=x^4+kx^2+c might not have a solution but (x)=x^3+kx+d must have a solution
@lime hill Has your question been resolved?
kcer?
@lime hill Has your question been resolved?
All cubics cross the x axis because they tend to infinity in one direction and negative infinity in the other direction as x goes to positive and negative infinity. Not all quartics cross the x axis because they tend to positive infinity together or negative infinity together, never opposite.
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The diagonals of a rhombus bisect each vertex angle. The diagonals of a rhombus bisect each other at right angles.
@alpine sable Has your question been resolved?
thanks
what does it mean
when it says
sum of two adjacent angles of a rhombus is always 180 degrees
so lets say angle a is of 58 degrees
so 58-180
122
so thats the angle B?
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.reopen
this isnt your channel anymore lol
ik i forgot
thanksss
lol
Anyone able to help with this? I tried taking slicing in the x direction and using similar triangles i got an expression for the side length of some cross section s as xa/h, i then subbed that into the equation for the area of an equilateral triangle getting that the area of some slice s is given by sqrt(3)/4 x^2a^2/h^2
integrating that gives me that the volume should be a^2h/4sqrt3 but its not, the volume of a regular tetrahedron is a^3/6sqrt2
so im not sure why i have 4sqrt3 when it should be 6sqrt2
my question again since the other guy hijacked the channel
i also tried taking slices in z but im not entirely sure how to relate the length of the side of a slice at some height z to the side of a
<@&286206848099549185>
also the slicing method just refers to finding the volume of a solid by finding a formula for the area of a cross section and integrating it, just if anyones unsure what it is
@humble ferry Has your question been resolved?
<@&286206848099549185>
@humble ferry Has your question been resolved?
The area of the bottom multiplied by height then divided by 3
Thats entirely unhelpful, i want come up with the formula for its volume as a function of the side legnth a using an integral
i know how to calculate the volume of a tetrahedron
.close
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I’m really struggling with this related rates problem I came up with 30 mph/h but it’s wrong, any help is appreciated
@carmine harbor Has your question been resolved?
not sure if this solves your problem, but
$15 \cdot 2 \cdot \tfrac{1}{\sqrt{2}} \neq 15$
riemann
,calc -45 + 15 / sqrt(2)
Result:
-34.393398282202
$\frac{2}{\sqrt{2}} = \frac{}{\sqrt{ }}$
EndTimes
Okay cool cool I got it wrong I thought the process was wrong altogether and I was confused I’ll try part b now thanks 😄
@carmine harbor that was facetious
don't take what I just posted seriously please.
But you should realize this:
x/sqrt(x) = sqrt(x)
Because:
Sqrt(x) * sqrt(x) = x
Nah you’re goodd man I appreciate the help
I got part b as well I’m all done with it
👍
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What does ratio like a : b : c actually mean
Example :
When we say
a , b , c are in ratio 3 : 4 : 5
does it just mean
a : b = 3 : 4
a : c = 3 : 5
b : c = 4 : 5
Because
a : b : c = 3 : 4 : 5 is false and just makes no sense
This is a yes/no question
Im just goona assume it is
how is this false
to clarify it means "for every 3 of a, there is 4 of b"
this carries onto "for every 3 of a, there is 5 of c"
and on again: "for every 4 of b, there is 5 of c"
@dense sleet Has your question been resolved?
I mean sure its "True"
$$\frac{a}{bc} = \frac{3}{20}$$
Pluton
let a , b ,c = 3x , 4x , 5x
$$3x : 4x : 5x = 3 : 4 : 5$$
$$\frac{3}{20x} = \frac{3}{20}$$
Pluton
x here needs to be 1 but it can be any number
Unfortunatly the way its wrotten
,calc 3/4/5
Result:
0.15
,calc 60/80/100
Result:
0.0075
thats not what it means though
Not same
.................
That was the whole question
Are you purposely being thick or what
You make no sense just saying this
It's like saying this makes no sense$$a\leq b\leq c$$
Just because it means a =< b and b =< c
a : b : c just indicates the ratio these numbers are in
Ok i agree it was inaccurate of me to say that makes no sense. I was applying that
If a , b , c are in ratio 3 : 4 : 5
a : b : c ≠ 3 : 4 : 5
Unless it is exactly 3 , 4 and 5
I mean that doesnt mean it litteraly which just makes my head question why its wrotten like that
why not????????/
'a : b : c = x : y : z' is equivalent to 'a : b = x : y and b : c = y : z'
It's just shorthand
and clearer in terms of conveying meaning in a lot of cases
it doesnt
in the 3+ case
another way of thinking about it its just saying
(a b c) and (x y z), the vectors, are parallel
They have the same direction
Can y’all help me with mine 😅
My bad
So to end the question using : is basically just a convention that is used to apply a : b : c = d : f : g is shortcut for a : b = d : f , b : c = f : g
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i need to find the area
qt = ts
qr = rs
qt and ts are both root 17
and qr and rs are both root 5
I mean just by looking at cubes you can calculate the area
hm?
the area of a right triangle is half of that of the square
there is no right triangle
you just need to be creative
uh
idk what your talking about
can you explain what i should do to solve this problem??
Everything here is a right triangle if you draw it
no?
yes
the squares on the perimeter
well i mean
even if I find
the area of that
i cant figure out the area of the figure
Best solution at least i think calculate area of 4×4 squares = 16 and remove all other area. All of them are perfect right triangles
ok i see that
wdym by remove all the other area?
what is the "other area"
the right triangles that are formed
my friend, do you have pen and paper?
out of it?
Area outside the figure you have but inside 4*4 square
now outline the different right triangles that makeup the perimeter
there are 4, correct?
so now i basically find the area of all the triangles
yes
wait what
The green outline should be cube
Red area is the one you need to remove from the cube
yes
ok i understand
ty
@dense sleet
i cant figure out
the top right shaded area
Split it in 3 pieces
i tried
i keep getting a decimal
it doesnt make sense
I see 1 cube and 2 right triangles
in that shaded region?
oh wait i think ik what you mean
wait lemme try again
i got the answer @dense sleet !
its 9
thx for your help man
Np
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What did you try
I was gonna take the conjugate but idk how to do that with this problem
You could maybe use LHopitals rule. But im not sure
What is Lhotpials rule
Actually I’ll search it up
@dense sleet the first one? And khan?
Ye
Ok
Maybe khan would be better
@hardy geyser Has your question been resolved?
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first one is correct, yeah
alr
think about what you're solving for
yeah
so i think that one is right too
yeah second one is right too
@alpine sable Has your question been resolved?
For the soccer problem u have to find when the ball hits ground again so after it lands. Ground level in this case is 0. As f(x) is height and x is time u have to find the time (x) when f(x)=0
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Hey, I'd like some help with geometric progressions
How can I determitate r (what multiplies the numbers, in case you call it different) only having 2 terms (for example a2 and a8)
$a_n=ar^n \
a_m=ar^m$
Mosh
And then calculate the first term with another one and the r? Like with a8 and r get a1?
Oh I think I'm not understanding that
the general term of a geometric sequence (WLOG starting at n=0) is $a_n=ar^n$
Mosh
$a,ar,ar^2,...$
Mosh
What is the ratio of $a_n$ and $a_m$?
Zybikron
Now I need to do an equation to get r?
Ok let me try to explain again
I only have 2 terms, a2 = 3 and a4 = 27. With that, I need to get the r
right.
Yeah
.
what is the ratio of a_n and a_m?
What do you mean with ratio?(sorry I'm not very good at english)
$\frac{a_n}{a_m}$
Zybikron
fuck joined here trying to understand more and now I understand even less
Nevermind, thanks for trying to help, I'll try to find a spanish sv or something cause I'm not getting it in english
Thanks tho
take this, divide a_n by a_m. That's all I'm asking right now. We can go from there
Ah wait wait, i understood
I'm getting 9
right, and what should 9 be equal to in terms of r?
.
Yeah that is giving me s result of 9
Take exactly this. Not your values for a_n and a_m, Exactly these ones. What is a_n/a_m?
I don't know, we've never done something like this with just letters
ok, let's look at an example. What is x^10/x^7?
x^3?
yeah, why?
Cause the 7 rests to the 10 as they are both elevating the same coeficient and they are dividing
Not sure if you call the things the same way as I do but I guess you understand it
I more or less follow
So when dividing, with the same coefficient (or base), what you subtract the exponents
so $\frac{x^{10}}{x^7} = x^{10-7} = x^3$
Zybikron
Right
So if $\frac{a_n}{a_m} = \frac{a\cdot r^n}{a\cdot r^m}$ what should you get?
Zybikron
Ah, a•r^n-m
the 'a' should cancel, but yes!
So in general, $\frac{a_n}{a_m} = r^{n-m}$, and you have $\frac{a_4}{a_2} = 9$. Can you put those together to get r?
Zybikron
r^4-2?
which can be simplified a little
so then I'd get r^2
and r^2 = 9....
then r is 3
Yep we're using only positives
cool! then yes, r = 3
yes
How do you get from a_1 to a_2?
oh i was getting confused with the other progressions
I just need to divide a_m by the r?
yep
a_2 / 3 in this case?
yes
@gaunt finch Has your question been resolved?
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guys can someone check my work
yea can u check if i got the right answer
oops i meant 85
yes you're good now
do u like my drawings of the picture
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how do I find the inverse of this matrix?
I have no idea where to begin, the teacher only taught us inverse of 2x2
which was a formula
do you know how to do gaussian elimination / row reduction?
basically do elementary row operations on $\begin{bmatrix}0 & 1 & -3\ 4 & 1 & 0\ 1 & 0 & 5\end{bmatrix} $ to get it to be the identity matrix. apply the same order of row operations you used to the matrix $\begin{bmatrix}1 & 0 & 0\ \0 & 1 & 0\ 0 & 0 & 1\end{bmatrix}$ and the result will be the matrix inverse
elemen
yea
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hi i have a hw question!
Professor Rogers has found that the grades on the nursing final exam are normally distributed with a mean of 75 and standard deviation of 6. Your answer should include (i) a sketch of the normal model that illustrates the question being asked, (ii) a statement of the proportion you are calculating, and (iii) an answer in complete sentences.
A) What proportion of the exam grades are between 72 and 87?
B) What grade are 15% of final exam grades above?
Do you know how to calculate a z score?
yes
Where are you stuck?
on a and b like how i would solve it. do i use the z score equation or the drawn out normal model?
So you need to do 3 things
Is there any part of 1,2,3 that you do not understand
well 3 is kinda a qualifier
so 1,2
lol i guess i wouldnt know what to say for 2
what do u mean? sorry im really not good at this stuff
Yeah so can you just like solve part a) without worrying about the rest of the nonsense
just pure math
im not sure, i dont think so?
Well you need to convert it to a z score
so would i do two separate z scores and use those as the observed?
so i would do 72-75/6 and then 87-75/6 to figure out the range? or am i way off
so that would be the z score yeah
for that
So you can use the z-table to calculate the area
what is a z-table
wait is that the same thing as a normal model?
we havent used those yet, just z scores and the normal models!
@wheat cloud Has your question been resolved?
no
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You need a table or something to convert from z-scores to probability
That’s what the question is asking for
i dont know anything about tables, we weren't taught that
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nope
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im not sure about c and d, thank u 🙂
the answer is 168 and 342 respectively, but i dont know how to reach the answer
would u guys mind explaining the rationale behind the answers? many thanks
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Find the three consecutive odd integers such that four times the middle is equal to two less than the sum of
the other two.
Representation:
Working Equation:
Solution:
ive already gotten the working equation but i'm not sure how to solve for the odd number thingy
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I don't know where to start, videos in youtube doesn't make sense to me.. How do I graph all of these ;-;
Start with 1. and then 2. and then 3. …
What does 1. mean? Do you know that?
like
the number 1
the negative thingy
I think you have to put asymptotes there
since theres infinity
but idk yet
Yes
wdym yes ;-;
What does $\lim_{x\to -\infty}$ mean?
wait before that
ScapeProf
how do I graph g(#)= #?
what are the coordinates?
for example
g(-1)=1
how do I graph that?
x-axis input, y-axis output
Yes
If I’m meant to ignore the point at (1,1)
Yes there is also a point at the correct place
so its the zero then?
Yes
so this ones wrong huh
ok I think I'm getting the hang of this
so this is correct?
No?
You just did g(0)=1 above?
I just told you yes one of the points you made is correct
What is input?
Yes
Yes if I’m meant to ignore the other point again
A point is a single point
cuz it's gonna be (0,0)?
So no a point should not be two points
Looks good (ignoring the double points again)
I still don't know what I'm doing wrong
in the double points thingu
I believe I sent a single point
without touching rhe zero
Oh thats prob just from stuff you erased, but g(-2)=0 has 2 points
oh I think it just marks of the marker at. the back
lemme put these coordinates to desmos and show you later on
brb
thoughts?
<@&286206848099549185>
@spice wasp Has your question been resolved?
@spice wasp Has your question been resolved?
What’s the problem
what do I do next
how do I graph
the remaining
especially with the infinite ones
You see the first one
I think that’s just a reciprocal function
Except it’s y = 1/x-1
so there's an asymptote right?
Ok wait lemme put the equation in desmos
That should be right
Because this graph is a reciprocal function
1/x
Let’s say y = 1/x
What does x never equal?
Can get infinity close to
But never equal?
answer my question first
oh.
OH I SEE
Can get infinitely close to
That’s what limit functions mean
I see..
so 1 over x since it cannot be undefined
Because you cannot ever divide by zero
However x can get infinitely close to zero
Now if you want it to be infinitely close to -1
You just translate the graph down 1 unit
Hence the 1/x and then - 1
To translate it down one unit so it fits the condition of getting infinitely close to - 1
You see the “limit”
The notation
Of the first question means
The limit of the function g(x) as x approaches infinity
oh
okok I think I can help myself with that later
but
what if it's
the other way around?
like the next example?
there's a raised to negative
so which means
its on the left side
right?
Is this precalc?
Okay
I forgot how to read these lmao
Which example you taking baout?
So you see the 3-
The negative above the 3
It means the x value approaches from the left
So question 3 means
The limit of the function g(x) as x approaches -3 from the left hand side is infinity
Yeah
correct?
Because it has prositve
The positive and negative sign in the place where the exponents are meant to be indicates from which side
Hmm let me think
sure take your time
oh
You might have to ask someone that is well experienced
precal is quite easy to me tbh
I see
Yeah
I’m in a car right
Let me get home and experiment with some functions
And see if I can find a right one
You have the find the function that fits the entire expression
I'll update you somehow
Okay
so deriving ...
Pretty much
But it’s like hella simpler than finding derivatives of like parabolas or whatever
As in the algebra should be simpler not that it’s actually complicated
I’m just not good at this because I’m dumb
I should be the one saying that
Nah you probably just don’t study
joining a discord server, desperately seeking for answers
This is some pre calc stuff
Your meant to be well versed in what this notation at least means and stands for
like she only showed us about
finding
the limit
with graphs given
but never explained the opposite
I see what I can do
I'm still searching in the internet but I don't think I can apply those to these
the equations are pretty complicated if you ask me..
After pre calc you should be extremely comfortable with different functions
Like exponential, reciprocal, logarithmic
Etc etc
And how to translate/dilate functions
Which I’m not good at
@spice wasp Has your question been resolved?
The same for question 4
Yes
It is plus 3
You may think it should move to the right
But that’s common mistake
Basically when you plus a value to the x
Ahh yes
I see
The function g(x) = 2^x whole thing - 1
Also works
Oh yeah
I made an error in the first one
If we were to use the reciprocal function as solution
It should be g(x) = -(1/x) - 1
Not g(x) = (1/x) - 1
oof I was waiting in our dms
sorry for rhe late reply
oh I think this one makes sense
because I believe you can:t cross
the asymptotes
and somehow
you need to xonnect the dots
based on the videos I've seen..
Oh shit
Lol
I thought this was dms
But yes
So for question 1
I think 2 different functions work
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I am lost and cannot figure out this question
Let's look at the second question first
We have
$$y = \frac{\mathrm{constant,of,variation}}{\mathrm{number,of,workers}}= \frac{k}{x}$$
Navix
Try to plug in the information we've been given: 4 workers and 60 hrs
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Can you retake the pic
.close
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can someone help explain this proof to me?
In which line you have problem?
between b) and i)
i don't know how they got the x^2 >= 0 and y^2 >= 0
and why they're saying y<= -2 or y>= 2
squares of real numbers are non-negative
oh so they are trying to get the interval in which the equation will be true?
also why did they choose y
and not x
ohh so it really doesnt matter which we choose?
we will get the same answer with both?
you'd reach the same conclusion in the end
no, it'd be indirect
ohh I see now, thanks
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