#precalculus
1 messages · Page 286 of 1
Good wow okay
And now this pattern is the same, so we have a line
and that line is slowly curving to the right and rapidly moving down
It never stops because we are letting $0\leq t< \infty$
oh okay cool good
dackid
There we go
yep okay infinite
and you did a triangle
so it cant change into a different triangle
The triangle was more of a visual aid
cant curve a triangle
It let me know how much we were moving up and down
But the red line is our actual graph
okay so whats the big deal about parametric equations if theyre just linear?
Let's try a different one. Let's see what you can gather from it.
also why is subscript 0 a thing
$x(t)=t^2$
$y(t)=t^3$
dackid
Try to graph that with just the tools we have
We'll let $0\leq t\leq 2$
dackid
so I draw y = cuberoot(x)
False. Ignore this elimination process for now. Do what we did with our line. Develop the intuition
No no. It goes up by t^3
For $x(t)=t^2, x(1)=4$!?
dackid
I call lies
no its ^4?
Well, technically right, but just because x(1)=1
-_-
or 2^2
If $x(t)=t^2$ what is x equal to when t=1?
dackid
just 1^2
Which is?
1
Yes
For x(t), yes
Let's actually do from $-1\leq t\leq 2$
dackid
3 is gonna be massive
Ooo, this is actually really interesting
27
Let's actually do $-2\leq t\leq 2$
dackid
okay is that better?
There is something really interesting going on in this interval
its going up and to the right a lot
Like I said, focus our t values on the interval above now
can be -2 or 2
t can be between -2 and 2
but nothing lower or higher
So check (x(t),y(t)) when t=-2,-1,0,1,2
That will give you a good idea fo what will happen
it will be the same as when -2 and 2 it is the same
because squaring removes negative
Ah, x will. But what about y?
Your graph will end up looking something like this
I like that description. Pretty much 😁
But something that may seem strange is it is symmetric across the x-axis
whats that
Do you know what the x-axis is?
So if you look at the horizontal line. The top looks like it is a mirrored version of the bottom
But one of the first things you learn in algebra 1 and 2 is the vertical line test
If you draw a vertical line anywhere, and two points on the graph are on the line, then it's not a function
but center can be 0,0 though?
I mean, that's not really relevant for the vertical line test
The problem is two points on the graph hit the red line
yes
So, technically... this isn't a function
you tricked me all along!
But it is a parametric function 
😦
Parametric functions allow you to represent any curve as a collection of functions over time. So any curve you draw on a graph, function or not, can be parametrized!
so no more graphs then?
No one said that
Sure
Well, A is given to be 40°
So theta is given
Yep, and so is v
why do they give meters when we have feet for answer?
No no, gravity is $32 \frac{ft}{s^2}$
dackid
And speed is $14\frac{ft}{s}$
dackid
Read the problem. Everything we need is given to us
X_0=0
10.7246222t just this yes
If that's what it comes out to, yeah
okay good good
now y
is tough
but g is gravity?
t^2 we need to get rid of the square somehow
-1/2gt^2 + 8.999026536t + 63
Also, just gonna say it right now, never plug numbers in until you are at the final stage
oh
And I can guarantee you 14sin(40) os perfectly acceptable for this program
okay I do that then
It is also more accurate than your approximation, as yours is just an approximation
Yep
-16t^2 + 14sin(40)t + 63
$y(t)=-16t^2+14\sin(40°)t+63$
dackid
and no approximation
Nope. This answer is as exact as it gets
wow thats fire
So now we now how high the canteloupe will be for any time t, and how far away it will be for any time t.
You bet. Parametrized functions are simply a way to measure things with respect to time.
$f_y$ where f(x,y) means what exactly? $df(x,y) \over dy$?
Daemon
Nothing actually
Now $\frac{\partial{f(x, y)}}{\partial{y}}$ does mean something
dackid
No worries. I just wanted to make that clarification
$\frac{d}{dx} [f(x,y)\frac {y'}{\sqrt{1+y'^{2}}}]$
Essentially what you're doing is looking at a slice of the surface in the y-z plane and seeing what the derivative of f is with respect to y.
Daemon
So say we have this amazingly drawn surface by yours truly
haha. I think I got it :) So $f_y$ is taking a slice of f(x,y) and find it's tangent on the y-axis?
Daemon
On the y-z axis
the above derivative is more calculus though right? :S
oooh. right. you're doing it on xyz axis!
or that :P
So when you are taking a slice of the graph, you are looking at the y-z plane where x is a fixed number
cooool :D
Does that idea make sense?
yeap
it's hilarious that I'm doing an MSc on applied math and I'm excited when I understand these things XD
Here is a quick example
Let $f(x, y)=xy$. Then $\frac{\partial f}{\partial y}=x$, since x is considered a constant
dackid
and $\frac{\partial{f}}{\partial{x}} = y$
Daemon
ha!
There ya go
Also, some shorthand notation for that same thing is $f_y$ if it's a y partial and $f_x$ if it's an x partial.
dackid
Quick question, why are you asking this in #precalculus 😆
I thought it was precalculus :S
Oh goodness no. This is multivariable calculus
And this is? $\frac{d}{dx} [f(x,y)\frac {y'}{\sqrt{1+y'^{2}}}]$
Daemon
for #multivariable-calculus ?
Again, you are taking a partial here.
wait...
It's part of the euler-lagrange equation. It's written as d/dx. No θ/θx :\
Gahhh. I'm calling it a night... WIll think again on it tomorrow.Many thanks for the help dackid :))
aye aye o7
dack my guy I did the hard part of this problem but now they're asking for distance
<@&286206848099549185>
so i have solved this question but i just want to make sure that i did it right
so first i started off by listing out all the things that are given which are, A=58750, r=0.05 and t=4
?
then i used the A=Pe^rt formula and plugged everything in and rearranged the eq accordingly to find P and the answer i get is 48100.43 or simply 48100, i just want to ask that did i do everything correctly?
Looks good to me
so the formula is correct and just want to make sure just in case that 58750 is the A value (the future value) right?
The formula is correct but did you plug in the right numbers?
58750 is the A value yes
thats your start
ok, thank you so much for your help
np
Hey dack you understand how I can get the distance?
Of course. Solve for when y(t)=0 and plug that t value in to x(t).
Also, stop writing the approximations!
Oh perfect so it'd be just 86. Also, I have to write the approximations! They say its wrong when I dont its weird ik!
then 18.70283481(86)
No, it is not 86
I didn't say when solve y(t) when t=0, I said solve for t when y(t)=0
Then you need to tell the program to stop being approximately wrong! I'm sure it'll listen to you 😆
I wish I could haha
Also, for approximations, you probably only need to round to the first two decimals
so y(t) equals 0 it will be -4.9 + 18.06.... + 86
Oh true it says 4 for this one but I never round for some reason
$h(t)=0=-4.9t^2+18.06t+85$
Solve for t
dackid
Ah, do 4 then.
Well, this is a quadratic equation
oh so factor
Time for the Quadratic Formula!!!!
And one of them should be negative 
A negative time does not have any meaning
so pick the positive
yes!
Now plug in that t in to x(t)
oh okay will do
After all, you're trying to show how far it traveled when it hit the ground. Well, it hit the ground at the time when y(t)=0
I mean sure. I'm not plugging it in
Okay thanks for the carry
Yo my guy congrats on the promotion, well deserved.
I asked for it 😆
and you deserve it haha
Thanks, that's very kind of you :)
,w x^4-2x^2-24=0
Can someone help me with my hw?
Yes, but post it
Why ping?
You said to post it earlier
Ok
x=log7^8-5/2, what does it mean to have log present after you have solved for the unknown? im having trouble understanding what a log truly is. i know that its used to find the unknown exponent but why keep log present once we have solved for x?
You know that from a half rotation, the height of the stone goes from 3 (the maximum height) to 0 (the minimum height). You need to figure out at which height the stone starts to model your graph. You know the span of one period since 0.4 seconds is one revolution.
I’d fix the graph first and see if you can determine what equation to use after that.
How would you get rid of the log?
I'm sure this is pretty simple and I'm just missing something here but everything I've thought of to solve for t would just contradict eachother when getting ln to the other side
they isolated t by taking just the 4 and the ln
because its like 4 times t times ln
so they just divided 4 and ln to leave the t out
hi guys anyone know how to do question b? 
quotient + chain rule
that works for b too?
yes, cause f is a quotient of functions
but how do i get the g function? it's not 2gx right?
you're given enough information about g
differentiate g(x^2) using chain rule
sorry i just dont understand it huhu
okayy i got it thanksssssss
Do what Ramonov said
anyone know where i went wrong here
f is increasing on (1,inf) @still quarry
i suppose i would do the opposite steps that i took to get to the log
also that is increasing from 1 to inf
in its derivative
can you divide by 0?
obviously not lol but i tried 0 and its wrong
well when is x+5 = 0?
-5, there we go, now it makes sense thanks
How can i prove this to be true long hand with out a calculator? i am not sure i truly understand logarithms.
@thorn moat look up logarithm rules
Can someone please help me with the 2 I have circled? I don't know how to transform them based off of D and C and I also don't understand how to know where to put the line of the graph through
You are aware of this, right?
For example, question 37.
If you let your x --> +-infty. What are you left with? 🤔
I understand how to get those but I dont know how to graph it
I was going to write a lot here, but there are so many videos on YouTube. I will refer you to one. I don't know if I can post the link here, so, check your pm.
do lim x-> 0- and 0+ exist
yes they exist
and it's 0 right?
yes they both equal 0
yes
kk ty
but f(x) is not continuous at x=0
right
I'm not really sure but I tried it and I just multiplied both sides by 4 and got that it was equal
so probably factor out 1/4
also in polar equations of conics is p directed distance or absolute value
Original problem for context/.
i'm getting the same answer as them but (sqrt 3 -1) in parentheses
I just factored out 1/4 then -sqrt 2
wow dude thank you so much. So odd that that isn't taught in my book or by the teacher yet is expected.
could you also show me this one?
yeah that’s taught in algebra but expanded on in precalc
uhh try it first by multiplying by 3/3
step 2 to step 3 is just substituting tangent values
and step 3 to 4 is expanding and multiplying by 3/3 which is 1 so it doesn’t change the value
last step to final answer is multiplying by (3 - sqrt 3) divided by itself
i just need help with finding the start and end pt, for some reason I get the same number for both
go through w/ first principles?
what’s that
I just got in calculus with no context and they randomly give this hw to me
the limit in the question
$f'(x)=\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}$
moshill1
👀
so what's f(x+h)?
If you want me to be completely honest, I have no idea
They put me from algebra one, to calculus
ok so plug in x+h in for x and that's f(x+h)
Cause they said I had talent or something
$\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}=\lim_{h\to 0}\frac{3(x+h)^2-5(x+h)-3x^2+5x}{h} \ =\lim_{h\to 0}\frac{3x^2+6xh+3h^2-5x-5h-3x^2+5x}{h}$
moshill1
Do you cancel out 3x^2, -5x, -3x^2?
after expanding the brackets stuff will cancel, yes
lost some 3's while distributing
almost like that's what I was referring to
$\lim_{h\to 0}\frac{f(x+h)-f(x)}{h}=\lim_{h\to 0}\frac{3(x+h)^2-5(x+h)-3x^2+5x}{h} \ =\lim_{h\to 0}\frac{3x^2+6xh+3h^2-5x-5h-3x^2+5x}{h} \ =\lim_{h\to 0}\frac{6xh+3h^2-5h}{h}$
Hmmm
moshill1
👀
Almost there :)
I’m so stuck 😣
dackid
Do you cancel h now?
I don't see why not
yeah, and as h approaches 0...
6x-5?
Bingo!
Thank y’all!
hello,new here. i am really bad at these type of Qs where it asks of me to prove something is something, it would be really appreciated if someone could help me out a bit with the process
<@&286206848099549185> apologies for the ping. This type of question really confuses me a lot
isn't it a straight line?
english not my 1st language,so I do apologize for my crappy eng lol
Yeah so we know that inverses are reflected along y=x
y=x is just a tilted line going straight through at a 45 degree
Yeah but also
and the y=1/x is an even function
If you flip the graph over the line y=x
You get the same exact graph
That’s what symmetrical means
oh so it's a reciprocoal?
One side is identical to the other
It’s an inverse
A special property of 1/x is that it is its own inverse
is y=x
Basically the question is asking you to prove that expression is it’s own inverse
Do you know how to find inverses?
isn't it like
you get the function
then switch the y and x values
to solve for f-1(x)
I had to serve a mandatory military service and everything about math is jumbled into a mess in my head...
Nah bro you’re good
That’s exactly it
You flip the x and y and solve for y again
Basically a neat thing about the function it gave is that it is it’s own inverse and the question is just asking you to prove that fact
Interestingly, that function is significantly linked to a 2x 2 matrix's determinant
Which I dunno, I find super interesting
I really appreciate the help guys, but I'd like to be a bit selfish and ask for just the first step in as to how to begin
so what I got down so far
dackid

i know we have to single out y
but i am not sure what number to multiply both sides by,in order to single out the fraction
so then x(cy-a)=ay+b
dackid
Quick algebraic reason as to why we do that
Correct
then...divide by a...?
So the trick you wanna do is distribute x on the LHS
Then see of you can get terms with y in them on their own side. That is:
$cy+ky=\dots$ where c and k are some random constants.
dackid
But of course, they are very specific in this problem
So now that we got (cy-a)x=ay+b
We can inverse the x and y to get the value
This is how I interpreted it based on you fellas” hints
You got it!
Also keep in mind, this is the inverse, so $f^{-1}(x)=\frac{ax+b}{cx-a}$
dackid
But since $f(x)=f^{-1}(x)$, f is symmetric across y=x
dackid
aha,i see thanks bro!
Can someone help me with 37 please
give the inverse sine function some arbitrary value y. so sin^-1 (x-1) = y
build a triangle where one of the angles is 'y' and then find the sides of the triangle
do you need further explanation?
sorry I was away from my computer for a bit. I don't understand how to find the sides of the triangle from that equation. Also can I cancel out the sin^-1 with sin so it is sin(x-1)=y
sin^-1 is an inverse function. so if sin^-1 (x) = y, then sin y = x
so with sin(y)=x I make the x x/1 so then my b side ill be x and the hypotenuse will be 1?
and then from there I get all the sides and then get the tan of the triangle?
I got the right answer! You are a legend thanks for the help!
awesome. np!
can I ask you another question real quick? Its okay if not
go ahead
from the picture I posted earlier for number 41 I messed up on the x+1/2 but I don't know how to correctly do it. I know that I need to combine them somehow so I can get my 2 sides but I got x+2 which is wrong
I did (x+1/2)/1 and then multiplied the 1/2 and denominator by 1/1 and got x+2
wait what
so your opposite side is x + 1/2 and your hypotenuse is 1
(idk what your step did, but x+ 1/2 would simplify into (2x+1)/2)
wait I can just leave it as (x+1/2)/1?
yes
and ohh I was way off with the simplifying
its a ratio so it doesnt really matter
for some reason I thought I had to combine them
sorry for the bad question thank you for helping!
again, no problem lol
Yo what topics are under precalculus?
read the channel info
Prove that if a^2+bc≠ 0, then the graph of f(x) = ax+b/cx-a is symmetric about the line y=x. Can you help me with this problem please?
assuming that's x+4 on the right hand side, collect the x terms
is this a test?
everybody hates i. try rationalizing the denominator
and wrong category
It's review for a test
the paypal part makes this skeptical 
The teacher didn't upload his lectures for that week
I mean, I have the textbook. But my friend comes over in an hour or less. I'd much rather buy someone a coffee to get it done tonight and not worry about it. But I can just go through my textbook as well
welp, just like el chupacabra suggested
divides them and get rid of the i in the denom
try to use conjugates in the process as well
God, I have no idea what that even means. Guess it's textbook time
@arctic walrus im assuming you know how to rationalize complex fractions
no i dont XD
do you know what i^2 is
I don't want to waste anybody's time to teach me an hour for a cup of coffee
An imaginary number or a vector
Im so sorry, hold on, I did not expect such a quick reply. I am reviewing a previous section
I do have a question though
How do i distribute the second part correctly?
is it -9i - 12j?
WTF
There's a distributive error here, is there not?
The 2j was distributed with a negative, and re-distritubed again..
OH WAIT. It makes sense.... They distributed it to the second part first, then the first part last
just seems there's a stray )
the () doesnt include the 4j anymore after the first distribution
That's what was confusing.....
theres an extra ) for no reason
Thank you you guys are great lol
complex time
post this shit in the right section bruh
this isnt precalc
#geometry-and-trigonometry would be better imo
Hi guys! this week i started learning complex numbers, but it's a huge confusion for me. So i don't understand the part why negative roots exist since we learned that we don't have a solution for the quadratic equation when the answer is negative. Can someone pls explain me a bit? Thankyou!
we just define sqrt(-1) as i
and fundamental theorem of algebra says there are always 2 roots to a quadratic
Your teacher likely said no R roots exist if b^2-4ac<0
exactly
and how come i^2=-1
by definition
can i find the def on wiki or ...
yes you can
You'd be surprised just how expansive math gets by letting i^2=-1
It seems so simple, but complex numbers is like a whole new world in comparison to the reals.
A WHOLE NEW WORLD
they are unreal
Welp, someone had to do it 😆
Hey guys, i have a calculus question about a integral rule and i wonder is it ok to ask here or should i wait for a question channel?
i just need the name of the rule :3
?
what is this rule called?
its unclear what the rule is but are you thinking of u sub
basically you use it when you want to integral a rational function
quotient rule?
all i get is partiell integral
let me look it up one sec
yuuup
that its
thank you!
I knew how to use it before but i totally forget about it for some reason lol
i just can't seem to get it to work
i knew how to do it before but for some reason it does not make any sense to me
rederive it
and all i see on youtube is partiel integration and u-substitution which is something that i don't need for this course
$\int \frac{ f(x) }{ g(x) } \dd x $ ?
$\int \frac{ f(x) }{ g(x) } \dd x$
steppaz
fugc
u sub
i remember something about moving out the denum outside of the integral but that doesn't seem to work and stuff would cancel out
$2 \cdot \frac{1}{2} = 1$
jan Niku
youre only looking at the 1/2
consider the 2 as well
i guess really theyre also applying the constant multiple rule
$\int x = \int \frac{1}{2} \cdot 2 \cdot x = \frac{1}{2} \int 2 \cdot x$
jan Niku
which you want there because 2x is the derivative of x^2+1
alternatively, you could do u sub first and get to a similar answer
yeah i'm with you with the 2x is integral of x^2+1
which is probably better since the approach yo showed requires you to have some foresight
well
this is my problem
x^2 + C is the integral of 2x
tell that to my teacher haha
Wolfram Alpha doesn't understand your query!
Perhaps try rephrasing your question?
Click here to refine your query online
there is literally 5 or 6 pages about the substitution method in my book
😄
u sub is really just algebra disguised as calculus

AH
found it
it's called "Reciprocal rule" or just "Reciprocal"
there is a perfect 2 minute video that explains exactly how it works 
This isn't quite a rule, it is just a lucky u-substition
yeah it's just u-sub
That is not the reciprocal rule. That is just a standard integral recall that in highschool we were taught that the derivative of ln(x) = 1/x. This integral is just a generalized version which you get through u-substitution.
Reciprocal rule is a rule for differentiation not integration.
Pic related is kvotregeln.
^
could someone please help w the polar equation of a parabola with its focus at the pole and vertex at (1, -pi/2)?
I don't really understand why p is 10 instead of 5 and how the directrix is to the left of the pole
Then how would you take the derivative of a rational function without using the u-substitution? Because in my book we have been taught that rule. Where you basically derivative the function and you put it in the denum and you re-write it as "ln I f(x) I + C". But that don't seem to work for me as i am missing one step and i am not sure what it is lol
I was just saying that
$\int{\frac{dx}{x}} = \log{\abs{x}} + C \
\int{\frac{f'(x)}{f(x)}} = \log{\abs{f(x)}} + C$
Isn't called the reciprocal rule, reciprocal rule is for differentiation. This integral is just a standard integral, an identity that pops up when solving some integrals which you can reuse. There are a list of standard primitives you have to your use when solving integrals. I assume your book has a proof of the integral somewhere.
rts
For example, this integral
$$\int{\frac{e^{x}dx}{1+e^{x} } }= \log{\abs{1+e^{x}} } + C$$
I identified that the numerator is the derivative of the denominator so i applied the standard integral $$\int{\frac{dx}{x}} = \log{\abs{x}} + C$$ to solve it
rts
Oh
It says that any rational function has the integral of f'(x)/f(x)= ln I f(x) I + C
Yeah no biggies, you can say it is rule i just didnt want you to confuse it with the reciprocal rule in the youtube video you linked which was him just differentiating a rational function
how would you graph overall shape of this by hand
What's 9+10
Find their asymptotes x intercepts y intercepts
So u can plot a rough graph using that info
And see as x tends to -inf and +inf
If f(x) tends to 0 or inf or whatever
Did you factorize the denominator and then check for vertical asymptotes for those x where the denominator equals zero?
You find the intercept points, find the stationary points by having the derivative, then solve the limit as x approaches infinity and negative infinity
lastly
check for vertical asymptotes by checking what happens to a function as it approache a singularity. (a singularity in this case is divison by zero). You have singularities at x = -8 and x=3, Solve the limit of the function when x approaches 3 and when x approaches -8 both from left and from right.
If it equals infinity you have a vertical asymptote.
If the limit exists from right but it equals infinity from left then the function approaches an open endpoint from right but it will be a vertical asymptote from left.
Ok thanks
What’s the end behavior of this function?
Is it as x approaches -infinitely, y approaches positive infinity and as x approaches infinity, y approaches negative infinity?
technically true, however it seems like an oblique asymptote would best represent what's happening
can uh
someone help me with this
i know you can factor it
cosx(sinx + 1)
set that to 0
cosx = 0
sinx = -1
you can do inverse sin/cos here
then consult the graph to find the other values between 0 and 360 degrees
or unit circle
Looks, good, so for what x is cos 0?
So what is the problem? 😄
Can I get help with this question please?
Remember that trig functions are periodic so when they ask for all solutions you add with 2pi right
I see
ye
Well if x=3pi/2 implies sin(x)=-1
Then i can say sin(x)=-1 for x=3pi/2 + 2*n*pi
where n is an integer since sin is periodic.
hm
yeah you get zero whenever cos is zero aswell
alr so imma put 90 n' 270
remember to include all solutions since it is periodic
it says 0 < theta < 360
Well then should be those two then
oki
Yo, if you have dy/dx of two graphs, how do you use that to find where the gradient is the same?
you mean slope?
if f and g are two function, just solve for x
where
f'(x) = g'(x)
what does simplest radical form with a rational denominator mean..
my answer is sqrt30/10
what is the question
Part B. Do I just do 1=-2x and then solve for x?
ye
does x = -1/2 seem right for that? idk if thats right at all lol
Well the derivative of a function at point x=c will give you the slope of the line that tangent the graph at x=c
The function x is its own tangent, recall the equation of a linear function being kx+m where k represent the slope
and k = delta y / delta x
-1/2 is the slope for the tangent cause x is the slope of that norm right?
yeah
sorry man, i am not sure what they mean by rational denominator
I agree with your answer but then again im not sure
do you know double angle formulae?
oh ok then
ln(1/2)/-27 can anyone simply just help me on how do you simplify this?
i know that the answer is ln(2)/27 but i just need a little help on how do you get from ln(1/2)/-27 to ln(2)/27
apply power rule to ln(1/2)
so how do i do that?
so what i have been trying to do is taking the reciprocal of the denominator meaning i did ln(1/2) times -1/27 which gives me ln(-1)/54, but this isn't the correct answer
1/2 = 2^(-1)
sorry i don't get what does that mean?
$\ln(\frac12) = \ln(2^{-1})$
ℝamonov
power rule (for logs)
so how would i start, if you could help me?
do you know your log laws?
yes
i know them but i just can't remember them at the moment
do i do like ln(2^-1/27)
as i've mentioned power rule/law (for logs) 5? times already
no
now you also need to review your order of operations
you could start with
2x + b = x^2 -4
and then consider the value of the discriminant
no
Hi, i just have a question about limits as they approach +/- infinity. I was wondering when you want to examine how a function behaves when it goes towards +/- infinity is there some condition that the function has to fulfill for *you * to examine how it behaves when it goes towards +/- infinity?
If this question should go under question channel lmk :p
Like, as i understood it, the values will still be the same whether it goes towards +/-
For example if we look at this function, i believe they have done some polynomial division to figure out the asymptote. Is this just some type of preference to write it as +/-?
if you'd answer please tag me 
so for this question this is what i have done so far, so i think i have solved half of the question
so i have solved for k but now i don't know what to do next, like what is my next step going to be.
if anyone is there that can please help me?
i also have the answer key for this so the answer key says the answer k=ln(2)/27, which i have gotten already and then the actual question finding the time which is 54 years which i don't know how to find, like i don't know the next step to find it?
anyone there to help please?
anyone there...?
U could start by modelling the question into an equation first!
You have three cases:
One where if x approaches a value c implies f(x) approaches value C then the limit is C however if the function approaches infinity when x approaches c then you have a vertical asymptote (lodrät asymptot). You also have to consider two-sided and one-sided limit when studying the limit as x approaches a singularity. (Singularities in calc 1 are for those x where the function isnt defined, for example, division by zero, negative argument to squareroot or logarithm , or x-values that are outside the domain of certain trig functions for example x<-1 is undefined for the explicit function arcsin(x).
The third case is when x approaches infinity, this is when you study if the function has a horizontal asymptote(vågräta asymptoter). If x -> infinity implies f(x) -> C then C is a horizontal asymptote of f(x). However if x->infinity implies f(x)->infinity then you dont have a horizontal asymptote.
To sum up:
-
When x->c you are checking for vertical asymptotes at x=c (You always check left and rightside limit.)
-
When x->infinity (from left and from right) you are checking for horizontal asymptotes.
As to how you compute certain left-side and right-side limit i will link a post where i explained an informal way of doing it. The right way is using epsilon-delta proofs.
@timber ice
shit
We can begin by just doing one of the limits
so when i check for vertical asymptotes i check for x as it approaches infinity from left and right
Yeah
and for horizontal it's when it approaches infinity from left and right
And c in this case is the x that makes the function undefined
Exactly
Ye np,
That's very well written, i always just check for infinity
If we look at this one, what does "+infinity då x ->-3^-"? if thats not a complex question to ask
does it mean it goes towards -3 from the left side?
Yes
3^- can be interpreted as
3 - d where d is a very small number
And 3^+ is 3 +d where d is a very small number
and the values don't really change tho right? when you check for infinity from left and right, you could just add ^- and ^+ as soon as you have figured out what value it goes towards
oh ok makes sense
For example, does e^x have horizontal asymptotes?
Solve limit as x approaches positive infinity
And now solve the limit as x approaches negative infinity
The limit is infinity when x approaches infinity right
But when you are going towars negative infinity you will have the limit equal 0
Therefore y=0 is a horizontal asymptote to e^x
Which is just the x-axis
försöker bara förstå vad som står :p en sekund xd
oh
juste
because e is defined for e>0
so right side is infinity whiles as minus infinity is 0
so it can differ
e is defined for all x
Hold on i will draw
Ok let me ask, how do you evaluate the limit 1/x as x approaches 0 from left?
let me get paper
it goes towards +/- infinity if x=/0 or x=/1
it goes towards 1
because like
it becomes -1000
it goes towards -infinity, i'm not sure how to explain it but it get's bigger and bigger
Exactly
but negative
Or well 0-0,01 is -0,99 right
And the smaller i make d the larger a negative
And if i go from right
x->0^+
It is 1/(0+0,01) which is 1 divided by a positive very small number
Which gives you a positive infinity
Now
yeah
well it goes towards +infinity right?
the numbers decrease but never reaches negative
no
it goes towards 0
e^-x = 1/e^x right
So it goes towards 0
Since x is approaching infinity we know that 0 is a horizontal asymptote
yeah please
Consider the function: 1/(x-5)
let me actually check which is which one sec
What is it domain? Is it defined for all x?
it's not defined for when x=5
At 5 we have a vertical asymptote
oh yeah i remember now, vertical asymptote is when the nämnare is 0 and horizontal is as it approaches infinity.
Yeah, so for x=5 the function isnt defined, x=5 is a singularity we want to study
usually it implies there is a vertical asymptote but that is not always true
You have to confirm it by solvind the limit
So lets solve what is the limit when we approach 5 from left respectivelt from right?
it's 5^- and 5^+, no?
it approaches minus infinity right?
if we plug in 1/(4.99-5) we get -100 and it continues to decrease
Since we have infinity from left and right
We have confirmed that there is a vertical asymptote at x=5
Now lets see of our function has a horizontal asymptote
Lets start with positive infinity
Solve 1/(x+5) when x approaches positive infinity
Both from left and right ye
since we can't breake out any 0's
One divided by a very big number gets us zero
And one divided by a very big negative number gives us 0 aswell
and these asymptotes are basically these values that the function never touches
Yeah
So vertical asymptotes are at valdes where x approaches a value that is in the domain
While x when approaching infinity we are checking for horizontal asymptotes
in this one
she is looking for when x=c which was our scenario one
Yeah and ske confirmed that we have a vertical asymptote at 3 and at x=5
alright, tack så sjukt mycket igen 
Du är fan tvär bra 😳

hmm
so for this question this is what i have done so far, i think i have solved half of the question
so i have solved for k but now i don't know what to do next, like what is my next step going to be
if anyone is there that can please help me?
i also have the answer key for this so the answer key says the answer k=ln(2)/27, which i have gotten already and then the actual question finding the time which is 54 years which i don't know how to find, like i don't know the next step to find it?
if anyone is there that can please help me out?
You didnt take into account that the substance is four times the safe level
so i don't get how would i do it?
like have i done everything correctly so far because i have only solved for k so far?
Let $N_{0}$ be the safe level of the substance. We know it is four times the safe level, so $Q_{0} = 4N_{0}$ We know that $Q(t)= Q_{0} \cdot\left(\frac{1}{2}\right)^\frac{t}{27}$
then solve the follwing equation.
$$Q(t) = N_{0}$$
$$ N_{0}= 4N_{0}\cdot\left(\frac{1}{2}\right)^\frac{t}{27}$$
rts
so i don't have the initial value which is No so how will i solve for t(time)?
$$ N_{0}= 4N_{0}\cdot\left(\frac{1}{2}\right)^\frac{t}{27}$$
$$ \frac{1}{4}=\left(\frac{1}{2}\right)^\frac{t}{27}$$
$$ \log{(\frac{1}{4})}=\log{\left(\left(\frac{1}{2}\right)^\frac{t}{27}\right)}$$
rts
sorry, where did No go?
I divided both sides with 4N
oh i got it
then i log both sides
yes your right
so after taking the log of both sides, are you left with log(1/4)=(1/2)^t/27?
Im left with the latest row in above pic
Should be straightforward now on how to isolate t
the t is your unknown
Recall that:
$$\log{x^a}= a\cdot \log{x}$$
rts
so is it log(1/4)=(t/27) x (1/2)?
what happened to the log on RHS?
doesn't it go away when i bring down the exponent?
nope
oh no, my bad
