#help-13
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yes
hmm what if you made a basis with e^x and cos(x)
they are linearly independent
and then created a differentiation matrix
when you get Ae^(2x)cos(3x) for some constant A
nvm that wouldn't work
haha im sure one could figure out some interesting linear algebra way to solve this
Tabular?
haha yeah
also known as DI method (shout out to bprp) - basically just IBP
keep doing tabular until you get an expression which includes e^(2x)cos(3x)
just write it out tbh
that's where ur messing up
well sin is alterating
and e^2x doesn't cchange
so like 2 times
yes
also don't use this method
just write it out
yes you erase the last line and you would be done really quickly
pencil don't blame others for trying to help you
I would check your work
once you get a better answer lmk
hmm
just write it out again
pencil
I'm trying to help you
remember the formula for integration by parts
and please write it out!
it's not recommended for you
it can be done with tabular
just write it out properly
and don't use the shortcut method for now
solve it using the standard integration by parts method, and I'll let you know
okay, so do it and ping me
after you solve it normally, I will tell you
Good job!
Now
Expand it out
And bring the last term over to the other side
Okay so almost there
The last line is incorrect
Bro help me what happens in here im new
Idk
Sometimes we do like hs math like here
Sometimes we do like college level stuff
I’m a freshman in university
Aight bro you’re kinda being an ass
I wanna get into programming ngl
Dayum
I’m not helping you further but just look at both sides of the equality
On the step before the last one
Bring the last term on the right hand side over the left hand side
I’m guessing ur like a sophomore or sm
And bro you gotta calm down
You’re taking like basic calc
You’re privileged to get any help
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I'm sure I went through the process correctly to get the answer but it's still saying I got it wrong
would you like an image of my work
yea
hmm
I forgot the extra part with $f_{xy}(x_0, y_0)$ so I added it at the bottom, but I checked everything and it feels right from what I see
hanzoh
In the Q(x,y) formula I needed to use another line to finish the formula, when solving I forgot that part on the extra line at first but added it in later
that part is fine
hm
good
I also looked it over like four different times, I don't think there's a mistake in my work, but if there is it wouldn't be easily noticable
idk man
that's alright, I'll probably just email my professor
aight
Yup
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I'm confused, does graph like these have inflection points, I understand that inflection point occur when the graph goes from concave up to concave down, vice versa. to me the graph doesn't swap concavity, it only looks like it is increasing, so would this graph not have an inflection point at (0,0)?
only the interval included?
but yea, i think youve got it
you can firm this because f'' = -f
there are no interval given
the graph does seem to be concave up at the start and concave down at the end
I was taught to read the graph from left to right, to me it look like it's only increasing, is there any better way of understanding it
well reading increase is only going to get you critical points
what you should look for is if theres a maximum of the rate of change
it does seem like near the left side, the rate of increase starts increasing
then it maximizes around x=0
then it starts to slow down
if we increased the graph in either direction it seems like wed see the function turn around
however we are clearly looking at an interval where the function begins to increase, tops out, then starts to increase much more slowly, nearly stopping
so any small changes of increasing/ decreasing can indicate that graph potentially has an inflection point
you want to look for places where it seems like the rate of increase of the function tops out and turns around
like here, the function becomes more steeply increasing towards x=0
but after x=0 it looks like its becoming a much more slowly increasing function
this suggests x=0 is an inflection point
would it be bad to visualize it with tangent lines? also are there function in which inflection points don't exist in?
no, as long as you know what you are looking for
ok, I think I understand, in this case my graph will have an inflection point at (0,0) because the rate of change decreases after passing that point
yes
also are there function in which inflection points don't exist in?
yes
not to be crass but you should invent one
can you think of a function where the rate of change only increases?
hint: ||what if it was just a positive constant?||
ohh
and loosely you should be able to visualize what these look like
i guess really loosely 
yup an function like f(x) = x
yea thats sort of a uhh
i mean thatd be like a dummy example
heres a function with no curvature
y=2 works in the same way
you might consider a less trivial example like x^2
(the rate of change only increases)
and like wise maybe x^2+4, x^4 + x^2,
got, may I ask another question separate to the one above
I was given a function f(x) = (x+1)^5-5x-2 and it asked whether it was concave up bewteen interval (-1, infinity), I got x = -1, but I confused on how I would draw an line of interval and understand the right hand side of the interval
understand?
What do you mean in this context
what do you mean understand the right side?
can you add more context here, what do you mean you got x=-1
was given a function f(x) = (x+1)^5-5x-2 and it want me to find whether concave up bewteen interval (-1, infinity), to find concavity at the point I learned that we must differentiate the function twice, which I did
okay, so you differentiated f(x) to get f''(x)
yea, I got x from simplifying f"(x)
so you mean that you started from f(x), you obtained f''(x), and you found that x=-1 is a solution to f''(x)=0
can you classify the point x = -1 in the context of this discovery? what kind of point is it?
I think it, that this point is potentially a point of inflection, but the question wants us to determine whether it is concave up
so you found an inflection point
I lost on how to do that
inflection points are places where the concavity of the function changes
potentially
lemme see theres an image that might be helpful
im gonna toss a few
whats important to know is that the concavity is given by your second derivative
so you can create some equivalent statements, like
if f'' > 0 on an interval, the function is concave up there
the function has positive concavity i guess you could say 
just like how we might say, if f' > 0 on some interval, the function is increasing there
all of this to mean, you found the place where the concavity changes, right
you solved f'' = 0 and got x = -1
does f'' change at x=-1 to become positive?
aka, does the function have an inflection point at x=-1, and then become concave up?
@white isle
doin okay?
I'm confused
how would we interept the left side and right side of the inflection point
f'(x)?
yea like
if i said oh heres some function
find where its increasing
give me all the maximum and minimums using the derivative
find where its decreasing
conceptually do you feel okay with that process? how the derivative helps you to find these intervals and points?
yea
so, one way to think about all this inflection point stuff, is to just kind of use blinders, and apply all of this intuition again to a new function (the derivative of f)
you feel good with being given f, and using f' to find all that stuff
so now pretend f' is just some g, and we want to look at g'
so we interpret it just like with f'. if f' was 0 somewhere, and to the left it was negative, and to the right it was positive, youd have found a critical point
and to the left f would be decreasing, and to the right f would be increasing
you just change the words around
if f'' was 0 somewhere, and to the left it was negative, and to the right it was positive, youd have found an inflection point
and to the left f would be concave down, and to the right f would be concave up
idk if this is helpful
i promise im trying lol
I understand what you are saying, but what confuses me is mainly the definitions, I guess, for example f'' > 0 on an interval, the function is concave up what am I suppose to do with my x value?, once I get f'(x) or f''(x) and the values of x, I don't really understand what i suppose to do with the values of x that I get from solving these functions
well its like this
you have f'', so you can answer questions about concavity
they ask you if f is concave up somewhere
so all you need to answer is if f'' > 0 there
these are equivalent
presumably you found all the places where f'' = 0
its on the edge of the interval
so all that remains to check is that f'' > 0 somewhere on our interval
so we plug in any number into our f"(x) function to see whether positive or not
yea, which works here because there are no 0s on our interval, right?
you have this nice, continuous f''
it has no 0's on our interval
so if its positive somewhere, it has to be positive everywhere
because otherwise itd have to cross through 0 to become negative
it doesnt matter what theorem it is 
intermediate 
intermediate value theorem 
oh got it, if postive then concave up, if negative concave down. for critcal numbers they just local minimum and maximums, but what happens when f'(x) = DNE, what does that tell use about f"(x)?
I am butchering everything you said sorry about that
hmm can you think of a f which is defined at some x=a but f'(a) is not defined but f'' is defined

mostly f' tells you about f'' in the same way that f informs you about f'
that is, maybe, its more helpful to think of them in the other way around, if youre hunting for intuition
higher derivatives give you information about lower derivatives, not the other way around
idk if that makes sense, but thats how id think about it
critical points of the derivative of the derivative are inflection points
critical points are to f' as inflection points are to f''
and if f' being DNE somewhere means f'' is DNE there i think it could be an inflection point too 
but just by definition
see i think like
1/x is maybe an example
f'(0) is not defined
neither is f''(0)
and in fact the curvature of this function never changes
youd call x=0 a critical point because f' does not exist there
if i remember rightly 
but the curvature doesnt change, so its not an inflection point
and actually i think that a point where f'' is not defined is not an inflection point even if the concavity changes sign there 
these are pathological cases though
or maybe better say they arent interesting because they are either defined to be or not be
sorry im babbling 
ok, i got it
the curvature can change over a point where f or f' or f'' is not defined
or it can not change
its not enough information
f(x) = 1/x^2 has a change in curvature at x=0
f(x) = 1/x doesnt
just depends
thanks for your help, it has been a pleasure
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Practicing for extracurricular math test, these are the questions i'm completely stuck on and made no progress
- Let a be a number such that a^4 + a^3 + a^2 + a + 1 = 0. find a^2000 + a^2010 + 1
- Polynomial functions satisfy f(y)=3y^2 - y + 1 and F(G(y))= 12y^4 - 62y^2 + 81
what are all possible values for the sum of the coefficients of G(y)
-
Cuz i don't understand the symbols. Define f : {x|x<=0, xER} => R with f(x)=|x| and find inverse
-
Prove or disprove that the graphs y=f(x) and x=f(y) must intersect
-
For what values of a is the function f(x) = x/(x-a) its own inverse
on 3, the problem is saying: Define a function f, which maps non-positive real numbers to the reals, by f(x) = |x|
you should be able to figure out 4 by just guessing
how
no im asking
like
lets design one
im telling you its false
they say x=f(y) and y=f(x) always have to intersect
its not true
whats the problem with f=2
i know
so x=2 and y=2
this is just a preliminary guess, its the easiest guess
if it doesnt work, maybe we can qualify the reason why it doesnt work, and make a better guess
why doesn't it work
something slightly less easy but better informed
right, why doesnt it work
what does the graph of these two functions look like
what quality of the graphs make it not work
x=2 is just a line
i'm kinda confused
its all the places where x is 2
right
so any y value, but x is 2
so, x=2 is a vertical line, its straight
y=2 is the other way, all x, but anywhere y =2
ad y=2 is horizontal
but they intersect
whats the problem here
yea
at (2,2)
but i mean
what do you expect, theyre straight, right
yeah
yeah
so, really, we want a function that kind of bends up and away
can you think of a function like that
sqrt
something that maybe sort of bottoms out, and goes up towards infinity on each side
okay, we can try that
+5
,w plot y= x^2 + 5 and x=y^2 + 5

yay
OH
WAIT
i'm kinda dumb
they're basically two things
that are
like
perpendicular
i just can't visualize it
i get what you mean
this x=f(y) and y=f(x) thing flips the functions over the line y=x
yeah
so, if you can find a function that doesnt cross that line
the functions wont intersect, either
can yo uwork me through the polynomial one
Let a be a number such that a^4 + a^3 + a^2 + a + 1 = 0. find a^2000 + a^2010 + 1
i feel like i just missed a concept
not supposed to be a hard question
k it's fine
for 5, im sure theres some way to guess

but, you could just use the definition of inverse
you want f is its own inverse
so f(f(x)) = x
its not fun, but this will get you the answer
i got x^2-ax^2+a^2x=x from that 💀
wait i didn't do it right i think
we want this to be true regardless of x value right
so i think we can just match up coefficients
write it x(1-a) = 0 and a^2 -1 = 0
require both equations be true
this gives 1-a=0 and a^2 = 1
(a = 1)
if we did good, the function should be symmetric about y=x
(because f(y) must equal f(x))
3 says, you have a function that takes in a non-positive number and returns its magnitude
f-1(x)=-x where x>=0 right?
so given the magnitude of a number, what function maps the magnitude back to the corresponding nonpositive number?
negative
yes
its just negative
this is actually part of the definition of |x|
but the domain has to be a certain thing right?
well, you can see it there
right
well, you can see this too
you know for an inverse to exist, what youre really looking for is that like
say you write f(x) = y
you want that f(y) = x is also a function
yeah okay
if you rotate this thing 90 degrees
i gtg
it fails the vertical line test
sorry
not a function
yeah
youre good
but the range
have a good one
if we just take half the pointy function
its just a line
it does fine
@lunar radish Has your question been resolved?
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For this problem, I use the tan sum identity but i am confused because tan(pi/2) is undefined. I am not sure how to work out (tan(theta)+tan(pi/2)) / ( 1 - tan(theta)tan(pi/2). This is the tan sum identity after everything was plugged in. can i have some direction?
I would do it in terms of sin and cos
$tan \left(\theta + \frac{\pi}{2}\right) = \frac{sin(\theta + \frac{\pi}{2} \right)}{cos(\theta + \frac{\pi}{2}\right)}$
MellowDramaLlama
$tan \left(\theta + \frac{\pi}{2}\right) = \frac{sin(\theta + \frac{\pi}{2} \right)}{cos(\theta + \frac{\pi}{2}\right)}$
```Compilation error:```! Missing \endgroup inserted.
<inserted text>
\endgroup
l.57 ...right)}{cos(\theta + \frac{\pi}{2}\right)}
$
I've inserted something that you may have forgotten.
(See the <inserted text> above.)
With luck, this will get me unwedged. But if you
really didn't forget anything, try typing `2' now; then
my insertion and my current dilemma will both disappear.```
how would tan(theta + pi/2) be equivalent to sin(theta + pi/2), can you explain that, i dont understand?
its not hold on I'm getting syntax errors
oh i see
lemme know if you get stuck
no that worked out perfectly, i didnt ever think to use the quotient identity in this problem. thanks a lot!
.close
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i need help with factorising using common factors
please post a specific postition you need help with
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Could someone help me out?
apply that
Although does the 3 go to the numerator or denominator?
in combo with exponent laws
stuff gets multiplied to numerator
$a\times \frac bc = \frac{ab}{c}$
ℝαμΩℕωⅤ
Here is the full question
Thought I could do it, but really confused on how to integrate it.
this did not require you to express sec in terms of cos
Yeah, I was just overthinking it
its recommended that you ALWAYS post the original at the very start
Will do 👍
Still getting a different answer when I enter it on my calculator
Is this the correct way to write it?
<@&286206848099549185>
poor notation, that may be interpreted differently be certain calculoatrs
if the calc doesn't recognise cos^2(x),
use more (): (cos(x))^2
is this purely for checking an answer you got?
Yeah
show what you're getting
I'm getting 0.87189
and a pic of what the calc is pumping out
,w integrate from π/6 to π/4 \frac{3}{cos(x)^2}
When manually integrating I get this
But when I check my calculator I get this
what are you entering into your calculator
^
poor notation, that may be interpreted differently be certain calculators
yeah that's fair
I kinda assumed they were inputting (cos(x))^2
seems like it might be computing
$$\int_{\frac{\pi}{6}}^{\frac{\pi}{4}} \frac{3}{\cos(x^2)} \dd{x}$$
ℝαμΩℕωⅤ
,w integerate 3/cos(x^2) from pi/6 to pi/4
yeah
Isn't that correct?
no
no
they're very different
What is wrong with it?
square in the wrong place
$\cos^2(x) = \cos(x)\cdot \cos(x) = (\cos(x))^2 \redneq \cos(x \cdot x)$
ℝαμΩℕωⅤ
Oh yeah I see now
@tired inlet Has your question been resolved?
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i dont get it
im trying to calculate for question 16
but its telling me that justin has to lower his mark to be in a higher percentile ???
like what
please help
you haven’t given any information that lets us help you other than something’s clearly gone wrong
im good now
use .close pls
.close
@cursive thicket Has your question been resolved?
.close
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if this grid represents that fraction (4 column x 3 rows) what number equals to that diagonal line ?
Also how would one define math ? What is it ?
that diagonal line divides the grid in half, maybe you'd call it 2/3
however this doesn't really have an answer
It does
and neither does your second question
I may be missing the context
you are
Okay i give you a time stamp
Unlock the mysteries and inner workings of the world through one of the most imaginative art forms ever -- mathematics -- with Roger Antonsen, as he explains how a slight change in perspective can reveal patterns, numbers and formulas as the gateways to empathy and understanding.
TEDTalks is a daily video podcast of the best talks and performan...
Help me understand what he said.
he is asking about the length of the line
it is a triangle
and a special type of triangle
Equilateral ?
where you know the base lengths are 3 and 4
so the length of the hypotenuse must be 5
Why ?
There is no definition for math ?
Then what does mathematics even mean ?
Study of a word ? -.-
this is not a specific math question, if you have a problem you need help with, post it, otherwise close this channel as this is not the point of them
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the second is more useful if you are looking for one specific side, while the first is better for finding the angle A or other sides if thats what you meant
but they are essentially the same
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Hi I have a question it was e^(2ln(y)) = y +12 and I got two answer y=4 and -3 but I am confused whether -3 is a correct solution as in this form its a math error but can't it be rewritten as (-3)^2 because e and ln cancel
so y^2 - y - 12 = 0
(y-4)(y+3)
y = 4 and y = -3
but then
recognize
ln(-3) IS NOT DEFINED
so y = -3 is not a solution
yeah i was just wondering about whether the form would make it (-3)^2 but it doesn't, thanks for the clarification
yep
.close when ur done
.close
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I have two pouches, each with five seemingly identical coins, but we know that in the first pouch, there is one fake coin, and in the second pouch, there are two fake coins. We randomly drew one coin from each pouch, and then from this pair, we randomly selected one about which we confirmed that it is fake. What is the probability that the second selected coin is also fake?
Solution: 4/15
@rugged tusk Has your question been resolved?
Let F1 denotes that 1 coin is false and F2 denotes that two coins are false.
We want to find out $P(F_2 \vert F_1)$.
From the Bayes theorem we can get $P(F_2 \vert F_1) = \frac{P(F_1 \vert F_2)P(F_2)}{P(F_1)}$
then i dont know how to move forward
Michal
in this case and in majority of cases i've seen bayes theorem doesn't help you
you have enough information to do this
bayes rule pushes you back one step
there are three ways you end up with a false coin picked:
it comes from the first pouch: (1/5)(3/5)(1/2)
it comes from the second pouch: (4/5)(2/5)(1/2)
or they are both false: (1/5)(2/5)
added together, they give P(B)
if P(A) means that i picked 1 false coin, what is P(B)?
and how to calculate the intersection? if A and B are independent we can calculate it as a product of P(A) and P(B), otherwise bayes...
yeah i can see that, I'm implicitly multiplying (1/5)(2/5) by 1 to get P(A & B)
thanks
$P(A\vert B) = \frac{P(A \cap B)}{P(B)} = \frac{P(A)P(B)}{P(B)} = P(A)$ ?
Michal
then why we calculated P(B)
maybe i'm not doing that
Let F1 denotes that 1 coin is false and F2 denotes that two coins are false.
We want to find out $P(F_2 \vert F_1)$.
From the Bayes theorem we can get $P(F_2 \vert F_1) = \frac{P(F_1 \vert F_2)P(F_2)}{P(F_1)} = \frac{1 \cdot \frac{2}{25}}{P(F_1)} $
Michal
i think that this was pretty good start, now i need to calculate only the denominator
$P(F_2 \vert F_1) = \frac{P(F_1 \vert F_2)P(F_2)}{P(F_1)} = \frac{1 \cdot \frac{2}{25} }{ 1-\frac{2}{25} - \frac{12}{25} } = \frac{2}{11}$
Michal
hmm, its still incorrect
First, your $P(F_1)$ is incorrect. It should simply be 1 - 12/25 = 13/25.
Second, $P(F_2 | F_1)$ is not the probability you are looking for. You need to account for the probability that you pick a false coin. ie. you are twice as likely to pick a false coin from two false coins than from a false and true coin.
chencking
So I don't get it how to calculate that
Try making $F_1$ the outcome that you pick a false coin from your two coins and $F_2$ the outcome that both coins were false. You want to find $P(F_2 | F_1)$.
chencking
Yes. Those are the outcomes the problem gave in the start.
He mistakenly used incorrect outcomes. That is why he got the wrong answer.
He was calculating the wrong probability.
i copypasted (1/5)(3/5)(1/2) twice in my solution
sorry
(1/5)(2/5) + (1/5)(3/5)(1/2) + (4/5)(2/5)(1/2) is the denominator, 1 − 3/50 − 4/25− 12/25 if you want to subtract instead
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how do i find the critical point of this
its gonna be -(t-5) and t-5
i find the derivative of both
gonna be -1 and 1
-1 & 1 = 0 is underfined
now what
What are the instructions of the question
find the critical point
What is your definition of crticial point
idk the definition
critical point c means f'(c)=0 or f'(c) is not defined
so 0 is the critical point?
the answer key says 5 tho
we need to find a point where the f'(x) is not defined
means it is not differentiable
oh so the critical point is what value we substitue is f`(x) to get 0 or underifned?
yea
if you see the normal |x| function
it is not differentiable at x = 0
so we need to make t - 5 = 0
do u get it?
sure if i can help
48
i got this
so only critical point is 0, right?
because if we substitute 0 , we get undefined
i dont think this is correct
what is it
wait let me get a pen and paper and solve on my own
wait fr?
so in rational functions
like we dont just set the whole equation to 0
actually ill get 1-x=0
yea
but still isnt 0 a critical point
you just take the denominator to the other side
not always
but here it is
since if the denomiator is 0 g'(x) becomes undefined
can you find the domain of thr given function?
i forgot how to get domain 😅
its a sqaure root func
so whatever is inside of it
cant be negative
2x - x^2 > 0
whatever x satisfy this
are in the domain of the func
can you solve this now?
x= 2
yea you set it equal to 0
we need to make it 0 ot greater than 0
when will it be greater than 0?
when its = to 3?
wait no i mean 2 and less
because x< =2
we change the direction when negating
look
so endpoints is finding the domain of the denominator
no the whole function i think
nope
Idk how they got only 1 as the critical point tho
0 should also be a critical point i think
i didnt understand this
i just solved the inequation
the domain is [0,2]
so 0 and 2 are included in the domain
since root0 is defined
i think this is called 'the wavy curves' method of solving inequalities
i have more questions can i send 😅
umm how many?
2
okay
i read this 1000x times
plenty of people here to help you here even if i go
i didnt understand how it only have 1 real solution
Do you get the part where it says "it crosses the x-axis"
yes i get it i can explain
But you need to ask specific ques
see if it even had 2 real solutions
if would mean that f(x) is zero at 2 points
and if in a continuous function there exists 2 points a and b where the function gives out the same val
there must exists a c between a and b such that f'(c) is zero
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i have done this with arg properties
It took some calculations
but in the solution they did something with geometry i dont get the solution
How do they know z is on the arc
I dont know what arg(z1/z2) actually means graphically
wait actually i know what arg(z1/z2) means its just the difference of angles but in here something different happening i think

(z + beta) - beta = z, as well as (z + alpha) - alpha = z. In other words, those triangle side lengths represent z + beta and z + alpha
uh lemme get this hold on
i dont understand how we can conclude its the side length

It's like vector addition yknow
The ones that have the angle pi/4 in between
There it'd be z - (z + alpha) = -alpha
oh
I am messing up the directions
how do you know its that direct
like the way they point out
i understand how you pointed them
But i dont know why that
So if you have a vector PQ then that represents a vector in the direction from point P to Q right? so if z represents point P, and Q represents point -alpha, then PQ = (z - (-alpha)) = z + alpha represents the vector pointing from z to negative alpha
it's aight
thanks
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Pls give reasoning for q1 part (a)?
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Sorry for this, it just hit me now u meant here the qp vector is z + alpha right , cause the pq vector is -alpha - z
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Umbrella Corporation hired 87 employees, which increased its stff by 40%. What was the original number of employees? How many do they have now?
Set up an equation
One side is 87 employees
Other side is = to a relationship and 140%
wdym relationship?
it is 87 = 40% from original number or smth
Do you round the numbers?
ye, the number is odd
's what makes me think im wrong with this answer
but quora says the same equation so 🤷♂️ thank you!
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how do I convert this into cosine or sin?
I know how to work with the sum difference identities but I've only done it with sin and cos values
You don't have a sum/difference identity for tan? There's a popular one
Tan is sin/cos
yes so is it sin 19pi12/cos 19pi/12?
But indeed if you don't want to use it, it's enough to get sin(19π/12) and cos(19π/12), then divide them.
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anyone know why its wrong?
Im guessing its something like 19999 💀
how can i do that? sorry not too good with this calculator
its ti-84+
i don’t have that model
If you make t go to infinity the equation become 9450/(0.5 + 0(because it gets smaller)) if im correct
yea i did x at 499,999 and it came out to 18900 or so
Just think of what happens to the number as it gets bigger
The number you add to the bottom gets way smaller
Cus it 1/26.5e^t
Which if t = infinity 1/infinity is 0
Well not true
But u get my point
As it approaches
I did it in my head by just assuming t is an infinitly big number
yeah 💀
thank u 🙏
:3
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how do you find the closest approach of two particles A and B?
my notes say that rB|A(t) * vB|A = 0 but we don't have a velocity for the two vectors im trying to find
"The position vector of particles A and B, t hours after 12 noon, are r = 12i + 3j + t(3i + 4j) and r = -3i - 5j + t(2i +6j) metres respectively. c) FInd when A is closest to B and find this distance."
Already found the distance in terms of t and when A and B are 18 m apart
it says in the answers that |AB| is minimised when t = (-2)/2(5)
but i have no idea how that works
i tried solving for the vB|A using the parts that are t(3i + 4j) and the other one in the position vectors and solve that against the vB|A(t) but that didnt work either
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..?
this is the question?
u used vector subtraction yet?
u can simply use the distance formula here
then u get the distance as f(t)
from there u could get the answer
like [12+3t-(-3+2t)]^2+[3+4t-(-5+6t)]^2=distance^2
d^2=5t^2 - 62t +289
???
@heady sierra
t = -2/2(5)
which i dont get
t=-1/5?
how did u get distance 18
yes
my distance is like 22/sqrt5
I know using differential calc with methods but I don’t think we’re expected to know dif calc for this
right
well first we would right the equation as a square of something
Would dif calc work too just to know for later
yes
ok 5t^2-2t + 289 can be written as 5(t-1/5)^2 + 289 - 1/5
i dont know its name but to get the minimum value of a quadratic equation , u just have to do x=b/2a where a is positive
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Hello
I'll just get an image lol.
well use the fundamental thm of calculus
yeah.
mhm
@versed fulcrum Has your question been resolved?
you can use leibnitz rule
notamy
ah sorry, didn't see that you've already sent it
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Yeah. Just checking for each option is the simplest way.
Doing analysis for the question is probably an overkill.
but my inequality is wrong right
since when was 1/2 < 1/3 lol
Yeah. Lol
the teacher wrote that
no the other way doesn't conform the question's specification?
lol
i write it as two i guess?
Actually it's two separate inequalities.
yeah so i think there's something i can exploit
1/x + 1/y < 1/3
1/x + 1/y > 1/2
wait that doesn't make sense again
lmao
1/x + 1/y is less than 1/3
but is more than 1/2???
If it satisfies anyone, it is in solution set again.
There is an "or" in the question.
It needs to satisfy any one of them.
Since it can't satisfy both.