#precalculus
1 messages · Page 194 of 1
cya
or later idk
how do I find the maximum and minimum of y=sinx+sin2x
what have you tried and where are you stuck
ok
I tried adding the amplitudes of both
didnt work
factoring out sin doesnt work since it changes the equation
and it's the last problem on my math homework
and I wanna go play CSGO
hang on. given that you're posting this in #precalculus rather than #calculus, i suppose you're not supposed to use derivatives
is that correct
forget it
iidk I take calculus next year
why not use a sum to product identity then
The process of converting sums into products or products into sums can make a difference between an easy solution to a problem and no solution at all. Two sets
$\sin(x) + \sin(2x) = 2\sin(\frac32x) \cos(\frac12x)$
Ann:
so it is 2
maybe
0.o maybe
the maximum value cannot be greater than 2
because sin and cos are both bounded by 1
so $2\sin(...)\cos(...) \leq 2$ no matter what the contents of those sin and cos are
Ann:
if it so happens that there exists a point for which 2sin(3x/2)cos(x/2) is equal to exactly 2, then congratulations, that's your maximum value
what part of what i said is confusing?
Ann may I say something
i'm saying $\sin(t) \leq 1$ and $\cos(t) \leq 1$ for all $t$ @viscid thistle
Ann:
@lilac pier what
nvm
by how is sin(...)cos(...) less than or equal to 2
Ann:
$2\sin(...)\cos(...) \leq 2 \times 1 \times 1$
Ann:
ftr, it doesn't look like this is gonna be enough to find the actual max value
and like sinxcos2x+cosxsin2x
and like graph it
you are not starting with sin(x+2x)
sin(x) + sin(2x) is not the same thing as sin(x + 2x)
starting with sin(3x) is going to be pointless
I saw my teacher do sin+cossin=sin(1+cos)
sin(x) + cos(x)sin(x) = sin(x) * (1 + cos(x)) sure
why what
$a + ab = a(1+b)$, this is just algebra and has nothing whatsoever to do with trig
Ann:
I know
I'm not stupid I'm just uhh
Are you finding min/max?
fuck blame it on the sprite
yes sir
Hmm
@willow bear
I think knight has a soluuttion
And I’m assuming you don’t know calculus?
yyep
how'd u know ❤️
Hm
calculalusssss
my precalc book is shit
utter garbage
Well
...
Since y=sinx and y=sin2x have a phase difference, we can't add 1+1.
what
explaining calculus without calculus
they don't have a fucking phase difference
they're not phase-shifted wrt one another sup
0.o oh damn
They are?
no they're not
theyy dont
they're fucking sin(x) and sin(2x)
even i know that
they have fucking DIFFERENT FREQUENCIES
0.o
Yeah my bad
honestly i don't know
😢
this problem is inaccessible at your level. i really doubt that there's a way around it.
u think it wants me to graph it and wright down what I see
here i can even give the exact answer
which i guarantee you is impossible to arrive at w/o calculus
1.76 or something
it's 1.76ish yes but unless you're asked to find that value to two decimal places this won't do
he does not
i'm not about to give a calculus 1 lecture in ten minutes
it's more than just "the slope or something"
I mean real genius can explain anyyhting in 10mins
no
you can't explain a phd thesis in 10 minutes in its entirety to a five year old
i was not referring to you specifically
nor was i likening myself to a phd, which i'm not
yes ma'am
the exact answer is $\frac{(3 + \sqrt{33})\sqrt{30 + 2\sqrt{33}}}{32}$, and you'd find that by setting $\dv{x} (\sin(x) + \sin(2x)) = 0$ and evaluating $\sin(x) + \sin(2x)$ at those values of $x$.
Ann:
The metaphor is you can’t explain something a little more advanced to a beginner without providing more background
And that background will be given to you in further courses
my precalc class supposed to be like around half a semester long
uh yeah you were given a calculus problem in a precalc worksheet and you don't have the tools necessary to solve it
there really is nothing else to be said here lol
Uh can you show us the question from the book
yeah it has that graph symbol
what's that mean
just say ur pencil wrote it and ur brain agreed
You gotta graph it to get the maximum and minimum
@willow bear how do i do it by hand
just draw
squiggles
but then
like rly close
but then
make it so that one little box is like 1000 pi
so they cant say ur wrong
you can't
its just a lot of squiggles mushedtogether which lookes like ||||
what does that graph icon next to the question mean
It just means you have to get it by graphing it. Typically, it means you have to use some gdc
Looking at the rest of the questions, they don't seem to lend themselves to precalc methods. You probably have to use a gdc to graph them and get the maximum
it says it right there
0.o
we just got this book
read it
:/
all of it?
it ain't that much
That entire conversation above took place for absolutely nothing
unless your reading comprehension only allows you to grapple with about a dozen words at a time
bruh why u roast me like that
It's not a roast
kinda is
Dude
it is thick
If it doesn't apply to you, it's not a roast.
how hard can it be to read ONE (1) paragraph containing PRECISELY the information you need
yeah great
these symbols are trippy
I think some people use desmos or something
a graphing calculator or a computer with graphing software.
I'm just saying it's expensive
READING COMPREHENSION BRUH
If you have one use it to your advantage
this man has the biggest brain
I did better on the math sat part
YA GOTTA GET SOME AT SIXTEEN YEARS OF AGE DONTCHA THINK
I can agree with you: they're really expensive and very dumb
english is hard
yeah english is hard
ann r u 30?
Ann, he didn't say he couldn't use an online software.
20
is it a top uni?
i think so
harvard?
no
yale?
Vietnam?
is it in asai?
no
Asia*
is it in europe
uhh poland?
closer but no
hungary?
no
Germany?
saint petersburg state university, in russia
Lmao
....
very nice
"piveat"
moyo emya jager
like how many hours a day
hw
ok uh
avg
Skoko vremine u vas?
Take this to chill
can we like not do poorly transcribed russian
I like russia
also yeah
it has snow 😄
Take this conversation to chill, guys
I can speak, can’t read/write );
no thats too little
lol
TAKE THIS CONVERSATION TO CHILL
ttatt wont work
maybe 5 hours?
OK LEMME BRING IT BACK TO MATH
what's the arc length of the curve in p
p is russia
cause priveat
no ones going to respond
What
TAKE THIS CONVERSATION TO CHILL
pootis
Another misprint?
Nope
$-ct = \ln(\frac{B}{cD}) \implies t = -\frac{1}{c} \cdot \ln(\frac{B}{cD}) = \frac{1}{c} \cdot \ln(\frac{cD}{B})$
Abhijeet Vats:
There we go
basically, the stuff inside the logarithm was flipped
@summer monolith
ln(B/cD)=-ln(cD/B) ?
log properties
mmmh that was the property that was used
log properties
Can't see this one in the list
$-\ln(x) = \ln(x^{-1}) = \ln ( \frac 1x )$
ramonov:
application of power rule
what do you mean you 'can't see this one in the list'
you don't just have a piece of paper listing all the laws that you've encountered so that you can just pull one or two laws from it when you need them
try to actually follow the logic of the argument and you'll live a happier life
NO, THIS IS WHAT I MEAN
DO NOT SIMPLY HAVE A LIST THAT YOU'RE TAKING FORMULAS OFF OF.
Is this an imperative or a statement?

And why not?
It makes life easier
Wew
I didn't realize that 1/(a/b)=b/a
Not sure though. I need to check again.
??????????
Nevermind
I was just thinking about the derivative of ln(cD/B)
Lol
I've just waisted hafl an hour trying to comprehend how c^2De^-ct derives from 1/c*ln(cD/B)

$\dv{S}{t}=B-cDe^{-ct}\\\dv[2]{S}{t}=\dv{t}(B-cDe^{-ct})=,?$
RokettoJanpu:
👍🏾
$\lim_{x\to 1} \frac{x^m - 1}{x^n -1}$ hello I'd appreciate some help
CoolShot:
what am I supposed to do exactly
Find the limit, if it exists
one of the few cases where LH makes it possible to avoid having a shitton of different cases
wdym different cases?
natural, integer, rational, arbitrary real
ohh ok
wait you're learning derivative but don't know log rules what
I mean, i guess it is but it is not a prerequisite to understanding the basic idea of a derivative or an integral
how would u do the graph on the right?
f(g(x))
how would i fine the points for that?
or find the equation?
can anyone help with that
oof
Well, what do you think?
You're trying to find f(g(x)), where the input is now g(x), rather than x
What can you do with that?
oh
uh
idk ;-;
I do this?
is there an easier way tho :c
well faster*
@fluid shore
Well, how's that gonna help you here, though?
oh is it not?
When you suggest a method of doing something, you need to consider the reasons for why it's gonna help you.
uh u can
Did i say it wouldn't? I'm asking ya to think through it and see if it does help you.
Well, you could do that, certainly
Since f(g(x)) = 2g(x) + 1 = 2(3x-2) + 1 = 6x - 3, you can also do it that way.
oh then
simplify?
after making them equal?
so x-3?
@fluid shore
would be
f(g(x)) ?
No
oh
I just found f(g(x)) for you
Yes
Keep in mind, the input has now changed from being x to g(x) instead.
oh ok
so it would be 6x-3?
OH yay
thats what u got
so that would be the function for f(g(x))
so i could just plot it?
What do you think?
question tho how does this relate to the mapping thing?
i think : yes
but i dont really understand why we do this
can u explain how they are related or something
😛
What do you mean
Well, i mean, there's a bit of work that does go into all of this
There's a bit of theory so you'll just have to read up on it. Then, you can ask questions if you're confused.
Yes
oh
Lol
and the next thing?
That last bit?
yes
They're asking you to compare g(f(x)) with f(g(x))
question th
u know when they asked to graph
was i expected to just do it without
solving for it?
ok
uh
for the last bit
is the answer no
coz its not the same equation?
@fluid shore
Idk, you tell me
Yeap, so if they don't give the same result, they're not the same
Yay
im self teaching myself this
before school starts which is why im so clueless LOL
u know whats sad
i did what u taught me
i got
x^2+2x+1
but sadly i forgot how to Graph quadratics thats super sad
@fluid shore
lol
oh wait
i can complete the square
but i think i forgot how to
rip
@fluid shore Am i doing it right so far tho?
Lmao
lol
f(g(x)) = (g(x))^2 = (x+1)^2
No, you asked about completing the square
oh
That's the completed square
First of all, graph x^2 and x+1
i did
Then, graph (x+1)^2 by plotting points
ok
Legit, if you're not confident about doing it straight away, just plot points
There's nothing harmful about that
okk
hmm
is it the same graph
no right?
wait tbh for
i think they are does it count if
actually nvm
they aren't lol
right?
@fluid shore
What
You mean is (x+1)^2 the same as x^2
No they are not the same, my dear
But
They do look the same cos they're both parabolas
yes
lol
ok so
i did this part on my own
and other points I got were
using g(1) point (1,4)
using g(2) point (2,9)
using g(-1) point (-1,0)
are those right
@fluid shore
Do you expect me to do the calculations in my head?
Check the calculations you have done. If they're correct, then they're correct. If they're not, redo them.
Then, plot the points.
Did you follow the steps given correctly? Did you find every value that you need to calculate correctly?
Yes.
waitttt
x^2 is equal to
(x+1)^2
its the same graph
but translated
so they are equal? @fluid shore
they're not equal
why?
Is 4^2 = 3^2?
shifted
yes
Yes, they look the same. They're both parabolas
Is 4^2 = 3^2?
answer this
Okay, so have you solved the problem?
Good.
have fun and feel free to ask questions
I prob will
ask
LOL
i self teaching which does't help when ur just answering questions from class notes which u would do with the teacher but
annywayssss
i wanna get ahead so i can stay in winter break mode when school starts LOL
coz ill be done the work 😄
Are you in high school?
cool beans
like unicycle? everyone is scared of a unicycle, you're not alone
jokes aside, just have a positive attitude and roll with it know what i mean
yeah ik
ik 😛
What do you want to study in uni?
Engineering
or computer science
i would honestly just do math but apparently u cant really do much with just math so rip
are u guys american?
I'm Singaporean. I believe Publius is American.
yes
ur from Singapore?
oh ok
OK TIME FOR THE NEXT LESSON
😛
ok then i guess im
doing that
isn't that what we were doing
@fluid shore
making them equal?
?
oh that
i think i forgot how to rip
;-;
@pale bison uh u know how
it says solve
does that mean

that's meant for MrBioFex
How'd you get that
f(x) x g(x)
say you have $f(x)=x^2+2x$ and $g(x) = \sqrt{x}$
Publius:
then, when you say f compose g, what that means is that:
take the function g(x), and plug it into f(x)
so, you have f(g(x))
so, whenever you see x in the function f(x), you replace it with g(x)
yes, that circle
exactly
oh..
that makes so much sense
i thought the circle was
multiplication coz sometimes a dot represents that
multiplication is mostly likely a dot
ye
only losers use X
Its not X
lol
Its ×
lol
the true meaning of multiplication is to expand it to addition
To multiply a and b means to find the area of a rectangle with side lengths a and b
question
Kind of like "crossing" the side lengths if you will
x^2-12+3=x^2-9
Lol this is what precalc is nowadays?
Im just old ig
oh
lol
It matters not how hard it is. It only matters that you understand what's being presented.
tho I HAVE TIME
wellllllllll
uniiiii caressssssss
about the markkkkk
;c
which hurts but its fine..
this pre uni section of discord is really mixed up
what do u mean?
huh
well, because they're all "basic" and i don't think it matters that much that we have four different channels for it
so g composite of f is x^2 +6x -3?
Nah 4 different channels is so that we can help different people with different questions
😦
jk
yes you are correct that "so g composite of f is x^2 +6x -3" for a)
i think there's a typo
yees
what's your reasoning?
hmm
if i have f(x) = x+1 and g(x)=x-1
then f compose g and g compose f are the same, despite them being different
huh
so them being different is NOT enough to finish the problem
im so confused now ;-;
do the dirty work and calculate it
how
just like how you did in question i
oh..
i did tho
okay, then good, that's the right way to do it
where did those equations came from?
f composite of g(x)
and then g composite of f(x)
i jus used my answers for i and ii for iii
can I not?
ohh
i read the question wrong
i thought i is for a)
ii is for b
and iii is for c
my bad, yes
you're right
yeah
and say yes or no
ok lol
u really made that
complicated thats
very funny 😛
lol
... okay
yes
2nd
so far so good
but then i compare my self to people here and i feel like i'm a big dumb
oh rip
honestly idk if im dumb or smart
coz im good at math but lol sometimes Im just
very stupid
always happens, to anyone
my marks dont show that im good at it ;-;
it did before
which is why i dont find marks a fair way to
judge someones intelligence
coz i was at a 87 now look im at a 77
CAUSE: STRESS DURING TESTS
well, test scores don't measure intelligences first of all
it measures how well you understood the concepts (at least it tries to)
one test brought me down 7%
so just work on it
then i dropped 1 each time lol
but i do tryyyy
i do practice i just
stress out during tests and i blank out coz all thats in my mind is u gotta do this if u wanna go to uni and then
i panic when i dont get something then my confidence goes ⬇️
well yeah, that happens
but does uni care
NOPE
im scared ;c
lol
hey so for
b
i would be x+2
and ii would be x
right?
how did you get x+2 in b/i
oh ok so
(square root of x+1)^2 +1
the square cancels the square root
so then
x+1+1
which equals x+2
right?
alright first off
don't write square root like that
second, $g(x)$ is not $\sqrt{x+1}$
like what?
Ann:
third, you really should write sqrt(x-1)
oh ok
f(g(x)) = (sqrt(x-1))^2 + 1
wellits hard to say what u wanna say
with the parentheses
for math on
messages
its right on my paper
LOL
oh btw the answer should be x
these equations are equal YAY
b/ii is not x, ftr
would what be x - sqrt(2)?
the answer for b/ii
no
well show your work
ok
sqrt(x-1)
sqrt(x^2-1-1)
sqrt(x^2-2)
cancelled square with square root for x which gave me:
x- sqrt(2)
okay so
first off
f(x) is not x^2 - 1
and second
not only is sqrt(x^2) not equal to x in general, you also pulled a fucking freshman's dream
oooooooof
OMG
why am i copying these wrong
LOL
wait no
wait ye
rip
hey so i was
right before
it was x?
no you weren't
$\sqrt{x^2} = x$ is not true in general!
Ann:
if $x = -5$, then what is $\sqrt{x^2}$?
Ann:
5
exactly.
true
ok
my bad i thought it was outside coz
idk
lol
no wait i messed up
i guess i just did it without actually considering where the square was
so the final answer is just sqrt(x^2)
or i can fo
cant i do
x^(2 x 1/2)
and i get x^(2/2)
which is just x?
@willow bear
no! that only works if x is positive! which you cannot assume!
oh
you literally just demonstrated that $\sqrt{x^2}=x$ is false in general, since for example it is false for $x=-5$ !
Ann:
think! think about the things you say!
$x^{2^\frac{1}{2}}=\sqrt{x^2}=|x|$
Publius:
ok
square that number
neat
bad tex
the - will always become
a positive right?
so then u dont have to deal with
square rooting a negative number?
which is why it will be
absolute?
coz then u get the same number
umm
but positive since u square then cancel that with the square root
square root of a negative number is called imagenary