#help-17
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vengeance
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2^m+2^n=520, how do i solve for m and n?
Find pairs of 2^m and 2^n such that their last digits add to 10
so tell me the pattern
pattern?
for last digit of powers of 2
the question on my paper was If 520=2^m+2^n, where m and n are integers, then m + n is equal to
im meh at math so i dont really understand what you're talking about
ok
so 2^1=2
2^2=4
2^3=8
2^4=16
2^5=32
so on
so we can say the last digits have a pattern of 2, 4, 8, 6, 2
let me bold it for you to see
oh ok
but how do i use that to solve for the question
well, which pairs add up to 0
and
2 and 8
bet
so we can say that a solution must be in form 2^(4k+1)+2^(4j+3) for k, j natural numbers due to our generalization
its probably easier to note that either 2^m or 2^n must be at least half of 520
which powers of 2 are between 520/2 and 520
i am le thinker
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struggling to understand how to know what directions to plot arrows in for phase portrait
the null clines is making sense to me
just dont know how you can know which direction the arrows go in with th 3 different null clines
why do the phase portrait arrows circulate around the fixed points (+-1,0) but tend away from the fixed points (0,+-1)?
what’s your vector field?
2D in x,y
yeah sure but do you have an explicit formula for it like x’ = f_1(x,y) and y’=f_2(x,y)
yeah but what’s the vector field you are plotting now is it a) c) of g)?
I am doing 3b
so f=2xy g=1-x^2-y^2
srry not really sure what youre asking
new to this topic
It’s C^1 at least so you can linearize your system around the different fixed point
then the resulting linear system Ax=x’ can be studied and will have the same behavior as the nonlinear one around the different fixed points
if you’re not familiar with that yeah you have to get a feel for the vector field and plot it like you did
Oh is A the jacobin matrix here
yes
Jacobian*
the jacobian evaluated at the fixed point you want to study
So that way I find where the FPs are stable/ unstable?
yeah, if it’s a sink attractive or repulsive
Okay I see, thank you
@white palm how would I know the directions of the arrows in the quadrants outside the circle like where I highlighted below
you could go quadrant by quadrant pick x and y big in this quadrant and get a feel for the direction this way because like polynomials from R to R from my little experience playing with these vector fields the interesting behavior is around the origin.
this empirical conjecture applies when your vector field is defined by polynomials, this won’t do if there is a sinx in your vector field
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Anyone know how to do this question?
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can sopmeon explain
i get up to the 3rd line
and after i dont get it
do you understand up to here?
the fourth line is literally just transposition
yes
literally just transposition then mate
well the left hand has an annoying m there which you dont want
so youd divide by $m$
and thats it
Percy
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I can't figure out why we have the $+ \pi$ in the second piece.
Graphically I get it, algebraically I don't see it.
Percy
I have like
\begin{align*}
y&=\arccot(x) \
\cot(y)&=x \
\tan(y)&=\frac1{x} \
y&=\arctan \left(\frac1{x} \right)
\end{align*}
and I don't see why we need the piecewise function
Percy
i mean, $\arctan(x)$ has a domain of $\mathbb{R}$ so I don't see why we need anything here-?
Percy
im at my limit now lol
@calm pecan the reason it is there is because of the way we have done the branch cut
uh huh?
So tan and cot are not one to one, right?
So when we take the inverse we need to decide which part actually gets mapped back as the inverse
I see, how do I do that?
It's just convention
Someone somewhere decided that the function would be more useful if it inverted one region vs the other
To be clear, having tan^-1(1/x) does make an inverse of cot
Okay yeah well, how do I introduce the + pi though?
And like, justify its necessity
Just not the principal one, okay
fair enough
But it doesn't make the function arccot, because arccot is defined as the inverse of the domain (0, pi) not (-pi/2, pi/2)
That's just what we need to do to make the numbers work
How do I show that my graph is shifted down by pi compared to the principal arccot
Well, the period is pi
okay and here we have a negative value for 1/x which doesn't work
i follow i think
Negative values of 1/x are not a problem
no? it'd be outside the domain for the principal arccot though?
wait nvm
tfw i get confused between range and domain
So I get that, like, $\arctan( \text{some negative value})$ would be a negative value, which wouldn't be the principal range of the arccot function, and shifting it up by $\pi$ solves the issue
Percy
To be fair, talking about the inverse you pun them a lot
Exactly
Can I just write 'adding pi gives the principal range so ill do that', or is there a more rigorous way to like, i dunno, derive that we need to shift by pi
So if we want to talk about rigor, your definition of arccot is incomplete
Because it is undefined at x = 0
That's also fair
So I think maybe mathematical rigor isn't terribly important for this problem.
(this isn't accusatory, just knowing when to pick your battles)
(yes i get it, going overkill isn't always the best idea)
So you would need to define arccot as the inverse of cot limited to the domain (0, pi)
And also use the fact that cot is periodic with period pi
Then if you can show some function, such as arctan(1/x) maps to some other part of the cot domain, then you can use the fact that cot is periodic to show a vertical shift of kpi where k is an integer also maps some other part of cot
And then you show for k = 1 and k = 0 it maps the parts that you want
Then you have to cover the case where x = 0
But like
There's no rigor in why we choose the part of cot to inverse
It's just what we have decided is most useful to us for most applications.
So in a sense the choice is arbitrary, so the selection of k is also arbitrary.
This applies to arctan as well
Anyway, the above is rigorous enough for a proof
Yeah, there's no problem here, other than the point wise discontinuity at x = 0
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If I understood it correct it, deposited means that she loans money to a bank.
Meaning that she will earn money from the bank
Do I do 300x1,05squared
and 200x1,05powered to three
and calculate how much they earned and see who earned the most
and the girl in the green earns the most?
since she earns 31.525 and the other 30.75
Woah, the last time I’ve touched interests was like 8 years ago.
I’m assuming this is Compounding.
$A = 200(1+5/100)^3$ and $A = 300(1+5/100)^2$
Maddie
,calc 200(1+5/100)^3
Result:
231.525
Thank you brother or sister @ruby jungle
I just got this as a new unit
Im new to it too
In a solution there are 50 bacteria per ml. The number of bacteria increases by 15% each minute. How many bacteria are there in 5 ml after 4 minutes?
@ruby jungle
So basically initially you have 50bacteria per mL.
So, 5 ml would have errrr 250 bacteria.
oh
Bacteria*
No, you’re fine.
wAit
Okay no more trolling.
So initially you’d have 250 bacteria.
Yes
Result:
437.2515625
yes
437 Bacteria
Also
Scientifically…
Bacteria shouldn’t be in decimals.. So i’d round to the nearest whole:)
Ty
this question too
@ruby jungle
You are making a sauce and the recipe calls for vegetable stock. 1 litre sauce must contain 4% of stock. How much sauce can you make out of 180 ml stock?
Its so confusing, I dont understand it at all
Okays, so 1 Litre of sauce -> 4% Stock
Means that per Litre, 40 mL is stock.
Do you understand?
4% =0.04
0.04 x 1L =0.04 Litres or rather 40 mL.
So, 180/40 will give u how many times you can make the sauce.
Yes
Do you understand up to here?
yes
Instead I used king henry does usually ..
converted 180ml to liter
and I got 0.18
40 mL Stock -> 1 L sauce
180 mL Stock = 180/40 x 1
Then that divided by 0.04 gave me 4.5
Yes. That works too
Yes
What I did is valid because of unit consistency.
180 mL/40 mL would result in a dimensionless value. Which can be multiplied by a unit to give you the final unit.
^ Additional information.
so with 180 mL of stock, you can make 4.5 TIMES of 1 Litre sauce.
So, the volume of Sauce you can make with 180 mL is?
Precisely 
Ty
The local lake in a town started to freeze one Sunday during the winter. The thickness increased by 2 cm each day. On a Sunday a couple of weeks later, the ice thickness has increased by 25% compared to the Sunday before. How thick was the ice then?
@ruby jungle the last questions I had some kind of idea how to do them but this just made my brain freeze
Hm…
So the difference is 25% increase in thickness… And we know that 2 cm each day, so 7 x 2 = 14cm.
Interesting
Wtf
Ok nevermind..
Nah, something was wrong
No, no
So percentage change is $\frac{(x+14)-x}{x} = \frac{25}{100}$ … Soo… x is the initial height and x+14 is the final height. The difference would be 14 cm as we know…
Yes
So.. unrealistically the height of ice is 70 cm 😂😂
Maddie
The equation?
Ok im trolling 😂😂 the change is simply 14/x
So 14/x actly the difference between one sunday and the sunday after
Yes
So the initial is x, final is x + 14.
The difference 14/x * 100% MUST be equals to 25% change
So solve for x.
My equation was 14/x = 25/100.:)
Solving for x will give you x = 56cm.
X+14 (Final height) is 70 cm.
You understand? 
I dont understand at alll
😂😂 I figured
Are you familiar with equations?
% Change is = Final - Initial/Initial * 100%
But then I dont understand why you add another 14
When you have already added 14 to the equation
Oh no, because I was looking for difference using the full formula 😂😂
Then i forgot 14 is the difference
But irregardless, x+14 is the Final height and x is the INITIAL height.
Let me write it properly
\begin{align*} \frac{Final - Initial}{Initial} &= \frac{25}{100}\ \frac{14}{x} &= \frac{25}{100}\ \therefore \text{ x = 56 cm}\end{align*}
So basically, Final - Initial is simply 14 Because for each day, it increased by 2 cm. After 7 days the difference between first and 7th day is 14cm Hence Final - Initial can be represented as 14.
Maddie
I’m in mobile
But as you mentioned, you can use x+14 = 1.25x:)
What you’re doing is you’re finding the 25% increase of x. 0.25x = 14 and x = 56 same thing.
Understand? 
The initial is x = 56 and final is x + 14 = 70 🙂
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Do i ask for help here?
yes
yeah
quelle question?
ok
You can also write in english its only that the tasks are in french
la première il faut regarder que la somme des proba est égale à 1
Okay merci
et aussi que toute les proba sont entre 0 et 1
Donc si c’est p.ex -0.5 c‘est impossivle?
une proba n'est pas négative
Okay
pour la deuxième il suffit d'ajouter les probas qui vérifient la condition
donc pour P(X <= 1) tu as que c'est la somme des probas pour X valant -3,-2, -1, 0, 1.
oui 0.80 pour celui que j'ai dis
oui
Okay merci
interpreter n'a pas vraiment de sens comme il n'y a pas de contexte
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polynome du second degre
tu sais que la somme c'est 1
donc p² + p + 0.44 = 1
résoud pour p
il devrait y'avoir qu'un seul p dans [0, 1]
parmis les deux que tu trouves
Mais comment est ce que je calcule ca?
tu ne connais pas les polynomes du second degré avec delta = b²-4ac ?
Oui
c'est sur celui ci qu'il faut faire delta
Mais comment est ce que j‘utilise le delta la?
Mais c‘est plus que 1?
Mais je fais quoi avec la 3.24?
Bro I reallllyyy dont understand anything in math i just want to solve the fw excercices dont you wanna do them quickly?
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Hello! Quick differential equations question
it doesn't matter
oh okay good to know
generally you put it on the right though
we only write one because the +C for both integrals can be combined into one constant
i guess you could do + C with both integral?
but then you would subtract the costant
which would still be a constant
because the constants wouldn't cancel out?
gotcha exactly
so the constants get combined
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Pulling my hair out
$\dv{y}{x} = -\frac{2xy^2 - 18}{2x^2y} = \frac{9 - xy^2}{x^2y}$
knief
yea you got that
knief
yuck
now
$\frac{x^2y(-2xy \cdot \frac{9-xy^2}{x^2y} - y^2) - (9-xy^2)(x^2\cdot \frac{9-xy^2}{x^2y} + 2xy)}{x^4y^2}$
knief
you had all this so far right
Yes but my two was in the front
$\frac{-2xy(9-xy^2) - x^2y^3 - \frac{(9-xy^2)^2}{y} - 2xy(9-xy^2)}{x^4y^2}$
knief
man these people are evil fr
let’s cancel xy
oh nevermind
that term doesn’t have it
Have been working on this for over a hour 🤣
you had this?
It’s a pretty evil problem for sure
$\frac{-4xy(9-xy^2) - x^2y^3 - \frac{(9-xy^2)^2}{y}}{x^4y^2}$
knief
I still had a 4 in the denominator since I’m not sure where it canceled out
i canceled the factors of 2 here^
$\frac{-4xy^2(9-xy^2) - x^2y^4 - (9-xy^2)^2}{x^4y^3}$
knief
ugh
then distribute i guess
$\frac{-36xy^2 + 4x^2y^4 - x^2y^4 - (9-xy^2)^2}{x^4y^3}$
knief
Thank you for helping me btw I greatly appreciate it
$\frac{-36xy^2 + 3x^2y^4 - 81 + 18xy^2 - x^2y^4}{x^4y^3}$
knief
$\frac{-18xy^2 + 2x^2y^4 - 81}{x^4y^3}$
knief
,w factor 2x^2 - 18x - 81
bruh
I shed a tear
lmao
I thank you🤣🤣
Wow what a problem, I’m giving him hell when I see him Monday
yea that’s just tedious work
Thank you so much
you’re welcome sir
I just type .close right?
yea
.close
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lil bit of a dumb question, but how do you simplify cos(arctan(x)?
try drawing a right angle triangle
label an angle theta
tan(theta) = x/1
so the opposite of that angle is x and the adjacent of that angle is 1
i hope u can carry from there
ykw that's extremely less convoluted than the unholy method i was trying 😭
i was trying to reverse a silly thing i did to get the derivative of arcsin(x) kind of similar ot logarithmic differentiation but w sin and then itnegrate to somehow get f(x) back
but
uhhh
that wasnt working at all 💀
tysm for your help!
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How to simplify?
might be sophie-germain
What's that
$x^4 + 4y^4 = ((x + y)^2 + y^2)(x^2 + 2xy + 2y^2)((x - y)^2 + y^2)(x^2 - 2xy + 2y^2)$
it is indeed sophie germain
hi fungus
Oh ok, I'll try using it
just an intuition, i would try only examining a small part of the fraction to apply sophie germain
the first term in each tesseract follows a linear pattern, i.e. 6x + 4
$\frac{(6(x + 1) + 4)^4 + 4\cdot3^4}{(6x + 4)^4 + 4\cdot3^4}$
try applying the identity on this first. see what you get
Ok
Actually wait, I don't get the tesseract part
Uh, just explain to me in highschool terms
another name for fourth power
Oh
like, squared, cubed, tesseracted
I see
since a tesseract is a 4d cube
Ah, make sense
Well, after playing around with the sophie-germain formula, I think I have an idea now
Anyways, imma take it from here myself, I'll close the channel now
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Part (b)
Very rough diagram
So we know that m and n have slopes of 2
And if we get where the slops of the tangent to the circle are equal to 2 we get their locations
But I dont really know how to find where the slopes of the tangents are equal to 2
Do I just take the derivative of the circle and set x = 2? (im just guessing)
yes
plus or minus
if algebraic distance is found
if you put modulus in the distance formula then it's already sorted
1 moment working things out
How do I do this with the c being unknown though
0 = 3(-1/2) + c
c = 3/2
2x + c = -x/2 + 3/2
c = -5x/2 + 3/2
x = 3/5 - 2c/5
do you know the formula for distance of a line from a point?
No I didnt know there was a formula
I always did it this way
oh
then that was a given method in the book you followed?
Im not following a book 😅
I dont have a teacher you guys are my teachers hehehe
But I would like to know this formula that sounds useful
WAIT I do know this one I just googled it
|ax + by + c|/sqrt(a^2 + b^2)
yes
this is the one
basically
take all the coefficients of the equation on one side
So x = 3, y = 0
yes
a = 0, b = 2, c = c
wait hold on
And the distance is all equal to sqrt(20)
what did you say the slopes of the tangents were?
2
-1/2 is the red line slope
then your line equation should be y - 2x - c = 0
a is -2
Oh
and b is 1
Okok
|(-2)(3) + (1)(0) + c|/sqrt((-2)^2 + (1)^2) = 2sqrt(5)
|-6 - c|/sqrt(4 + 1) = 2sqrt(5)
just substitute 3, 0 here
yes
|-6 - c|/sqrt(5) = 2sqrt(5)
yes
|-6 - c| = 2(5)
yes
-6-c can be 10 or -10
first check the solution for 10
that gives one line solution
Wait how sry
I get that |-6 - c| cant be negative
But how does it give us 2 solutions
there are two tangents to a circle with the same slope
like a sandwich
|x| = 10 means x can be at -10 or 10
Ahhh yeyeye
for example
if we needed to equate it to 5
for EXAMPLE
|-6+1| = |-6+11| = 5
so c can be -1 or -11
same way for 10
a normal line equation is a straight line
but the modulus for a single variable is a V
so one solution in the y axis cuts through two possible values in the x axis
Ok I thiiiink I get it
So -6 - c = 10 and -6 - c = -10
-c = 16 and - c = -4
c = -16 and c = 4
So the equations of the line are y = 2x + 4 and y = 2x - 16
(x - 3)^2 + y^2 = 20 is the circle equation
So sub in (x - 3)^2 + (2x + 4)^2 = 20 and (x - 3)^2 + (2x - 16)^2 = 20
And that will give us the x values of the coordinates
Then get the y values using those x values
and you should get a perfect square
then done?
(ax + b)^2 = 0 form for both
yes
Okokok I get it now 😄
Thank you so much for explaining!! You are a really good teacher
❤️
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How do i differentiate the end part
2pi^2r^3
Do i take both powers down by 1?
Ohhh im doing derivative with respect to r
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can anyone help me with part a & b
how do i find the value of a? in the right angled triangle?
ohh alright i get it now
and for part b do I just find the area of the rectanglular prism and add it to the triangular prism?
surface area of rectangular prism + surface area of triangular prism - the area of common face
what do you mean by the area of common face?
there's a face common to both the prisms
that wont be included in surface area to giftwrap
the 42 x 15 face
so ur net surface area is 4 trianhles + 5 rectangles
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take combinatorics
does looking at f'(x) give us anything
we can find maxima and minima by looking at f'(x)
i cannot simplify f'
@paper depot
Ann
you have f(x) defined in this form
by taking the derivative we can check at what points is the function f(x) minimum
or maximum
and how do we do that
how do we find those points
we have f(x)
i mean i assume you guys know application of derivatives / monotonicity
yes but do YOU know them
yes ofcourse !
exactly what computation with f' lets us find the min?
THATS THE POINT AFTER DIFFERNTIATING I AM NOT ABLE TO MOVE FORWARD !
f'=0 at the min
yes then
show us what your f' is
wait a min i ll send a photo of my working
you could have sent that at the beginning and saved us some effort
yep
yep
this can let you get rid of a lot of the complexity of the equation f'(x)=0
i ll try it wait a min
can you just tell why arctanx is always greater than equal to zero
for x less than zero it will be ...?
if x is negative then arctan(x) is negative also.
oh i see
so denominator is always >=0
and also e to the power everything
@paper depot i have got a smaller term but cant simplify it further
<@&286206848099549185>
show
@paper depot
bad transformation
arctan(x) + x/(1+x^2) = 0
note that you have here the sum of two numbers which are always of the same sign
either both positive or both negative
how can it ever happen that their sum is zero?
no, it means the only solution is x=0.
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no fractions don't turn from addition to multiplication
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hello, a friend sent me this because she couldn't find the mistake, and its supposed to be solved without substitutions, so idk what to do
how did tan²x become sin²x in the 4th step?
oh
never mind
misread
its cos⁴x in the denominator
There's no mistake
he had basically undone what he did tho
you just get back to F = F
yeah thats what I thought
you just get F(x) = F(x)
but that's useless
Why not simplify sin^2 / cos^4 to sec^2 tan^2 ?
or convert using double angle?
what's the point of that
then you have u = tan x and du = sec^2 x dx
its supposed to be solved without subs
no substitutions
oh
apparently no subs
my bad
):
Are you allowed to use the general form for \int sec^n x
no 😭
I saw it somewhere
do you think people who do not know about substitutions would know this formula lol
would it be possible to reduce this using the double angle formula for cosine?
trust me
i tried
cos²x = (1+cos2x)/2 ?
this behemoth though
cos^4 x = 1/4 (1 + cos 2x)^2
that lowkey seems harder to solve
maybe you can then do a partial fractions?
probably
hey hey HEY
i think
i did something similar
but was it with cos⁴
im not sure
brb

What works?

@paper panther does the answer have tan³x somewhere?
I mean, this is where I got to, but without a substitution you can't eval tan^2 sec^2
oh yeah
I guess so
,ask integral 1/(cosx)^4
why does it write it like that
that is tan³x yes
now how do we get there
im getting $\tan x + \frac{1}{3} \tan ^3 x$
that's the same as this?
,w differentiate tanx + 1/3 tan^3(x)
nice
sec^4(x) = sec^2(x) + sec^2(x)tan^2(x)
idk if this is any easier tho
oh its what we had before
nvm
i suggest splitting tan³x
can we use IBP?
Idts 😭
@paper panther
That'd leave us with exactly 0 applicable rules

i think so
but like atp just drop it im probably just wasting ur time
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why do we add two gradients in 2 constraints Lagrange optimization problems, what is the geometrical interpretation of it? I understand in the case of one constraint, level curves of two function touch at some point and in that point gradients are parallel, but cant wrap my head around when there are two constraints
So imagine you have two spheres, the place where they intersect is a circle
This circle is a level curve where both constraints are satisfied.
Unfortunately, with more constraints and more dimensions of the underlying function, we rapidly stop being able to effectively visualize these things because they start requiring more than 3 dimensions.
@pulsar dome ^
I'm sorry if it's not entirely clear
thank you for explaining, but it is still not entirely clear why do we add ,in this example, gradients to the circle
I see
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@pulsar dome sorry I went AFK
The idea I was trying to illustrate is, say for instance, you have f(x, y) and a constraint that makes a circle, like x^2 + y^2 = 4
your constraint reduces the number of dimensions of the valid output by one.
typically, this is true of any constraint.
now in the second case, you have f(x, y, z) and the two constraints each make a sphere.
let's say (x-2)^2 + y^2 + z^2 = 4, and (x-1)^2 + (y-1)^2 + z^2 = 9
these two constraint surfaces together have an intersection. And this intersection is the mutual constraint surface
This is typically (but not always) each reducing the number of dimensions of the possible solution space by one.
But the way they interact with the function is different.
so they take two different legrange constants.
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even though the answer to the first box should be negative cube root of y-3 in the site my homework is wrong there is no cube root
have i done something wrong
??? where is my cube root
Can't you type a fraction with the x^... ?
If yes you can do ^(1/3)
Else your answer seems correct so i advice you to contact them to ask
missing a - sign
I want to isolate I
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i can only check two times on the site
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so next try i wont know if i got it wrong
Riemann point it, missing a minus
that is true
should this be the proper formatting
you took the cube root before multiplying by -1
(-x)^n is not always the same as -x^n
idk then because the google ai begs to differ
then follow google ai and close your channel
.close
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i need visualizing -660 degrees. would appreciate to be taught how to draw them
Think circle. Start at the rightmost end, a quarter turn clockwise is 90 degrees. After doing 4 quarter turns, you will end up back where you started and at -360 degrees. This shows that -360 degrees is = 0 degrees. Keep going for -660.
and the opposite for positive?
yup, anticlockwise
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thank you very much! now it is much more clear
.close
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today we did graphing quadratics in factored form but i had a doctors appointment today and this is a new unit we started today
What exactly do you need help with?
well since i missed todays lesson I need help with all of it
no
its a new subject we started today
yeah its where y = 0 and the line touches the graph
yup, so when would f(x) equal 0 for the equation above
when y = 0?
i dont think i get the question
do you know exactly what y means?
up and down
vertical
yeah, but in this case it also means the Output
huh
do you know what x is?
yeah, but it is also the input
so for example if you have y=2x+1
what is y when x is 2
when F(X) = 0
yeah
now set the equation (x-2)(x+3) equal to 0
do you know for what input values (x) the equation equals 0?
yep
oh wait its not a singular point hold on
btw ive got a answer key to check with just in case
do you know what AOS stand for?
axis of symmetry
yeah, now do you know how to find it?
if you don't mind me asking what level math is this
add all numbers and divide by amount of numbers
ok vertex time
remember to set it equal to x
its just X=-1/2
yup
the vertex should be pretty easy to find now with this new info
do you know what exactly the vertex is?
the maximum or minimum
its the AOS
yeah
yup
so vertex is (-1/2 , -6.25)
yup
ok then, open and domain are easy because domain is pretty much always all real numbers and its positive so it opens up
yup
last thing is range
elaborate pls
it only affects the y-values
yup
aos is 2.5
yup
you have to multiply it by 2 now
so not much changes
yeah
just same steps + multiplying
yup
yup
