#help-28

1 messages · Page 303 of 1

narrow ermine
#

This is used a lot for multi-variable limits because if you can show $\abs{\text{inside of your limit}} \le (\text{limit of something you know goes to 0})$, then you can conclude straight away that your limit goes to 0.

glossy valveBOT
#

Azyrashacorki

narrow ermine
#

It's often easier than checking paths and such

full forumBOT
#

@bitter tree Has your question been resolved?

bitter tree
#

ohh oke thx so much

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#
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upbeat tiger
#

\begin{document}

\textbf{Problem 6.}

In the accompanying figure is represented the cube ( ABCDA'B'C'D' ), with ( AB = 8 ) cm. The diagonals ( AC ) and ( BD ) intersect at point ( O ), and the lines ( A'B ) and ( AB' ) intersect at point ( E ). Point ( F ) is the midpoint of segment ( CC' ).

\begin{enumerate}
\item[(2p)] \textbf{a)} Show that the volume of the cube ( ABCDA'B'C'D' ) is equal to $512$ cm( ^3 ).

\begin{center}
\( V = l^3 = \dots = 512 \) cm\( ^3 \)
\end{center}

\item[(3p)] \textbf{b)} Prove that the lines \( FO \) and \( DE \) are perpendicular.

\end{enumerate}

\vspace{1cm}

(Note: The figure shows a cube in perspective with points ( O ), ( E ), ( F ) marked, together with the space diagonals and some face diagonals.)

\end{document}

glossy valveBOT
#

Allstars
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upbeat tiger
#

This is the figure

#

<@&286206848099549185>

torn jolt
upbeat tiger
#

My first time using help

mossy stratus
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# upbeat tiger <@&286206848099549185>

Please only use the <@&286206848099549185> ping once if your question has not been answered for 15 minutes. Please do not ping or DM individual users about your question.

pearl thicket
upbeat tiger
#

I need help with B

#

Soooo?

balmy dust
#

wait

#

a sec

#

yk vectors?

upbeat tiger
#

No

balmy dust
#

@upbeat tiger

upbeat tiger
#

Pure geometry only

balmy dust
#

right

#

idk tbh

solid anchor
#

hi

balmy dust
#

seems pretty elementary with vectors

solid anchor
#

whats the doubt?

balmy dust
#

dk about geo tho

solid anchor
#

wait is geometry?

balmy dust
solid anchor
#

nah not my type gng ✌️

#

sorry gng

torn jolt
upbeat tiger
#

Like pure geoemetry

torn jolt
#

🥀

upbeat tiger
#

Im in 8th grade

torn jolt
#

hm..

upbeat tiger
#

Romanian not american

#

Soooo noone?

#

😕

balmy dust
#

!status

full forumBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
mossy stratus
#

for question A since its a cube so base line height and width equal

#

set those equal l, then volume = l^3 = 8^3

balmy dust
#

he only has doubt in B supposedly

mossy stratus
#

o let me see

upbeat tiger
mossy stratus
#

proof OF parallel to AC'

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@upbeat tiger thats the first step

upbeat tiger
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It is the middle line so it is parallel

mossy stratus
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median line in triangle

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now prove AC' perpendicular to DE

upbeat tiger
#

Ok tx

#

Love u

#

.close

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torpid perch
#

which kind of functions have empty image

mossy stratus
#

Empty function

torpid perch
#

what?

#

care to elaborate

mossy stratus
#

Function f: empty symbol -> B

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You know a function is when given any x only return exactly one y value for each x right

#

Alo, care to respond? -.-

torpid perch
#

you mean a function with a empty domain

mossy stratus
#

Yep

torpid perch
#

that is a empty function

mossy stratus
#

If no domain then no codomain to image

torpid perch
#

any x in domain

mossy stratus
#

My bad for respond long i was typing translate and do code

torpid perch
#

what?

mossy stratus
#

You nailed it

mossy stratus
torpid perch
#

i see

mossy stratus
#

Do you understand now bro

#

Or more explanation

torpid perch
mossy stratus
#

If you have a domain that have no elements, then you cant have an output

torpid perch
#

that the domain is empty

mossy stratus
#

Like putting no fruits in blender and expect to have smoothies

mossy stratus
#

Function (empty symbol)

torpid perch
#

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subtle thorn
#

I have a couple of PDE-related problems i should be able to solve but am too brainrotten to rn, and deadline is today. If someone could nudge me in the right direction, i'd be very grateful.

1

I have proven a result showing for $x\in\mathbb{R}^3$, $R>0$ [
\int\limits_{|y|=R}\frac{dy}{|x-y|}=\int\limits_{|y|=R}\frac{dy}{\max{(|x|,R)}}.
]Using this, i need to show the following: for $0 \leq f \in L^1(\mathbb{R}^3)$ a radial function, prove that there exists $M>0$ such that for $|x|$ large
enough, we have
[\int\limits_{\mathbb{R}^3}
\frac{f (y)}{
|x - y|} dy \leq \frac{M}{
|x|}.]

glossy valveBOT
#

🇵🇸μ🔆
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subtle thorn
#

i think the idea of this problem is to split the integral by $|x|>|y|$ and vice versa, so we integrate over a ball (or its complement) for fixed $|x|$, there the radiality of $f$ should prove useful

#

but just some step isn't clicking

glossy valveBOT
#

🇵🇸μ🔆

subtle thorn
#

it is also obvious the constant will be a multiple of the L1 norm of f

#

<@&286206848099549185>

solid anchor
#

Yeah?

subtle thorn
#

here's an idea of what might work as a solution but i don't think it makes sense.

\begin{align*}
\int\limits_{\mathbb{R}^3}
\frac{f (y)}{|x-y|}
\leq \int_{|x|>|y|}f(y)/|x|dy+\int_{|x|<|y|}f(y)/|x|\leq 1/|x| (\int_{|x|>|y|}|f(y)|dy+\int_{|x|<|y|}|f(y)|dy)\leq ||f||_{L^1}/|x|
\end{align*}

glossy valveBOT
#

🇵🇸μ🔆

subtle thorn
#

:/

full forumBOT
#

@subtle thorn Has your question been resolved?

neon rivet
subtle thorn
#

<@&268886789983436800>

subtle thorn
neon rivet
#

inflicting sensitive topics?

sterile jungle
#

Good for you, but don't spam in random help channels please

austere cove
#

Why you invading a help channel if you don't have anything useful to say?

cunning sapphire
#
  1. don't troll, and 2) this is someone else's channel.
full forumBOT
#

@subtle thorn Has your question been resolved?

full forumBOT
#

@subtle thorn Has your question been resolved?

subtle thorn
#

no it hasn't and i don't expect it will be.

full forumBOT
#

@subtle thorn Has your question been resolved?

fringe siren
#

In the first equation the right part is supposed to be infinity, so there is a mistake, i think

fringe siren
#

you integrate over R^3 the constant, it is infinity.

subtle thorn
#

sorry about that

#

<@&268886789983436800>

fringe siren
#

in the second equation also the same?

subtle thorn
fringe siren
#

what you mean by f- is a radial function, it depends only on radius?

subtle thorn
#

yes, ie it's rotationally invariant

fringe siren
#

the conditions still seem strange to me because for equations shouldn't matter how big x is

#

i suppose you should rewrite equation in radial coordinates to better understand behavior of integral

#

$dx dy dz =r^2 \sin(\theta) dr d\theta d\phi$

glossy valveBOT
#

mikhail_kolesnikov

fringe siren
#

if f is a radial function it will be actually $L^1(\mathbb{R})$ and and the analysis will be reduced to integration over one variable am not sure how to write |x-y| but i suppose y shoulduse formula |x|^2=(x,x) where (x,x) is a scalar product

glossy valveBOT
#

mikhail_kolesnikov
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subtle thorn
#

like the computation is very much analogous

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like i can WLoG rewrite f(y_1,y_2,y_3) =g(|y|)

fringe siren
#

the problem that f(r) can have pole in r=x

subtle thorn
#

but it's a removable singularity so do we mind

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that's why we split the integral right

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and since f is L1 then the integral is finite

fringe siren
#

honestly idk

subtle thorn
#

now i'm just not 100% sure what to do on the ball's complement

subtle thorn
#

(on the ball)

#

so multiple by L1 function is no problemm

fringe siren
subtle thorn
#

exactly

fringe siren
subtle thorn
#

well, i'm just tryna find the upper bound, right?

#

so, [
\int_{|x-y|<R}f(y)/|x-y| \leq \int_{|x-y|<R}|f(y)|/|x-y|\leq ||f||{L_1}\int{|x-y|<R}\frac{1}{|x-y|}]

glossy valveBOT
#

🇵🇸μ🔆

subtle thorn
#

am i making a logical leap

fringe siren
#

f(y) is a vector function?

subtle thorn
#

well $y\in\mathbb{R}^3$

glossy valveBOT
#

🇵🇸μ🔆

subtle thorn
#

the whole time $x,y\in\mathbb{R}^3$. Idk if that wasn't super obvious, sorry

glossy valveBOT
#

🇵🇸μ🔆

fringe siren
#

no am asking if $ f:R^3\to R$ or $f:R^3\to R^3$

subtle thorn
#

right dude im so fucking spent lol

glossy valveBOT
#

mikhail_kolesnikov

fringe siren
subtle thorn
#

no the codomain should be R

#

just Lebesgue measurable functions

fringe siren
#

sr gotta go

subtle thorn
#

ofc, thanks for your time anyways

fringe siren
subtle thorn
#

you're the only one on here who actually gave big effort it's v appreciated :3

subtle thorn
#

i give up

#

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robust knoll
noble plover
#

wth

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fresh dune
#

I need help with proving this problem

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fresh dune
#

I tried doing some calculations but got stuck

#

What am I supposed to do in that problem?

spiral vigil
#

s^2 + c^2 = 1

fresh dune
spiral vigil
#

what's your goal again?

fresh dune
spiral vigil
#

with all of these problems the correct thing to do is to immediately convert both sides into sin and cos

#

using s^2 + c^2 = 1 and t = s/c

fresh dune
#

Alright, I'll try right now

fresh dune
#

Thank you

#

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empty tangle
#

am I the only one who think this is worded a bit ambiguously ?

empty tangle
#

to me it sound like shes earning 300 per trip

spiral vigil
#

that does appear to be what it says

lost python
#

I think it would be 300 + earnings for apples each trip?

empty tangle
lost python
#

or actually, it doesn't say only one truck goes per week

#

that is def ambiguous

empty tangle
#

ye its so annoying

lost python
#

but it could be 5 trucks going on 15 trips per week getting $4500?

empty tangle
noble spade
empty tangle
#

saying "for each trip lennox earns 300 dollars" would not be accurate then

noble spade
#

Why not

#

Does it give any other meaning?

empty tangle
noble spade
#

Its not ONLY 3t/W its 3t/W x no.of trucks

empty tangle
#

ye I missed that part lol, will read more carefully

#

tnx

#

will close

#

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foggy prairie
#

Can someone explain to me why velocity is going downwards

foggy prairie
#

I’m confused

foggy vapor
#

as the acceleration is pointing downwards, it forces the velocity to (eventually) also start pointing down

#

or were you looking for a more mathematical explanation?

foggy prairie
#

But I don’t even understand why acceleration is pointing downwards

foggy vapor
#

gravity

foggy prairie
#

Acceleration is supposed to be the instantaneous rate of change of velocity right ?

#

So how is it that

foggy vapor
#

yeah?

#

gravitational acceleration is just taken as a constant system condition

#

you are always going to have -9.81 m/s^2

foggy prairie
#

Again this isn’t explaining how that’s acceleration comes about from what we understand the derivative is

#

That’s gravity but I don’t get why that’s acceleration which is the instantaneous rate of change of velocity

foggy vapor
#

i am saying that you should be looking at it from the opposite direction

#

given the acceleration, what is the velocity at any time t?

foggy prairie
#

Integrate it

foggy vapor
#

yes

foggy prairie
#

Yeah

#

But I’m just not getting the motion sill

foggy vapor
#

Since there is no horizontal acceleration, the horizontal component remains constant

#

ok i mean

foggy prairie
#

Yeah Idk man

foggy vapor
#

we can be proper about it too

foggy prairie
#

Can you explain it in terms of how acceleration is the rate of change of velocity

dusty scaffold
#

well we know that the acceleration is the rate of change of the velocity, and we also know that the acceleration is -9.81 m/s^2 (because that's how gravity works), so we compute the velocity from that

#

more explicitly the thing we end up with is v = (initial velocity) - 9.81t

#

if you differentiate that then you get -9.81 m/s^2

#

(which is the same as how gravity should work because we specifically chose this formula to make it work out that way)

foggy vapor
#

your position at any time $t$ is going to be [
\vv r(t) = \vc xx(t)+\vc yy(t)
]
if you launch the projectile from an initial height $h$ with an initial velocity $v_0$ at an angle $\theta$, the components are going to be
\begin{align*}
x(t) &= (v_0\6\cos\theta)t \
y(t) &= h + (v_0 \sin \theta)t - \412gt^2
\end{align*}
due to the standard kinematics equations. Differentiating those, you get:
\begin{align*}
v_x(t) &= v_0\6\cos\theta \q(\t{note it being constant}) \
v_y(t) &= v_0 \sin \theta - gt
\end{align*}
Take the derivative once more, you get:
\begin{align*}
a_x(t) &= 0 \
a_y(t) &= -g
\end{align*}
Although, truth be told, this is like circular reasoning as the kinematics equations are derived from the above procedure done in reverse, so...

glossy valveBOT
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@foggy prairie Has your question been resolved?

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foggy vapor
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foggy vapor
#

DAG: Directed Acyclic Graph

I don't understand the fourth bulletpoint of this proof. What was taken to be the inductive hyptohesis?

split hatch
#

I guess all DAGs of order <n have a topological ordering

foggy vapor
#

strong induction?

split hatch
#

well it's weak induction since we only use the fact for n-1

#

but it doesn't really matter

foggy vapor
#

ok thanks

#

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tame sundial
#

im so confused rn, i should be getting x+4-4 but im getting x-4-4

delicate torrent
#

,rccw

glossy valveBOT
tame sundial
#

and i’ve tried using ai to explain it to me but i lwk need human help

noble spade
delicate torrent
#

and the original question too

tame sundial
#

crap i did it again

delicate torrent
#

,rccw

glossy valveBOT
delicate torrent
#

i think you wrote your $x$ as $y$

glossy valveBOT
#

1 divided by 0 equals Infinity

tame sundial
#

forget the <-4 that’s me bent a dumbass

delicate torrent
#

i kinda notice that for a long time

tame sundial
#

like wdym i switched x and y to find the inverse

#

im stuck on trying to prove it’s an inverse

delicate torrent
#

huh?

noble spade
#

which one are you doing gang

tame sundial
#

im doing a

delicate torrent
#

oh yea

#

note that

#

$\sqrt{(2x + 8)^2} \neq 2x + 8$

glossy valveBOT
#

1 divided by 0 equals Infinity

delicate torrent
#

it's $\abs{2x + 8}$

#

that's the thing

glossy valveBOT
#

1 divided by 0 equals Infinity

tame sundial
#

well yeah and?

noble spade
tame sundial
noble spade
#

i mean what is the answer supposed to be

tame sundial
#

ik im not crazy

#

and i asked ai and it says that too but it’s talking abt some absolute value and changing the sign to negative for some reason and idek

sacred cloak
#

,w f(x) = -3(2x+5)^(1/3) +4, find f inverse

#

ah yes

sacred cloak
#

????

#

gee thanks

delicate torrent
#

bruh

noble spade
tame sundial
tame sundial
#

2x^2 + 16x +29

noble spade
#

WOW

noble spade
sacred cloak
tame sundial
#

i got +29

noble spade
#

mb forgot to divide by 2

tame sundial
#

i already know that part i just wanna know how to verify that it’s an inverse

sacred cloak
tame sundial
#

and im genuinely right there but like im stuck right here

noble spade
tame sundial
noble spade
tame sundial
#

🫩

#

i js wanna verify it’s the inverse but i swear this is so stupid

noble spade
#

its not its the f inverse function lol

tame sundial
#

it is tho

noble spade
#

its better than swapping x,y

tame sundial
#

lwk man i give up idek

noble spade
#

.close if ure done

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@tame sundial Has your question been resolved?

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timid shore
#

Hellooo
Does anyone understand why this is?

X² becomes 2x

& -2x becomes (2-1) since x is 1 & it basically is the same thing when you multiply it??

But how did they get -1×2x^0

gritty rose
#

Do you know power rule for derivatives

timid shore
gritty rose
#

,tex .diff rules

glossy valveBOT
#

riemann

gritty rose
#

More or less you'll need to memorize those. Certain the second and third for this problem

timid shore
#

Oh

#

Okay tysmm

gritty rose
#

yes

timid shore
#

What's the difference between () & []?

gritty rose
#

nothing

timid shore
# gritty rose yes

Oh! & Its an increasing function if x/y + & decreasing if the x/y is - rigjt?

gritty rose
#

no idea what you just said

timid shore
timid shore
gritty rose
#

?

sonic stratus
#

For a certain function f which has a derivative, if f ' is positive, then f is increasing (upwards slope), and viceversa for negative values.

#

if f ' = 0, then the original function f is constant.

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pulsar kiln
#

\textbf{Problem (English).} Let $f=f(x,y)$ satisfy the partial differential equation
[
\frac{\partial f}{\partial y}=\frac{\partial^2 f}{\partial x^2}-2\frac{\partial f}{\partial x}.
]
Show that one can choose real numbers $a,b\in\mathbb{R}$ such that the function
[
u(x,y)=e^{ax+by},f(x,y)
]
satisfies the simpler equation
[
\frac{\partial u}{\partial y}=\frac{\partial^2 u}{\partial x^2}.
]
Also determine the values of $a$ and $b$.

glossy valveBOT
#

Quantie

pulsar kiln
#

so idk what im supposed to do

do i first solve the last equation du/dy = d^2u/dx^2

#

then show that that also solved the first equation

gritty rose
#

you plug u(x, y) into the last equation and show it's true

pulsar kiln
#

well it could be, the dudes that wrote my literature love to do that kind of stuff

gritty rose
#

i don't know what you mean by factiod

pulsar kiln
#

i could try to solve it too

gritty rose
#

no. it's a given property that f satisfies

#

not all functions satisfies that PDE

pulsar kiln
#

ok but imma solve the last equation

after deriving and simplifying i get

bf + df/dy = a^2f + 2adf/dx + d^2f/dx^2

#

which i think is wrong

#

do you know how id go with starting to deriving

#

this is just deriving u(x,y)

gritty rose
#

the word is differentiating

pulsar kiln
#

oh right yeah, my prof talked about that

in swedish, differentiate and deriving are two different things lol

pulsar kiln
#

dope

#

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iron pond
#

I asked chatgpt and looked online but I cant understand how to integrate two unrelated trignometric functions. Can anyone explain how I'm supposed to do this?

gritty rose
#

integrate by parts thumbsupanimegirl

iron pond
gritty rose
noble spade
iron pond
noble spade
#

v is generally the one which is easy to integrate and u is the one which gives simple things on differentiation

gritty rose
noble spade
#

in this case, better to take u=x and v=sinx

gritty rose
#

it follows from product rule for derivatives

iron pond
gritty rose
#

f' = derivative of f yes

noble spade
iron pond
#

okay I'll try

#

thank you

rugged void
#

!done

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iron pond
#

!done

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#

(if you think you'll need help keep it open)

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rugged void
#

ah

#

okay then

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hoary ember
#

theres alot of useless info here

#

number of bathrooms and time in the shower

#

well i mean, from what i sse in your writing, you used those informations? honestly im not even sure what im seeing right now as its incredibly messy. also making sure again, your only using divisions right as a challange?

#

honestly i reccomend trying to do it normally, then trying to fit the challange for division after you solved it regularly

#

cause honestly trying to do it directly is just an extra headache

#

basically i would try and just spam a×b=a/(1/b)

#

as doing it regularly should be much simpler

knotty grail
#

were you able to find a formula for the total money spent first?

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#

@empty tangle Has your question been resolved?

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#

@empty tangle Has your question been resolved?

noble spade
#

the 3 bathrooms and 480 minutes information is practically not used at all

#

i mean not needed

#

72 litres per person, meaning 432 litres for 6 people from there u can calculate

#

i dont understand it either how did you get here?

noble spade
#

x6p

knotty grail
#

works i guess

#

people normally find multiplication more intuitive though

#

in case i had 8 boxes with 9 pencils in each i would do $8 box \times \frac{9 pencil}{box}$ rather than $\frac{8 box}{\frac{box}{9 pencil}}$ due to how we describe things in english

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sly anchor
#

this is a Magnetic flux density-time graph the figure related to it is on top.can some one explain me plz why E2 is reduced? why it is not being added ,as area increase?

neon silo
#

Physics server might be slightly more helpful

sly anchor
#

yes

#

but i have no any other option to seek help

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cyan trellis
#

Can I get help at b? Im quite stuck. It says to bring the expression to its simplest form (for context tg is tan and ctg is cotangent)

indigo drift
#

Are you trying to prove both sides are equal to each other?

cyan trellis
#

No, there's an expression and i need to bring it to the simplest form

balmy dust
#

do you know the identity $a^2 - b^2 = (a+b)(a-b)$

glossy valveBOT
#

parthisjoking

flint hull
#

remember that cos^4(x) = cos^2(x) * cos^2(x)

cyan trellis
#

Hmm let me see

#

So uh at the part with (cos²x-sin²x)²/(sinx*cosx) do i apply that for (cos²x-sin²x)²? Or at the last thing i wrote

balmy dust
#

doing cos and sin is a waste of time

#

solve it in tan and cotangent

cyan trellis
#

Oh, indeed I see it now

#

My teacher usually told us to do sin cos at the beginning bruh

#

It's easier working with tan and cotan, thanks for the idea, ill see what I do

#

Is this alr?

balmy dust
#

looks perfectly fine to me

cyan trellis
#

Alr, thanks for help!

#

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remote bronze
#

What is this formula and how can I use it?

gritty rose
#

show the full context

remote bronze
grave elm
#

have you read that example

gritty rose
#

and also understand what alpha_i represents

prime forum
#

Alpha I is basically the power of (in 2^7, 7 is alpha I

remote bronze
#

what is the symbol from i=1 to k?

#

It looks like pi?

grave elm
#

product, you multiply all the numbers from i = 1 to i=k

grave elm
remote bronze
#

ai+1 ways to choose how times it appears in the factor why?

gritty rose
remote bronze
#

Yeah

gritty rose
#

did you understand that

#

,calc 2^7

glossy valveBOT
#

Result:

128
gritty rose
#

try listing all the factors of 128

remote bronze
#

I'd be here all day lol

rugged void
#

no you wouldn't

#

try it

#

there aren't as many as you'd expect

rugged void
# gritty rose ,calc 2^7

i don't know why but i expected you to just have memorized all the powers of 2 upto like 32 ngl

remote bronze
#

1,2,4,8,64,128?

gritty rose
#

amazing

rugged void
#

missed a few

gritty rose
#

jsut missed two

rugged void
#

two

#

actually

remote bronze
#

16

rugged void
#

and

#

one more

remote bronze
#

18

rugged void
#

... no

remote bronze
#

32

rugged void
#

correct\

rare dock
#

AA_Sus the reason why the formula works is just basic combinatorics. which nobody has explained for some reason

rugged void
#

ngl, just following riemann's lead

rare dock
#

to make divisors of n you can pick some number between 0 and alpha_1 to be the exponent on p_1. similar with all the other primes. there are 1 + alpha_1 choices for the exponent on p_1

elfin crescent
#

1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048
Hey 2048 taught me something

rare dock
grave elm
rare dock
#

yes

remote bronze
#

i just don't understand why this is even a part of this book

#

like anyways youd have to know the prime factorization of the nubmer

rare dock
#

yea

remote bronze
#

why would we even select a number less than alpha?

rare dock
#

because doing that makes more divisors

remote bronze
#

So 0 | n always right, but if you have a choice between 0-alpha every single time, aren't you counting 0 multiple times?

#

for each prime

rare dock
#

0 does not divide n

#

also when you pick 0 on all the exponents, the corresponding number is 1

#

not 0

#

when you don’t pick 0 on all the exponents, the corresponding number will not be 1

#

there is no double counting going on but maybe that takes a little bit of convincing

#

it’s basically just that prime factorization is unique and so each distinct choice of exponents gives a distinct product

remote bronze
#

Oh mb x | 0, irrelevant here though mb

remote bronze
rare dock
#

are you suggesting that like… picking (1,2,5) as exponents will give the same number as when we pick (2,1,5) for exponents

remote bronze
#

Like for the example 84, the prime factorization is 2^23 * 7. We can do 2^03*7 to produce 21 as a factor? Is that the purpose of the formula?

rare dock
#

yes?

remote bronze
#

That typed out really weird mb

rare dock
#

every triple (a,b,c) with 0 <= a <= 2, and 0 <= b, c <= 1 corresponds to a unique (positive) divisor of 84

#

there are 3 * 2 * 2 such triples

remote bronze
#

Okay I think I understand this now

#

Thank you

rare dock
remote bronze
#

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lyric field
#

problem in probability
I dont understand why this isn't a "stars and bars" problem where we put the green tomatos first which is x_1+...+x_n=n then complete the rest with red tomatos. I might be making this too combinatoric..

rare dock
#

what exactly are you going to count with stars and bars?

#

you can do it with stars and bars but kinda complicated for no reason

lyric field
#

number of ways to distribute green tomatoes then complete the rest with reds

lyric field
rare dock
#

the thing is that a constraint like 0 <= x_i <= 2 is maybe more difficult to deal with than you’re imagining

lyric field
#

i forgot to bound them by 2

rare dock
#

it can be done. just not as easy

lyric field
#

that changes it alot

#

does doing that solve the question though?

rare dock
#

honestly it’s pretty irrelevant

lyric field
#

im pretty sure i was wrong by assuming the tomatos of same color are indistinguishable

rare dock
#

the answer will be the same whether you treat them as distinguishable or not

#

but if you get into some messy combinatorics instead of taking a probabilistic approach, you do need to decide whether to make them distinguishable or not

lyric field
#

got it

#

though just to be clear, if we treat them as indistinguishable then there's only 1 configuration for this event, and thus the probability is 1 over the size of the sample space right?

#

which is the answer to the stars and bars calculation

rare dock
#

the “total configurations” are not all equiprobable i think

#

when you look at it like that

#

can i give you a suggestion on how to do the problem

lyric field
#

yes please

#

some more probabilistic approach than this

rare dock
#

start with making 1 basket. what’s the probability there is one red and one green tomato?

#

you pick one tomato at random, then another from amongst the rest

lyric field
#

n choose 1 times n choose 1?

rare dock
#

no

#

that’s not even a probability. it is not a number in [0,1]

lyric field
#

oh right

#

1/3?

rare dock
#

it should be depend on n

#

we pick a tomato. then the probability we pick a different color tomato to go with it is n/(2n -1)

#

there are 2n-1 total tomatoes left after after we pick one, and n are the other color tomatoes

lyric field
#

yes i understand

#

you set one then figure the probability of getting the other

#

so we start with 1 basket and then?

rare dock
#

go on to the next basket

lyric field
#

(n-1)/(2n-3)

#

then the probability of this event is (n!)/(2n-1)!!

#

alright i think i got enough to go on from here, thanks

#

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dusky sand
#

Question
2 circles of radii 2cm have their centres 2√2 cm apart. Find the perimeter and the area of the shaded region (as shown in diagram)

dusky sand
#

My solution, what went wrong and where and why?

balmy dust
#

how did u know that

#

the angle is right

#

hmph

#

it is right

#

but howd u know

dusky sand
balmy dust
#

u took

#

,, \theta = \pi

glossy valveBOT
#

parthisjoking

balmy dust
#

while calculating

dusky sand
#

Oh that

balmy dust
#

area of sector

balmy dust
dusky sand
dusky sand
balmy dust
balmy dust
dusky sand
#

Lemme recalculate

balmy dust
#

ye

dusky sand
dusky sand
balmy dust
#

umm

#

me personally

#

vector component

dusky sand
balmy dust
#

are you familiar with vectors

dusky sand
balmy dust
#

atleast the projection of a vector on another

dusky sand
#

Yea

balmy dust
#

dot product to be specifc

#

it is a projection

#

of a vector

#

on another

dusky sand
#

Have learnt it only formula oriented wise actually

#

But yes have learnt it

dusky sand
balmy dust
#

you agree this is true?

dusky sand
balmy dust
#

yes

#

similarly

#

in the question

#

try splitting the length of 2sqrt2

#

into two parts

dusky sand
#

Thanks for the assist again

#

.Close

#

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quick aspen
#

How do I find the vertex with a standard quadratic form?

sudden condor
glad plover
# quick aspen How do I find the vertex with a standard quadratic form?

Using the vertex form: since the squared term has a minus next to it, then the maximum of f is when that term is 0. Meaning for x=0.5, f is max, which makes f(x)=6.25
The vertex form is simply a clear way to see the max/min of the function
Without the vertex form:
The vertex is
(-b/2a , f(-b/2a))
That is just always truee

minor sail
#

because if vertex form is a(x-h)^2 + k, expand:
ax^2-2axh+ah^2+k,
ax^2 = ax^2, bx must equal -2axh, c = ah^2 + k,
bx = -2axh,
b=-2ah,
h=b/-2a

minor sail
#

yeah

#

did i not write that

sand bone
quick aspen
#

I was able to find 2 points (0, 6) and (1/2, 0)

minor sail
#

wrong guy to ask

quick aspen
#

Or is that just for finding A

minor sail
#

im even a bit intimidated

quick aspen
#

How would I find thr 6.25

#

Because i was able to find 6 but not 6.25

sand bone
sudden condor
quick aspen
sudden condor
quick aspen
#

No

sudden condor
#

Why not?

quick aspen
#

The x intercept is where X=0

#

Wait

#

Nvm

sudden condor
#

It’s the reverse
If a point lies entirely on the x-axis
The y value of said point is 0

quick aspen
#

Yeah

#

Thats what I meant

sudden condor
#

You took linear equations before yeah?

quick aspen
#

Yeah

sudden condor
#

y=0 is the same as the x-axis entirely

#

Moreover, x=0 is the same as the y-axis entirely

quick aspen
#

Huh

sudden condor
# quick aspen Huh

When you plot the line y=0
this line lies entirely on the x-axis
Since you vary x, but y is just 0

quick aspen
#

Yea

sudden condor
#

same with the x=0
y varies but x is always 0
So the line lies on the y-axis
Is that clear?

quick aspen
#

Yes

sudden condor
#

So from this conclusion we can have two rules
x-intercept is where the y value is 0
y-intercept is where the x value is 0
clear?

quick aspen
#

Yes

#

I substituted those

#

But for some reason i could not find 6.25

#

Even though it says it on the vertex form

sudden condor
#

Are you familiar with completing the square ?

quick aspen
#

Yeah

sudden condor
quick aspen
#

Would I be subtracting thr 6 or do I keep it

#

I forgot

sudden condor
# quick aspen

Add on subtract to in the same side
+6-6 (is still 0 so the expression is equivalent)

  • there was a mistake on my part
    It was supposed to be -x^2+1x+6
quick aspen
#

What

#

Wdym add on subtract to

sudden condor
#

When completing the square think of a scale where the weights are equivalent.

Suppose I took away or added extra weight.
The scale side won’t be equal anymore so we try to make up for the lost weight to preserve the equality by adding what we took away, or taking away what we added.

In completing the square the idea still occurs
We add the square of the middle term divided by 2 but we also subtract to keep both sides equivalent

quick aspen
#

Ok

#

I get it now ty

#

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past path
#

I don’t understand how this integral is divergent. Wouldn’t the limits make those terms go to 0?

sudden condor
past path
sudden condor
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glossy tapir
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What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
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7. None of the above
glossy tapir
#

3

mossy stratus
#

Tính delta

glossy tapir
#

bài 3.1 anh ơi đ phải 3.3

mossy stratus
#

Đúng rồi

glossy tapir
#

3.1 delta j hả a

mossy stratus
#

Có 2 nghiệm nên delta lớn hơn 0

#

À 3.1 à

glossy tapir
#

bài bất đẳng thức mà

#

xe lăn ấy a

mossy stratus
#

tiền lãi 1 xe là bn

#

=giá bán - giá sản xuất

#

Tính ra rồi thì đó là lãi 1 xe, rồi lấy tổng tiền vốn chia tiền lãi 1 xe là ra số xe cần

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left moon
#

Why isn’t tan2x equal to 2sinxcosx

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left moon
rugged void
#

tan^2 u + 1 is sec^2 u

left moon
#

Yes

rugged void
#

not 1 - tan^2 u

left moon
#

Oh

#

Oops

rugged void
#

lmao

left moon
#

💀

rugged void
#

happens

#

dw seriously

#

i make mistakes like this

#

all the goddamn time

left moon
#

Lololol

#

Hopefully not on tests

#

😔

rugged void
#

i ripped half my hair out on a problem before realising i forgot to divide by 2

#

😭

rugged void
rugged void
#

anyway .close if ur done

left moon
#

Yuh

rugged void
left moon
#

.close

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rugged void
#

alr

torn jolt
#

<@&268886789983436800>

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fair ocean
#

hi!!! just checking if my work is correct

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fair ocean
sturdy valve
#

,w integrate sqrt(y+1) from 0 to 3

woeful girder
#

Dang man good handwriting

sturdy valve
#

,w integrate t^3(1+t^4)^3 from 0 to 1

visual kiln
#

do u guys know anything abt binomials and inverse and norm distributions and all

fair ocean
sturdy valve
woeful girder
#

Cooked

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woeful girder
#

Good thing i misspelled

fair ocean
#

fhank you sonmuch !

woeful girder
#

Ahem no one saw that

sturdy valve
#

👍

fair ocean
#

!close

#

wair how again

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kh.

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.close

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woeful girder
#

.close

visual kiln
#

y do u guys use ! this sm

woeful girder
visual kiln
#

ow

#

lol

sturdy valve
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warped frost
#

! is a bot command prefix to call up various text snippets

#

like that

visual kiln
#

oowww

woeful girder
warped frost
#

either way, if you want to ask your question, please use an available channel

visual kiln
#

thats acc cool ngl

sturdy valve
woeful girder
#

Are you still upset at me about the pre uni remarks 😭

sturdy valve
#

YES

woeful girder
#

Oh

sturdy valve
#

im a valued member of the preuni community

woeful girder
#

You are

sturdy valve
#

:)

woeful girder
#

I value pre uni community too cough

torn jolt
#

tuff members of pre uni gng

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lethal trout
#

I need help i have a division test tomorrow on math from 1st quarter to 4th quarter lessons, I'm grade 10

balmy dust
#

give a list of topics

#

also what mention what you need help with

lethal trout
#

Well mostly i need help with circle, tangent and secant

lethal trout
sterile sinew
#

Wow looks hard

lethal trout
#

I'm a fast learner but I want to ace this lol

sterile sinew
#

Dangg, i believe in u, keep going

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drifting summit
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drifting summit
#

Hi

#

can someone view my proof?

#

i'm not sure if i'm doing transfinite induction correctly

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@drifting summit Has your question been resolved?

trail barn
#

This looks fine to me (although it's been a while since I've done set theory)

#

I assume "$V_\beta^$ is transitive by $()\beta$" is meant to be typeset more like "$V{\beta^}$ is transitive by $()_{\beta^*}$"?

glossy valveBOT
#

Edward II

drifting summit
#

ye mb

#

.solved

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misty garden
#

Hi, given that a general quadratic polynomial around two variables to be f(x, y) = ax^2+bxy+cy^2+dx+ey+f. I know that cross sections of this polynomial form a parabola. How can I prove that the minimal point of all the cross sections also form a parabola?

gritty rose
#

kinda vague but you can parametrize the "minimal points" and show that the resulting eqn is a parabola

misty garden
#

This is what I am working with

wise tartan
misty garden
misty garden
wise tartan
misty garden
#

Sorry, I still don’t understand. May I know how we pick the constant y? I thought we were using all cross sections in the form of y=#

gritty rose
#

maybe find two or three non overlapping parallel parabolas first and write them here along with the conic with actual constants

misty garden
#

Sure, I can do that! Just making sure, do you want me to find the vertex of three cross sections parabolas to find the parabola containing all the vertices?

#

<@&286206848099549185>

wise tartan
glossy valveBOT
#

CherryMan

wise tartan
#

If I let g be the minimum value of f(x,y) for a specific y, then $g(y) = a(\frac{-by+d}{2a})^2 + b(\frac{-by+d}{2a})y + cy^2 + d(\frac{-by+d}{2a}) + ey + f$

glossy valveBOT
#

CherryMan

wise tartan
#

that means, the minimums do form a parabola

#

and the plane the parabola is formed in is defined by x = -by+d /2a

#

(consequently the same holds for cross sections with x constant)

#

idk i might have made a mistake

misty garden
#

Ok, that makes sense to me! So you first took the partial derivative to find a general equation of a cross section vertex. Then you plugged it back to the original function and it was still a general quadratic right?

wise tartan
#

yes

#

also

#

it should be -by -d/2a

#

not -by+d/2a

misty garden
#

Got it, thank you so much! May I know if the same logic applies when determining if a general cubic equation around three variables have cross sections that satisfies the property of a general quadratic?

wise tartan
#

i dont know

#

its harder to check using this method

misty garden
#

Oh ok, I think I got it for quadratics, but have not understood how to generalize it for high degree polynomial

#

<@&286206848099549185> can anyone help me prove or disprove the generalization of this problem? Greatly appreciated!

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@misty garden Has your question been resolved?

neon surge
glossy valveBOT
#

k
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

neon surge
#

so points (+-sqrt(1-y^2), y, some z)

misty garden
#

I understand, thank you for showing a counter example! 🙏

misty garden
#

.close

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azure bridge
#

Matrix matrix multiplication?

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azure bridge
#

@fathom saddle im ripping my hair out with this

#

anyone?

nova briar
#

X(n) = M^n V where M is your matrix, and V is your vector

#

Do you know how to find the nth power of a square matrix?

azure bridge
#

i just started this unit

#

Do I have the right setup?

#

ive been stuck on this question for an hour 😭

fathom saddle
#

The numbers are a bit jumbled. Currently, you've got a 20% chance that a juvenile becomes a juvenile, where you want a 20% chance they become an adult

azure bridge
#

but isnt it under the A(t+1)

#

A(t+1) = .2J(t) no?

fathom saddle
#

J is the top row

#

You've currently got:
J(t+1) = 0.2J(t) + 0.9A(t)

azure bridge
#

yeah

#

no wait

#

my J(t+1) is just .15A(T)

fathom saddle
#

Knowing how to mutiply a vector by a matrix is needed for this problem, make sure you know how to do that

#

But, even further, you are going to multiply two matricies together too

#

Are you studying ahead? This is a bit far from the beginning of a course

azure bridge
#

im only one lesson ahead sadly

fathom saddle
#

Jeez they're not taking it easy on you haha

azure bridge
#

ah okay I got it now, i thought I was doing matrix matrix multiplication

azure bridge
#

easy probability and easy recurrence solving + bernoulli's equation

#

and now after the midterm they have us doing expectation, variance, std dev, and now this

#

in a week

#

😭

azure bridge
fathom saddle
#

Yes! A vector-matrix multiplication is still just a matrix-matrix multiplication

#

Or, a matrix-matrix multiplication is where you take the right matrix, break it into column vectors, multiply each by the left matrix, then reassemble the result

azure bridge
#

i’m done looking ahead for today

fathom saddle
#

I also like this graphic for visualizing matrix multiplications

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tacit token
#

How to solve x^{5}+10x^{4}-16x^{3}+7x^{2}-10x+1 = 0?

mossy stratus
#

$x^5+10x^4-16x^3+7x^2-10x+1=0$

glossy valveBOT
cinder thorn
#

Wolframalpha?

tacit token
#

No machines allowed.

mossy stratus
#

He need to understand how to get to that answer

cinder thorn
#

You won't have rational roots here

mossy stratus
#

Not to rely on AI or digital tools

tacit token
cinder thorn
#

Do you know galois stuff maybe

tacit token
#

nope

cinder thorn
#

And how have you solved quintics until now?

#

Because I'm not even sure this is possible

tacit token
#

wdym

tacit token
cinder thorn
#

Where did you find this problem

tacit token
#

self-question

mossy stratus
#

This one doesnt have beautiful coefficients.

#

This involves complex solutions for sure.

cinder thorn
#

Yeah i kinda expected it

mossy stratus
#

At least 2 conjugate pairs

tacit token
#

can't it have all roots real

cinder thorn
#

No

#

I mean it could

tacit token
#

reason?

mossy stratus
#

Cuz it have real coefficients

cinder thorn
mossy stratus
#

Maybe 1 pair minimum

tacit token
#

isn't that just a guess?

mossy stratus
#

You can use conjugate pair root theorem, but it must have complex sols

cinder thorn
mossy stratus
#

I just chucked random x values in my calc, i only approximate a real sols in the interval -11, -12, so i assume the rest of 4 are complex, then 2 pairs, could be wrong

tacit token
cinder thorn
#

No

#

Especially for degree 5 and above

#

You could be in a special case but then you'd have to use galois and such

tacit token
#

oh

#

ok

#

thanks

#

no formula?

atomic hare
#

An entry to #SoME2. It is a famous theorem (called Abel-Ruffini theorem) that there is no quintic formula, or quintic equations are not solvable; but very likely you are not told the exact reason why. Here is how traditionally we knew that such a formula cannot exist, using Galois theory.

Correction: At 08:09, I forgot to put ellipsis in betwee...

▶ Play video
tacit token
#

thanks

#

.close

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mossy stratus
#

Thats a great video

#

👍

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craggy tapir
#

for part b, how do i calculate P(X = 10) if i am approximating as a normal distribution?

balmy dust
#

total probability theorem?

craggy tapir
#

how is it applicable here?

craggy tapir
balmy dust
#

is 5% the prob of a board being defective or is it the percentage of the total boards that are expected to be defective

craggy tapir
#

i don't see the difference

balmy dust
wide sundial
craggy tapir
#

i briefly read about it when the formula when the formula for P(X <= x) to approximate bin dist is introduced

#

but i'm not sure how to apply it to calculate P(X = x)

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neon rivet
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neon rivet
#

I need to check my answer

noble spade
#

a bar is not the hypotenuse

noble spade
neon rivet
#

what did i do wrong

noble spade
neon rivet
#

what is not perpendicular?

noble spade
#

Bro its not a right angle triangle u cant use pythagoras here

neon rivet
#

the triangle

#

oh

turbid tinsel
#

simple vector addition works

neon rivet
#

then a vector is 10 + 5

#

which is 15cm

#

NE

prime pier
glossy valveBOT
#

حسیب ♥

noble spade
#

They are not in the same direction

turbid tinsel
#

add them in vector form

#

so 10j + 5j

#

then take the magnitude