#help-23

1 messages ยท Page 41 of 1

short sparrow
#

damn, howd u do it

toxic stratus
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the construction is using one of the quintessential properties of sups/infs over the reals

solar hazel
#

i did it how i explained already lol

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idr how i "came up with it" back then

short sparrow
flat frigateBOT
toxic stratus
#

this is one of the key properties of sups over sets of real numbers

#

you use this exact property to construct the sequence you want

short sparrow
toxic stratus
#

something that converges to sup A

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the above property says there are elements in A which are arbitrarily close to sup A

short sparrow
#

yeah i get that

toxic stratus
#

this is the same as saying a sequence converging to sup A exists

short sparrow
#

okay

toxic stratus
#

thats all there is to it

short sparrow
#

can u help me find out what to do with it

#

cause im not so sure myself

toxic stratus
#

layla has explained the core parts of the solution

short sparrow
flat frigateBOT
toxic stratus
#

thats how you conjure up new elements for your sequence

#

written exactly here

short sparrow
#

hmm okay ill try connecting it all now..

short sparrow
flat frigateBOT
#

Levens

toxic stratus
#

do an epsilon-N proof

short sparrow
#

with that? how

toxic stratus
#

typically i would take not 1/n but 1/10^n

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so

flat frigateBOT
toxic stratus
#

so then the question is

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if you want an element of the sequence within say the 59714th decimal place of sup A

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then you can go along 59714 elements of the sequence

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and find the 59714th element

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and by the way its been constructed

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itll be within the 59714th decimal place of sup A

flat frigateBOT
toxic stratus
#

so basically to do an epsilon-N proof

flat frigateBOT
short sparrow
#

wait why -k

toxic stratus
#

?

short sparrow
#

oh oh

#

lol mb

#

ok im still reading give me a sec

toxic stratus
#

usually you do if epsilon > 0 then there exists N such that ...

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im just saying in the specific case epsilon is 0.0.....01 you can do something like this

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and actually thats all you need

short sparrow
#

thanks.. for infA, can I choose $\epsilon = \frac{1}{n} +10$?

flat frigateBOT
#

Levens

toxic stratus
#

for inf you just switch all the inequalities around

short sparrow
#

oh

flat frigateBOT
toxic stratus
#

or if you want to think of it as decimal places

flat frigateBOT
safe radishBOT
#

@short sparrow Has your question been resolved?

short sparrow
#

thank u snow, helped a lot

safe radishBOT
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safe radishBOT
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warm dune
#

two families rent a helicopter. The cost for the first family of 5 was $520. The cost of the second family of 3 was $432.
Write an equation to represent the cost per person and the base cost.

safe radishBOT
#

@warm dune Has your question been resolved?

trim swan
#

"Write an equation to represent the cost per person and the base cost."

#

This is what the directions say?

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I think a system of equations makes more sense

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@warm dune

warm dune
trim swan
#

Ah, okay. But first we need to find m and b

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And we can do that by solving a system of equations

warm dune
#

oh

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how do i do that?

trim swan
#

Do you know what I mean by a system of equations?

warm dune
trim swan
#

Yeah, except I'd say 5m + b = 520

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m and b are what we want to find

warm dune
#

oh ok

trim swan
#

That's one equation, what's the other one?

warm dune
#

3m + b = 432?

trim swan
#

Yeah

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So

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Do you know how to solve the system for m and b?

warm dune
#

b = 520-5m?

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and b = 432-3m?

trim swan
#

looks good

warm dune
#

5m + (520-5m) = 520

trim swan
#

Close, but you substituted one equation into itself

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You want to substitute one into the other

warm dune
#

ohh

#

5m + (432-3m) = 520?

trim swan
#

Yep

warm dune
#

2m + 432 = 520
2m = 88
m = 44

#

is that right?

#

5x44=220

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520-300=220

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so the equation is f(x) = 44x + 300?

trim swan
#

Yep ๐Ÿ‘

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You can check it yourself by seeing that f(5) gives 520 and f(3) gives 432

warm dune
#

yeah your right

trim swan
#

Sure thing ๐Ÿ‘

warm dune
#

.close

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frail wraith
#

hello?

safe radishBOT
#

@frail wraith Has your question been resolved?

obsidian bone
#

Its correct.

frail wraith
#

Ima submit this and if Im wrong itll be on you

#

I really. need the points, no pressure

obsidian bone
#

If you intend to submit that, you should define what F is

frail wraith
#

F is the function that represents the matrix.

obsidian bone
#

Yep. Then thats fine

frail wraith
#

Thanks, if theres nothing more.

safe radishBOT
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safe radishBOT
safe radishBOT
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@frail wraith Has your question been resolved?

safe radishBOT
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solemn vault
#

Can you do a quick check??

safe radishBOT
solemn vault
warm rose
#

And 10/18 x 8/17 = 80/153?

solemn vault
#

Oh ye

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Expect that is everything fine??

#

@warm rose

warm rose
#

Yeah looks fine

solemn vault
#

Ok thx

#

.close

safe radishBOT
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bold void
#

help

safe radishBOT
bold void
#

im stucked

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at this problem

#

help

thin bridge
#

what problem

bold void
#

HEY

#

HERE

#

im stucked for like 20mins

safe radishBOT
#

@bold void Has your question been resolved?

rigid inlet
#

@bold void still stuck?

safe radishBOT
#

@bold void Has your question been resolved?

safe radishBOT
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wild trout
#

Can someone explain all 3 of these questions? The process to get the roots of the function.

flat frigateBOT
sonic spruce
#

Okay so

wild trout
#

It all equal to 0

sonic spruce
#

If you let x^2=y for first it should be doable

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Same way

wild trout
#

Then I put the biggest ^ number in brackets to be ^2?

sonic spruce
#

x^5 = y

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And x^(1/3) = y for third

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The main takeaway is

wild trout
#

Part b has 4 roots apparently

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I need x E R

sonic spruce
#

Solve for y

wild trout
sonic spruce
#

There should be 2 solutions for y

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And further 4 solutions for x

wild trout
#

(Xยฒ)ยฒ-12xยฒ+32

sonic spruce
#

Ye

wild trout
#

X=0 x=0 x=4 x=8?

#

Hmm

#

How do i get the roots?

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I'm confused ๐Ÿ˜• can you help me factorise?

sonic spruce
#

Can you factorise that ?

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For y?

wild trout
#

Ohh

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(Y-4)(y-8)

sonic spruce
#

So y is?

wild trout
#

Is that correct?

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Y is 4 or 8

sonic spruce
#

So x^2 = 4 or 8

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Right cause y= x^2

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Right?

wild trout
#

Sorry

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My mom called me

#

Yeah

sonic spruce
#

So x is?

wild trout
#

So u square root them

sonic spruce
#

Yessir

wild trout
#

X is 4, can be negative 4

sonic spruce
#

No

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Square root?

wild trout
#

I mean 2 and negative 2

sonic spruce
#

And?

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When x^2=8

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What about then?

wild trout
#

Sqrt 8 and negative 8

sonic spruce
#

Which is also?

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But yes

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Good job

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The next ones are the same logic

wild trout
#

Ty

#

Makes much more sense now

sonic spruce
#

Can you do the next one?

wild trout
#

Yeah

sonic spruce
#

Great:)

wild trout
#

Ty

sonic spruce
#

Also also

#

What does you name mean?

#

Username i mean

wild trout
#

It's just a code

sonic spruce
#

Okay okay

#

Have a good day

wild trout
#

You too

#

Tysm

sonic spruce
#

Np:)

#

Close the channel when you are done

wild trout
#

.close

safe radishBOT
#
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#
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dusky marsh
#

sasa..

sonic spruce
#

Lol this channels gonna close soon

safe radishBOT
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remote kernel
safe radishBOT
remote kernel
#

Things got worse rq huh

#

I could loop forever and ever here

#

What went wrong?

quasi bison
#

...what even is going on here?

#

2x+y = 5
4x+z = ?

is this EXACTLY how the problem was given to you?

remote kernel
lean otter
#

new variable just dropped

quasi bison
#

then there's so, so, so little information.

#

you literally cannot say anything meaningful.

remote kernel
#

What?

quasi bison
#

if all you know about the variables x, y and z is that 2x+y = 5, then you cannot say anything about the value of 4x+z

remote kernel
#

Oh

#

Im gonna try and find the original equation

#

I got online

quasi bison
#

should have gotten your hands on that to begin with tbh

lean otter
#

im guessing you mistook some number with ? or something

remote kernel
#

Gosh dangit i forgot a y

#

๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€๐Ÿ’€

#

Let me try again

lean otter
#

yeah that changes things

#

a tinsy weensy bit

quasi bison
#

...

#

well i mean like. yeah.

#

but also taking this sort of thing directly from Google is sus

lean otter
#

never thought google maths practice was a thing

remote kernel
#

Epic

lean otter
#

๐Ÿ˜ญ

#

where is the y again

remote kernel
#

10 is right

#

This next one is interesting

lean otter
# remote kernel 10 is right

fun fact, you could've just simply multiplied the whole original equation by 2 and that would've saved you a lot more time

remote kernel
lean otter
lean otter
#

multiply by 2

#

4x + 2y = 10

#

you are done

remote kernel
#

Oh

#

Theres a trick

#

I forgor the y again

#

Lol

remote kernel
#

Not a z

#

Lol

quasi bison
#

i gathered as much

remote kernel
#

Anyways with 2 instead, would it still be solvable?

#

Anyways

#

This one is interesting

#

And yk i have an evil devious idea

quasi bison
remote kernel
#

The forbidden technique

quasi bison
#

this is really bad on many levels

remote kernel
#

Why?

quasi bison
#

the first of which is that you actually went out of your way to write $2 \divisionsymbol 3$ instead of $\frac{2}{3}$ (and likewise in two other places)

and the second line is simply nonsensical

flat frigateBOT
quasi bison
#

granted, the problem itself was also written poorly; it should have been $$\frac{2}{3} x - \frac{3}{2}x = \frac{1}{12}$$

flat frigateBOT
remote kernel
#

How do you know its (2/3)x and not 2/3x?

quasi bison
#

you mean how i knew it wasn't $\frac{2}{3x}$?

flat frigateBOT
quasi bison
#

i had to make an assumption. you were studying linear equations so i assumed the equation you posted here was also meant to be linear.

remote kernel
#

Isnt 2/3x linear too?

#

I mean no exponents= automatically linear

quasi bison
#

no

#

2/(3x) has x in the denominator

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you cannot have that in a linear equation

remote kernel
#

Hmmmm may i ask why?

quasi bison
#

allowing x into the denominator puts you in the wider class of rational equations, which can get considerably more complicated in their behavior than linear ones

#

i mean for example $\frac{1}{x} + x = 5$

flat frigateBOT
quasi bison
#

this is not linear anymore

remote kernel
#

Ohh thats scary

remote kernel
quasi bison
#

you can try to ask me but i will be unable to answer except to repeat that it is nonsensical

remote kernel
#

Alright....

#

I mean technically nothing was wrong?

#

Normal tranposing rooles

quasi bison
#

no,

#

there is no such thing as "transposing"

#

you did some symbol manipulation that ultimately does not mean anything

#

like

#

ok no nevermind

#

there is nothing more i can say here.

remote kernel
#

I guess i just butchered math so badly lol

quasi bison
#

yes

#

yes you did

safe radishBOT
#

@remote kernel Has your question been resolved?

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dark pike
#

here is my process for finding the derivative of 1 over x

dark pike
#

apparently the end result should be negative 1 over x squared instead of positive 1 over x squared

#

why is this?

fresh remnant
#

From step 3 to 4 you dropped the negative sign

#

You keep it

dark pike
#

surely it should be -x^2 instead of -{1 over x squared} though right?

#

ah

#

wait

#

yeah i think i get why now

final halo
#

The minus out front and the minus in the power aren't interacting in any way

#

Perhaps you thougut they were cancelling somehow

dark pike
#

alright thanks you two ๐Ÿ™‚

#

.close

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crude star
#

is inf^0 = 1?

safe radishBOT
final halo
#

No

#

Infinity is not a number

crude star
#

I rmbr seeing a post where one said that

#

got it doe ty

#

.close

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reef galleon
#

can i add and remove pi from something like cos(3pi-x) like if its in a form of +2kpi sorry if my vocabulary is bad i study maths in french

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@reef galleon Has your question been resolved?

safe radishBOT
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@reef galleon Has your question been resolved?

reef galleon
#

<@&286206848099549185>

safe radishBOT
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@reef galleon Has your question been resolved?

clear blade
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lean otter
safe radishBOT
lean otter
#

do you know how to change 12cosยฒ(a)

#

in sina idk

pseudo scroll
#

sin^2 A + cos^2 A = 1

lean otter
#

ah ok ty

#

.closer

#

.close

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fiery escarp
safe radishBOT
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safe radishBOT
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@fiery escarp Has your question been resolved?

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lean otter
#

<@&286206848099549185>

safe radishBOT
lean otter
#

nvm

uncut cloak
#

Nice

safe radishBOT
#

@lean otter Has your question been resolved?

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worn cairn
#

I am completely lost on this question right now, Three vectors, x,y, and z satisfy x+y+z=0 . Calculate the value of x. y+y.z+x.z if lxl =2 , lyl=3 and lzl=4

worn cairn
#

I've tried applying properties and manipulating the formula, but nothing works and i don't know what to do

safe radishBOT
#

@worn cairn Has your question been resolved?

worn cairn
#

<@&286206848099549185>

safe radishBOT
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clear ingot
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lethal creek
safe radishBOT
lethal creek
#

honestly i just need help working through it bc i have no idea how to solve it

#

then i have 1 more like this

solemn vault
#

Find such numbers when you multiply them it becomes 60 and when you add them it becomes 23

lethal creek
#

oh goodness

#

you multiplied a and c right

worthy hemlock
#

Yes

lethal creek
#

k

#

oh 20 and 3!

worthy hemlock
#

Here's a video on how to factor when a isn't equal to 1
https://www.youtube.com/watch?v=f0GqRY1ORbQ&ab_channel=BrianMcLogan

๐Ÿ‘‰Learn how to factor quadratics when the coefficient of the term with a squared variable is not 1. To factor an algebraic expression means to break it up into expressions that can be multiplied together to get the original expression.

To factor a quadratic trinomial where the coefficient of the term with a squared variable is not 1, we find tw...

โ–ถ Play video
lethal creek
#

ok thank you

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sick matrix
#

A 43-foot rope is tied to the top of a 31-foot vertical cliff face. When pulled so that it just reaches the ground, what is the angle of elevation to the top of the cliff?

sick matrix
#

This is how I interpreted the angle

sudden birch
#

U can construct a right triangle with this (triangles are every which is awesome, I know). What does it look like? The height of the cliff and the rope belong to which of the legs and hypotenuse?

#

Oh yeah

#

Now apply trig stuff. Soh Cah toa stuff

sick matrix
#

I did Tan -1 (43/31) but it got marked as wrong.
So I'm trying Cos-1(31/43) But I don't know if I'm interpreting the triangle in the problem properly.

thin bridge
#

the triangle is correct, you choice of trig function is not

sudden birch
#

^^

#

Hint:

#

31 is a side thatโ€™s opposite to the angle

#

41 is the hypotenuse

sick matrix
#

So Sin-1 (31/43)?

sudden birch
#

One is the o and the other is the h in soh Cah toa. Yes u r correct

thin bridge
#

yes

sick matrix
#

Thats weird, we didn't use Sin at all for any of these problems.

sudden birch
#

Sin = opposite side / hypotenuse

sick matrix
#

Ye I know.

thin bridge
#

use whatever the problem calls for

sudden birch
#

Just making shots

#

Shore

sick matrix
#

46.13

safe radishBOT
#

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crude ledge
#

A 125-foot tower is located on the side of a mountain. In addition, a 170-foot-long guy wire is attached to the top of the tower which is anchored at a point 55 feet downhill from the base of the tower.

What is n โˆ A

worthy hemlock
#

Apply law of cosines

crude ledge
#

How?

#

Iโ€™m completely lost on it

#

๐Ÿ˜…

worthy hemlock
#

Do you know law of cosines?

crude ledge
#

Partially

worthy hemlock
#

The law of sines helped us solve for all the sides and angles in SAA, ASA, and SSA triangles, but now we have to learn the law of cosines if we want to solve for SAS and SSS triangles. This one is kind of like the pythagorean theorem, just for oblique triangles instead of right triangles, so it has trig functions in it. Let's check it out!

Watc...

โ–ถ Play video
crude ledge
#

This one right?

#

Being the law of cosines

#

Would be writing

#

170^2 = 55^2 + 125^2 - 2(55)(125) cos C

#

?

worthy hemlock
#

Not quite

crude ledge
#

Wrong placing?

worthy hemlock
worthy hemlock
crude ledge
#

No โ€ฆ itโ€™s 125

worthy hemlock
#

Yes

crude ledge
#

A = 170
B = 55
C = 125

#

Right?

worthy hemlock
#

Technically the angle you are looking for is angle A, so across from angle A is side A

#

I just noticed that your problem labeled that angle as A

#

And not C

crude ledge
#

Yeah!

#

Iโ€™m guessing that would change

#

The number

#

Right?

worthy hemlock
#

You would just need to swap some numbers around

crude ledge
#

125^2 = 55^2 + 170^2 - 2(55)(170) cos C

#

?

worthy hemlock
#

Yeah

crude ledge
#

Thank you!!! A LOT

safe radishBOT
#

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lean otter
#

Uhhh where would I start with this problem, the limit goes to 0, and Iโ€™m pretty sure I canโ€™t do the integral test, all Iโ€™ve learned is p-series, integral test, comparison test, divergence theorem, and smth else, I havent learned the ratio test tho, any help?

safe radishBOT
#

@lean otter Has your question been resolved?

lean otter
#

<@&286206848099549185>

safe radishBOT
#

@lean otter Has your question been resolved?

stray bluff
#

u can use comparison test

lean otter
#

O okay Iโ€™ll try Ty

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lament flare
#

hello can someone help me with this?

safe radishBOT
#

@lament flare Has your question been resolved?

marsh walrus
lament flare
#

The letter c

marsh walrus
#

what do you mean?

#

thats what you think is the answer?

safe radishBOT
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@lament flare Has your question been resolved?

lament flare
#

yes

safe radishBOT
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@lament flare Has your question been resolved?

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flint python
#

this is my global minimum when it asks for the coordinates for the x value would i write it between my domains like for exmaple (x,-20) where x is 20<x<40

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halcyon stump
#

Can anyone have alternative solution for this question. Q) If x=a(cost+tsint) and y=a(sintโˆ’tcost), find dx^ 2/ d ^2y โ€‹

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eager cloak
#

who can help me

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noble sail
#

if a man has to work 5 days in 31 days, without working 2 consecutive days, how many arrangements are possible for his days of work?

untold sky
#

if they have to work for 5 days, how many days must they not be working?

then can you simplify the problem in terms of arranging working and non-working days?

noble sail
#

i dont think this can work

#

i tried it

untold sky
#

it can

starter: how many ways can you fit the first working day into the block of non-working days?

buoyant shadow
#

it works but you need to try it the right way, it's a trick

noble sail
#

there are 5 working days

untold sky
#

you get that the man has 26 non-working days

how many ways can you insert 1 working day into the 26 non-working days

then, while satisfying the condition that the man is not working 2 consecutive days, a second working day

noble sail
#

no

#

but i dont see the point

#

this is very difficult

untold sky
#

the point is that this generalizes for any number of working days :p

instead of computing directly, try to fit working days between non-working days

noble sail
#

why? why are we fitting working days into non working days? to avoid having 2 consecutive days of work? if yes how are we achieving that

buoyant shadow
#

there's 27 slots when you have 26 days

#

it goes in between

noble sail
#

how?

#

each day represents one slot no?

buoyant shadow
#

no, they are flexible like that

#

you imagine slots in between

#

and unimagine them back after choosing

noble sail
#

I dont get what you mean

buoyant shadow
#

like if you have two non working days and you add a working day
.X.X.
the dots are where you can fit it

#

WXX, XWX, XXW

#

and this solves the problem in one step

#

if you;re slotting many working days at once, they will automatically be non consecutive

#

it's a trick, iv just hoped you'd invent it

noble sail
#

I still have a hard time understanding this

noble sail
buoyant shadow
#

yeah

noble sail
#

and the dots my possibilities?

#

for work

buoyant shadow
#

you keep them both, you add a W in between

#

yes

noble sail
#

so i am attempting to fit 5 W between 27 X

#

fuck

#

i see

#

very clever

buoyant shadow
#

when you add a second day, the dots will literally stay like that

#

so it's a one step choice

noble sail
#

i dont get why the dots are necessary

#

we're just starting with 27X and then seeing how many ways we can fit a W between 2 X right?

buoyant shadow
#

well yeah they don't carry information

#

just visual aid

buoyant shadow
#

i can add them back WXX โ†’ WX.X

#

and it recreates the pattern before removing

noble sail
#

Ah i see the point of the points

buoyant shadow
#

you would think it's literally stars and bars but I don't see a way to make it like that

untold sky
#

it is, a+b+c+d=2 nope, a+b+c+d+e=22

#

then stars and bars

#

oh actually might be 22

noble sail
#

i want to understand how we went on to think about this

buoyant shadow
#

someone probably spoiled it to me i don't remember

noble sail
#

so there is nothing that can help me in future problems, some pattern to spot

#

i was helpless in front of this one

buoyant shadow
#

and then also into 6

untold sky
#

no it's 5 bars, give me a second, my brain is dying .-.

fair hound
#

it's 5 bars yeah

buoyant shadow
#

but how

#

you're allowed to have one group empty, or the other one or even both

untold sky
#

ok it's 5 bars and 22 stars, that took too long to wrap my head around

fair hound
#

by making a change of var

#

yep

buoyant shadow
#

ahh

#

yes

#

it clicked

#

thank you both

fair hound
#

you have 5 bars and 26 stars
but 4 of the bars can't directly follow each other, so you sub these 4 bars by a shift of 1

#

and you get 5 bars and 22 stars

buoyant shadow
#

26โˆ’4 yeah

noble sail
#

is this something i should know :/

buoyant shadow
#

yes please :D

noble sail
#

great, a wiki article

untold sky
#

it's a neat trick that will save you a lot of time if you get it into memory

when i was doing math comp and undergrad combinatorics we had a saying "if it looks too hard transform it into stars and bars"

noble sail
#

looool

buoyant shadow
#

yeah that's lame i know, i don't know youtube links

noble sail
#

lool no i wasnt sarcastic i spend most of my time on wiki

#

but wait didnt we actually transform this problem to make it easier

#

like it isnt easy, but we seem to have added a spot to make it easier

#

no?

#

our month became 32 days

#

of which we need 31

#

I just cant see how this overwhelming problem is suddenly a simple one

#

and instead of picking the days of work and non work... we instead fixed the days of non work and simply bothered with our days of work right?

untold sky
#

the not-so-rigorous answer is that you transform the problem in a way that you won't be counting in a way where previously arrangements drastically changes count formula

if you try to brute force by saying "okay day 1 can be a working day, then 3,5,7,9, then if you fix 1,3,5,7 you have 23 more choices" you get massive nested sums

noble sail
#

That 1,3,5,7 and 1,3,5,8 are drastically different?

untold sky
#

if you try to count by "if work day 1 is here how many ways can i place work day 2, then how many ways can i place workday 3"

you can immediately see that the number of ways to place say, workday 3 depends on placements of workday 2 and workday 1 in a not very nice way (and gets much worse for days 4/5)

so you want to either 1. make the dependency less nasty or 2. hopefully skip the dependency thing altogether

fair hound
#

another way to see it for dazzle:
a sequence of working and non working days is a sequence of w and x, where w are working and x non working
you have 5 w and 26 x
but two w can't be next to each other
so we make a little transformation: we couple 4 of the x with 4 of the w, to form couples Y = (x, w), and now Y can follow w and Y can follow each other
now we have 27 symbols: 1 w, 4 Y, 22 x where w and Y are of the same object "working day to place in the sequence"

untold sky
#

the method frog introduced, where you insert work days into the 26 non-work days, makes the dependency less nasty (you just get 27 * 26 * 25 * 24 * 23, and you can determine how many ways to insert more)

#

stars and bars skips that dependency altogether, by observing the structure:
there must be at least 4 non-work days between the first work day and the last work day, since no work days can be consecutive

#

therefore when we say 5 bars and 22 stars, it's equivalent to treating there being only 22 non-working days, and removing the constraint that workdays have to be non-consecutive, because we implicitly add 4 more non-work days, one after each of the first 4 work days

noble sail
noble sail
noble sail
#

just incredible

untold sky
#

what frog's method does is it ignores the order of the work days

because when you try to brute force, you label work days "first work day", "second work day (after the first)", etc

by inserting workdays between non-workdays you're saying one of the workdays can be here, .. etc

noble sail
#

Ah

#

I see why this would simplify a ton the work

untold sky
#

also that method to count under the restriction of no two identical items together is one of the earlier tricks you'll learn in combinatorics probably in the first lecture or two

#

worth remembering because it's easy to apply

noble sail
#

Okay

#

how did you get so good at combinatorics

#

you seem to have understood it to its core

untold sky
#

did math comps back in middle/highschool and read a decent amount of brilliant/art of problem solving

noble sail
#

waaw

#

whats brilliant/art of problem solving

#

can i access them?

untold sky
noble sail
#

are they free?

fair hound
#

artofprobemsolving is

untold sky
#

aops is, brilliant no

noble sail
#

and do they explain core intuitions?

#

or just solutions

fair hound
#

depends tbh, aops has problems + people who gives solution

fair hound
#

some people are clearer than others

noble sail
#

okay i see

#

thanks a lot this was super helpful

#

.close

safe radishBOT
#
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misty belfry
#

statistics question: Can you have an estimate with no bias and high variance?

misty belfry
#

doesnt "no bias" imply ur estimate is the same as the population parameter?

#

so for example if i want to estimate the mean of something using a sample data what does it mean for my sample mean to have bias zero?

fair hound
#

no bias means the expected value of your estimate is the real expected value for your parameter

misty belfry
fair hound
#

yes, the impossible task is to have both no bias and low variance

misty belfry
#

why would it have high variance? high variance means if i get another sample data i would get a different result right?

#

and if i keep repeating the results will differ largly

fair hound
#

high variance means the probability of getting data far from the expected value is high

#

like a flat distribution instead of a condensed one

misty belfry
#

but doesn't no bias mean that what im estimating will be close to what is real?

#

nvm is ee

safe radishBOT
#

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night sparrow
#

How to prove AD bisect angle BAC?

safe radishBOT
fair hound
#

AD is diameter so ABD and ADC are right triangles and share two sides since BD = DC

night sparrow
#

angles in semi circle?

fair hound
#

I don't understand what you're trying to say

#

I'm talking about similar triangles

#

ABD and ADC are congruent

night sparrow
#

i see

#

thx i can solve it now

#

.close

safe radishBOT
#
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safe radishBOT
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hidden rose
#

how would i go about multiplying a rotation martix for the Xs and Ys here? i havent learned aboht matrices yet but im trying to understand what im supposed to do when given such a thing

hidden rose
#

just out of pure curiousity

hidden rose
#

is it supposed to be a matrix with xyz coords and then i would need to multiply it like 2 matrices would be multiplied

obsidian bone
#

$\begin{bmatrix} 1 & 0 & 0\ 0&\cos{\theta}&\sin{\theta}\end{bmatrix}$

hidden rose
#

$\matrix{x, y, z}$

#

like this?

obsidian bone
hidden rose
#

ah so its literally just 2 matrices being multiplied

#

that was the only thing i didnt undestand, whether it was supposed to be just x multiplied, but that would be weird and not propper, so i was confused as to what exactly to multiply

#

thx

#

.close

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crisp lodge
#

hey guys
I was tasked with solving the diff equation, f''+f=(cosx)^2
I managed to arrive at the solution f=1/2-1/6(cos(2x))

crisp lodge
#

however, im not sure if those are indeed all the solution, not am I sure how to compute it to account for all possible solutions

#

can anyone calrify this for me ?

white relic
#

help

solid shell
safe radishBOT
#

@crisp lodge Has your question been resolved?

safe radishBOT
#

@crisp lodge Has your question been resolved?

safe radishBOT
#

@crisp lodge Has your question been resolved?

safe radishBOT
#
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lean otter
safe radishBOT
lean otter
#

when given a function like this

#

how do I find the zeros?

glass carbon
lean otter
#

it wont touch at y = 0

#

thats for sure

glass carbon
#

u want to solve

lean otter
#

yep

glass carbon
#

?

flat frigateBOT
glass carbon
#

or what

lean otter
#

yes

glass carbon
#

then think about it - can it achieve positive value? (I mean function)

lean otter
#

the x can be positive

glass carbon
#

well, other question, can sqrt( something ) be negative?

lean otter
#

i solved it on a calculator, just wanted to know how the process is with such functions

lean otter
#

if i remeber

glass carbon
#

yes, it can't

#

so

#

it can be 0 or positive

lean otter
#

yes

glass carbon
#

let's consider it's even zero, then if we subtract 4 we'll definitely get negative value

raw pivot
glass carbon
#

wait, you're asking about complex? ;d

raw pivot
#

just generally asking

glass carbon
#

but still

#

it works

lean otter
#

isn't it add ?

glass carbon
#

in other words you have:

#

$$\sqrt{4-x^2}=-4$$

flat frigateBOT
glass carbon
#

you've said square root is always NON-NEGATIVE

#

on LHS u have negative 4

#

so is there any x such that equation is true?

lean otter
#

this equation is false

glass carbon
#

yes

#

this means function - 4 - sqrt(4-x^2) has no zeros

lean otter
#

ok with functions that dont touch at y = 0

#

how do we do it ?

#

i imagine this parabole touches -4

#

or something

#

y = - value

#

@glass carbon do I do trial and error to see which x value the function stops ?

nova creek
#

If the function has no zeroes

#

Then it has no zeroes

#

Full stop

lean otter
#

this is the function here, it stops at x = - 2

#

x = 2

nova creek
#

But it never touches y = 0

lean otter
#

ok so I have to trial and error with the y

nova creek
#

No

#

It will never touch y = 0

lean otter
#

i know

nova creek
#

You're asking for the zeroes of that function

#

There are none

glass carbon
#

maybe formulate your question properly

#

Are you thinking about y-intercept or what

#

domain maybe??

lean otter
#

the points -4, -2 ; -4, 2

#

ok domain

#

thats the one that gives these points

#

it works

#

thanks

#

.close

safe radishBOT
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mortal kernel
#

Can someone help me with this? My professor wants it done with Plurality with Elimination AND Pairwise Comparison .

safe radishBOT
#

@mortal kernel Has your question been resolved?

mortal kernel
#

.close

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sharp wharf
safe radishBOT
sharp wharf
#

I donโ€™t really understand what the function g does

#

By g(f) is it referring to a general function f in B_n?

#

But then what is f(1)โ€ฆ representing?

obtuse jackal
#

f is in Bn yes

#

It's based on the idea that an n-periodic function is uniquely defined by its first n values

#

So this associates the function to these values

#

And proves it's a bijection

sharp wharf
obtuse jackal
#

Say you want to find f(k).
You can just use euclidian division to write k = qn + a
Then because f is n-periodic, f(k) = f(a), with a in [1, n[.
Therefore f is entirely defined by its first n values. The rest is found by repeating it

sharp wharf
#

I see, thanks. Essentially this g function is just mapping f to its n tuple so f(1)โ€ฆf(n) before it repeats

#

What is f and f over score though?

#

I also donโ€™t really get how it is injective

#

Since take for example a function f with f(1) to f(5) as (2,4,6,2,8,)it has period 5 but, f(1)=f(4)

obtuse jackal
#

You don't want f to be injective. You want g to be injective

obtuse jackal
sharp wharf
#

I see on the very last line shouldnโ€™t it also be f over score(p)

#

But I donโ€™t really see how I would efficiently come up with this in an exam haha, are there any tips to do so?

obtuse jackal
obtuse jackal
#

How do you describe periodic functions ? First by their period. That gives you the union of the Bn

#

Then you know that it is sufficient to prove each Bn is countable (or uncountable since it's an open question)

obtuse jackal
#

So if you understand the material, I wouldn't say there's a single hard step for coming up with this proof. I came up with the same thing before looking at the solution and took me a few seconds. Which is not meant to be boastful, but to argue that it's quite a straightforward proof for a countability problem

safe radishBOT
#

@sharp wharf Has your question been resolved?

safe radishBOT
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fiery escarp
safe radishBOT
fiery escarp
#

<@&286206848099549185>

safe radishBOT
#

@fiery escarp Has your question been resolved?

tropic schooner
#

What's the first part of the question that you find confusing?

fiery escarp
#

I computed the wronskain determinant and got -3

#

So Iโ€™m not sure how to get the dimensions

tropic schooner
#

As far as I can tell, the Wronskian determinant (that I had to look up, because I hadn't seen it before) isn't necessary to solve this problem.

fiery escarp
#

I was thinking the dimensions of the subset h is 3

tropic schooner
#

I do get that dim(H) is 3.

fiery escarp
#

And for part b I said it is a basis for p2

#

And for part c I got some fractions then o I donโ€™t know what to do

tropic schooner
#

What is dim(P_2)?

fiery escarp
#

The question doesnโ€™t say the dimensions of p2

tropic schooner
#

Hm. I guess I can explain it a different way too. You said that the three polynomials are a basis for P_2, what does that mean?

#

(I'm looking for a particular idea, or an equation, that follows from the definition of what a basis is.)

#

What is the span of a basis?

#

Why did you say for part b that it is a basis for P_2?

#

(As in, what led you to decide that.)

fiery escarp
#

Hereโ€™s my working out

#

Wait so it doesnโ€™t spam p2

#

So itโ€™s not a basis for p2

tropic schooner
#

FYI it's -4, not 4, for the matrix you wrote in the middle there.

#

What's the standard basis for P_2?

fiery escarp
#

O

#

So I messed up

#

I canโ€™t be asked anymore

tropic schooner
#

In this case, it does span P_2.

#

The standard basis for P_2 is {x^2, x, 1}. It shouldn't be too hard to convince yourself that span({x^2, x, 1}) will give you every polynomial of degree at most 2. Therefore dim(P_2) = 3.

#

How I solved the problem: Since dim(H) = dim(P_2) = 3 and H is a subspace of P_2, this means that H = P_2. This makes answering b and c easy.

safe radishBOT
#

@fiery escarp Has your question been resolved?

fiery escarp
tropic schooner
#

I... can't deduce what you're doing for most that image.

fiery escarp
#

Oh

tropic schooner
#

The only thing I could recognize was the matrix made of the three polynomial's coefficients (with 4 instead of -4).

fiery escarp
#

I'm confused how to answer c

tropic schooner
#

If you have that H = P_2, and the three polynomials are a basis of P_2, what is a basis of H?
If you have that H = span({three linearly independent polynomials}), what is a basis of H?

#

Hint that gives away what I tried to get you to remember/say: ||A basis of V is a set of linearly independent vectors (in this case polynomials) that span V.||

safe radishBOT
#

@fiery escarp Has your question been resolved?

safe radishBOT
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white crow
#

so for (a), I got 1 as my gcd using the euclidean algorithm. How do I apply that to question (b)? Do I just solve for s or t?

misty coral
#

when you worked out your gcd

#

you got something like a=bq+r right

#

and r is 1

white crow
#

mhm

misty coral
#

you can think of it as going backwards

#

if r = a-bq

white crow
#

37 x 2 + 1

#

oh

misty coral
#

eight

#

right

#

so express one in terms of 37 and 75

white crow
#

so 1 = 75 - 37 x 2?

misty coral
#

exactly

#

,calc 75-(37x2)

flat frigateBOT
#

The following error occured while calculating:
Error: Undefined symbol x2

misty coral
#

oop

#

,calc 75-(37*2)

flat frigateBOT
#

Result:

1
misty coral
#

seems legit

white crow
#

but how do I know what the values of s or t are based on this?

misty coral
#

you've done it

#

1=37(-2)+75(1)

white crow
#

ohh

#

its because you subtracted

misty coral
#

for the negative? yes

white crow
#

right

#

thanks for the help

#

.close

safe radishBOT
#
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pastel kite
#

What would 5x+6=56 be?

safe radishBOT
foggy salmon
#

um

#

first u want only x on 1 side

#

im guessing u r solvin forx

#

so we can start with -6 on both sides

#

what do u get after that?

safe radishBOT
#

@pastel kite Has your question been resolved?

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safe radishBOT
plain gate
#

i answered iii) only

#

im just unsure if thats correct

#

im 99% sure it is

turbid raven
#

They are all discrete I think @plain gate

stray bluff
#

yeah seems right

turbid raven
#

Well it's not how much gas it is, it's the number of litres

trim swan
#

same with the age and weight, they are continuous

turbid raven
#

Idk the task seems extremely ambiguous.

trim swan
#

I disagree

#

I think you could go real brainiac and count the number of molecules of gasoline and say it's discrete

#

But that seems counter to the spirit of the question

#

And the age and weight are unquestionably continuous

#

Looks good

plain gate
#

.close

safe radishBOT
#
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white crow
#

So i did (a) and (b), got 1 as the gcd for (a), and s = -2 and t = 1 for (b)

white crow
#

for question (c), I did 1 == 75(1) + 37(-2) (mod 75) and since 75 mod 75 is 0 I'm left with

#

1 == 5(-2) (mod 75)

#

oh wait

#

is 10 supposed to be the answer

drowsy moss
#

where did the 5 comes from?

white crow
#

that's a good question why did I write 5

#

uh

#

let me go fix it

#

ok so

#

what i have now is

#

1 == 37(-2) (mod 75)

drowsy moss
#

yeah

#

so what's the inverse of 37 (mod 75)?

white crow
#

-74?

drowsy moss
#

nope

#

what's the definition of an inverse (mod n)?

#

or really any multiplicative inverse

white crow
#

37(x) == 1 (mod 75) right

drowsy moss
#

yeah

white crow
#

well 37 and 75 could be any number

drowsy moss
white crow
#

oh

#

-2?

drowsy moss
#

yes

white crow
#

one question

drowsy moss
#

or 73 if you want to make it positive

white crow
#

why is -74 mod 75 1?

drowsy moss
#

two numbers a and b are equivalent (mod n) if n | a-b

#

well, 75 | 1 - (-74)

white crow
#

oh

#

makes sense now

drowsy moss
#

another way to think about it is a and b are equivalent (mod n) if a = b + kn

white crow
#

ah

#

and k is integer

drowsy moss
#

yep

white crow
#

right

#

thanks for the help

#

.close

safe radishBOT
#
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opaque sorrel
safe radishBOT
opaque sorrel
#

@toxic stratus hi

#

for the characteristic equation is it just lambdaA - I

#

how do i find lamda

drowsy moss
#

characteristic equation is det(A-Lambda*I) = 0

toxic stratus
#

hi

opaque sorrel
#

where do i spawn in lambda tho

#

or is it an arbitrary value

#

oh wait

#

it is

drowsy moss
#

arbitrary

opaque sorrel
#

cuz the equation roots are the eigenvalues

#

oh

toxic stratus
#

lambda is just some number

#

like

#

you get a polynomial

opaque sorrel
#

ohhh

#

lemme do it

#

thx

#

did u miss me

obsidian bone
#

Two snows?

flat frigateBOT
opaque sorrel
#

yes

toxic stratus
#

itll just look like that

#

a polynomial

opaque sorrel
#

yesmaam

#

the roots are the

toxic stratus
#

e-vals

opaque sorrel
#

egyenvalues right?

toxic stratus
#

ye

opaque sorrel
#

nice

#

lemme do it rq

#

wait

#

its det(A - lambdaI) = 0

#

can it be

#

det(lambdaI - A) = 0

toxic stratus
#

doesnt really matter since its just a possible sign change

opaque sorrel
#

o

toxic stratus
#

if you do lambda first the coefficient in front of the largest power of lambda will always be 1

opaque sorrel
#

how do i type lambda in latex

toxic stratus
#

so idk

#

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