#help-26

1 messages · Page 6 of 1

neon iron
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@half pike I'm guessing you just didn't see the minus sign

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Notice it says y=**-**2, not y=2

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Pro tip: Close the dollar signs before writing text

safe burrow
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huh

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wdym

neon iron
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The ", so " part

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That's just regular text

safe burrow
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oh right

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tbh i dont care all that much its clear whats meant

half pike
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ohh

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wait what’s wrong abt 8c

neon iron
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You once again ate the minus sign

half pike
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whats Sox

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OH

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hang on

neon iron
half pike
#

would it be 1^2 - (-2)^2 or 1^2 - (-2^2)

neon iron
safe burrow
half pike
#

okk

neon iron
#

In case of doubt, when replacing a variable with its value, put parentheses around the value

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@half pike You can now .close this channel

half pike
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real quick

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8a is -3
8b is 9
8c is -2

neon iron
half pike
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yay

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culd u help with this one

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idk how to do this

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like is it x + 5 < 0

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?

neon iron
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Yes

half pike
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how do u do the other ones

neon iron
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First of all do question a, it should be easy

half pike
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idk how to do 1b or 1c

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it doens tmake sense

neon iron
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Do you know what the "solution set" is?

half pike
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not rlly

neon iron
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It's the set of all numbers that satisfy the equation/inequality

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@half pike Does that make sense?

half pike
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can u give an example

neon iron
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Because x=1 and x=-1 are the only solutions to this equation

half pike
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ohh ok

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how do i graph the set

half pike
neon iron
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I'm saying that either x=-1 or x=1

half pike
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ohh

neon iron
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@half pike What do you think the solution set is for the inequality x > 0?

half pike
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-1

neon iron
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?

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That's not a set

half pike
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-1,1?

neon iron
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...?

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x > 0

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Are you still thinking about x^2=1?

half pike
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yea

neon iron
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Because that was an earlier quesiton

half pike
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oh

neon iron
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That's a number

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Not only that, but it doesn't even satisfy the inequality

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-infinity is not greater than 0

half pike
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whats a set again

neon iron
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Just a collection of things

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Although because we're talking about a solution set it must be a collection of numbers specifically

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GG to the guy who just got automodded

half pike
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oh ok

lucid bridge
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Wait

neon iron
lucid bridge
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Do u know what the form of a solution set is

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Just yes or no

lucid bridge
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Id call it a form

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That's how I've always called it

neon iron
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Any set of numbers can be a solution set

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So I don't see what you're talking about

lucid bridge
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It can be represented in multiple ways

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Thus it's a form

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(it's not actual terminology, I just think stuff like this)

neon iron
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Yeah sure but I think if they knew this they'd be able to answer

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@half pike So should I take that to mean that you don't know the solution set for x > 0?

half pike
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yes

lucid bridge
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Then you gotta teach them how to make a solution set

neon iron
lucid bridge
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Fair

neon iron
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Just testing their background knowledge first

neon iron
half pike
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what si what

lucid bridge
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I think they mean take it as they don't know

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Anyway

neon iron
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Oh broke

lucid bridge
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Also sorry if u find my tone rude or anything, I'm bad at communicating

neon iron
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@half pike The set is (0,infinity)

lucid bridge
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What

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Bruh wtf

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That's interval notation

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My guy

lucid bridge
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Nooooo

neon iron
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thonk An interval is a set of numbers

lucid bridge
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It's interval notation, I learnt it as solution set is a set

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Like

neon iron
# half pike oh

Does it make sense that we're using an interval rather than {}?

lucid bridge
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Idk if they learnt it like me so I would do it in the set notation

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Not interval

neon iron
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Ok...?

neon iron
lucid bridge
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I have no idea where the set thing went

neon iron
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0 > infinity 📝

lucid bridge
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${ {x \in \mathbb{R}; 0 < x <\infty} }$

neon iron
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@half pike Last attempt, are you there?

half pike
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yes

lucid bridge
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Shit

thorny flameBOT
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Kai The Doge

lucid bridge
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Finally

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Omfg

neon iron
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@half pike So does it make sense to you that for x > 0 we used an interval instead of the regular set notation with curly brackets?

half pike
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i guess?

lucid bridge
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Both work*

neon iron
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Like for x^2=1 there are finite solutions

lucid bridge
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But if there are infinite, you cannot just give a few numbers or list them all, thus u have to use set notation

neon iron
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Hence we can write them all down like {1,-1}

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But for x > 0 there's an infinite amount of solutions

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So instead of spending an infinite amount of time writing them all down we just use an interval

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@half pike Does that make sense?

half pike
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yea

neon iron
half pike
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-5, - infinity?

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or -6?

lucid bridge
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It's -5

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Also is -infinity smaller or bigger than -5

half pike
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uhhh

neon iron
half pike
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[-5, -infinity)

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?

neon iron
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Is -5 a solution to x+5<0?

half pike
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it would be =

neon iron
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Yes

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So is it a solution or not?

lucid bridge
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Is 0<0

half pike
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no?

lucid bridge
neon iron
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Therefore -5 is not part of the solution set

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So it should be (-5,-infinity), not [-5,-infinity)

lucid bridge
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Also (-infinity,-5)

half pike
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Ohhh

lucid bridge
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Since smaller number...

neon iron
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I don't think it's a rule to do that but it's the convention

lucid bridge
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Follow convention, teachers may mark wrong

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Better to be safe imo

neon iron
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Yes, teachers hate students

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So you gotta be careful

lucid bridge
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Also is both or one correct? @half pike (-6,infinity] and (-6,infinity)

half pike
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one

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it’s the second one

lucid bridge
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Why

half pike
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cuz infinity is suppose to end with ) always

lucid bridge
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Yep

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Since infinity is a concept and not a number

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It cannot be =

neon iron
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Riemann spheres:

lucid bridge
neon iron
lucid bridge
half pike
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wait so for my question

neon iron
half pike
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how do i graph hit

neon iron
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Are you familiar with graphing intervals?

half pike
half pike
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and idk how to

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thr space is kinda small

neon iron
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Yeah, it is

neon iron
lucid bridge
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It's a line

half pike
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okk

neon iron
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I found this on Google

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Does that ring a bell?

lucid bridge
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Like a bad number line basically

half pike
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ohhh

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so how do i do that

neon iron
half pike
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and do i jsut write it on the line?

neon iron
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By the way because your interval goes all the way to -infinity you will only draw one parenthesis

neon iron
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Well do it on another piece of paper or in paint (the program not actual paint) first

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So that I can check what you did

half pike
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ohh

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i dotn get it

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doesn tlook right

lucid bridge
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I thought you were supposed to do it with dots like this

half pike
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do i use the third one?

neon iron
neon iron
half pike
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okk

lucid bridge
neon iron
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@half pike Any progress?

half pike
half pike
neon iron
half pike
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yay

neon iron
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To remember this notation, you can think of a circle as an "open dot" and a point as a "closed dot"

half pike
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yes

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but it doesnt include -5 so

neon iron
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Yes

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Hence it must be open

half pike
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open dot is excluded right?

neon iron
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Hence it's correct

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Yep

half pike
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oh yay

neon iron
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You may now .close this channel

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Unless you have more questions

half pike
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can we do the other one

neon iron
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Oh I forgot about the other one

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Right

half pike
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x + 1 <= -2

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is that right

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?

neon iron
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Yes

half pike
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how do i write the soultion set

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@neon iron help monkagiga

neon iron
half pike
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idk

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uhhhh

neon iron
half pike
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-3, infinity

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?

neon iron
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Yes

half pike
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wait rlly

neon iron
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Wait no

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Not infinity

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Think about it for a moment

half pike
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oh what would it be

lucid bridge
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Is infinity less than -3

half pike
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no

neon iron
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I don't really know how to make you realise this yourself

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All I can say is wrong direction ⬅️ other way

half pike
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oH

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(-infinity, -3]

neon iron
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Yes

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Why'd you choose ] this time?

half pike
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did i use brackets right

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cuz it includes -2

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because its <=

neon iron
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-2?

half pike
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not <

neon iron
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Why are we talking about -2?

half pike
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oh sorry

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-3

neon iron
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Yes

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That's the reason

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Now I think you won't have any problem graphing it

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@half pike Did you graph it?

half pike
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not yet

neon iron
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If that's it, you can now .close this channel

half pike
neon iron
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That's a lot of work you have there

half pike
neon iron
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Or maybe I'm just not used to it because I'm lazy

half pike
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the question is

neon iron
half pike
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Solve the linear inequality.

neon iron
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I can't believe neither of us is paid to do this

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Anyways

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Tell me the first one where you get stuck at

half pike
neon iron
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For example, something such as x <= 3 is considered solved

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Because x is alone

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@half pike Does that make sense?

half pike
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idkk

half pike
neon iron
half pike
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okk

neon iron
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Basically in 2x <= 7, x is not alone

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There's a 2 next to it

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So you need to find a way to make it alone

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Do you know how to do that?

half pike
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yes

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so is x = 14

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?

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wiat

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sorry

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my bad

neon iron
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= thonk

half pike
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= 3.5

neon iron
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14 thonk

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= thonk

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How the frick did <= become =?

half pike
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oh yea

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so is x <= 3.5

neon iron
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Yes

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I think my teachers would accept this as an answer, not sure about yours

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In theory both this and solution set form should work fine

half pike
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oh ok

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what abt the other ones

neon iron
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Well same logic

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Just do them all the same way and tell me if you get stuck at any of them

half pike
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so x > 4

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?

neon iron
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Yes

half pike
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oo yay

half pike
neon iron
half pike
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-x >= 5 -7

neon iron
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Oh there you go

half pike
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-x>= -2

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but u cant have a negative varible like that right?

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so is it

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x >= 2

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?

neon iron
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If you're going to negate both sides the symbol flips

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Like picture the number line in your head

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Or even better, take a piece of string or a pen or pencil and think of it as the number line

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Then flip it, which represents negating a number

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Notice how everything that was on the left is now on the right and everything that was on the right is now on the left

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That's why when you negative both signs of an inequality the symbol flips

half pike
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ohh so its <=

neon iron
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Yes

half pike
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ohhhh

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can u help me with the hrad ones pls

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like the fraction ones

neon iron
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Which one specifically?

half pike
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21, 23, 33, 34, 32, 24, 22

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i'd say those ones

neon iron
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@half pike The fractions don't make it hard at all

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Typical numerophobia or whatever the frick its called honestly

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Students do be like that

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It's just the same as what you already did but you have to write more stuff down

half pike
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oh

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okk ill try

topaz sinewBOT
#

@half pike Has your question been resolved?

#
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topaz sinewBOT
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desert pulsar
#

Is this correct?

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@vernal matrix thanks

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.close

topaz sinewBOT
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rich rampart
#

Does this series have a name?

topaz sinewBOT
rich rampart
#

I’m having a hard time finding the sum of this series but I can’t match it to any on Wikipedia

neon iron
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could you show the original question

ionic oar
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Seems to be something special

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There is a pattern though

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$T_n = \frac{n}{n(n + 1)}$

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Bot broken

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The nth term is n/[n(n+1)]

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Which is just 1/(n + 1)

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Which is a harmonic progression

rich rampart
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On shoot that’s right

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I forgot about the term out side the series

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If it’s harmonic doesn’t that mean there’s no sum.

ionic oar
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Well

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There's no neat and tidy formula for it

rich rampart
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So this series just goes to infinity

ionic oar
#

Yes it diverges

rich rampart
#

I probably did something wrong

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this was the original question

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for a I found it to be (1/k)(1/k+1)

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Thanks for the help!

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Really appreciate it

molten raven
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I don’t think you did something wrong, I got the same

rich rampart
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so this is basically saying my expected value of getting a white is an infinite number of tries?

molten raven
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Yea this is weird let me see if I made a mistake

rich rampart
#

I guess it kind of makes sense for it to be infinite

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cause the more black I choose the white basically just disappears

molten raven
#

I guess

rich rampart
#

to the point where i keep drawing which just hurts my chances of getting the white

molten raven
#

Yea that makes sense

rich rampart
#

Thanks for the help!!

#

.close

topaz sinewBOT
#
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lyric mountain
#

what would be a good hint for the anti deriv of tan x?
I'm trying to rewrite it but I got a product still in the end. Assume calc 1 knowledge

pastel oracle
#

try substitution

lyric mountain
#

ohhhhh

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good idea

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would you rewrite tan first as sin x / cos x

pastel oracle
#

yes

lyric mountain
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then rewrite sin x / cos x as sin x * sec x

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let's see

pastel oracle
#

that's not how I'd do it

lyric mountain
#

oh

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you'd stick with sin x / cos x?

#

.close

topaz sinewBOT
#
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finite mortar
#

for 8c

topaz sinewBOT
finite mortar
#

i dont get why u need the line after this one --> i thought u can find probability that B scores first from there

pastel oracle
#

what do you mean?

finite mortar
#

i dont get why theyve done the last bit

pastel oracle
#

to find that probability

finite mortar
#

so theyve done the first part to get enough information for the last part

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this question always confuses me

pastel oracle
#

yes

finite mortar
#

oh mb you can't say that the probability of A winning = 0.3 because that has the condition of B scoring first?

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ohhh so u consider A winning if they do score first and if they dont

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ohhhhhhhhhhhhhhhhh

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thanks

pastel oracle
#

they might be using the law of total probability in the denominator

finite mortar
#

whats dat lol

pastel oracle
#

google it, there should be plenty of resources on it

vernal matrix
finite mortar
#

h

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*oh

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yh

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oh i see

#

ill keep that in mind

topaz sinewBOT
#

@finite mortar Has your question been resolved?

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lucid oak
topaz sinewBOT
gusty bane
#

!status

topaz sinewBOT
#
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'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
lucid oak
#

2^x=5

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how do i know what is x?

gusty bane
#

do you know what a log is

lucid oak
#

no with out it

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can we?

gusty bane
#

we know x is between 2 and 3

lucid oak
#

okay

gusty bane
#

2^2 = 4, 2^3 = 8, and 5 is between those

lucid oak
#

so how do we know exacly?

lucid oak
gusty bane
#

know what

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know what exactly or close

lucid oak
gusty bane
#

you just need to be able to estimate it is between 2 and 3

gusty bane
lucid oak
#

how do we write x?

gusty bane
#

they gave you that x + 2y = 6

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the smallest value to consider is x = 2

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and the biggest is x = 3

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plug them in and see the largest and smallest values for y

karmic monolith
#

huh

lucid oak
karmic monolith
#

It only takes like an hour

lucid oak
#

i will

gusty bane
#

@karmic monolith this is an estimation question

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they want you to use the fact that x is between 2 and 3

karmic monolith
#

I don care

gusty bane
#

?

karmic monolith
#

Logarithms make it easier

gusty bane
#

what is log_2(5)?

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without using a calculator

karmic monolith
#

okay

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let me open libre math

gusty bane
#

i don't understand why you are being combative when the intended solution is clear

karmic monolith
gusty bane
#

this is again more complicated than it needs to be

topaz sinewBOT
#

@lucid oak Has your question been resolved?

topaz sinewBOT
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wispy mulch
#

Can someone give me the steps to solve this one please, my teacher only wants us manipulating one side.

wispy mulch
#

It’s the one question I haven’t been able to figure out

radiant tapir
#

if you expand out tan(X) as sin(x)/cos(x), then simplify, you'll see that becomes a trig identity

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you were on the right track

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here's a hint

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$\frac{tan(x)}{sin(x)cos(x)} \\= \frac{\frac{sin(x)}{cos(x)}}{sin(x)cos(x)} \\ = \frac{sin(x)}{sin(x)cos^2(x)}$.

thorny flameBOT
#

MellowDramaLlama

radiant tapir
#

now simplify and bob's your uncle 🙂

topaz sinewBOT
#

@wispy mulch Has your question been resolved?

wispy mulch
topaz sinewBOT
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clever cloud
#

Are vector fields just the gradient of some level curves?

knotty ledge
#

not all

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ones that are are "conservative"

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or are you not on about vector fields that are gradients of just some function?

clever cloud
#

By conservative, do you mean that whose partial derivatives of g and f with respect to x and y respectively?

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Damn, I guess i'd have to go way back and read the textbook.

knotty ledge
#

conservative vector fields are those whose line integrals over them only depend on the end points

clever cloud
#

Yeah, I've learned the same concept in Calc-based Physics as well.

knotty ledge
#

yeah those are precisely the vector fields that are gradients of some function

clever cloud
#

Okay, so if those "some functions" are non conservative, then there can't be a gradient of any sort?

knotty ledge
#

if the vector field is not conservative, it is not a gradient of a function

clever cloud
#

Those are "vector fields," am I correct?

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I know these are the gradients but

knotty ledge
#

those arrows are some of the vectors in the vector field yes

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and because this vector field comes from the gradient of phi, all the vectors are normal to some level curve

clever cloud
#

Got ya...

#

Thanks.

topaz sinewBOT
#

@clever cloud Has your question been resolved?

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static jacinth
#

I want to prove that the space of convergent sequences in $X$ is closed in $(X^\mathbb{N}, d_{\infty})$. $X$ is a metric space.

thorny flameBOT
#

Casiel368

topaz sinewBOT
#

@static jacinth Has your question been resolved?

static jacinth
#

<@&286206848099549185>

fringe kernel
#

wth

#

i dont know about this

#

wait for another helper

topaz sinewBOT
#

@static jacinth Has your question been resolved?

topaz sinewBOT
#
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prime meteor
#

.reopen

topaz sinewBOT
#

prime meteor
#

I saw this wasn't solved yet so I reopened it

#

<@&286206848099549185>

empty sail
#

.close

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neon iron
topaz sinewBOT
neon iron
#

How do I do part a?

loud oasis
#

use newton's third law

half edge
#

I’d consider it as a system

neon iron
neon iron
#

How would I relate that to vectors

loud oasis
#

draw a free body diagram showing the forces acting on each block as a vector

half edge
#

The outstanding forces are the gravitational forces

#

The tension is equal and opposite as cloud posited

thorny flameBOT
#

Stephen

neon iron
#

I’m still confused

half edge
neon iron
#

Does tension in the string equal downwards force+upwards force?

topaz sinewBOT
#

@neon iron Has your question been resolved?

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thorny ice
#

Don't know how to find the non-trivial solution for this to get Kn and thus K3

topaz sinewBOT
#

@thorny ice Has your question been resolved?

topaz sinewBOT
#

@thorny ice Has your question been resolved?

topaz sinewBOT
#

@thorny ice Has your question been resolved?

halcyon slate
thorny ice
#

Alright

#

.close

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neon iron
#

Why didn't i need to flip the intergral to have the lowest value on the bottom.

neon iron
#

oh

#

nevermind

#

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magic night
#

Uh I attempted but don't know how to get it to it's antiderivative

magic night
#

My attempt led me to 1/2 x (x-5)^-1

#

Now I'm gonna take a guess and say that's not it

neon iron
magic night
#

Oh

#

Wait what do I do with du

#

keep in mind I'm very new to antidifferentiation 😎

neon iron
#

If you let u = that, then differentiating u gives du = 2 dx

#

So your integral becomes

#

1/(2x-5) dx
= 1/u * 1/2 du

#

Integral of 1/u is ln|u|

magic night
#

so

#

I let u equal the denominator

#

and then there's 1/u (from the x-5) and 1/2 from taking out half, multiplied by du

#

Then by antidiffing it, I get ln|x-5| x 1/2 x 2?

neon iron
#

its 2x-5 not x-5

magic night
#

Whcih gives 1/2 x 2 ln|x-5|?

#

Oh ye

neon iron
#

And where are you getting the 2 from?

#

we get the 1/2 because

#

du = 2 dx
dx = du/2
But we are integrating 1/(2x-5) dx

#

dx = du/2

#

Or 1/2 du

magic night
#

Uh

#

I think I'm a bit confused sorry-

#

I get defining u and then getting du as 2

neon iron
#

du is not 2

#

du = 2 dx

magic night
#

wait what 💀

#

oh

neon iron
#

u = 2x-5

#

D(u) = D(2x-5)
D(u) = D(2x) - D(5)
du = 2 dx - 0

#

You can YouTube search "u substitution for integration"

#

To learn more about this technique

#

But essentially

#

We make a dummy variable by substituting the expression as something which we can easily integrate

#

Its all just algebraic manipulation of the expression

#

We know integral of 1/x is ln|x| but
1/(2x-5) is annoying to deal with

#

But if we could somehow mold this expression

#

Into something which does look like

#

1/x dx we would be able to easily integrate it

#

So we let u = 2x-5 and check if we are transforming from the x world to the u world

#

How will that affect dx and the integrand as a whole

#

Any integral has 2 parts

#

Integral of f(x) dx
The two parts are f(x) and dx

#

We know that 1/(2x-5) becomes 1/u

#

So replacing that we get

#

Integral of 1/u dx

#

Uh well we cannot really integrate this

#

variable in u but integrating in the x world

#

So we have to change dx into something du as well

#

u = 2x-5
means du = 2 dx
Or, dx = du/2

#

Now replacing that

#

We get

#

Integral of 1/u dx
Becomes
Integral of 1/u * 1/2 du
Or,
1/2 * Integral of 1/u du

#

Does that make sense?

#

If not, I highly encourage checking YouTube

#

U substitution

magic night
#

I follow everything before that though

#

and I get rearranging the equation to make dx the subject

neon iron
#

Try to solve similar problems like integrate sin(3x-9) to see if you have really understood it

magic night
#

Oh that'd be -1/3 Cos (3x-9) right

neon iron
#

Right

magic night
#

I think I get the usual antidiff for ex, basic variables and circular, I just can't grasp the du changing thing

neon iron
#

,w integrate sin(3x-9)

thorny flameBOT
magic night
#

9-3x?

neon iron
#

And wolframalpha is weird

magic night
#

Oh ye, I thought that'd only give the -1/3

#

oh wait

#

Nevermind that comment I just realised what that meant

topaz sinewBOT
#

@magic night Has your question been resolved?

magic night
#

uh ye

topaz sinewBOT
#
Channel closed

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magic night
#

I figured it out

#

Sorry for the trouble 💀

topaz sinewBOT
#
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craggy shoal
topaz sinewBOT
craggy shoal
#

we got value of PR from a previous question, which gives us 8

dapper lantern
#

Find PR first

#

And then use trigonometry

craggy shoal
#

we have s = 60

shut vigil
#

That's pythagorean theorem

#

For the 60 degrees

#

that is a special angle

craggy shoal
#

i have PR, i dont have ps or pr

muted spire
craggy shoal
#

sin 60 is root 3/2

shut vigil
#

If you do something like this, that is an equilateral triangle so all sides are the same

shut vigil
craggy shoal
#

i didnt quite understand

#

just started trigonometry this year

#

sin s = pr/rs

sin s = 60

sin 60 = root 3/2

#

understandable

#

then what?

#

8/2?

#

4?

muted spire
craggy shoal
#

yes

shut vigil
shut vigil
craggy shoal
#

tf is this

muted spire
#

its just some multiplication

shut vigil
shut vigil
shut vigil
# shut vigil

This picture shows an equilateral triangle, a triangle with the same three sides

shut vigil
#

if we add two of these together we have

shut vigil
craggy shoal
#

so 16?

shut vigil
#

ah no

shut vigil
#

so sub it

#

x whatever I wrote = 16

#

find for x

craggy shoal
#

16/root 3

craggy shoal
#

but yeah

#

ty

#

.close

topaz sinewBOT
#
Channel closed

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shut vigil
#

It's wrong

topaz sinewBOT
#
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craggy shoal
topaz sinewBOT
shut vigil
#

nah

#

its 16 = x sqrt(2)/2

#

so it's 32/sqrt(2) = x

#

or 32 sqrt(2)/2 = x

#

or 16 x sqrt(2)

#

18.48

craggy shoal
#

that aint even a option bruh

shut vigil
#

Ah bruh I made a mistake there

craggy shoal
#

16/root 3 which makes it 16 by root root 3 * root 3 / root 3 which is 16/3 * roott 3?

shut vigil
#

AHHH

#

I know where the mistake is

#

It's here

#

Maybe I'm too tired
It's x^2 / 4

#

so 3x^2/4

#

or xsqrt(3)/2 = 16

#

so 16/sqrt(3)

#

yeah it's D

#

cause that's just the same but rationalized

#

so 16sqrt(3)/ sqrt(3)^2 or 16 sqrt(3)/3

#

Yah

#

I'm just too tired maybe I should play rest first

craggy shoal
#

yep

#

.close

topaz sinewBOT
#
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severe bramble
#

Integrate x^(-a/b)*sin(x) dx from 0 to 1. Do it with partial integration (Done) and then by variable substitution with x=y^p for a well choosen p. Now whenever I try to select, 1, -1, 2, -2, +-5, +-10, +-9, +-10/9 I keep getting a thing I do not want when I get the dx/dy part. I think I'm missing something obvious. It's ok if we need to solve the integral with numerical methods after the substituion.

topaz sinewBOT
#

@severe bramble Has your question been resolved?

topaz sinewBOT
#

@severe bramble Has your question been resolved?

topaz sinewBOT
#

@severe bramble Has your question been resolved?

topaz sinewBOT
#

@severe bramble Has your question been resolved?

brazen plover
severe bramble
#

Ok so I think I solved it but still get a wrong answer when I calculate it. So dx = py^(p-1) so $integral_0^1 p y^(2p-19/10)cos(y^p) dy, if I take p = 19/20 lots of the things cancel out and I can numericaly solve it in matlab with '''matlab integral(@(y) (19/20).*cos(y.^(19/20)),0,1)'''

#

so if I integrate, from 0 to 1 of (19/20) .* cos(y.^(19/20)) I get 0.7943

#

so if I integrate, from 0 to 1 of (x.^(1/10)) .* (sin(x)) I get 0.4369

#

But they should give me the same value

topaz sinewBOT
#
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rugged idol
#

I struggle with the following math exercise:
You can have friends from town A and Town B.
You can have at max 4 friends from A and unlimited friends (like N) from B
X is a random variable representing the number of friends you have from B
You can only have friends from B if you have 4 friends from A.
X is Zipf distributed.
Whats the probability that you have at least one friend from A

My approach was we introduce Y that represents the number of friends I have from A and calculate
P(Y=4 & X>0)
But now I struggle with calculating Y. I dont have any probability given for someone from A being my friend.
I just know that X is Zipf distributed with parameter 4.
Can someone maybe give me a hint or something like that ?

topaz sinewBOT
#

@rugged idol Has your question been resolved?

rugged idol
#

.close

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#
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lyric mountain
#

Assume Calc 1 Knowledge.
For questions like these, aren't I just finding the first deriv and C, then I just plug in -1 into f'?

lyric mountain
#

idk what FTC is 🙂

silver trench
#

i’m assuming it stands for fundamental theorem of calculus

lyric mountain
#

OHHH

#

Yeah

#

I tots do

winter egret
#

The idea is that f(x)=F(x^2)-F(2) for some F that has the property that F'(t)=t/(t+1)

#

But if f(x)=F(x^2)-F(2), then certainly f'(x) = F'(x^2) - 0 = x^2 / (x^2 + 1)

lyric mountain
#

this solution doesn't make sense to me

#

it looks like he subbed the upper and lower limit

#

like

#

when I do my u sub, I know I have to change the upper and lower limit

#

but he used those to sub his integrand??

#

idk why my Professor would include parts of a solution where he hasn't taught us how to do

floral bison
#

Ok

lyric mountain
#

Like, I did u sub on t + 1

floral bison
#

$\frac{d}{dx}(\int_{a}^{f(x)} (g(x)) dx)$
=$g(f(x))(\frac{d}{dx} f(x))$

#

Oh lord

#

Hold up

lyric mountain
#

sure

thorny flameBOT
#

% Openglobe %

floral bison
#

There it is

lyric mountain
#

do I have to do it that way

floral bison
#

That’s an alternate way

lyric mountain
#

that looks like chain rule

floral bison
#

But much easier

#

It’s the reverse chain rule

lyric mountain
#

LOL

#

yeah

#

mf never taught us about reverse chain rule

#

ty

#

at least now I know what he did

floral bison
#

This “u” stuff is confusing

topaz sinewBOT
#

@lyric mountain Has your question been resolved?

lyric mountain
topaz sinewBOT
#
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neon iron
#

what are we talking here about ? it is permutation right?

alpine mist
#

no, the n things are all the same. So the number of values of r is n+1

#

so there are n+1 ways to choose r things from n identical things

neon iron
#

okie

#

.close

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#
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neon iron
#

p & q are alike objects and s is distinct object... in how many ways can we select object in this ?? i know when one group are alike the eq is (f+1)(h+1)-1 and when distinct it is (p+q)!/p! * q!

neon iron
#

.close

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elfin dagger
#

did i do this right?

topaz sinewBOT
#

@elfin dagger Has your question been resolved?

elfin dagger
#

<@&286206848099549185>

visual wedge
#

0

#

It should be 0

elfin dagger
visual wedge
#

Wait

#

Cross product gives you a vector that is perpendicular to the plane of the crossing vector i.e p and r here

neon iron
#

Shouldn't it be up the plane?

visual wedge
#

In my diagram, no

neon iron
#

Why not?

visual wedge
neon iron
#

Oh nvm its the right hand rule

#

Im dum enough to repeat the same mistake over n over again

elfin dagger
#

im not just doing cross product the question asks me to do a dot product of r too

visual wedge
visual wedge
elfin dagger
#

oh so is there no calculations needed then?

visual wedge
#

No

#

Simple observation, will save you some labour

#

These are trick question

elfin dagger
#

so i did my cross product wrong then?

visual wedge
#

Let me check

elfin dagger
#

since if i do the dot product with r it has to equal 0

visual wedge
#

I got 2,2,1

#

🤔

#

Do it like this, it is cleaner

elfin dagger
#

is my method bad? it's what was taught in my lesson

visual wedge
#

Determinant

visual wedge
ivory swallow
#

actually it would be 3i+2j+k

visual wedge
#

Can you kindly point out the mistake in my image?

ivory swallow
#

(4-1)i

visual wedge
#

Right

#

My silly mistakes are still there then

ivory swallow
elfin dagger
#

ok what was it?

ivory swallow
#

1 X 0-(-2 X 1) that will be 0+2=2

elfin dagger
#

ohh i see it thanks

#

real dumb mistake my bad

#

thanks for the help guys have a good night

#

.close

topaz sinewBOT
#
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velvet phoenix
#

I'm going through some solutions to a past paper (at uni) and I don't understand the solution given

velvet phoenix
#

Let $\chi$ be a non-trivial Dirichlet character modulo an integer $m > 1.$ Prove that the sum of the values of $\chi$ at the first m non-negative integers equals 0

thorny flameBOT
#

LeftySam

velvet phoenix
#

Solution:

#

Since $\chi$ is non-trivial there exists an invertible $b$ such that $\chi(b) \neq 1$

thorny flameBOT
#

LeftySam

velvet phoenix
#

(this is the first step, not the whole solution); I don't get this? Why is this true?

odd pagoda
#

well thats what non-trivial means

#

trivial sends all invertible elements to 1

topaz sinewBOT
#

@velvet phoenix Has your question been resolved?

velvet phoenix
odd pagoda
#

bezouts lemma

#

or well, thats the other direction

#

if gcd(n, m)>1 then it is clearly a zero divisor

velvet phoenix
#

Idk what that means

#

I'm confused what we're even talking about with regards to invertible here too

odd pagoda
#

has a multiplicative inverse

velvet phoenix
#

But what field are we talking about here?

#

$\mathbb{R}$?

thorny flameBOT
#

LeftySam

odd pagoda
#

not a field

#

a ring

#

mod n

#

Z/nZ

velvet phoenix
#

It's mod m no?

odd pagoda
#

same thing

velvet phoenix
#

Or why that implies the result

odd pagoda
#

if m=dk with d=gcd(m,n) and n=dt, then nk=dtk=mt=0 mod m

#

an element can only be a zero divisor or invertible

#

exclusive or

velvet phoenix
odd pagoda
#

then k=m=0

#

so you are multiplying by 0

#

which isn't interesting

#

but if d>1 then k is nonzero so you are multiplying by a nonzero element and get 0

#

which means zero divisor

velvet phoenix
#

Okay, the next is

#

As $a$ runs through all residue classes modulo $p,$ so does $c = ab$ as $c = ab$ has a unique solution in $a$ for every given $c.$ Hence $$\sum_{c=0}^{m-1} \chi(c) = \sum_{a=0}^{m-1} \chi(ab) = \chi(b) \cdot \sum_{a=0}^{m-1} \chi(a)$$ shows that $\sum_{a=0}^{m-1} \chi(a) = 0.$

thorny flameBOT
#

LeftySam

velvet phoenix
#

So a i'm assuming is what? A generator?

odd pagoda
#

you have (thing)=(something not 1)*(thing) so (thing)=0

#

just the sum index

velvet phoenix
#

No I get that, but I don't get the wordy bit

#

What does it mean that "a runs through all residue classes modulo p" anyway? A generator? Contained in the set {1,2,...,p-1}?

odd pagoda
#

if you let a be every element mod m, then also c=ab will hit every element

#

not sure why you switched to mod p now?

velvet phoenix
#

I meant m mb

#

Bruh this is crazy I can't believe this was an exam question

odd pagoda
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this is an easy question

velvet phoenix
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Seems unnecessarily difficult

odd pagoda
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no offense but you dont seem to know any basics

velvet phoenix
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I'm in third year

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It's just "a runs through all residue classes" is a very vague statement to me at least

odd pagoda
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it's a very classic math statement

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just look how its used in the sum

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you also say that sums run over some numbers

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every number from 0 to m-1 is used

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for a

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and then also for c because b is invertible

velvet phoenix
#

Does it mean a generates the group mod m {1,2,3,...,m-1}?

odd pagoda
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a is not a fixed element

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it is a running index

velvet phoenix
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So what does it mean, you have a in {1,2,3,...,m-1} mod m and you sum over each possible a?

odd pagoda
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do you know how sum notation works

velvet phoenix
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Yes

odd pagoda
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you keep excluding 0

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a runs from 0 to m-1

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just like in the sum

velvet phoenix
#

Sure, then include 0 in that, is that correct?

odd pagoda
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yes

velvet phoenix
#

.close

topaz sinewBOT
#
Channel closed

Closed by @velvet phoenix

Use .reopen if this was a mistake.

#
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hallow garden
#
  1. Water flows through a cylindrical pipe of internal diameter 7cm at 5m per second. Calculate:
    i) The volume in litres, of water discharged by the pipe in 1 minute.

Here's what I'm doing

π * 300 * 3.5
11545.35/1000
11.545

hallow garden
#

Am I doing correct?

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I don't have any marking scheme which I can check against

mellow arrow
topaz sinewBOT
#

@hallow garden Has your question been resolved?

topaz sinewBOT
#

@hallow garden Has your question been resolved?

topaz sinewBOT
#
Channel closed

Closed due to timeout

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#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

neon iron
#

i need help with this

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im kinda stumped

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i did ratio thing

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for first one

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i got mod x <1

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so r is 1

#

?

topaz sinewBOT
#

@neon iron Has your question been resolved?

neon iron
#

help

topaz sinewBOT
#

@neon iron Has your question been resolved?

neon iron
#

help

sour bloom
#

yeah looks like left one is r=1

sour bloom
neon iron
#

i did that one too

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can u look at my solutions

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ill send them

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@sour bloom

sour bloom
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main ideas are there, presentation can be more formalised

neon iron
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of course

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i will do

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is it correct?

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@sour bloom

sour bloom
#

yeah seems so

neon iron
#

ty

topaz sinewBOT
#
Channel closed

Closed due to the original message being deleted

topaz sinewBOT
#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

ivory cradle
#

ok I have geometric equations, I'm at Tn=6600(0.825)^n-1 to model the value of a machine after n years of depreciation, how much was the machine originally worth

ivory cradle
#

after looking I am just stuck idk what I'm doing to start

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<@&286206848099549185> ?

fickle oracle
#

It hasn't been 15 min yet

ivory cradle
#

yes it has ....

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I'm not quite that bad at math

fickle oracle
#

Oh sorry, I didn't see the time

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It's 11:28 already

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OK let's see}

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Is this your equation

pastel oracle
#

find the value when n=0?

fickle oracle
#

$T_n = 6600 \cdot (0.825)^{n-1}$

thorny flameBOT
#

Max Hetfield

ivory cradle
#

yes

fickle oracle
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What is the n?

ivory cradle
#

i mean for the initial value 1 ??

fickle oracle
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n is the years of depreciation

ivory cradle
#

or is that for after 1 year of depreciation

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okay

fickle oracle
#

If the machine is new, how many years of depreciation have passed?

ivory cradle
#

so then its just 0

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yeah

fickle oracle
#

Yes

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n = 0

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Replace and solve