#help-10

1 messages · Page 261 of 1

timid silo
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Need help, stuck with Q2c

obtuse pebbleBOT
pliant grove
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hi

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emmm..

timid silo
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Hi :))

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How do I show that F(k+1) is 2^k

pliant grove
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mmm.. the alternatives

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?

timid silo
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Strong Induction, the TA is gonna be picky if I pick another method

pliant grove
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ahh ok ok

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mmm.... wait

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I don't know I'm not sure I think 25

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;<

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need help

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please

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i don't know

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please help me

timid silo
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You know normal Induction?

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Induction with inequalities?

pliant grove
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No, I don't know, only the exercise says to calculate, that's as far as I know.

pliant grove
timid silo
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Strong induction applies more to recursive functions

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This is example with strong Induction

pliant grove
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ahh, yes I know but it doesn't work for me or maybe there is another solution please help

pliant grove
timid silo
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I have trouble with this form of induction too 😓😓

pliant grove
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but i need a your help please

timid silo
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I need help too 🤣

pliant grove
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xd

timid silo
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We in this together 😂

pliant grove
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yess

timid silo
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So... how gonna get help 🤔

pliant grove
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I think the same

timid silo
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.close

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late roost
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Hi so im learning how to find the perticular solution to this equation, The lecture is saying that because G(x)=x^2, y has to be a polinomial of degree 2. Can anyone explain why that is?

obtuse pebbleBOT
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@late roost Has your question been resolved?

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patent marten
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Ok so I'm confused as to what the answer for this problem is. My professor said it is zero, but I said DNE because it's breaking one of the limit laws.

obtuse pebbleBOT
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@patent marten Has your question been resolved?

patent marten
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<@&286206848099549185>

vernal spear
patent marten
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Yeah this will be the 3rd time sadly just going to give up on this one

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timid silo
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low key confusing 9th grade math

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im kinda bad sry just learned this todayu

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nvm solved on my own lmao

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timid silo
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.close

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umbral hornet
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why must n be a positive integer?

obtuse pebbleBOT
zenith raft
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'must' is the wrong word here

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it's not saying it must be an integer and otherwise the equality doesn't hold

umbral hornet
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I'm not quite understanding what you mean

violet sentinel
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you used the word "must" but it's not saying "must".

umbral hornet
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okay that i understand but

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why does it say n is a positive integer?

zenith raft
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under the right hypotheses you can extend that to n being a real number and still have the equality

umbral hornet
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this is my first time doing limits so sorry if i sound dumb here 🥲

zenith raft
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but it's making it easier for you

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(i assume the question is asking you to prove that)

brave bramble
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There's cases where the equation might fail, if n is not an integer

umbral hornet
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oh i see

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may i have an example?

brave bramble
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lim[x -> 0] √[x] is undefined

But √[lim[x -> 0] x] = 0

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The problem is the discontinuity of √x, at the limit point.

umbral hornet
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i see

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thank you 👍

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calm axle
obtuse pebbleBOT
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@calm axle Has your question been resolved?

obtuse pebbleBOT
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gritty swallow
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hello, how would you go about part c in this question

brave bramble
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Simplify 5 - r/10

gritty swallow
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oh i have to use a trig identity i see

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bright geyser
obtuse pebbleBOT
bright geyser
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not really sure

tough bolt
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The part that you colored blue is the part that B-A and C-A shares, so given that B-A=C-A mean that the C-A-B region and B-A-C region are empty

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Or else there will be elements that are in B or C that isn't in the blue part

obtuse pebbleBOT
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grim wharf
obtuse pebbleBOT
grim wharf
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It would be helpful if someone can explain the concept behind this sort of problem as well it would be much appreciated

obtuse pebbleBOT
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@grim wharf Has your question been resolved?

grim wharf
#

<@&286206848099549185>

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narrow garnet
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how do you solve using hyperbolic functions? I tried integration by parts but i got stuck. u = tanh^-1(x), du = 1/1-x^2, dv = x and v = x^2/2. when i do the integral of v du, im not sure how to proceed

obtuse pebbleBOT
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@narrow garnet Has your question been resolved?

vivid compass
narrow garnet
#

tysm

#

.close

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uneven otter
obtuse pebbleBOT
uneven otter
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now idk how to find for what values

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it would be inconsistent

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Ik this wont have any solutions because second last row concludes that 0 = 1

kind hawk
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whenever you divide by something, make sure that the something isn't zero

uneven otter
kind hawk
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if a-2b=0, then you can't divide by it

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so there are two cases

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either it is zero or it isn't

uneven otter
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shit im confused

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so do I split it into two cases

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before doing that

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but ltte say

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if a - 2b neq 0

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then the rref would be the same as what I got right

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and the rref I have is incosistent too right

shrewd wasp
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I guess you are right, it is inconsistent

uneven otter
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brah so its correct

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but

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the question

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is askin

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for what values of a, b

shrewd wasp
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$\forall \alpha, \beta \in \mathbb{R}$

warm shaleBOT
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adzetto

uneven otter
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why

shrewd wasp
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because this is present regardless of the values of α and β

uneven otter
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mhm alr

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@thin star whats funny doe?

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😭

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do u think i fuked up

kind hawk
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I am a bit worried that the program gives that rref

uneven otter
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i checked on another

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website

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and got same

kind hawk
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it should absolutely depend on the values of alpha, beta

uneven otter
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as mine

kind hawk
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instead of alpha and beta plug in zero

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what do you get then

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(you should obviously get a consistent system because the last column is the zero column)

uneven otter
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so all 0s

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on the right side?

kind hawk
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yes

uneven otter
kind hawk
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there we go

uneven otter
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🤔

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i dont get it

kind hawk
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online calc can't handle variables correctly

uneven otter
kind hawk
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yes

uneven otter
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alright imma do case 2 rq and show u brb

uneven otter
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uhhh another question

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I was thinking about dividing row 3 by a

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but i will have to split it into cases again right so is there a better way

kind hawk
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just do it

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you have two variables so it's not a huge surprise that you have to split it into cases two times

uneven otter
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so a = 0 and a neq 0

kind hawk
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yes

uneven otter
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shit alr brb

uneven otter
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im stuck

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what should I do next]

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wait could I do

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row 1 - row 4

kind hawk
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well now the third row is 0 0 0 0

uneven otter
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and then say its inconsistent

kind hawk
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and if a=0 and a-2b neq 0, then b has to be neq 0

uneven otter
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no no

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this is case 2 for a - 2b = 0

kind hawk
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ah

uneven otter
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so a = 0 and a - 2b = 0

kind hawk
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well then b has to be zero

uneven otter
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ohhhhh wb

kind hawk
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so fourth row is also 0 0 0 0

uneven otter
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row 4 + row 3

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to get row 4 as 0 0 0 0 a - 2b

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and row 3 as 0 0 0 0 a

kind hawk
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you are overcomplicating this

uneven otter
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ah mb

kind hawk
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you can just plug a=0 in

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and b=0

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you don't have to do any more row operations

uneven otter
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but

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im confused

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how did u conclude

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that b = 0

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from thsi

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oh because

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a - 2b = 0

kind hawk
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a=0 and a-2b=0

uneven otter
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and a = 0

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ahhhhh

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so

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1 0 1 | 0

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which is inconsustent

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right

kind hawk
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what

uneven otter
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brah

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like

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1 0 1 | 0 is never true

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u said

kind hawk
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anything with a zero on the right is always consistent

uneven otter
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to plug in b = 0

uneven otter
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this matrix is consistent?

kind hawk
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if a=0 and b=0, yes

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but that is in fact the only case

uneven otter
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so the answer would be for all a, b in R s.t a and b neq 0?

kind hawk
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yes

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wait

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the and is wrong

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a neq 0 or b neq 0

uneven otter
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but

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our final case

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was

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a = 0 and b = 0

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because look at this

kind hawk
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yes and the negation of that is a neq 0 or b neq 0

uneven otter
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oh for inconsistency

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for a b in R s.t a neq 0 or b neq 0

kind hawk
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yes

uneven otter
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for all a, b in R s.t a neq 0 or b neq 0?

kind hawk
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again, yes

uneven otter
#

ty

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.close

obtuse pebbleBOT
#
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obtuse pebbleBOT
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verbal sluice
#

can anyone help me with how to prove a Cobb-Douglas function is homothetic

royal basin
#

what's a homothetic function

fossil crag
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a homothetic function can be written as $f\circ g$ where f is monotonic and g is homogeneous (ie $g(sx_1,...,sx_n) = s^kg(x_1,...,x_n)$)

verbal sluice
#

yes, but now it's like I know u = $f\circ g$ but I dont know f and g , and I need to prove u is homothetic

warm shaleBOT
#

CCCCClaire

fossil crag
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yes, well you have to find f and g such that it works

verbal sluice
#

here i should be 1

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so can I say if (the partial derivative of tx1 / the the partial derivative of tx2 )= (the partial derivative of x1 / the the partial derivative of x2), then u is homothetic?

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t is a constant

warm shaleBOT
#

rafilou2003

fossil crag
#

you should be able to write the utility function as $(x_1^{\frac{\alpha}{\alpha+\beta}}x_2^{\frac{\beta}{\alpha+\beta}})^{\alpha+\beta}$

warm shaleBOT
#

rafilou2003

verbal sluice
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ahhhh

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and here the f is the inside function and g is ()^a+b

fossil crag
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uh the opposite

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f(g(x1,x2))

verbal sluice
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ooh right

solar trellis
fossil crag
verbal sluice
#

and btw if I want to show u() is qusai-concave can I use its borded Hessian determinant ?

solar trellis
#

wth i've never heard of these words

verbal sluice
#

or just use its second order derivative and say if it is concave, then it is quasi-concave

fossil crag
#

I think that's the case here

verbal sluice
#

thank u so much!

obtuse pebbleBOT
#

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hushed jasper
obtuse pebbleBOT
hushed jasper
#

oops never mind

#

.close

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rocky pebble
#

Need help with this functional equation: f(x^2 + f(y)) = x•f(x) + y

timid silo
#

Don't use multiple channels

obtuse pebbleBOT
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storm kayak
obtuse pebbleBOT
storm kayak
#

Where do i even start?

kind hawk
#

do you know some other sets that generate A_n?

storm kayak
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This is all information that was given

kind hawk
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this can't be the only thing you know about A_n

storm kayak
#

ill give the full question for clarity:

warm canopy
#

What is your definition of A_n?

storm kayak
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It is not defined anywhere so i dont really know

polar fossil
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surely your book defines the symbol A_n at some point

storm kayak
#

Im trying to look for it right now

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okay i found it A_n is the set of all even permutations

warm canopy
#

And what is an even permutation

storm kayak
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definiton from the book says: A permutation that can be written as an even number of transpositions

warm canopy
#

So do you see how the s_i s_j generate A_n

storm kayak
#

not sure

obtuse pebbleBOT
#

@storm kayak Has your question been resolved?

obtuse pebbleBOT
#

@storm kayak Has your question been resolved?

obtuse pebbleBOT
#

@storm kayak Has your question been resolved?

storm kayak
#

<@&286206848099549185>

obtuse pebbleBOT
#

@storm kayak Has your question been resolved?

wide star
#

Why did the bot just stop asking?

tepid mountain
#

@wide star
It only asks for few times then it just stops

slate zephyr
#

I think it keeps asking but the waiting interval increases exponentially, right?

timid silo
#

im in hs ineed help with my algebra

viral blade
obtuse pebbleBOT
#

@storm kayak Has your question been resolved?

urban dawn
#

i have to find AC

#

<@&286206848099549185>

#

<@&286206848099549185>

spring steeple
obtuse pebbleBOT
slim cove
# storm kayak

Idk if you're still here, but #groups-rings-fields is probably a better place to ask future abstract algebra questions, more knowledgeable people will be there

#

Which part are you confused about though? Can you show that that set generates S_n?

obtuse pebbleBOT
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wanton carbon
#

How would I prove that the directrix of the quadratic function of the form y = ax^2 is vertical?

obtuse pebbleBOT
#

@wanton carbon Has your question been resolved?

wanton carbon
#

<@&286206848099549185>

#

also i want to show uniqueness

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prove that there is no other directrix for this quadratic function

shrewd wasp
# wanton carbon How would I *prove* that the directrix of the quadratic function of the form y =...

Let $P(x, ax^2)$ be an arbitrary point on the parabola $y = ax^2$. Let $F = (f_x, f_y)$ be the focus of the parabola $y = ax^2$, and let $d$ be the directrix by $y = c_1 x +c_2$. Use definition $$\mathcal{P} = { P \in \mathbb{R}^2 \mid d(P, F) = d(P, d) }.$$ Then find $f_x, f_y, c_1, c_2$ using the polynomial equation. This can be algebraically tiring. You can then use a reductio ad absurdum argument to prove uniqueness. Having found $F\left(0, \frac{1}{4a}\right)$ and $\left(c_1, c_2\right)=\left(0, \frac{-1}{4a}\right)$, using the same definition, assume $y=c$ and $c\neq \frac{-1}{4a}$ and show that there cannot be such a $c$.

warm shaleBOT
#

adzetto

obtuse pebbleBOT
#

@wanton carbon Has your question been resolved?

wanton carbon
#

this is part of a large proof

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so we don’t know it’s a parabola yet

wanton carbon
shrewd wasp
#

If you want a complete proof, do you want to define/demonstrate algebraic elements, real numbers and many more?

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I think it would be quite redundant

wanton carbon
#

ok fair enough

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is there a way other than just the definition of a parabola to show that it can only have one focus

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@shrewd wasp

shrewd wasp
warm shaleBOT
#

adzetto

wanton carbon
#

I’m an amateur

shrewd wasp
#

It should already have a single focus by definition, but if you want, assume that it has two foc such as F1 and F2. Write the equation for both focus using the definition. You will see that F1 and F2 must be the same point.

shrewd wasp
obtuse pebbleBOT
#

@wanton carbon Has your question been resolved?

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Show your work, and if possible, explain where you are stuck.
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wet badge
#

help is (4,38 )correct

obtuse pebbleBOT
latent walrus
#

!status

obtuse pebbleBOT
#
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
wet badge
#

i jus need to verify my aswnser

#

(4)

#

^i didnt do the equation yet, since i want to check if i got the coords correct

latent walrus
#

aha, lets see
y=8x+4, m=-1/8
f'=-1/x^(3/2)=-1/8
x^3/2=8, x=4

wet badge
#

yes, after i get the x, do i plug it into the orginal equation

#

or the derived one

latent walrus
#

original if you want the y coordinate

wet badge
#

because when i plug into the orginal i get 32

#

oh okay tytyt

#

32 looks like a devious number, so i wasnt too sure

latent walrus
#

how do you get 32?

wet badge
#

y=8(4)+4

latent walrus
#

thats 36, but also thats not the equation of the graph my guy

wet badge
#

wait so what do i do

latent walrus
#

the graph has the equation f(x)=2/sqrt(x) +1

wet badge
#

oh my god i jus relised

#

thanks bro

latent walrus
#

np

wet badge
#

wait i dont wanna bother, but can you also explain this question

#

(you dont have to, but i was jus confued on it)

latent walrus
#

you can check the limits in either direction (+ or - infinity)
if f(x) is convergent to a value rather than infinity or - infinity then that can be considered an asymptote

wet badge
#

wait, but how would i use it with the limit method

#

lim h->0,( f(x+h)-f(x))/h

latent walrus
#

im not sure how youd use that formula specifically for this honestly, ive only ever used it for differentiation

#

ill do some reading though and come back if i find anything

wet badge
#

its okay i can give u a differnt problem ! (i was jus confused on how to factor out the x^2 for this one )

latent walrus
wet badge
#

ah okay tyty

obtuse pebbleBOT
#

@wet badge Has your question been resolved?

#
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#
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timid silo
#

Hello I am doing Statics homework which requires some Calc 3 vector math. I have unlimited attempts and I have been using them to check my answers. I am stuck on questions 4-9. I have my work but will include a picture of the question first.

** Note: It's just one question, but divided to 10 steps
Question:
Force F1 has a magnitude of 473N and force F2 has a magnitude of 514 N. h = 3.9 m,

1- Determine Force F1's x-component in N ? = 0
2- Determine Force F1's y-component in N ? = -216 N
3- Determine Force F1's z-component in N ? = -421 N
4- Determine Force F2's x-component in N ? = 210.7 N (incorrect)
5- Determine Force F2's y-component in N ? = 422 N (incorrect)
6- Determine Force F2's z-component in N ? =-206 N (incorrect)
7- Calculate the Resultant force's magnitude in N ? 693N (incorrect)
8- Calculate the resultant force's coordinate direction angle θx in Deg ? = 72 degrees (incorrect)
9- Determine the Resultant force's coordinate direction angle θy in Deg ? = 67 degrees (incorrect)
10- Determine the resultant force's coordinate direction angle θz in Deg ? = 155 degrees

so what i have done:
find the unit vector of F2 (direction vector of length 1)
multiply each component of the unit vector by the length of F2
obtaining F2's components using the unit vector

timid silo
#

u2 is a unit vector, of length 1, in the direction of F2.
when i multiply the magnitude of F with u2 i get the components of F2.

trail cloak
#

Alright are you given the value of h?

#

h = 3.9 m okay

timid silo
#

look, if i take the magnitude of F2's components i get 514 N,
and when i take the magnitude of u2 i get 1.

#

i think my teacher might be wrong so i want to double check

trail cloak
#

Hmm

#

For F2 I got this

#

$\bar{F_2} = \left \langle250.832, 376.25, -244.664 \right \rangle \mathrm{N}$

timid silo
#

okay, where do you think I might have gone wrong?

trail cloak
#

In the unit vector of F2

#

You used 8 instead of 8-2

timid silo
#

okay, accounting for z being -z direction, i used the components you found and it was correct

warm shaleBOT
#

VulcanOne

timid silo
#

i see what you are talking about, except my teachers notes confused me because of a problem similar to this where he did not do 8-2 = 6

trail cloak
#

I think from there you can redo your work and you'll hopefully get the correct answers

trail cloak
#

So I always write my ending coordinates and starting coordinates to tell myself where the vector was going and where it started

timid silo
#

thank you very much btw VulcanOne

trail cloak
# timid silo

Just writing the results is pretty confusing to me. Not sure where the shortcut is.

trail cloak
#

Also the notation is a bit off

#

For the magnitude, you'd use this

timid silo
#

true

trail cloak
#

$\norm{\overrightarrow{r_{AB}}}$

warm shaleBOT
#

VulcanOne

timid silo
#

yeah, the notation has been really messing with me. Since in Calc 3 we use one notation, and in Physics they used another one, and my engineering professor is just barely using any proper notation 😅 🥲

trail cloak
#

Wait are you structural engineering?

timid silo
trail cloak
#

Ooooo

timid silo
#

got me like this🧟

trail cloak
#

Same lmao

timid silo
#

its a very humbling experience

trail cloak
#

Hope we make it into the big leagues soon xd

timid silo
#

are u doing structural?

trail cloak
#

Yep. Civil engineering. But structural is like 80% of the entire career so yeah :)

timid silo
#

That sounds awesome and also very humbling 😅

trail cloak
#

It is indeed

timid silo
#

so i was wondering what points u used for the starting coordinates

trail cloak
#

I used the point where the forces where exiting

#

Point A

#

And the other 2 points I used as the end points

#

Since direction matters

#

And the forces have their arrows pointing that way so ye

timid silo
#

if i use A (0,2,3.9) how is it when i get the vector AB, it is <0,-2,-3.9>? when the z point of A was positive?
i am just confused on where i need to do the book keeping

#

ooooh wait i see it now....i was counting point A as (0,0,0) idk why

#

i was trying to use free body diagram technique

trail cloak
#

Well it can get messy if you relocate your origin

timid silo
#

so i just keep the origin at the original given one? no shortcuts?

trail cloak
#

Yep

#

It's better that way

timid silo
#

okay

trail cloak
#

You won't lose track easily

#

And you can look at the diagram and it will be your reference

timid silo
#

You're right and I think everything messed up when i found the magnitude of AC = <4, 8,.-3.9>, since it should be AC = <4, 6, -3.9>

#

that little difference ruined everything after that

#

i swear these little things are going to keep me from getting A's this semester

trail cloak
#

You'll get an A I'm sure letsgoo

#

Keep things as simple as possible

#

You'll get the A+ in the bag

#

Also time yourself and know where you are messing up and try to fix them

#

No shortcuts until you understand the process

#

After that you will shortcut automatically

timid silo
#

thats some great advice that didn't know i needed...

I just finished the homework and got everything correct, thanks again bro

#

idk if ur accepting FR's but u should add me if you ever need another eye or helping hand!

#

.close

obtuse pebbleBOT
#
Channel closed

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#
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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>.
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untold cove
#

Is this correct?

obtuse pebbleBOT
cunning breach
#

You should write negative sign in step 2 instead of absolute value. $$\int_{-1}^1 -\frac{3}{4}x+\frac{3}{4} dx - \int_{1}^2 -\frac{3}{4}x+\frac{3}{4} dx$$

#

Since $$\int_{1}^2 -\frac{3}{4}x+\frac{3}{4}x dx$$ has a negative area.

warm shaleBOT
cunning breach
#

Hmm, the value I got is 9/8

untold cove
#

Oh okay

#

Thanks

#

Tbh k don’t understand half of that stuff

cunning breach
#

From step 4 to step 5, you forgot your negative sign.

untold cove
#

My teacher just suddenly started writing wrong equations and I got confused lol

#

Thanks!

cunning breach
#

Welcome.

untold cove
#

Why is there 3/4x dx? Thought it was 3/4 dx…?

#

@cunning breach

warm shaleBOT
cunning breach
#

My bad, since I copy-pasted it.

untold cove
#

Oh okay, thought I was trippin

#

.close

obtuse pebbleBOT
#
Channel closed

Closed by @untold cove

Use .reopen if this was a mistake.

obtuse pebbleBOT
#
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Ask your math question in a clear, concise manner.
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After 15 minutes, feel free to ping <@&286206848099549185>.
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proper kelp
#

if f(x)=1+xlnx for (0,5], what is its minimum and maximum value within the domain

hidden compass
#

Min/max should ring you a bell about derivatives, right?

proper kelp
#

right, so the minimum i found to be 1/e by simply equation the derivative to 0

#

but for the maximum, im not tpoo sure

#

intuitively, i would say x=5 but without proper working out

median spoke
#

f'(x) = lnx + 1

#

f'(x) = 0, x = 1/e as you say

#

so you should test x = 0, 1/e, 5

proper kelp
#

ah

#

so how would i word this

#

as x increased, f'(x) increase, therefore the greatest x would yield the greatest f(x)

#

but this is kinda weird to write in a maths problem

median spoke
#

it wants you to explain?

proper kelp
#

no

#

but i think i should have some working explaining why its 5

median spoke
#

You always test the highest and lowest values in the domain

#

so 0, 5, and then the value in the domain where f'(x) = 0

proper kelp
#

well i cant test 0 since lnx

median spoke
#

0 technically isn't in the domain, but as you approach 0 from the right you get 1

proper kelp
#

the limit approaches 1?

median spoke
#

it does, but I guess that's not obvious without looking at the graph

#

but the derivative is negative between 0 and 1/e

#

so the minimum is def 1/e

#

so yea it's 5 because that's the one with the greatest value of the 3 significant values

proper kelp
#

i see

#

can i ask another question?

median spoke
proper kelp
#

x^2+xy+y^2=1

#

what is the max and min y values possible?

#

i found the derivative to be -(2x+y)/(2y+x)=0

fervent cradle
#

i think you can just rearrange for y explicitly

#

like, you can get y = f(x)

#

and then go normally

proper kelp
#

how would you do that

fervent cradle
#

ok suppose you had 1 + y + y^2 = 1, how would you solve for y

proper kelp
#

quadratic

fervent cradle
#

right

proper kelp
#

or just factorise

fervent cradle
#

so just do that for x^2 + xy + y^2 = 1

#

i mean ok

#

you don't need the quadratic formula for this, it's actually nicer to use completing the square when you have algebra i find

#

maybe slightly simpler

#

but both work

median spoke
#

(1 - 2x - y)/(2y + x)

#

getting that for derivative

#

wait no

#

nope you're right

fervent cradle
#

ok wait i'm dumb

fervent cradle
#

for now let's just multiply through by the denominator

proper kelp
#

wait i meant y'=that

fervent cradle
#

and then you just have -(2x+y) = 0

#

oh

proper kelp
#

yep

#

yeah its still the same thing

fervent cradle
#

i mean ok but you want y' = 0

#

yeah

#

so yeah you have -(2x+y) = 0

#

and then you can just substitute that back into the original thing

#

and then it's just quadratic again

#

that's probably how you're intended to do it

proper kelp
#

i tried that and got y= plus minus 2/root7

#

which was not right on the graph

fervent cradle
#

oh

#

ah i see your problem maybe i think

#

so let's just do it

#

y = -2x and x^2 + xy + y^2 = 1

so x^2 - 2x^2 + 4x^2 = 1

so 3x^2 = 1

so x = +-1/sqrt(3) and then y = +-2/sqrt(3)

#

simple sign error

#

you probably had like y = 2x instead of y = -2x

proper kelp
#

oh yeah you're right

median spoke
#

getting 3x^2 = 1

fervent cradle
#

yup

median spoke
#

x = ±1/sqrt(3)

proper kelp
#

ok so im having trouble on which to substitute, x=-1/2 y or y=-2x

fervent cradle
#

either works

median spoke
#

shouldn't matter should it?

fervent cradle
#

solve for either x or y and then you can just use y = -2x to get the other one

proper kelp
#

but would x= something y be faster

fervent cradle
#

sure whatever

#

you'd have to deal with fractions tho

#

so i didn't

proper kelp
#

i see

#

so i simply sub x=plus minus 1/root3 into the original equation

#

and find y

fervent cradle
#

no

median spoke
#

yes

fervent cradle
#

i mean ok you can

#

but it's much simpler to use y = -2x

#

once you have that

proper kelp
#

oh true

#

also since x^2+y^2+xy means the values of x and y can be interchanged, would y just be the same answer

fervent cradle
#

yyyes

#

like ok

proper kelp
#

right what is this called again?

fervent cradle
#

y is maximum at x = -1/sqrt(3), and then y has max value 2/sqrt(3)

proper kelp
#

actually no scrap what i said

fervent cradle
#

and then x is maximum at y = -1/sqrt(3) and x has max value 2/sqrt(3) there

proper kelp
#

oh wait nvm

fervent cradle
#

so like, you can swap them in that respect

proper kelp
#

yeah thats what i meant, im confusing myself

#

actually

#

wait why is y max at -1/sqrt3 instead of the postive version

median spoke
#

graph looks like this for reference

fervent cradle
#

so we have y' = 0 when x is either 1/sqrt(3) or -1/sqrt(3)

for x = 1/sqrt(3), y = -2/sqrt(3)
for x = -1/sqrt(3), y = 2/sqrt(3)

so one of these is a minimum and one is a maximum

proper kelp
#

oh i see

#

ty i understand now

#

🙂

#

.close

obtuse pebbleBOT
#
Channel closed

Closed by @proper kelp

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obtuse pebbleBOT
#
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Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
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• Be polite and have a nice day!

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proven zephyr
#

Suppose there are 2 real integers with a difference of 10. The smaller integer is a multiple of 3 whereas the other is a multiple of 7. If the sum of all the prime factors of each of the integers is 17, find the value of those 2 integers.

proven zephyr
#

So.... the sum of the other prime factors would be 17 - 7 - 3 = 7

#

Which limits the possibilities

#

But I don't know how to start

tender stratus
#

doesnt this imply both must be having 5 as a factor

#

because otherwise you dont get 10 as the sum

#

3 and 7 already taken, and 2 + 8 isn't possible

proven zephyr
#

it can also be
2, 3, 5

tender stratus
#

hmm I guess that's possible hmmCat

#

wait

#

the sum of the prime factors is including both right?

proven zephyr
#

yes

#

prime factors of the larger integer + the smaller

#

<@&286206848099549185>

obtuse pebbleBOT
#

@proven zephyr Has your question been resolved?

errant lark
proven zephyr
#

distinct prime factors

#

like for example

#

2^5 * 3^7 would be 2 + 3

#

= 5

errant lark
#

Okay.

errant lark
proven zephyr
#

Brb 5 min, my food came

#

no

#

wait yes

#

i mean yes

errant lark
#

Okay.

obtuse pebbleBOT
#

@proven zephyr Has your question been resolved?

errant lark
#

Are you certain that there is an answer? I think i ruled out almost all of them. Of course, i could have made a mistake.
Anyway, confirm if there is indeed a solution.

proven zephyr
#

But i can’t understand it

#

wait

#

i will translate

errant lark
proven zephyr
#

oh wait i did a typo

errant lark
#

😐

proven zephyr
#

but yes

#

i wrote it as 17 - 7 - 3 = 10

#

edited tho

_ _

#

For example:
the two numbers are (x, y)
x = 7m
y = 3n

since the difference is 10 and x>y
then:
7m - 3n = 10

the values of m and n can be determined by reversing Euclid's algorithm
7 = 2×3 + 1
1 = 7 - 2×3
10 = 70 - 60

thus obtained
m = 10
n = 20

Thus, the general solution
m = 10 - 3t
n = 20 - 7t
x = 70 - 21t
y = 60 - 21t

The satisfying pairs of two-digit numbers are ={(28,18),(49,39),(70,60),(91,81)}

Note that the sum of all prime factors of x and y is 17, hence 17=3+p+q+7.
Then p+q =7, so the only primes p,q that satisfy are 2 and 5.

So, it is clear that among the pairs x,y, the only ones with prime factor 5 are x=70 and y=60. So, the sum of these two numbers is
x+y = 70+60=130.

#

i don't understand how they got m = 10 and 20 = n

errant lark
#

70 = 2* 5 * 7
60 = 2 * 2 * 3 * 5

#

Sum = 2 + 3 + 5 + 2+ 5 + 7 = 24

#

Not 17

proven zephyr
#

wait yeah

#

what

errant lark
#

Or you told me wrong.

errant lark
proven zephyr
#

Okay I'm not sure now.

errant lark
#

According to what you said, there is no solution.

proven zephyr
#

Hm.... okay, maybe it doesn't count as separate.

errant lark
#

Other than that, approach is really simple.

#

You see that GCD of 3 and 7 is 1.

#

That means there are infinitely many numbers of the form 3n and 7m such that 7m - 3n = 10

#

Now, you just solve that using euclidean or diophantine equation.

#

You get general solution as m = 10+3k, n = 20 + 7k, where k is any integer.

obtuse pebbleBOT
#
Channel closed

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Use .reopen if this was a mistake.

proven zephyr
#

.reopen

obtuse pebbleBOT
#

proven zephyr
#

forgot to react mb

errant lark
#

Do you want me to show what i mean by euclidean method?

#

It's just reverse GCD process.

proven zephyr
#

I'm not sure i've learnt it.

errant lark
#

I'm pretty sure you have. At least the forward part.

#

So, we calculate GCD of 3 and 7.

#

$$ 7 = 3\times 2 +1 $$
$$ 3 = 1 \times 3 + 0$$

warm shaleBOT
#

Enemagneto

errant lark
#

GCD = 1

#

Clear as much?

proven zephyr
#

I can see that GCD = 1

proven zephyr
errant lark
#

You have never calculated GCD using this method?

#

How do you calculate GCD?

proven zephyr
#

I-

#

last time i did that it was at 4th grade

#

ima just go and relearn this after this

errant lark
#

Sure.

#

Also, learn how to represent GCD of a and b in the form ax + by, where x and y are integers.

#

That's all it is about.

proven zephyr
#

Okay!

#

Btw, an you continue with the explanation? I'll go back understand it after I've learned about it.

errant lark
#

Okay. So, basically you try to find such two numbers m and n such that 7m - 3n = 1.

#

We know that there are such numbers because 1 is GCD of 7 and 3.

#

It's easy to see in this case that m = 1 and n= 2 works for us.

#

So, we have 7(1) - 3(2) = 1

#

but we need 7m - 3n = 10. Right?

proven zephyr
#

yes

errant lark
#

We have 7( 1 * 10) - 3 (2 * 10) = 10

#

Which is just 7(10) - 3(20) = 10

#

Lucky for you, your answer is already there. 70 and 60. But i'll explain further for general solution.

#

So, once you have found one pair of m and n that satisfies
7m - 3n = 10, you can find all the infinite solutions of this equation where m and n are integers.

#

This is something you can also think on your own. Would you like to try or should i move on?

proven zephyr
#

You can move on.

errant lark
#

Alright. So, key to finding all the solution is to imagine that we'll have different m and n but the RHS will always be 10.

#

So, basically you can say that both the terms 7m and 3n are increasing/decreasing by equal amounts so that their difference stays equal i.e. equal to 10.

#

So, we have something like this:
(7m + l) - (3n + l) = 10

#

Our m and n are currently 10 and 20 respectively. Remember that.

proven zephyr
#

okay

errant lark
#

But if we take such a l which is divisible by 7 then we can factor 7 out from l.
So, we'll have something like:
7(m+ k) - (3n + l) = 10

#

So, you see - Here, we have kind of found another integer m' = m+k which will satisfy our equation. Only issue is that it's not our solution yet as we have not found a corresponding n.

#

So, think about how we can get n'. Well, for that l has to be divisible by 3. Then we can factor 3 out from it.

#

So overall, if l has 3 and 7 both as its factor, we will get new m' and n'.

#

Makes sense ?

proven zephyr
#

Why does n need to have 3 and 7 both as its factor?

errant lark
#

Not n

#

l

proven zephyr
#

ohh

#

okay i get it then.

errant lark
#

I fixed the typo.

#

Great.

#

So, l will basically have to have 21 as its factor i.e. l will be of the form 21k.

#

Now, we are almost there.

#

Let's put it in the equation.

#

(7(10) + 21k) - (3(20) + 21k) = 10

#

(7(10) + 7(3k)) - (3(20) + 3(7k)) = 10

#

7(10+3k) - 3(20+7k) = 10

#

Where k can be any integer.

#

So, m = 10+3k & n = 20+7k

#

Just for fun, let's try putting some value of k.

#

Any integer.

proven zephyr
#

3

errant lark
#

Okay

#

m = 19 & n = 41

#

7(19) - 3(41) = 133 - 123 = 10

#

So, you have found all infinite solutions.

#

Now, work on m and n as you need them to have your required factors.

proven zephyr
errant lark
#

Well, fun thing about number theory is that it's very intuitive and realistic. Who doesn't feel cozy with the simple natural numbers so hang in there.

errant lark
#

Look at your numbers.
You have 7(10 + 3k) and 3(20+7k).

#

You already have 3 and 7. So, remaining sum is 7.

#

Two possibilities:
2+5 OR 2+2+3

proven zephyr
#

But we don't count them as separate.

#

2 + 2 + 3 would be 5 no?

#

Since we're counting 2 once

errant lark
#

Ah. Yes. Still in mindset of original wording of the question. Lol

#

Only one possibility. 2+5

#

That makes it way more simple.

#

So, either 10+3k would be divisible by 2, and (20+7k) would be divisible by 5, or other way around.

#

Now try to think of k values which will make that possible.

#

Should be easy?

proven zephyr
#

0, 10, 20, .... , 10 * n

#

and so on

errant lark
#

Yes

#

All of those will give correct answers.

proven zephyr
#

So then I just test them one by one?

#

wait... all of those give correct answers?

#

so-

#

huh?

#

ima just take a random k like.. 40

#

7(10 + 3k) - 3(20+7k) = 7(10 + 120) - 3(20 + 280)
= 7(130) - 3(300)
= 910 - 900

#

Prime factors of 900: 2, 3, 5

#

Prime factors of 910 = 2 x 5 x 7 x 13 nvm

#

so just.... 0

#

okay

#

thanks

#

.close

obtuse pebbleBOT
#
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proven zephyr
#

t!rep @errant lark

sinful lightBOT
#

Reputation_Icon marvei has given @errant lark a reputation point!

errant lark
#

Lol

obtuse pebbleBOT
#
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timid silo
#

can someone help me understand this

obtuse pebbleBOT
timid silo
#

discrete math

onyx gust
#

I am struggling to understand the solution for case 2, mainly at why sqrt An + sqrt L disppear when they are showing the proof.

timid silo
obtuse pebbleBOT
timid silo
#

post on help-forum

blazing forge
timid silo
#

wym how formal

blazing forge
#

i'm not sure i could type out a perfect natural deduction proof

#

but if you just need to reason you way to ~q with the premises

timid silo
#

as long as i understnad we good

blazing forge
#

i can help with that

#

pog

timid silo
#

yes yes

timid silo
blazing forge
#

okay. so you want to somehow conclude ~q. the only premise with ~q in is is s v ~q. in order to get ~q from this, we need for ~s to be true

#

basically you can just reason backward, if you want

timid silo
blazing forge
#

you know that s v ~q is true. if you want this premise to force ~q to be true, you have to know that ~s is true. i guess you can also see this by noting ~a v b is equivalent to a --> b. so s v ~q is equivalent to ~(~s) v ~q, which is equivalent to ~s --> ~q

#

so if we know ~s is true, then we get ~q is true

#

since the only way for ~s and s or ~q to both be true is if ~q is true

timid silo
#

damm im lost asf

blazing forge
#

FeelsBadMan what are the argument forms in Table 2.3.1

#

this will likely help

timid silo
#

im looking at elimination

#

p V q

#

~q

blazing forge
#

pog yeah, you can use elimination

timid silo
#

therefore p

#

but lets swap this

blazing forge
#

you know s v ~q is true, so if you know ~s is true, you can conclude ~q is true

#

via elimination

timid silo
#

s V ~q
~s
shouldnt it be q instead of not q?

blazing forge
#

this is just saying for arbitrary premises p and q. ~q is an arbitrary premise

#

it would be better if they said a v b, ~a, therefore b

#

then you could say you have s in place of a and ~q in place of b

timid silo
#

okay so in any case, if the premise has not in elim

#

then the conclusion is also not

#

got it

#

i dont need tto understand why fuck it, i got a test in 30 min

blazing forge
#

you could have something like (p --> r) v (q --> s --> t) and if you knew ~(p --> r), then you could conclude q --> s --> t

#

with elimination

timid silo
#

right

#

i fuckin wish this prof would give hw

blazing forge
#

pog. so, if we do the reasoning backward method, we want to know ~s is true in order to do elimination on b. to conclude f.

#

so we have to somehow get ~s from the premises

#

e. tells us that if we know ~p and r, we will then get ~s (by using modus ponens)

#

so now we just need to know ~p and r is true from the premises

#

does this sort of make sense so far

timid silo
#

yes

blazing forge
#

pog. now a. tells us that ~p v q --> r, so if ~p is true, then ~p v q will be true (by generalization), so then modus ponens will tell us that r is true.

#

so in fact, we just need to know that ~p is true in order to know r is true (and therefore ~p and r is true, by conjuction)

#

c. tells us that ~t is true, and modus tollens on d. will tell us that ~p is true

timid silo
#

yes

blazing forge
#

then you just have to write it all in the other direction...

timid silo
#

how does ~t being true

#

tell us ~p is true?

blazing forge
#

d. says that p --> t, and you know that ~t is true, so then modus tollens says ~p is true. or do you mean why does modus tollens work?

#

an example might help. it is true that if it is rainy, then it is cloudy. so rainy --> cloudy. if somebody tells you that its not cloudy, then you can use this fact to conclude that it is not rainy

#

this would be an example of applying modus tollens in a case where its more intuitively clear

timid silo
#

yes got it

blazing forge
timid silo
#

are u able to talk rn?

blazing forge
#

no sorry FeelsBadMan

timid silo
#

😦

blazing forge
#

next to my gf who is in a call

timid silo
#

ill send u 5$ enough to buy her chocolate 😉

#

" yo babe if i talk with this guy, you get chocolate, deal?"

golden sand
#

@timid silo you are breaking the rules here

blazing forge
#

would be writing our backward reasoning forward

timid silo
#

sorry!

#

mod didnt say anything bout it yesterday

blazing forge
#

no because i assume its either going to be slowly telling you the answer again or we will run out of time before your test

#

use the process i've conveyed to you and your inbuilt human rationality to try to reason through the next one

timid silo
#

idk if its still breaking the rule

blazing forge
#

i feel like you just need much more practice doing these things to do well for your test

#

i can't help you enough in 20 minutes or whatever

timid silo
#

yes i was studying yesterday

blazing forge
#

did you do any on your own :o

timid silo
#

nope cus i had more things to go over bahah

#

okay how bout this

#

ill do the next one

#

and u check it

blazing forge
#

sure

#

hopefully you can do at least one on your own before the test FeelsOkayMan

#

i believe in you

timid silo
blazing forge
#

nice. so you have p and you want to get p and s in order to get t using modus ponens on c.

#

so you just need to somehow get s

#

there is only one premise that allows you to conclude s, which one is it?

timid silo
#

~q --> u ^ s

blazing forge
#

pog

#

so you just need to know ~q is true and apply modus ponens

timid silo
#

~q --> u ^ s
~q
therefore u ^ s

#

modus ponens

blazing forge
#

pog. now you can specialize to go from u ^ s to s

timid silo
#

yeah thats the part im stuck now

#

wait

#

so s

#

p ^ s --> t

#

idk

blazing forge
#

peepoHappy yea, you have p from the elimination you did earlier, so you can do conjunction to go from p and s to p ^ s

#

then modus ponens to get t

timid silo
#

ohh i can do that?

blazing forge
#

its called conjunction here

#

if you have p,q then you can get p ^ q

timid silo
#

what happens to

#

u ^ s?

blazing forge
#

theres one on the table called specialization

#

if you have p ^ q, you can get q (or p)

#

you have u ^ s, so you can get s

timid silo
#

right

#

damm

#

okay to p ^ s --> t

blazing forge
#

yeah. then you're done

timid silo
#

whaaa

#

fr?

#

shii so if i remember the table im gucci

#

i know these things intuitively but i might need to write down after i use it

#

on the test

blazing forge
#

you got p from elimination on a, and then you got s from specialization on u ^ s. so you get p ^ s by conjunction, then modus ponens p ^ s to get t

#

yeah

#

gotta know all the rules and their names i assume

#

part of being in a logic class FeelsOkayMan

timid silo
#

can i add you?

#

i gtg

blazing forge
#

idk probably not i don't wanna do tons of logic problems

timid silo
#

bahahah

blazing forge
#

i already did that 1-2 years ago

timid silo
#

😦

#

me sad

blazing forge
timid silo
#

Appreciate the help bro

timid silo
blazing forge
#

you can do it OOOOa

obtuse pebbleBOT
#

@timid silo Has your question been resolved?

obtuse pebbleBOT
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radiant moss
#

I have to turn this expression in the from asin(bx+c), I know I have to use Addtion thereom , but I'm not sure how. I'm thinking of using sin(x-y) = sin(x)*cos(y)-sin(y)*cos(x) but I am not sure how

tardy epoch
radiant moss
modern cedar
#

is this correct ? i didnt replace sin at the end but i get another answer on photomath and the math solvers
its integral of dx/rad(144+x²)

obtuse pebbleBOT
#

@radiant moss Has your question been resolved?

tardy epoch
#

use 3 = 2 + 1

obtuse pebbleBOT
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strong wigeon
#

yo

obtuse pebbleBOT
strong wigeon
#

How is this X less or equal to 3?

#

I know R\ makes (3) into [3], but does it also make the (->) into [<-]??????

#

-> means infinity

#

<-

obtuse pebbleBOT
#

@strong wigeon Has your question been resolved?

keen garnet
#

It’s say’s that x is real number inferior to 3 I think

obtuse pebbleBOT
#

@strong wigeon Has your question been resolved?

strong wigeon
#

But ty for attempting

blazing forge
#

its saying $x \in \mathbb{R} \setminus (3, \infty)$

warm shaleBOT
blazing forge
#

if i understand correctly

#

that's the set $(-\infty, 3]$

warm shaleBOT
blazing forge
#

and $x \in (-\infty, 3]$ if and only if $x \leq 3$

warm shaleBOT
blazing forge
#

or at least, that's how i'm interpreting it monkaS

#

the notation is not familiar to me

keen garnet
strong wigeon
#

Also since that E symbol say X before

#

I think it means X must be 3 or less

blazing forge
#

it means that x is in R, but x is not in (3, \infty). the set (3, \infty) is the set of all numbers y such that 3 < y

#

so its saying that x is a real number that does not satisfy 3 < x

#

so that means that x satsfies x <= 3

#

and then thats the definition of the set (-\infty, 3]

strong wigeon
#

Ok thanks

#

if there is R \ the infinity changed direction?

blazing forge
#

in this case, but i don't think that's how you should think of it

#

you should unravel the definition of the set to see what its saying

strong wigeon
blazing forge
# strong wigeon How i think of infinity ?

it seems like your first thought was "if you have R \ before an interval with an infinity in it, then this is equal to an interval with an infinity on the other side". and this is basically always true, but its probably better to understand why it happens than to try to memorize this

obtuse pebbleBOT
#
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obtuse pebbleBOT
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verbal niche
#

Oh

#

.reopen

#

.close

trail cloak
#

Next time don't delete the original message

#

Please open a new channel

obtuse pebbleBOT
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glossy temple
#

help

obtuse pebbleBOT
#

Please don't occupy multiple help channels.

glossy temple
obtuse pebbleBOT
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Please don't repeatedly close and claim a new channel with the exact same question. This erases all previous progress made towards your problem, and is confusing for helpers, making it more difficult for them to answer your question. We ask you to please be patient, even if your channel has not received much attention. If you are having a problem with a helper, please report it to <@&833154869451292722> rather than closing the channel and attempting to seek out another helper.

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@glossy temple Has your question been resolved?

tardy epoch
obtuse pebbleBOT
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daring cairn
#

Hi, I Had this question from a previous year test as im studying and im not sure if i got the right answer as the one filled in is wrong but no right answer is written.

using the digits0-9, find the number of natural numbers that are even, have distinct digits and are less than 5000

I got 1373

daring cairn
#

2* 8 * 7 * 4 = 448
2* 8 * 7 * 5 = 560
8 * 8 * 5 = 320
8 * 5 = 40
5 = 5
total = 1373

obtuse pebbleBOT
#

@daring cairn Has your question been resolved?