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1 messages · Page 308 of 1

winter light
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I believe there's a mistake, the very last bit should be dx not dt

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Nooo, this is one of the worst mistakes you can do in math 😭

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$$\frac{A}{B + C} \neq \frac{A}{B} + \frac{A}{C}$$

ocean sealBOT
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Alberto Z.

winter light
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Instead, this rule is correct: $$\frac{B+C}{A} = \frac{B}{A} + \frac{C}{A}$$

ocean sealBOT
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Alberto Z.

winter light
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If $y = \frac{1}{2 - x}$, what is $y'$ (or if you prefer $\frac{dy}{dx}$)?

ocean sealBOT
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Alberto Z.

winter light
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$$y = \frac{1}{2 - x} \implies y' = \frac{dy}{dx} = \frac{1}{{\left(2-x\right)}^2} $$

ocean sealBOT
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Alberto Z.

winter light
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Chain rule

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Because you have to multiply by the derviative of 2 - x, which is -1 (and this minus cancels the previous one)

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Yes

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$\frac{d^2y}{dx^2} = y''$ simply

ocean sealBOT
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Alberto Z.

winter light
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It's another notation for the second derivative

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Nope

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$$\frac{dy}{dx} = \frac{1}{{\left(2-x\right)}^2} \implies \frac{d^2y}{dx^2} = \frac{2}{{\left(2 - x\right)}^3}$$

ocean sealBOT
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Alberto Z.

lone heartBOT
#

@alpine sable Has your question been resolved?

lone heartBOT
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crimson tundra
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How do I find the quantile value of chi square with 5 degrees of freedom and 0.1 significance level

crimson tundra
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Using table

zealous lichen
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find out the p value

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then use the table

crimson tundra
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How do I find the p value?

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P = 1 - alpha and that is 0.9

zealous lichen
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umm

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that's for single tail

crimson tundra
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How would I calculate it for single tail then

zealous lichen
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so p =1-0.1=0.9

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then look for df =5 and p =0.9

crimson tundra
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In the table I have only degrees of freedom and level of significance

lone heartBOT
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@crimson tundra Has your question been resolved?

lone heartBOT
#

@crimson tundra Has your question been resolved?

crimson tundra
#

.close

lone heartBOT
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vapid shuttle
lone heartBOT
vapid shuttle
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I'm having trouble understanding this proof

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particularly starting at the last line, when it says, U intersect S closure is a subset of U intersect V closure equals the emptyset

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Also, I don't see why they ignore this case. How is it demonstrated that neither set intersects the closure of the other?

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this is my other confusion

oak perch
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S in V

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Therefore closure of S in closure of V

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take intersection with U both sides

vapid shuttle
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are you explaining the top image cogwheels

oak perch
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Your last confusion

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The one you put why under

vapid shuttle
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ah

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and U intersected with the closure of V is empty why?

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because we suppose U and V form a disconnection of S closure

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nevermind

oak perch
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Because closure of S is disconnected

vapid shuttle
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okay so what about the first confusion then, I understand that part now

oak perch
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Still I prefer to transform your condition of being connect to a equivalent but more convenient form

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What is your version of definition of being connected again?

vapid shuttle
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it is connected if it is not disconnected, and it is disconnected if it is the union of two nonempty sets that do not intersect the closure of eachother

oak perch
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So

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Intersection (U and cl(V)) is empty

vapid shuttle
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no

oak perch
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This gives us U contained in X-cl(V)

vapid shuttle
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that can't be true

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because U and V form a disconnection of S closure

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oh sorry you are right

oak perch
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I mean the condition of disconnectness

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Then X-V=U in X-cl(V) in X-V

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Therefore U=X-cl(V), meaning U is open

vapid shuttle
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what is X

oak perch
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Similarly V is open

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The total set X

vapid shuttle
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total set?

oak perch
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X is disconnected

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Then there exists subsets U,V of X satisfying your condition

oak perch
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Similar V is open

vapid shuttle
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I'm not following this

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I don't know what X is, or why it matters that any of our sets are open

oak perch
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… never mind then I use your notation then

vapid shuttle
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okay

oak perch
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Because if they are both not non-empty, and it isn’t a disconnection of S

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Then we have S=(S intersection U) union (S intersection V). S is union of two non-empty subsets. This isn’t a disconnection meaning

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Cap is notation for intersection, cup union right?

vapid shuttle
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yes

oak perch
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Then

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cl(S cap U) cap (S cap V) is non-empty or (S cap U) cal cl(S cap V) is non-empty

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Contradiction

vapid shuttle
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what is that contradicting?

oak perch
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Because cl(S cap U) cap (S cap V) is contained in cl(U) cap V

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The latter is empty

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So the former can’t be non-empty

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Similar for the another one

vapid shuttle
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why is it contained in cl(U) cap V

oak perch
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S cap U in U
S cap V in V

vapid shuttle
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I see

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so that is why neither of those can be nonempty

oak perch
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Yeah

vapid shuttle
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so then from this earlier

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we conclude that

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this means that U must be empty

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and that contradicts U union V forming a disconnection for S closure

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right?

oak perch
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Yeah contradiction

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Yeah

vapid shuttle
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this is very difficult to grasp

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but I feel closer

oak perch
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That’s why I was

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Trying to give you a more convenient equivalent definition of being disconnect

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But anyway you can prove it yourself

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X is disconnected <-> X is disjoint union of two non-empty open subsets <-> X is disjoint union of two non-empty closed subsets <-> X is disjoint union of two non-empty subsets who are both open and closed <-> X has a proper subset that is both open and closed

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But anyway, they are all equivalent, it’s just I personally feel these are more convenient to use

vapid shuttle
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Sorry Cogwheels I was just trying to completely wrap my mind around what'd we just done and get the proof all settled

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reading now

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ty

oak perch
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Np

lone heartBOT
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vapid shuttle
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@oak perch my completed proof if you were interested in seeing it

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ty again for your help

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I was having lots of trouble on that one

lone heartBOT
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rancid tartan
#

construct a box and whisker plot to display the number of pets owned by a number of randomly chosen students. The data are, 2, 0, 5, 1, 2, 1, 0, 8, 4, 3, 9, 1, 2, 3, and 1

lone heartBOT
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Please don't occupy multiple help channels.

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worn hinge
lone heartBOT
worn hinge
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...

tropic grail
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Nevermind, we posted a problem at the same time

worn hinge
# worn hinge

Hi, so why was ls 2 delta r^2 like that? shouldn't it have a pi as well?

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when it was distributed?

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or there is some rule I don't lnow about this

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it should be pi delta r^2

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this part

tropic grail
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Why is the left part delta A / delta x?

worn hinge
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idk as well

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it should be delta r right?

tropic grail
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I thought so

lone heartBOT
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@worn hinge Has your question been resolved?

worn hinge
#

<@&286206848099549185>

lone heartBOT
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@worn hinge Has your question been resolved?

lone heartBOT
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@worn hinge Has your question been resolved?

lone heartBOT
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flat roost
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is this the most simplified form or is there anything more i can do?

tacit arch
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That's fine as is

flat roost
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oh ok

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i have another problem

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The cells in a culture in a lab grow according to the logistic equation dP/dt=0.02P(1-(P/2000)). Initially the population of cells is 300. Estimate the amount of cells after 3 hours.

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I got 315.6, but the answer says its 315

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here are my steps

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,rotate

ocean sealBOT
lone heartBOT
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@flat roost Has your question been resolved?

lone heartBOT
#

@flat roost Has your question been resolved?

nimble fern
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except the part written p=1/2000
which should be B=1/2000

flat roost
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did you get 315.6 too?

nimble fern
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,calc 6000*e^0.06/(17+3e^0.06)

ocean sealBOT
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Result:

315.62340475972
nimble fern
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yea

flat roost
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oh alr

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thanks

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.close

lone heartBOT
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faint frost
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i have a lot of problems in geoemtry specifically triangle congruence. i have a worksheet that i have left mostly blank cuz i dont understand how to do anything at all.

faint frost
nimble fern
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wow so many

faint frost
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i just dont get it

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for the proof problem 7, i know i have to prove the triangles are congruent then use cpctc

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and for everything else i have aboslutely no idea

nimble fern
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oh okay, i never heard of cpctc

faint frost
nimble fern
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oh that

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so, you'll have to prove congruent triangles first 👍

nimble fern
faint frost
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we learned those in class

nimble fern
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that's good!

faint frost
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i know i have to use those

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but idk how

nimble fern
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let's start with Q7

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what do we need to prove BD=EA?

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(i use = instead of the congruence sign for ease of typing)

nimble fern
faint frost
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uh

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bdc and aec

nimble fern
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so, what info will we need?

nimble fern
faint frost
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its gotta be the included angle

nimble fern
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nah, we need to angle between 2 lines

faint frost
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between the 2 corrosponding congruent lines

nimble fern
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the given 2 lines

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yes

faint frost
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which one tho

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oh wait

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nvm

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bcd and ace

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wait a second

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@nimble fern since we already know that the corrosponding lines are congruent, bcd = ace

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right

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what reason is that tho

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not sure what the postulate or theorom would be

nimble fern
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we need 2 coorespdoning lines

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and

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the angle between them

faint frost
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yeah

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but what reason would that be on the proof

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to prove bcd = ace

nimble fern
faint frost
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is that what ur talking about?

nimble fern
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yea

faint frost
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how would i use that

nimble fern
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like we know, for now, the base angles of the inner triangle are same

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and base angles of the outer triangles are same

nimble fern
faint frost
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how do we know that the base angles of the outer triangles are the same

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and bcd and ace arent exteroir angles

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so i dont get it still

nimble fern
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ok, I'll go through step by step then

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ah, btw can you repost Q7 for easier reading?

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angleCDE = angleCED (base angles, isos triangle)
angleCBD=angleCAE (base angles, isos triangle)
angleCDE=angleCBD+angleBCD (exterior angle of triangle)
angleCED=angleCAE+angleACE (exterior angle of trianlge

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all good till here?

faint frost
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yeah i got it

nimble fern
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good

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next step will be

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angleCDE-angleCBD=angleBCD
angleCED-angleCAE=angleACE

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now that since
angleCDE=angleCED
and
angleCBD=angleCAE

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we have
angleCDE-angleCBD=
angleCED-angleCAE

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therefore
angleBCD=angleACE

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therefore we can finally prove triangle BCD congruent to triangle ACE

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all good till here?

lone heartBOT
#

@faint frost Has your question been resolved?

lone heartBOT
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vivid basin
#

If a²+1/a² = 786, then a-1/a = ?, I know it can be solved by adding/subtract 2 on both sides, but can it be solved by finding out the value of a, from the first eqn

ocean sealBOT
gray isle
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some people respect the order of operations

vapid shuttle
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I am not one of those people

vivid basin
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It's a²+(1/a²) and a-(1/a) sry

gray isle
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no need to apolgise

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those () weren't necessary

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it'd be pain to solve for a first

vivid basin
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As I'm good in just solving by linear equations in 2 variables that's why I asked to find a firs

gray isle
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you could convert the first equation to a quartic equation
for which you'd get 4 solutions, which may not necessaily be nice
and end up doing something like 4 cases

vivid basin
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I'm not so good in maths so I just know some basic techniques like solving using 2 vars, it would be very helpful if you could solve it using an efficient method and a method which would be in my context of understand like using linear eqns

tardy stag
lone heartBOT
#

@vivid basin Has your question been resolved?

alpine sable
#

what part of your question hasn't been resolved

vivid basin
alpine sable
vivid basin
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If I solve the first eqn for a I get √343

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Ok np I will use the efficient method

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.close

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vague iris
#

Do we always get the same derivative if we simplify the function first before getting its derivative in multiplication and division, and if we use the rules first before simplifying?

nimble fern
#

do you mean like
f(x)=(x+1)⁴
f(x)=x⁴+4x³+6x²+4x+1?

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and find f'(x)?

vague iris
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like f(x)=(x-4)^2 (2x=3)

nimble fern
lone heartBOT
#

@vague iris Has your question been resolved?

tardy stag
#

and yes you'll get the same answer

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although you may have to factor one or expand the other, to easily see that they're the same

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high mauve
#

Hey

lone heartBOT
high mauve
#

Trigger Warning: Arachnophobia

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A spider wants to crawl the shortest way from corner a to corner b

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So my book says 64 cm

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Idk how it got to that

pulsar laurel
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Is it like a box

high mauve
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Yes

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sqrt30^2+20^2 is 36.0555

pulsar laurel
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So then it can go up then across diagonally

high mauve
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yes

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That'd be

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Sqrt(30^2+40^2)=50

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50 + 20

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70

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But book says 64

pulsar laurel
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Maybe it can go straight from a to b

high mauve
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sqrt(40^2+20^2)=44.72

pulsar laurel
#

Pythogoras in 3d

high mauve
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No it can't, spiders can't fly 😅

pulsar laurel
#

Webs

high mauve
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Besides, 50^2(diagonal of box) +20^2 (height) is 53.85, so shorter than 64

pulsar laurel
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64 doesn't sound right

high mauve
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I have no idea what the book wants me to do

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It's a chapter about repeating the Pythagoras

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Nothing advanced

pulsar laurel
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Is there like a solution at the back of the book

high mauve
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Do you think 64 is an error?

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Yep

pulsar laurel
high mauve
#

6.28

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Ok I trust you @pulsar laurel thank you for your time!

#

.close

lone heartBOT
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chrome dagger
lone heartBOT
chrome dagger
#

How do I do this

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brb in 5

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dont leave if you come

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im back

alpine sable
#

\dm
I think it is to safe to start with the fact that
[
\s{a+b+c} \mathbin{\c r \ne} \s a + \s b + \s c
] in general

ocean sealBOT
chrome dagger
#

ok

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ohhh wait

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oops

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ok but what now

alpine sable
#

\dm
horizontal asymptotes are defined by an asymptotic/convergent behaviour in the function as it approaches $\pm \infty$

ocean sealBOT
chrome dagger
#

yeah

alpine sable
#

\dm i.e. check if $\ds \lim_{x \to \pm \infty} \map f x$ exists

ocean sealBOT
chrome dagger
#

were finding the y value as x aproaches + or - infinity

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that's what you said?

lone heartBOT
#

@chrome dagger Has your question been resolved?

lone heartBOT
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simple saddle
#

how interquartile range is calculated here?

simple saddle
#

here in image 1st one denominator is always 365 why so and in second case with replacement approach is used ? what is the reason for this denominator thing

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please help!

heady pollen
#

how is interquartile range defined?

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or is that the question

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hmm

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are your messages getting deleted?

simple saddle
#

yeah

heady pollen
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odd

simple saddle
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why so

heady pollen
#

idk

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never seen auto-deletion before

simple saddle
#

now its ok ig

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i thought for a sec i got banned lol

simple saddle
charred summit
#

This is a good video for your question

simple saddle
#

its understood for 10 and so terms but this i didn't understand

charred summit
#

If there is 2 terms
Then it is simply the difference between them

If it's for 3 terms then it is the difference between the final and the first one

charred summit
#

Yeah

simple saddle
charred summit
simple saddle
simple saddle
#

so instructor showed an exaple for 6 people

charred summit
#

To solve this we need to know how many ways can 2 persons have birthdays

So do you know about combination?

simple saddle
#

but i was thiking it would be like (365/ 365) *( 364/364)... like that as without replacement it is? right?

charred summit
#

Nice
So to get all the ways for their birthdays
We do a little easy equation

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,calc 365 * 365

ocean sealBOT
#

Result:

1.33225e+5
charred summit
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,calc 365^2

ocean sealBOT
#

Result:

1.33225e+5
simple saddle
charred summit
#

So now we want to know how many ways they can have the same birthday which will be
365 ways

simple saddle
charred summit
#

Getting the probability of two having the same birthday is
$\frac{1}{365}$

ocean sealBOT
#

Sherif Player

simple saddle
#

bro my doubt was why denominator was not altered like it is when no replacemnet case is there in the second q that happend

charred summit
#

Which gives us the percentage 0.274%
Meaning to get a 100%
That there is at least 2 people have the same birthday

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We do

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,calc 2 / 0.274%

ocean sealBOT
#

Result:

729.92700729927
charred summit
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So we need 730 people just to get 100 percent probility to have 2 people of the Same birthday

simple saddle
#

bro

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its 23 people

charred summit
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So I can't solve it ?

simple saddle
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but the ans is 23 thats what

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i wasn't asking the ans just the denominator concept

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noo need to solve

charred summit
#

Hmm I think that it is 365 which represents the year days

simple saddle
charred summit
#

Do you mean the way he said
$$\frac{364}{365} \times \frac{364}{365}$$?

ocean sealBOT
#

Sherif Player

charred summit
#

Look I think I understand it now
When
To calculate the probability that bunch of people doesn't share any birthday is easy
We will just take one out of them then say that
The second one needs to be different than this person so it will be
$$\frac{364}{365}$$
Then the third one needs to differ from both of these guys so
And as both of the conditions needs to be applied we will use multiplication
$$\frac{364}{365} \times \frac{363}{365}$$

ocean sealBOT
#

Sherif Player

charred summit
#

And so on

#

Now to get that at least 2 of them has the same birthday we will just say
1 - the result

#

So we get
$$1 - \frac{364!}{(365-K)! \times 365^{k-1}}$$

#

As K is the number of people

ocean sealBOT
#

Sherif Player

lone heartBOT
#

@simple saddle Has your question been resolved?

lone heartBOT
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vague iris
#

Where did I go wrong?

lone heartBOT
hot snow
#

honestly looks alright to me

vague iris
#

i think there was a mistake in the answer key. The denominator was raised to positive 2.

#

Thanks!

#

.close

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lethal belfry
#

I would like some advice on how to solve the following diophantine equation $x^2+y^2+x-y= 2021$( The question is actually to find the number of diophantine roots, but I would like to find the roots first

ocean sealBOT
#

physicsrocks

mellow grail
# ocean seal **physicsrocks**

dont take my advice too seriously, but solving for either variable in terms of the other using quadratic formula should allow u to place a few bounds on the values

lethal belfry
#

I have tried a few tricks. Like$(x+0.5)^2+(y-0.5)^2= 2020.5$ and $(x+y)(x+y-1)-2xy=2021$ But neither seem to help

ocean sealBOT
#

physicsrocks

mellow grail
#

in this case its possible your only option is my way

#

reason being its not factorizable

wind cloak
#

I mean isn't this just the equation to a circle

mellow grail
wind cloak
#

You can find the length of the intercept made on the x axis and calculate the distance from the x coordinate of the center

wind cloak
mellow grail
wind cloak
wind cloak
mellow grail
mellow grail
lethal belfry
wind cloak
#

square root of 2020.5

#

Is the radius

lethal belfry
#

.close

lone heartBOT
#
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frosty swift
#

I have doubts in this question's solution I found online.

frosty swift
#

Somebody did this:

#

Where did x + 1/x come from?

#

This is ref page I found from that person.

alpine sable
#

that's smart actually damn

frosty swift
#

But why though?

alpine sable
#

using the information from the four equations, you can see how they got to l+(1/l)=q-2

frosty swift
#

Yeah.

alpine sable
#

so they see that l+(1/l) is f(l) in this case and its range is [2,infinity)

frosty swift
#

Ok I see.

alpine sable
#

and then they're substituting for l+(1/l) in that inequality to get the range of q

frosty swift
#

But wait, shouldn't the range by -1 to infinity taking only natural numbers?

#

Or I'm mistaken?

#

(probably).

alpine sable
#

you can find the range of x+(1/x) by completing the square

alpine sable
#

wait

#

i think im massively mistaken

frosty swift
#

No.

#

You're right.

alpine sable
#

wait yeah

#

im right

#

ok no i was half right the range also includes the interval (-infinity,-2]

frosty swift
#

But wait, you can't complete the square for this I don't think so.

alpine sable
#

yeah that part was wrong

#

if l+(1/l) was less than -2, it would imply q-2 was less than -2 or q was less than 0

#

which isnt possible because q is given to be natural

frosty swift
#

Yeah I got that.

#

Oh wait.

#

1/x is a rational function.

#

So the minimum val. is 1 for natural numbers.

#

for f(x) = x + 1/x => f(1) = 2

#

So that's why they did that.

#

Ah that's acutally smart.

#

(That's what you said in the beginning).

lone heartBOT
#

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final mural
#

Hello, is this the right drawing of the situation

final mural
#

Orthogonal means independent here

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#

@final mural Has your question been resolved?

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@final mural Has your question been resolved?

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humble leaf
#

Let v1, v2 and v3 be distinct elements of a vector space V over a field F and let c1, c2, c3 ∈ F . Under what conditions is the subset {c2v3 −c3v2, c1v2 −c2v1, c3v1 −c1v3} of V linearly independent?

humble leaf
#

i think the answer is never cause c1(c2v3 −c3v2)+c3(c1v2 −c2v1)+c2(c3v1 −c1v3) is always 0

#

so they're always a linearly dependent set

#

someone pliz sanity check, thanks!

oak perch
#

$\begin{pmatrix}v_{1}&v_{2}&v_{3}\end{pmatrix}\begin{pmatrix}0&-c_{2}&c_{3}\-c_{3}&c_{1}&0\c_{2}&0&-c_{1}\end{pmatrix}$

ocean sealBOT
#

Cogwheels of the mind

oak perch
#

So only when v_i are linear independent and that matrix is invertible

#

Calculate its determinant

#

Oh seems like you did

oak perch
humble leaf
#

cool thanks 🫡

#

.close

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oak perch
#

Np

lone heartBOT
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alpine sable
#

hi can anyone help me with this probabilities question

alpine sable
#

hi

#

i know this is related to pascals triangle and ncr but i dont fully understand how to do it

waxen flame
#

The first sentence basically tells that you are using combinations of four fruit so 4C1 + 4C2 + 4C3 + 4C4.

#

The next line does not clearly define if Olivia is just adding one fruit to each of the possible combinations or there is an additional fruit to consider in the combinations above. The explanation given would indicate they intended the former.

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
#

thank you sm

#

i just got one more question, it might be dumb

#

but what i did was i looked at pascals triangle and i included 4c0 and 5c0 in my calculations so i did 32-16=16, why did you leave out 0?

#

4c0?

#

so i did (1+5+10+10+5+1)-(1+4+6+4+1)

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#

@alpine sable Has your question been resolved?

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viscid lynx
oak perch
#

I would do it like this:

#

y=rcos(u), z=rsin(u), 0<=r<=3, u from 0 to 2π, x>=0
The 3x-y+z=6 condition becomes sqrt(2)rsin(u-π/4)=6-3x

#

dxdydz=rdxdrdu

viscid lynx
#

starting with dy my friend

#

not dx

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#

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raven coral
#

Hi, I have a question about the definition of a gradient vector field. I know that $for a C^{1}$ vector field F, we have that $F = \nabla f$ (i.e F is a gradient vector field), then for any simple closed curve $C$, we have that
$$\int_{C} \textbf{F} \cdot d\textbf{S} = 0$$ . However; what if F is not $C^{1}$ continuous? For example, consider $$\textbf{F} = \frac{-y}{x^2 + y^2} \textbf{i} + \frac{x}{x^2 + y^2} \textbf{j}$$. When $C$ is the unit circle, $\int_{C} \textbf{F} \cdot d\textbf{S} = 2\pi \neq 0$. And yet, ... F is the gradient of -arctan(x/y).

ocean sealBOT
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#

@raven coral Has your question been resolved?

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@raven coral Has your question been resolved?

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winter current
#

Hi, guys! If someone could help me with this, that’d be amazing I’m so confused.

vapid shuttle
#

What have you tried?

#

What part(s) specifically are confusing you?

winter current
#

I thought I was supposed to use the contribution margin ratio but I’m not sure 🥲

vapid shuttle
#

When you tried labeling the fixed costs

#

what crossed your mind

lone heartBOT
#

@winter current Has your question been resolved?

winter current
#

I’m not even sure where to start if I’m being honest

lone heartBOT
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weak ridge
lone heartBOT
weak ridge
#

PLease how do you solve

oak perch
#

It’s the same as (2r+4)+(r-2)=18

weak ridge
#

how

oak perch
#

Because C(n,a)=C(n,b) iff a+b=n

weak ridge
#

What

weak ridge
oak perch
#

Wait sorry

#

n

#

Editing

#

18 not 19 my bad

#

Edited

weak ridge
#

Why do you have to add

twin nimbus
#

You familiar with pascals triangle and the relationship between it and the binomial coefficients?

weak ridge
#

What do you mean

twin nimbus
#

In mathematics, Pascal's triangle is a triangular array of the binomial coefficients arising in probability theory, combinatorics, and algebra. In much of the Western world, it is named after the French mathematician Blaise Pascal, although other mathematicians studied it centuries before him in Persia, India, China, Germany, and Italy.The rows...

weak ridge
#

i know it

#

but tell me what it has to do with the question

#

please

twin nimbus
#

So the coefficients of (1+x)^n are the nth row of this

weak ridge
#

ok

twin nimbus
#

For instance, the third row is 1 3 3 1, and (1+x)^3 is x^3 + 3x^2 + 3x + 1

#

Each entry of Pascal's triangle is C(n, k)

#

Where n is the row and k is the column

#

And it's symmetric

#

Meaning that C(n, k) = C(n, n-k)

#

So we know n = 18, because (1+x)^18

#

So we just need to find the appropriate k

weak ridge
#

why n-k

twin nimbus
#

Symmetry

weak ridge
#

from where

twin nimbus
#

Pascal's triangle

weak ridge
winter light
weak ridge
#

how

winter light
#

Using the definition of binomial coefficient (if you know it of course, otherwise forget it for now)

#

The one with the factorials

weak ridge
#

which one

twin nimbus
#

n!/(k!(n-k)!)

weak ridge
#

then

#

what please

weak ridge
weak ridge
winter light
weak ridge
#

what definition

#

the formula

winter light
weak ridge
#

2 and 18

winter light
#

Don't think about numbers for now

weak ridge
#

Then what am i doing

#

please

winter light
#

Btw I'm going to bed now cause it's quite late

#

There is for sure someone available to help you

weak ridge
#

wait

#

please

#

how you got the n and n-k is what i need help in

weak ridge
winter light
#

I was saying that in few minutes I'm going sleeping and I wanted to let you know that you aren't left alone, but instead a lot of helpers are available to help you

weak ridge
#

no sorry wrong reply

winter light
#

I thought @twin nimbus wanted to make you note that C(n, k) and C(n, n - k) are equal to eachother

#

And what I was telling you is one way to prove that

weak ridge
#

how are they equal

#

What does the k even mean

winter light
weak ridge
#

but how

winter light
#

And I'm trying to tell you how to do that 😅

winter light
weak ridge
#

What does th k mean

winter light
#

I don't know how to explain you if not in this way

weak ridge
#

is it 18

winter light
winter light
weak ridge
#

but why are we talking about symettry here

#

how does have to deal with equality

winter light
#

@twin nimbus can you explain it again please? I don't know how to help him blobcry

weak ridge
#

please explain the relationship between the equality and the symmetry

winter light
#

<@&286206848099549185>

winter light
weak ridge
#

just try please

winter light
#

The only thing I can suggest is going back to the messages and restart to read carefully what @twin nimbus told you

weak ridge
#

i did that

#

i came with this question

#

going back wont help

winter light
junior citrus
weak ridge
#

yes

junior citrus
#

do you know binomial theorem?

weak ridge
#

yes

junior citrus
#

then whats the issue?

junior citrus
#

if the term you are expanding is 1+x, then the coefficient would not change from either the a or b terms

#

therefore you could just set the nCr terms equal to each other and solve for r

weak ridge
#

why

#

so they are the same

#

;but term 2 and 18 are the same

#

but they dont give me same r

junior citrus
# weak ridge why

well each term, according to the binomial theorem, could be written as nCr (1)^r*x^n-r

#

and you want to find out the coefficients of the (2r+4)th term and the (r-2)th terms

#

since no matter what 1^r * x^n-r will not have a coefficient

#

you can ignore those

#

and you just focus on the nCr terms

#

so you would set them equal to each other

#

18C2r+4 = 18Cr-2

weak ridge
#

18C1 is the same as 18C18

junior citrus
#

yes

#

oh

weak ridge
#

Hello

weak ridge
junior citrus
weak ridge
#

so that means

#

what do you mean r starts at 0

junior citrus
#

like

weak ridge
#

why is that a condition

junior citrus
#

x^4 + 4x^3 + 6x^2 + 4x + 1

#

x^4 would be 0

#

4x^3 would be 1

weak ridge
#

ok

#

but how is thata useful

junior citrus
# weak ridge why is that a condition

i mean then if you want r to start at 1 you could have the coefficient of the rth term to be equal to the coefficient of the (n-r+1)th term doesn't really matter

junior citrus
weak ridge
#

why does be n-r+1 be equals to r

weak ridge
junior citrus
#

nCr = nC(n-r) => n!/r!(n-r)! = n!/(n-r)!(n-n+r)! => n!/r!(n-r)! = n!/r!(n-r)!

weak ridge
#

why are we substracting r from n

junior citrus
weak ridge
#

where

junior citrus
#

$nCr = \frac{n!}{r!(n-r)!}$

#

$nC(n-r) = \frac{n!}{(n-r)![n-(n-r)]!} = \frac{n!}{(n-r)!(n-n+r)!} = \frac{n!}{(n-r)!r!} = \frac{n!}{r!(n-r)!} = nCr$

ocean sealBOT
#

PyroShock

#

PyroShock

junior citrus
#

@weak ridge

lone heartBOT
#

@weak ridge Has your question been resolved?

lone heartBOT
#

@weak ridge Has your question been resolved?

oak perch
# oak perch Because C(n,a)=C(n,b) iff a+b=n

It’s simply C(n,a)<C(n,a+1), strictly increases for a<[n/2], because the latter is the former multiplied by (n-a)/(a+1)>1. And C(n,a)=C(n,n-a). So increases then decreases, So C(n,a)=C(n,b) we have only a+b=n

lone heartBOT
#
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terse fable
#

Can someone explain how I get from point a to b

terse fable
#

a being where the arrow starts and b the equation its pointing to

#

or if anything how I get (a^2-2a-2) from combining the two fractions

#

oh wait never mind

#

.close

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#
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terse fable
lone heartBOT
terse fable
#

how does factoring the denominator end up with (2a+5)(a+5)?

#

I'm referring to the second denominator btw

#

nevermind

#

my brain is being dumb today

#

.close

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lavish kelp
#

Ok ok this is a little dumb

lone heartBOT
lavish kelp
#

Me and my friend have been so confused on what to do

#

EVEN THOUGH WEVE DONE STUFF ABOVE OUR GRADE LVL

#

cnr+r/n

#

Can you reduce that into

#

Cr+r/n

near apex
#

c, n, r are variables?

lavish kelp
#

Yes

near apex
#

Then no. Not unless n is 1 which then makes division by n in second term redundant.

#

Wait...

#

c and C are same. Right?

lavish kelp
#

Yes

#

Capital was mistake

fallen verge
#

wheres your parentheses?

#

$\frac{cnr+r}{n}$ or $cnr+\frac rn$

ocean sealBOT
#

GarlicB

near apex
#

Lol. True. Maybe, they had the first one and ended up with cr + r/n.

lone heartBOT
#

@lavish kelp Has your question been resolved?

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alpine sable
#

hay

lone heartBOT
alpine sable
#

i wanted do dicusses about roudning to the next dollor but it doesnt add up

median oar
#

What is the issue?

fierce prairie
#

send your problem?

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#

@alpine sable Has your question been resolved?

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pale granite
#

i need help

lone heartBOT
pale granite
#

i got a calculus problem but idk if yall can do it in this section

#

this is the very last problem of the summer hw and me and my classmates (7 of us) dk how to even approach this

tardy stag
# pale granite

what are some observations you can make about the limit on the left?

pale granite
#

its approaching 0

#

i got to the point where i canceled out the x, but idk where to go from there

tardy stag
#

but do you mean the denominator is approaching 0?

pale granite
#

mb

#

the x is towards 0

#

which means that we have to somehow cancel out the x in the denominator with another x in the numerator otherwise this limit would be DNE

tardy stag
#

well... it means that the numerator has to approach 0 as well

#

or else yes it would be DNE (or infinite, and certainly not sqrt3)

pale granite
#

what i did was multiply by the opposite thingy

#

so instead of a+bx- root 3

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i did + root 3

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lemme send a picture of my messy work

tardy stag
#

i thought about doing that but i wasn't sure if it'd be useful

pale granite
#

what would be better?

tardy stag
#

i just used l'hopital's rule but your way is probably better

pale granite
#

i didn't solve for a and b tho

#

we arent allowed to use l'hopital's rule

#

because we havent learned it yet

tardy stag
#

so you ended up with $\lim \frac{b}{\sqrt{a+bx}+\sqrt3}$ if i'm reading that right?

ocean sealBOT
#

hayley!

pale granite
#

uhh lemme check

#

yea

#

then the bx goes away

#

cuz x=0

tardy stag
#

yeah

pale granite
#

then that is equal to root 3

#

and idk where to go from there because there isn't a system of equations i can use to solve for a or b

#

after that im just rearranging the equation

tardy stag
#

yeah you only found one equation so far

#

i used the fact that the original numerator had to = 0 to get another equation

pale granite
#

could u pls explain why it has to =0

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the numerator specifiaclly

#

specifically

#

w9

#

w8

#

a+bx=3

#

a=3

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then solve for b

#

and you get b -6

#

b=6

tardy stag
#

then what would our limit be

pale granite
#

w8

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this got me confuzzled

#

lol

#

but wouldnt that be the function

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aka the y-value

#

and the y-value has to equal root 3

tardy stag
#

hmm?

pale granite
#

the thing is = to f(x)

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aka y

#

which is root 3

#

so why does the numerator of it have to = 0

tardy stag
#

well

pale granite
#

is it a special rule idk

tardy stag
#

what's $\lim_{x\to 0} \frac{x^2+1}{x}$?

ocean sealBOT
#

hayley!

pale granite
#

idk lol

#

um

#

DNE

tardy stag
#

how do you know that?

pale granite
#

cuz you cant get rid of the 0 in the denominator

tardy stag
#

why not?

pale granite
#

can you?

#

x(x+1/x)

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over x

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then x+1/x

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its 0

#

i feel stupid

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lol

tardy stag
#

you are correct that it's DNE

pale granite
#

bet

tardy stag
#

and you'll note that if you plug in 0

#

you get 1/0

pale granite
#

yea

#

if i plug in 0 to the originial one its also gonna be DNE

#

but we know its not

tardy stag
pale granite
#

yea

tardy stag
#

thankfully we have some knobs to turn

pale granite
#

wdym

#

im just gonna resend the pic so i dont have to keep looking up

tardy stag
#

right, we have to stop that limit from not existing

#

we know the denominator is going to 0, we can't do anything about that

#

and if the denom goes to 0 but the numerator goes to some number that isn't 0, then the limit will not exist (or will be infinite)

pale granite
#

w8 no thats only if there is an x in the numeraot

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numerator

#

when the function is heading towards positive or negative infinity

#

w8

#

im so lost

#

is this a rule idk?

#

that the numerator and denominator have to approach the same number?

#

cuz how cany they both approach 0 if it says = to 3

tardy stag
#

well i mean

#

what's $\lim_{x\to0} \frac{3x}{x}$?

ocean sealBOT
#

hayley!

pale granite
#

3

#

obv

tardy stag
#

yes obv

#

but

#

the numerator and denominator are both approaching 0

pale granite
#

w88888

#

thats when you plug in for x

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then it is approaching 0

#

is there a yt vid i can watch

tardy stag
#

probably

pale granite
#

so

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basically

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just write the numerator = 0

#

solve for a

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plug into other one for b

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rightttttttttttttt???

pale granite
tardy stag
#

that is what i did yes

pale granite
#

ok perf

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what is the thing u were talking abt

#

what is it called

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so i can search it up

tardy stag
#

what thing

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uhh look at indeterminate forms

pale granite
#

ok thx

#

i appreciate it

#

have a good night

lone heartBOT
#

@pale granite Has your question been resolved?

#
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#

@trail summit Has your question been resolved?

lone heartBOT
#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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rapid gate
#

c

lone heartBOT
pulsar aspen
#

!status

lone heartBOT
#
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
pulsar aspen
#

@rapid gate

lone heartBOT
#

@rapid gate Has your question been resolved?

rapid gate
#

so

#

so either

#

i dont understand the english part

#

or the math part

#

but when it saids 13-19 inclusively

#

does it mean numbers 14-18 including 14,18

lone heartBOT
#

@rapid gate Has your question been resolved?

lone heartBOT
#

@rapid gate Has your question been resolved?

rapid gate
#

,w x^2-6x-27=0

rapid gate
#

,w log_3 (x-6)+log_3 (x)=3

rapid gate
#

.close

lone heartBOT
#
Channel closed

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#
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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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waxen seal
lone heartBOT
waxen seal
#

is my proof for a and b good enough?

#

<@&286206848099549185>

sour verge
#

Give me 15 minutes, Ill come back to it if nobody answered

waxen seal
#

ok thank you

#

here is number 3c

#

aw i think i read the question wrong

sour verge
#

I'm still doing something, but at first glance it seems you have the preimage definition a bit wrong for a)

#

(g dot f)-1 (E) = {a in A | g(f(a)) in E}

waxen seal
#

how about this? is my definition correct?

sour verge
#

That seems about right. Now I'd advise trying to pick an element from the first set and show that it must be in the second.

waxen seal
#

yes im doing it right now ill send it

#

here it is haha

sour verge
#

I get what you're trying to write down, but there's some things a bit iffy with it. I'll annotate it just give me a minute

waxen seal
sour verge
#

I think this might get you going a bit further

waxen seal
#

ok let me try yo fix it

#

i use g^(-1)(e) as elements of set g^(-1)(E)

sour verge
#

Again, x is not in g-1(E) since x is in A and g-1(E) is a subset of B.

waxen seal
#

ohhhh

sour verge
#

However, you can say that if (g dot f) (x) = e in E, then you have g(f(x)) in E, so f(x) is in g-1(E)

waxen seal
#

f(x) is in g(-1)(E)

sour verge
#

Yeah

#

But then that means this x is in A

#

With f(x) in g(-1)(E)

#

So it's also in f-1(g-1(E))

#

Makes sense?

#

It's not as short a proof as it could be, but it should do the trick.

waxen seal
#

f(x) is in B so there must be an x in A which is inside f^(-1)(g^(-1)(E))

sour verge
#

Yeah the x you picked to begin with is that specific x actually

#

But that's the reason yes

waxen seal
#

is it correct now?

sour verge
#

Yeah looks good

waxen seal
#

i can draw it or visualized it but i cannot say it mathematically

#

can i send more proofs?

sour verge
#

Yeah it takes some practice

#

Ofc

waxen seal
#

ok thank you very much im proving b and c now

lone heartBOT
#

@waxen seal Has your question been resolved?

waxen seal
#

here is my attempt at 3b and 3c

lone heartBOT
#
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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>.
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• 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.

wind hill
#

hello guys

lone heartBOT
wind hill
#

i want to learn, is there a way to answer rational function inequality fast?

#

like is there a shortcut?

vale wigeon
#

shortcut compared to what

wind hill
#

compared to the conventional, just a curious question, im fine with the conventional it's just that it takes me so much time when answering quizzes and test

#

for example let's have this

#

and this

vale wigeon
#

everything to one side then factorization?

wind hill
#

I just watched organic chemistry, i thought that was conventional sorry ^_^

#

any method you do?

vale wigeon
#

no, there is no shortcut around that.

wind hill
#

do you ahve a method u can share with me?

tardy stag
wind hill
#

ok ok thank you

#

im sorry if im asking too much can u show how that works, i do promise i'm just advance studying, this isn't out homework!

tardy stag
#

well like so for that second one

#

$\frac{(x-7)(x-3)}{(x-5)^2} > 0$

ocean sealBOT
#

hayley!

tardy stag
#

you can just multiply both sides by (x-5)^2; because it's always positive we don't have to change the sign of the inequality

#

so we get $(x-7)(x-3) > 0$ and we can easily solve that

ocean sealBOT
#

hayley!

tardy stag
#

and remember that 5 can't be a solution since it's not valid in the original expression (because it would be dividing by 0)

wind hill
#

thank you!

gray isle
#

that's applicable more generally too

wind hill
#

how did the answer went to this?

gray isle
#

e.g. in that first example you can multiply both sides by
(x+5)^2(x+6)^2

#

after multiplying both sides by (x-5)^2,
you'd get
(x+7)(x-3) > 0, (make sure to remember to exclude 5 from the solution set)
and the most intuitive way to identify the solution to that would be the wavy method where you draw a rough sketch of y=(x+7)(x-3)

alpine sable
gray isle
#

where the main features you care about are just the direction and x-intercepts

alpine sable
#

it's x + 7

wind hill
#

ok ok i see

gray isle
#

just a typo, idea still stands