#help-10

1 messages · Page 257 of 1

slate zephyr
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what about it?

gusty pelican
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is there a name for this process

slate zephyr
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I would call it finding a counter example by consturcting a model.

gusty pelican
#

ah okay thank you

slate zephyr
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have you noticed anything bhappy

gusty pelican
#

okay wait sooo the first statement was true

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and the second statement was also true

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so they are logically equivalent

slate zephyr
#

😧

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yes

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but

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only for this P and Q

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We chose bad P and Q.

gusty pelican
#

wottttt

slate zephyr
#

I will let you alter one of them in a way to make them different.

slate zephyr
gusty pelican
slate zephyr
#

So from our computation we might even start suspecting that they are same.

slate zephyr
#

but different P or Q

gusty pelican
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what do you mean by different P or Q?

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change P is true only when x=a

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to P is true only when x=b?

slate zephyr
#

We could define P always true or P also true when b

slate zephyr
gusty pelican
#

so that type of change

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hm

slate zephyr
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youz will need to try different variants

gusty pelican
#

I need to change it until I find a counterexample?

slate zephyr
#

yes

gusty pelican
#

if I don't find a counterexample

slate zephyr
#

OR you would need to proof that they are same.

gusty pelican
#

I can say that they are logically equivalent

slate zephyr
#

Probably eaisest to argue in some way why they are same.

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I assume you larnt some transofmrations where they stay identical?

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De Morgans rule etc

gusty pelican
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yes

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but I'm not really adept at them

slate zephyr
gusty pelican
#

why

slate zephyr
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(you probably already noticed but this is one of my favorite symbols to put)

gusty pelican
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I know P -> Q is ~P v Q

slate zephyr
gusty pelican
#

well I am only 8 days into this course

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so I don't know many things

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¯_(ツ)_/¯

slate zephyr
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one step at a time

slate zephyr
#

Here we do not need to transform

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it suffices to find some situatiosn where they disagree

gusty pelican
#

x from {a,b}
P(x) = {true if x=b}
Q(x) = {true if x=b}

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should I try with this

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I'm short on time tho

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😬

slate zephyr
gusty pelican
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I have to go to school tomorrow

slate zephyr
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generally rushing is bad for learning.

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:/

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You could try figure it out tomorrow

gusty pelican
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it's okay

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I think I've learned a lot today

slate zephyr
gusty pelican
#

thanks for the help

slate zephyr
gusty pelican
#

better than my professor

slate zephyr
#

still both true

slate zephyr
gusty pelican
#

change Q?

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Q true when a,b

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P true when a

slate zephyr
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It should be a good thing but you make it sound like a bad thing by putting "at least" bhappy

gusty pelican
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my bad

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I'll remove it

slate zephyr
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nah don't worry

gusty pelican
#

:B

slate zephyr
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yeah

gusty pelican
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professor doesn't go over these hard examples in class

slate zephyr
#

now it will disagree

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I think

slate zephyr
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Q=true, P only true for a.

gusty pelican
#

∃x(P(x) → Q(x))

P(a) -> Q(a)
true

P(b) -> Q(b)
true

so there exists is true

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∀xP(x) → ∃xQ(x)

for all x we have P(x)
but P(a) is true and P(b) is false

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and then....

slate zephyr
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yes

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SHIT

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they still agree

gusty pelican
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ah

slate zephyr
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perhaps you should put the "at least" back bhappy

gusty pelican
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are you sure there is a counterexample

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do you just know that bc you are good at this

slate zephyr
gusty pelican
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lol

slate zephyr
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Still I think they are different.

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Okay

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But at this point I need to fidn them...

gusty pelican
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how many combinations do we need to try

slate zephyr
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16

gusty pelican
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P only true when b
Q only true when a
is the same thing as before right?

slate zephyr
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4 for P and 4 for Q

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Some are very similar and hence redundant to try.

gusty pelican
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P only true when b
Q true for a, b

slate zephyr
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P = false does not work, becausew both sides true.

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Wait okay

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so we can see

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the statement on the left implies the statement on the right.

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we can only hope for the right statement true and the left statement false.

gusty pelican
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so the combination for that would be

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wait

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how do we make that false

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isn't there no way we can make that false

slate zephyr
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P = true also des not work.

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I am actually confused myself now.

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I think there is no reason why they should be the same but I also can't see the counterexample yet.

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wait

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they are the same.

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Proof

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Assume the left statement is true.

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This either means that one x have P(x) is false

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then the right is trivially also true

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otherwise the left statement implies that there exists a Q(x).

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Hence the right is also true.

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in the other direction.

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Assume the right statement is true.

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then if for all x P(x) is true

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we can find an x such that Q(x) is true

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This x will also do on the left

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Otherwise there exists an x where P(x) false

gusty pelican
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I see....

slate zephyr
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hence the left side is true for that x because of viscious truth.

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So they are the same.

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This really comes as a surprise to me.

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This goes to show how implications in the middle of stastements with discious truth can throth a wernch into our intiotion.

slate zephyr
gusty pelican
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O.o

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so you haven't found anything that makes it not equivalent

slate zephyr
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I believe i have actusally proven them to be equivalent.

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If you can show A => B

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and B => A

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then that means they are equivalent

gusty pelican
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ah

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I gotta go D:

slate zephyr
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I that case if one is true

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the other is true too

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So they cannot differ.

slate zephyr
gusty pelican
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thanks so much for your help

slate zephyr
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I think we finished anyway bhappy

gusty pelican
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have a good day

slate zephyr
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I need to digest my defeat also...

gusty pelican
#

loooool

#

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radiant spindle
#

how i can prove that a < f(x) < b if x is constrained by c < x < d? like the concept in general

wooden cipher
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This isnt always true

radiant spindle
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i meant more like

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for a specific function f(x) = ... , if it asks me to prove that f(x) < b for x < a specific number, how should i go about proving it algebraically?

tacit scarab
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find the maximum

radiant spindle
# tacit scarab find the maximum

so lets say
if 2 < x < 4 for f(x) = x^2, and it asks me to show that f(x) < 17
how should i go about finding the maximum without using limits? (this is a proofs course)

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like i can't just sub in 4 into f(x) to show this because x is defined as having to be less than 4?

tacit scarab
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If you can't use differentiation you can try to prove that f is increasing

radiant spindle
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can you elaborate on that

tacit scarab
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Prove that f is increasing at the interval 2<x<4

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Then plug in f(4)

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Which equals 16

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Then f(x) < 16 because f is increasing

radiant spindle
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ohh so you would still plug it in

tacit scarab
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Yes

radiant spindle
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thank you

tacit scarab
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No problem

radiant spindle
#

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radiant spindle
#

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obtuse pebbleBOT
#

radiant spindle
#

would u still need to plug in values for this? (aside from the final part where u plug in f(4)

tacit scarab
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An increasing function f have this property:
If a<b then f(a)<f(b)

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So if x<4 f(x)<f(4)=16

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To prove f is increasing, compare f(x) and f(x+a), where a is positive

radiant spindle
tacit scarab
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You need to prove it for all a

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So don't substitute a number to it

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Let's do f(x) = x as an example

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Let a be positive
f(x)=x and f(x+a) = x+a

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Obviously x<x+a

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thus f(x)<f(x+a)

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So f(x) = x is increasing

radiant spindle
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ohh

radiant spindle
tacit scarab
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Yep

radiant spindle
#

thus u have proved that f(x) < 4 for x < 4?

tacit scarab
#

Exactly

radiant spindle
#

thank you so much

#

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timid silo
#

When do you not need to use absolute value for ln|x|?

timid silo
#

My professor told me today that this is for particular solutions for differential equations (where you just need 1 solution)

sage geode
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Usually the absolute value is put there so that the domain is not so restricted

timid silo
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see, no absolute value there. is that train of thinking wrong?

sage geode
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Well yeah because |x| is the same as x for positive x

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So it doesn't really matter which one you write I suppose

timid silo
sage geode
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Well is it given that y(x) > 0 for all x? (or y(x) < 0)

timid silo
#

oh i see

#

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zinc tundra
#

Suppose we know that the number of items produced in a factory during a week is a RV with
mean 500. Find an upper bound on the probability that this week’s production will be at least
1000? If the variance of a week’s production is known to equal to 100, then give a lower bound
on the probability that this week’s production will be between 400 and 600? (Hint: Moment
Inequalities)

zinc tundra
#

should we use markovs inequality for the first part??

polar fossil
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the chebyshev ineq requires that the variable be nonnegative

zinc tundra
#

and?

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<@&286206848099549185>

polar fossil
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oh yeah i guess you can't produce negative units yeah that will work then

zinc tundra
#

markovs?

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what does it mean by upper bound ..at least thousand?

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P(X>=1000)<=?

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this?

polar fossil
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yeah

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and yeah Markov and Chebyshev are two names for the same inequality

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but Chebyshev sounds cooler lol

serene fossil
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technically they arent the same

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because markov is a special case of chebyshev im pretty sure

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actually thats not even true

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they are just different theorems

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in fact markovs is used to prove chebyshev

zinc tundra
#

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vast glade
obtuse pebbleBOT
vast glade
#

finding derivative using implicit differentiation

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what’d i do wrong here?

polar fossil
#

the chain rule wasn't done right

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derivative of sin(πx) is πcos(πx)

zinc tundra
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differentiation of sin(pi x)

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yeah

obtuse pebbleBOT
#

@vast glade Has your question been resolved?

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twilit onyx
#

how to do d ?

obtuse pebbleBOT
twilit onyx
#

rest is p easy but i am not able to eqaute x

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I get a eqaution in form of ax^4 - bx^3 +cx^2-dx

obtuse pebbleBOT
#

@twilit onyx Has your question been resolved?

formal wigeon
#

ie they intersect

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at least thats what i think the question asks

twilit onyx
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in which f(x)=inverse f(x)

formal wigeon
#

yeah

twilit onyx
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so is that just intercept

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?

formal wigeon
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i imagine so

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wherever they intersect take the x value there

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but its asking for exact value

twilit onyx
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cause they intercept at (1,1)

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and one more point

formal wigeon
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are you sure they intersect at 1,1?

twilit onyx
#

the solution sheet says says x=(3+underoot 5)/2

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oh wait they dont

formal wigeon
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so you would just set

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1 + underoot x

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equal to the inverse

twilit onyx
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they interest at some point beyond 2 before 3

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on both

formal wigeon
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yeah its ~2.68

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but i cant remember how to get that value

twilit onyx
#

hmm btw this is a non gdc question

formal wigeon
#

wdym gdc

twilit onyx
#

or digital graph

obtuse pebbleBOT
#

@twilit onyx Has your question been resolved?

obtuse pebbleBOT
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@twilit onyx Has your question been resolved?

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gusty wraith
#

Hi. I have a question:
"Let A, B, and C be three points that are not in line. Draw a point D which is equidistant from all three points!"
I asked chatgpt and the answer is on the picture. is that correct?

latent walrus
#

dont use chatgpt for maths

gusty wraith
#

any idea or keyword to find the answer?

kind hawk
#

surprisingly it is correct as far as I see. but yes in general dont use chatgpt

gusty wraith
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timid silo
#

In how many different ways can eleven people be seated at a circular table with eight seats, if three are left waiting?

timid silo
#

or maybe (11!/3!) x 7!

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Which one is correct and why? Or why they are all incorrect?

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I think it should be 10!/3!
Because in circular permutation you eliminate 1 for n, and n in this case is 11

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<@&286206848099549185>

wide rose
#

C 8 from 11?

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11x10x9x8x7x6x5x4?

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wait

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is it circular for rotational symmetry?

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then 11!/3!/8?

timid silo
#

to account for one fixed place

timid silo
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mm no

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P

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Is permutation right?

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The order matters

wide rose
#

isn't 11!/3!/8 right

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because there are 8 sets which cancel to only 1 for a circle

timid silo
#

Wdym

timid silo
wide rose
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is 1 2 3 4 5 6 7 8 = 2 3 4 5 6 7 8 1

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there

timid silo
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No

wide rose
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why?

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i mean as people

timid silo
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I mean yes
I thought you put 1 2 3 4 5 6 7 8 = 2 1 3 4 5 6 7 8

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Which matters is the order

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so it's not combinations

wide rose
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so

timid silo
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is Variations

wide rose
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so

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there are always 8 (7 other) variants

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for 1 ordered

timid silo
#

Also you need to take into account they are in groups of 8 and there's onw fixed place

timid silo
wide rose
#

-_-

timid silo
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so those are just the places available

timid silo
#

?

wide rose
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imagine

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a1 - a8 are selected people

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let's work with that

timid silo
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Yes I know

wide rose
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what is the ratio of a1-a8 to a1-a8 in a circle?

distant flax
#

can someone help me find the 3 quartiles for 5,2,1,12,6,9,9,10?

wide rose
distant flax
#

o

timid silo
wide rose
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and in a circle

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spoiler

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it is 8

timid silo
#

in a line
If you have only 8 people, there's 8!

wide rose
#

i mean

timid silo
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It's a variation wothout repetition

wide rose
#

in distinct order

timid silo
#

Yes
variations are for different orders

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Because it matters the order

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so you would have 8! different variations having 8 people in a line

wide rose
#

that's right

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and for circle?

timid silo
#

that is permutations

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and here

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you need to eliminate 1

wide rose
#

so we...

timid silo
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Having only 8 people

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no 11

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here the difference is that there are groups

wide rose
#

just do it for 8 people

timid silo
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a group of 8

wide rose
#

ok

timid silo
wide rose
#

lets make it super ez

timid silo
wide rose
wide rose
timid silo
#

Ok

wide rose
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how many ways for line and circle?

timid silo
wide rose
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i don't get it

timid silo
wide rose
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yes

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and

timid silo
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For variations you have groups ot you pick

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for permutations you don't have groups

wide rose
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i think i get it

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but

timid silo
wide rose
#

selecting 8 people

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and arranging them

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are 2 steps

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not a whole

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i mean, you multiply

timid silo
# timid silo

In both the order matters, but for variations n and k are different
in permutations n and k are equal

wide rose
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now I'm confused

timid silo
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mm but this is prior knowledge to solve this

timid silo
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I want to understand your point of view

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I want to learn

wide rose
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ok

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my point is

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we know all of the variants of putting 8 people in a line

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(forget about 11 rn)

timid silo
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Yes is 8!

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for a line

wide rose
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then you know in how many ways you put em in a circle

timid silo
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and 7! for a circle

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yes

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this is circular permutations

wide rose
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oh

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ok

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then multiply by the ways u select 8 people from 11

timid silo
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why would you multiply 11!/3!

wide rose
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because

timid silo
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why (11!/3! )x 7!

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how do I know that's correct

wide rose
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check for simpler examples?

timid silo
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ok

wide rose
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oh wait

timid silo
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n = 3

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k = 2

wide rose
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nvm

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good luck

timid silo
#

in a circle of two spots

timid silo
wide rose
#

why not

timid silo
#

because luck is not a factor to resolve a problem

wide rose
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I'm just being kind

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or life doesn't matter

timid silo
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why

wide rose
#

what why

timid silo
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life doesn't matter

wide rose
#

O_O

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cause you are asking why

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wishing luck is just a sing of kindness

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and gives motivation

timid silo
#

okay, good luck

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I 'll post it again

#

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sly gorge
#

hlo

obtuse pebbleBOT
sly gorge
#

i want to ask simply does this mean P(A/B) or P(B/A) i think theres some misunderstandin

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or way to interpret

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?

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?

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ik this is dumb q but still help me

tardy epoch
#

do you know the definition of independence?

sly gorge
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independence means when p(A intersection B)= P(A) * P(b)

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@tardy epoch i answered , sry for ping.

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@tardy epoch

tardy epoch
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and the intersection

sly gorge
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logically it should be like :- P(B intersection A)= p(b) *p(a/b) ?

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undone sentinel
obtuse pebbleBOT
undone sentinel
#

i got 4.6

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is that right

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my textbook doesnt have a solution for this example so idk if im doing it right

vast willow
#

,calc sqrt(29)

warm shaleBOT
#

Result:

5.3851648071345
vast willow
#

how do you calculate distance between 2 points ?

undone sentinel
#

oops i subtracted 4

#

the distance formula

vast willow
#

$\sqrt{(y_1-y_2)^2+(x_1-x_2)^2}$ right

warm shaleBOT
#

calculus is fun

undone sentinel
#

yea

vast willow
#

ok just sub

#

,calc sqrt(21)

warm shaleBOT
#

Result:

4.5825756949558
undone sentinel
#

okay so i did it right

vast willow
#

did you round ?

undone sentinel
#

ye

vast willow
#

ok wrong

vast willow
#

you have to add not subtract

undone sentinel
#

oh

vast willow
#

there is a + not a - between the paranthesese

undone sentinel
#

i accidentally subtracted

vast willow
#

yea

#

you should've added instead

#

thats all

undone sentinel
#

okay thanks

#

these problems are easy my eBook isnt displaying shit right so maybe im doing it wrong

vast willow
#

ohhh

undone sentinel
#

am i tweaking or is there not a single natural number here?

karmic heron
#

Is sqr of 36 not a natural number?

undone sentinel
karmic heron
#

All good

timid silo
undone sentinel
#

6

timid silo
#

so

undone sentinel
#

but its in square root form so doesnt that make it irrational

timid silo
#

how?

#

no

karmic heron
#

No

undone sentinel
#

okay

#

i understand

#

what about 0

karmic heron
#

1 to infinity

obtuse pebbleBOT
#

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obtuse pebbleBOT
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frail depot
#

Are these calculations right?

#

Mostly the $e^{(qx)^2}$ part

warm shaleBOT
#

SimonWin

frail depot
#

I forgot to put parenthesis on the picture but they are now

#

or shouldnt it be the whole thing actually

#

${e^{qx}}^2$

warm shaleBOT
#

SimonWin

frail depot
#

Aah... yes

#

so it's really

#

$(e^{qx})^2$

warm shaleBOT
#

SimonWin

frail depot
#

So like this, and then they cancel out, and I could possible even do it before the 2qx part...

#

But wolfram says they're equal

#

So

daring rock
#

Wolfram says what is equal?

frail depot
#

when i multiply in

daring rock
#

Yeah

frail depot
#

So, that should be fine, right

daring rock
#

Yeah, that looks good now

frail depot
#

Cooool! Aweeesome!

daring rock
#

You did need the brackets around the exponential, to answer your original question lol

daring rock
#

But yeah you got it

frail depot
#

Look (23)

daring rock
#

Oh ya I see now

frail depot
#

Which makes sense because it's (e^{qx})^2 not the q^2 too

#

So it completely makes sense!

#

Verry nice!

#

Thank you! ❤️

daring rock
#

Np 👍

frail depot
#

🫶

#

.close

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wooden edge
#

How can I evaluate the limit of the sum to infinity of (3^n - 2^n)/5^n

wooden edge
#

where n starts at 1

reef inlet
#

$\frac{3^n - 2^n}{5^n} = (3/5)^n - (2/5)^n$

warm shaleBOT
#

exophades

royal basin
#

^

#

what you have here is the sum of two geometric series

wooden edge
#

oh im so dumb.. sorry for wasting your time

#

.close

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wooden edge
#

.reopen

obtuse pebbleBOT
#

wooden edge
#

thanks though

#

.close

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round wing
#

Hey can someone guide me through this

obtuse pebbleBOT
round wing
#

I'm not sure what Im doing wrong

#

I multiplied te^t to each component and integrated

tepid mountain
#

You would be able to do it in an easier way if you considered
$$(-5i-j+5k)$$
As a constant vector that can be moved out of the integarl

warm shaleBOT
#

Sherif Player

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round wing
#

i got it

obtuse pebbleBOT
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drifting merlin
#

So I'm supposed to solve this system of linear equations. There are more unknowns than equations, so does this have a solution? Am I supposed to use the x = xp+xn thing here?

drifting merlin
#

Any help would be appreciated.

obtuse pebbleBOT
#

@drifting merlin Has your question been resolved?

sage geode
#

There are infinitely many solutions and in order to write them down you will need to express some amount of unknowns in terms of the other variables (in this case, you will have 3 unknowns dependent on other numbers)

#

E.g. x - y = 1 has infinitely many solutions for the same reason (there are not enough equations), but you can express every solution with the form (x, x - 1) once you see that y = x - 1

obtuse pebbleBOT
#

@drifting merlin Has your question been resolved?

drifting merlin
#

Ah so I need to express it in a general form.

#

Thank you.

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mortal lava
#

I just want to know whether or not ( 48m^2n) and ( 12mn^2) are like terms or not

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ashen perch
#

I just need help with PT2 No. 1

obtuse pebbleBOT
#

@ashen perch Has your question been resolved?

ashen perch
#

Help what do I do with number 1?

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@ashen perch Has your question been resolved?

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jovial fern
obtuse pebbleBOT
jovial fern
#

how would u factor this

tardy epoch
#

,w roots x^4 -24x^2 +x+132

tardy epoch
#

I suppose you plug in small integers to check

zenith spade
#

Rational root theorem and trial and error are your best friends

wispy wadi
#

^

tardy epoch
#

Then polynomial division

jovial fern
#

thought there mightve been a faster method

#

.close

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autumn marsh
obtuse pebbleBOT
autumn marsh
#

someone teach me how to do this please 🤞🙏

high lily
#

which one?

autumn marsh
#

all three

high lily
#

do you understand function notation

autumn marsh
#

yeah

#

idk what to do with the table

high lily
#

the table tells you the corresponding value f(x), g(x) value at each value of x

#

not really that different from other tables

#

e.g in that first table

#

first column of values

autumn marsh
#

how do i know which number to choose

high lily
#

1 and a 3 below it, indicates that
f(1) = 3

autumn marsh
#

yeah

high lily
#

you choose values based on what the question asks for

#

you are asked to find
$$g(f(2))$$

warm shaleBOT
#

ℝam()n()v

autumn marsh
#

OH

#

is that right

#

@high lily

high lily
#

yes

autumn marsh
#

AAAAAA

#

how about the bottom

autumn marsh
#

r they right

pale scaffold
#

,rotate

warm shaleBOT
pale scaffold
autumn marsh
obtuse pebbleBOT
#

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#
Channel closed

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warm reef
#

Can someone help me with this question

obtuse pebbleBOT
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empty cypress
#

yes, and all the notes are correct as well

open forge
#

Alright, thank you!

empty cypress
#

np

#

.close

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open forge
#

.reopen

obtuse pebbleBOT
#

open forge
#

I also want to confirm two other questions.

#

It is defined at 0 (0,0) so D and E are eliminated. B is simply the shape, A would be the shape of an absolute value graph so that's elminated.

#

I'm confused about C.

empty cypress
#

sure doesnt look like it has a vertical tangent

#

one of (A) or (B) is true

open forge
#

We haven't covered vertical tangents, and from what I see on Google, I think C should be eliminated.

empty cypress
#

answer: ||It has a corner because the derivative coming from the left is not equal to the derivative coming from the right||

#

cusp is when theres a vertical tangent

#

its a cusp if the two sides intersecting makes an angle of 0 degrees

#

the definitions are all a bit silly, but this one is clearly a corner

open forge
#

Oh, I understand it now.

empty cypress
#

i gotta go soon but if you have another quick one to check i have some time

open forge
#

Let f be the function given by f(x)=|x|. Which of the following statements about f are true?
I. f is continuous at x=0
II. f is differentiable at x=0
III. f has an absolute minimum at x=0

#

I have I and III since, both LH and RH limits equal f(0) and it has no transformations so abs min is 0 for the mother absolute value function.

empty cypress
#

yeah thats right

#

at x=0 its continuous but not differentiable

open forge
#

Alright, thank you for the help! Have a great rest of your day/night.

empty cypress
#

you too

open forge
#

Thanks!

#

.close

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proven musk
#

Uhh when you horizantally stretch a function by b is it stretched ed by 1/b or b?

karmic mural
#

makes it go "faster"

#

1/b stretches out

#

goes slower

proven musk
#

That doesn’t answer the question

#

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lean sedge
#

can someone help?

obtuse pebbleBOT
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uncut tree
#

.help

obtuse pebbleBOT
#

Commands:
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uncut tree
obtuse pebbleBOT
uncut tree
#

I was doing this ealier

#

And someone told me to find the mid point

#

I dont know how to figure out the other end point for this

unborn ice
#

Okay

#

It seems pretty simple

uncut tree
#

I think it is but our teacher didn’t go into depth about this😭😭

unborn ice
#

Do you got a graph of coordinate?

uncut tree
#

No I’ll graph it rn tjo

unborn ice
#

HMMM

#

Seems like it already told you where the mid point is located at

uncut tree
#

Yeah

unborn ice
#

Quadrant 3rd

uncut tree
#

I need to find the other end point

unborn ice
#

Wait

#

I get it

#

You can use the distance between the mid point and coordinate K

#

It says its a mid point of those two coordinates

uncut tree
#

Yeah

#

Then

unborn ice
#

Let me graph it

uncut tree
#

-17??

#

Yupp it is

#

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ebon tendon
#

I know I need to setup an equation and solve for the coefficients that multiply to equal the U vector but cant seem to get it right. Any Help.

obtuse pebbleBOT
#

@ebon tendon Has your question been resolved?

obtuse pebbleBOT
#

@ebon tendon Has your question been resolved?

hot sonnet
#

then solve for a and b

#

given that they are 2 unknowns, you just need 2 equations

#

find a and b, those values must make as1+bs2 = u for each component. If at least one component doesn't match, then there's no linear combination that satisfies a*s1+b*s2=u

ebon tendon
#

so take 6a+4b=6?

hot sonnet
#

yes

#

you need one more eq.

ebon tendon
#

-7a +6b = 25

hot sonnet
#

ok, now solve for a and b

ebon tendon
#

4b=6-6a

b=3/2-3/2a

#

Plugging that into the first equation

6a+6-6a = 6

#

0=0?

hot sonnet
#

you get 0=0 which is always true. It's like saying a=2, then plug that into "first eq." and get 2=2

#

That's why you need 2 different eq. , so you can use the other one for plugging in

ebon tendon
#

I got it! thank you so much!

#

.close

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stuck herald
obtuse pebbleBOT
stuck herald
#

can i consider two different rectangles like this or why not?

#

will it be either but not both at a time?

tacit scarab
#

both cases are possible

#

so you need to calculate both cases

stuck herald
#

x+2y=180 or 2x+y=180

#

but how should i go abt this?

#

@tacit scarab

tacit scarab
#

the area too

stuck herald
#

yeah its same 3600 =xy

#

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dire nacelle
#

Hi, I am currently stuck on this part of my question. I believe it is the fact that I don't quite understand what I am trying to do in this question.

dire nacelle
#

I am not sure what "Plot V as a function of R-naught" means

tacit scarab
#

we need more context

fathom flicker
tacit scarab
#

treat V as a function of R_0

#

and plot it

#

the function is given

#

V=1-1/R_0

#

it's the same as y=1-1/x

dire nacelle
#

.close

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stuck herald
#

50/3 how to convert this to mixed fraction

obtuse pebbleBOT
stuck herald
#

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spark wasp
obtuse pebbleBOT
spark wasp
#

can someone please explain the span of this vector
i spent over 5 hours trying to get help

#

and some dude would just ignore my questions

#

@grizzled shore

#

can you please tell me what hte span is

#

if ur still here

tacit scarab
#

span of a set of vectors v1,v2...,vn is the set of vectors of the form a1v1+a2v2+...+anvn

spark wasp
#

but i cant get a and c in terms of x y and z

#

so wtf do i even do in this case

tacit scarab
#

techincally this is the answer

#

except that they are linear dependent

#

so you can simplify them

spark wasp
#

what i dont get is the asnwer lol

spark wasp
tacit scarab
#

the span = {2a+b,a+c,2a+b}

spark wasp
#

yea

#

but we have to say

#

in R2

tacit scarab
spark wasp
#

R3

#

etc..

tacit scarab
#

oh you just need to determine the dimension

spark wasp
#

as well

tacit scarab
#

the dimension equals the number of linearly independent vectors

#

linearly independent means that if a1v1+a2v2+...+anvn=0 then a1,a2,...,an = 0

#

i.e. no vectors can be written as linear combinations of other vectors

spark wasp
#

like right here

#

i proved that you can get a and b in terms of x and y

#

meaning the span is R^2

spark wasp
#

if you get what i mean

spark wasp
#

they are dependent

#

2a+b=0

#

2a=-b

#

2a+(-2a)=0

#

0=0

tacit scarab
#

oh

#

mb

#

I meant to write dependent

#

why are you solving for A and B and C though

spark wasp
#

to see if you can get it interms of x y and z

tacit scarab
#

the span might not contain them

spark wasp
#

thats how to find the span

spark wasp
tacit scarab
#

it only works if the vectors span the whole space?

#

I think

spark wasp
#

so what do we do when it isnt

tacit scarab
#

how are you taught?

spark wasp
#

using this method

#

we havent covered

#

matrix and stuff

#

this is like the second lesson

#

we also have to say if its a plane

#

or a line

tacit scarab
spark wasp
#

to tell if its a line or plane we see eif its a multiple

spark wasp
#

in this situation

#

do you want to see my notes?

tacit scarab
#

find the maximum linear independent set of vectors

tacit scarab
#

you want to prove there are only trivial solution of ax+by=0

#

it comes down to simultaneous equations

spark wasp
tacit scarab
#

,rotate

warm shaleBOT
spark wasp
tacit scarab
#

I see

spark wasp
warm shaleBOT
spark wasp
tacit scarab
#

lol

#

so you know how to prove lienar independence

spark wasp
#

yea

tacit scarab
#

ok

#

find a linearly independent set of vectors

#

the dimension equals the number of remaining vectors

tacit scarab
# spark wasp

in your question the span is 2 dimensional for 3 dimensional vectors

#

so it's a plane in R3

spark wasp
#

how can i do that

#

when the vectors are dependent

tacit scarab
#

so you have 3 vectors x,y,z

spark wasp
#

yea

#

but one vector is a combination of the others

tacit scarab
#

yes

#

so pick any one of the vectors

#

and just remove it from the set

spark wasp
#

wdym

tacit scarab
#

repeat until you have a linearly independent set

spark wasp
#

could you provide an example

tacit scarab
#

let's say we have vectors [1,1] and [2,2]

spark wasp
#

ok

tacit scarab
#

obviously 2[1,1] = [2,2]

spark wasp
#

yea

#

so this is a line

#

not a plane

tacit scarab
#

let's choose [1,1] and remove it

#

we're left with [2,2]

spark wasp
#

ok

tacit scarab
#

so span([1,1],[2,2]) = span([2,2])

spark wasp
#

so we just solve for span of [2,2]?

#

x=2a y= 2B

tacit scarab
#

???

spark wasp
#

A[2,2] = [x,y]

tacit scarab
#

no

spark wasp
#

wdym no

tacit scarab
#

I don't get why you are doing tha

#

t

spark wasp
#

to see if we can get a in terns of x and y

#

x= 2a y=2a

spark wasp
#

but with [2,2] we know that it spans the entire R2

tacit scarab
#

R1

spark wasp
#

since we got a in terms of x

#

and a in terms of y

tacit scarab
#

I don't get what you're doing

spark wasp
#

Im doing what my prof is doing

tacit scarab
#

but if you get a linearly independent set, then the dimension of the span is the number of vectors in the set

spark wasp
tacit scarab
#

what's the point of it though

#

you should solve a[2,2]=[0,0]

#

to prove its linear independence

spark wasp
tacit scarab
#

it tells us the dimension of its span

spark wasp
#

how does knowing if its linear independence

#

show u its span

tacit scarab
#

the span is just ax+by+cz

#

but I thought you needed its dimension?

spark wasp
tacit scarab
spark wasp
#

man why is this so confusing

tacit scarab
#

idk man

#

ok let's organize everything

#

span(v1,v2,...,vn) = {a1v1+a2v2+...+anvn}

#

if the set of vectors are dependent, we can remove any from the set and have the same span

#

if v1,v2,v3 are dependent

#

then span(v1,v2,v3)=span(v1,v2)=span(v1,v3)=span(v2,v3)

#

once you have a independent set, the dimension of span = remaining vectors

spark wasp
#

how will it be the same

#

if depedent means the coeff is not all 0

#

for the vectors

tacit scarab
#

if a set is dependent, then any one of its vector can be written as linear combination of other vectors

#

say we have x = [1,1] and y = [2,2]

#

y=2x

#

span(x,y)={ax+by}={ax+2bx}={(a+2b)x}=span(x)

#

or geometrically

#

the vectors pointing at the same direction and thus describe the same line

tacit scarab
#

even if you remove 1 vector they still represent the same line

#

or thinking it backwards

#

if you add 1 vector on an already existing line you don't get more dimension

#

it's still the same line

spark wasp
#

where did u get y =2x

tacit scarab
#

[2,2]=2[1,1]

spark wasp
tacit scarab
#

?

spark wasp
tacit scarab
#

we are literally saying the same thing

spark wasp
#

so

#

i get this part now

#

now how can you tell if each other are indepdent or depdent

#

because i only know how to tell if the whole set is linearly independent

spark wasp
#

lets say

#

we remove

#

1 vector

#

span(v1,v2)

#

now we see if this is independent?

tacit scarab
#

yes

#

remove until independent

spark wasp
#

and that is also

#

dependent

tacit scarab
#

what's v1 and v2

spark wasp
#

[2,1,2],[1,0,1]

#

now we remove 1 vector

#

[2,1,2] is also dependent

#

so what do we do now

spark wasp
tacit scarab
#

no

spark wasp
#

but

#

v1 v2 v3 how are u gonna figure if that is independent

#

or depdent

#

since u get 0=0

tacit scarab
#

?

#

set av1+bv2+cv3=0

spark wasp
#

2a+b=0
a+c =0
2a+b=0

tacit scarab
#

and look for non trivial solutions

spark wasp
#

2a = -b

#

-b+b =0

#

0=0

#

-2a=b

#

2a-2a=0

#

0=0

#

a+c =0

#

so u cant do anything

tacit scarab
#

???

#

why you doing -b+b and 2a-2a

#

b=-2a

#

c=-a

spark wasp
#

b=2c

tacit scarab
#

thus we have solutions av1-2av2-av3=0

spark wasp
#

uh what?

spark wasp
tacit scarab
#

a+c=0 so c=-a