#help-36

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tranquil pine
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thanks man

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or shoudl i do cases

tranquil pine
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U just have to do it

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tranquil pine
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quiet garden
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quiet garden
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how u do this

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@quiet garden Has your question been resolved?

vernal fiber
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Because otherwise you would have to do a line integral for each segment

cursive bough
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pretty ugly for a green's theorem problem, I think it would suck either way lol

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but green's is easier i agree

vernal fiber
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Yeah but that's just the bounds at that point that are tedious

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wind flame
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.reopen

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i need help, i have a revision sheet but there is no answer key. i am wanting to know if my answers are correct.

wind flame
soft zealotBOT
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γ‚―γƒΌγƒͺγƒΌ

wind flame
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wdym? in which question and which statement?

hasty mist
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This here

wind flame
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opposite angles of a parallelogram are congruent

hasty mist
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Should be fine

wind flame
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im sorry if i annoy you, im gradually doing the worksheet so im gonna be sending stuff every few minute.

hasty mist
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Okay

wind flame
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naive wyvern
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I need help: (2π‘₯+1)(3π‘₯βˆ’6)=πŸ‘(πŸπ’™+𝟏)(π’™βˆ’πŸ) shouldn't the 3 go next to (x-2) instead of at the start? dosen't that change the value of the equation?

tired walrus
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multiplication is commutative

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so $(2x+1) \cdot 3 \cdot (x-2)$ and $3 \cdot (2x+1) \cdot (x-2)$ are one and the same anyway

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the 3 has no special emotional attachment to specifically the (x-2) bracket!

naive wyvern
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ohhh

worldly spruce
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Funny introducing cotangent

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πŸ˜‚

tired walrus
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oh\

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ffs typo

naive wyvern
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i understand now

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thank you : D

soft zealotBOT
tired walrus
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there we go

worldly spruce
naive wyvern
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okay so this makes sense but i do still need some help with something

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so the next exercise after is

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solve E=0

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e was the equation that was above

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so

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πŸ‘(πŸπ’™+𝟏)(π’™βˆ’πŸ)

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but

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on the correction it says

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(2π‘₯ +1)(π‘₯ βˆ’2) = 0

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so im a little confused lol

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maybe it was on the test like that

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and i didn't see it

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worthy radish
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Why does this person put -1 in brackets?

final saddleBOT
worthy radish
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What would it mean without brackets?

severe canyon
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Again??????

rich mesa
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Did you just ask the same question in a different channel?

rich mesa
worthy radish
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Instead of 5+-5?

rich mesa
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yes

worthy radish
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,w 5+(-5)

worthy radish
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,w 5+-5

worthy radish
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Alr

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Ty

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.close

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lethal drum
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lethal drum
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hi

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am stuck with this question

trail mango
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i can help

chilly pollen
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Try simplifying B a little @lethal drum using row operations

trail mango
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good idea

chilly pollen
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Taking the determinant directly would be painful ded

lethal drum
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if so then after changing the columns am stuck there, do we take every single number outside as cofactor since theyre similar in all the rows or what do even do

chilly pollen
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So really it won't be too much and you possibly get a neat relation

lethal drum
chilly pollen
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Try making each element one term

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Instead of regular echelon form

lethal drum
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element one term?

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element as in letter?

chilly pollen
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Element as in the entry in a row and column

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Like b 1,1 and so on

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Like a cell in a table

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Term as in a letter

lethal drum
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so 1 letter and 1 number?

chilly pollen
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Like each cellular block with one letter

shadow pewter
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Please i need help about this topic. Logarithm

chilly pollen
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!occupied @shadow pewter

final saddleBOT
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Someone else is already using this help channel. If you need help with a question, please open your own help channel/thread (see #❓how-to-get-help for instructions).

lethal drum
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but then it gets too complicated

chilly pollen
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Try going systematically

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Eliminate one variable at a time

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Also it suffices to do it for only one column @lethal drum

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Because of symmetricity

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meager hamlet
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should i memorize this

final saddleBOT
meager hamlet
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or am i better off conceputalizing this somehow

storm haven
worthy radish
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UwU

meager hamlet
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cuz rn i see some paterns but dont understand how it all corelates

storm haven
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Right?

meager hamlet
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yes

storm haven
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We know that when the derivative of a function is 0, that function is at an extrema right?

meager hamlet
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yep

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so like f'(x) = 0 f(x) has rel min or max

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u mean that right?

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ok perfect

storm haven
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So F''(x) = 0
F'(x) has a rel min or max

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Right?

loud sundial
storm haven
meager hamlet
storm haven
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And by definition, when f'' = 0, that's an inflection point catthumbsup

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That's for the first row

meager hamlet
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and potential inflection point

storm haven
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But if they said f'' = 0, NOT undefined, then it would be certain catthumbsup

meager hamlet
storm haven
meager hamlet
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and when f''(x) = 0 theres defo inflection/rel min/max

storm haven
meager hamlet
crystal schooner
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To add onto that, for an abs function, it is not differentiable at zero due to a "cusp" (Sharp point)

meager hamlet
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wait and then i think the bottom 2 clicked for me

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when f''(x) crosses the x axis, it measn theres a point of inflection, and then building off of previous knowlegde that when f'(x) changes from pos to neg f(x) has rel max so same thing is applied for f''(x) and f'(x)

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explanation might be not so good kekw

storm haven
storm haven
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For the F'' > or < 0, by definition F is concave up or concave down

meager hamlet
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so just memorize that?

storm haven
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I don't think you could put any intuition on that, cause that's literally the definition of concaveness!

storm haven
meager hamlet
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okay thats pretty easy to memorize thankfully

storm haven
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But, for F' u can use intuition

meager hamlet
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f''(x)>0 --> f'(x) is increasing

storm haven
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When a functions derivative is positive, then that functiin is increasing

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And F'' is the derivative of F'

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And that's it for your whole table catthumbsup
Simple wasn't it?? happy

meager hamlet
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yesss

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rly appriciate the help

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u explained it rly rly well happy

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.close

final saddleBOT
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meager hamlet
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when putting this table all together now

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i get something like this

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.reopen

final saddleBOT
meager hamlet
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if its asking about something different i can change the f into like f' and determine different stuff right?

pliant shore
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though if f'(x) has a point of inflection, that would be setting the 3rd derivative to zero, so the function better be easy to differentiate

crystal schooner
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i'd say that's fair game also

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This question is also nicer too. It already gave you the 1st derivative. So you need to take the derivative of that to determine concavity and/or inflection points of g(x)

meager hamlet
meager hamlet
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shouldnt expect nice questions on exam sadly

crystal schooner
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This may be different for you, but my exam for calculus (Assuming its hs math) was really straightforward. All the questions on the exam were questions that I have seen. Exams questions tend to be easier than tests.

pliant shore
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I think your teacher wants to test how well you know properties of graphs

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they're not going to have any crazy differentiations beyond the product rule, quotient rule, chain rule as you've seen before

meager hamlet
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yes most likely

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one more thing before i call it a day

meager hamlet
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u do (x^2+3)^3 = 0

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x^2 + 3 = 0

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x^2 = -3

pliant shore
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yep, and that's impossible for all real numbers

meager hamlet
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and then since that would give imaginary numbers there is no value?

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ok i see

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if it were to give real numbers

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then id use those in the table?

pliant shore
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or actually, wait you do for some instances

crystal schooner
pliant shore
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cause if you changed (x^2 + 3)^2 to (x^2 - 4)^2 for example

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the sign of that doesn't change: it's always 0 or positive

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but if you had (x^2 - 4)^3 instead, the sign of that changes

pliant shore
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the sign of that doesn't change, so you don't need to make a column for it in your sign diagram table

meager hamlet
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oh bc its always positive?

pliant shore
soft zealotBOT
pliant shore
meager hamlet
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okay i understand it now

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thanks for explaining

pliant shore
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no worries!

meager hamlet
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time to learn second derivative rule kekw

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ill be back if i have any questions

pliant shore
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good luck!

meager hamlet
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.close

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meager hamlet
#

this is just using second deriv rule

final saddleBOT
meager hamlet
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do i need to know my unit circle to find 7Ο€/6

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and 11Ο€/6

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or is there a way to find that by hand

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i normaly use the table method when it comes to trig

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but idk if i can use that here

vital crag
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,tex .reflect trig

soft zealotBOT
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riemann

vital crag
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Or maybe just

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,tex .sum diff trig

soft zealotBOT
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riemann

barren hound
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using a unit circle (even a small sketch of one) will far and away be the fastest way to find sin 7Ο€/6

vital crag
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With theta=Ο€

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Oh terminal or coterminal angles

warm python
meager hamlet
barren hound
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yes

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well at least memorising Ο€/6, Ο€/3, and Ο€/4

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and then you can kinda work with it from there

meager hamlet
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yea okay ill memorize it ig

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while im here... i have a question abt 2nd deriv test

barren hound
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for 7Ο€/6 for instance i'd scribble something like this

crystal schooner
meager hamlet
meager hamlet
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the midterm isnt till another month so i have time to learn that ig

soft zealotBOT
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riemann

crystal schooner
meager hamlet
# barren hound yup

okay i was confused cuz i didn't realize im meant to test all critical values

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so basically i can use 2nd deriv test any time?

barren hound
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the second derivative test says that if f ' (a) = 0, then:

  • if f '' (a) > 0 -> f has a relative minimum at a
  • if f '' (a) < 0 -> f has a relative maximum at a
  • if f '' (a) = 0 -> f has neither a relative minimum nor maximum at a (for example, x^3 at 0)
meager hamlet
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dumb question kekw but my brain is totaly fried today

barren hound
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ummmm i'm not sure what your question is. you can set f ' (x) = 0 by.... setting f ' (x) = 0

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like if f(x) = sinx + x^2

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then f ' (x) = cosx + 2x

crystal schooner
meager hamlet
meager hamlet
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ill need to do some practic e

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thanks for the help guys

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ive been studying since 9am and now its almost 2am i think im gonna call it a day today πŸ˜…

crystal schooner
barren hound
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oh actually i slightly misspoke --- if f ' ' (x) = 0 then it's inconclusive (e.g. x^4 at 0)

final saddleBOT
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@meager hamlet Has your question been resolved?

meager hamlet
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one tiny thing more

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when it says f"(x) is >0 it means above x axis right?

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and when f"(x)<0 it's bellow x axis

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or am i meant to look at the slopes

final saddleBOT
#

@meager hamlet Has your question been resolved?

formal trail
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means above x axis
means what is above the x axis? f(x), f'(x) or f''(x)?

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slate narwhal
#

?

scarlet lantern
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I think i may have done something wrong I'm not so sure

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so I'm checking over it again

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wooden marsh
#

In the figure, the curve y = 7 - x^2 A rectangle is drawn under the curve in the first quadrant according to the figure. Determine the largest value that the area of ​​the rectangle can take.

wooden marsh
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I got quite far but ended up doing something wrong idk what

leaden moon
wooden marsh
wooden marsh
viral jungle
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,rccw

soft zealotBOT
leaden moon
wooden marsh
#

Can someone rotate it

leaden moon
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,rccw

soft zealotBOT
wooden marsh
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Thanks

leaden moon
wooden marsh
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Oh alright

leaden moon
wooden marsh
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That’s nice

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Where did I go wrong

final saddleBOT
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@wooden marsh Has your question been resolved?

wooden marsh
#

<@&286206848099549185>

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Nvm

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.close

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worthy radish
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worthy radish
#

Really is the vertex (3,-11)?

severe canyon
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!1c

final saddleBOT
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Please stick to your channel.

severe canyon
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Why do you always open another channel immediately after closing the previous????

worthy radish
#

Stop it

severe canyon
worthy radish
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…

severe canyon
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If it is "because I have a question on another topic" you could have just said this and everything would be fine

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Instead, you chose to say "stop it" to a helper...
Why?

final tangle
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Different question, no multiple channel flag by the bot so it's fine unless I'm missing something

tired walrus
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the original question seems to be missing

severe canyon
tired walrus
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but judging by the a=1, b=-6, c=-2: did it ask to graph y = x^2 - 6x - 2?

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@worthy radish

severe canyon
tired walrus
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in this case yes, (3, -11) really is the vertex.

worthy radish
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It’s so weird that it is -11

worthy radish
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I’m not idiotic.

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.close

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severe canyon
severe canyon
worthy radish
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Ann always thinks so.

tired walrus
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nice mind-read

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if only it wasn't 100% wrong...

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just to be absolutely clear here: no, nenni, i do not consider you "idiotic" or anything similar.

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rustic light
#

Let V be an euclidean space with inner product <.,.> and T:V->V a linear operator
Show that if T is self-adjoint, then every eigenvalue Ξ» of T is real.

This question was given to us as an exercise by the professor, but I believe it to be misplaced and I need some conceptual clearing.
So far we have only been working with real inner product spaces, I'm aware of other definitions for complex spaces but that has not been mentioned yet.
Then the proof would be trivial because V is an euclidean space and from the definition of eigenvalue, Ξ» is in R. Am I missing something?

rustic light
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The fact that T is self-adjoint does not even seem to matter here

vital crag
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You use definition of self adjoint and axioms/properties of vector spaces

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Do you have a list of axioms for euclidean space

rustic light
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a vector space with an inner product (in this case the real inner product that we have been working with)

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that is the definition he gave

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of what an euclidean space is

vital crag
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Do you have properties of the inner product

rustic light
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The axioms?

vital crag
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Sure

rustic light
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<,>:V X V -> R
i) <v, v> >=0, and =0 iff v=0
ii)<u, v>=<v, u>
iii)<u,v+w>=<u,v>+<u,w>
iv)<ku,v>=k<u,v> with k being a scalar in R

gritty drift
#

You might be missing an important property (definition?) of hermitian operators:
If T hermitian, then <a, T(b)> = <T(b), a>

rustic light
#

if it meets those properties then it's a real inner product

desert mantle
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just treat the exercise as if you had a complex inner product

rustic light
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That hasn't been introduced yet, that's the problem

vital crag
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Yea idk how to do this without<u, v> = <v, u>*

gritty drift
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You need to know inner product space properties for complex IPs to disprove that it is complex... If you haven't covered complex IPs yet, how can you prove an eigenvalue is "real"?

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Like if we don't know what an complex number is, what other than "a real number" can a constant value be

rustic light
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Yes that's exactly what I said, I was just asking for guidance. I wasn't sure if I was missing something or not. But I guess the question was actually just misplaced

gritty drift
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Its a standard question if you can use properties like <cu, v> = c* <u, v> but you can't really disprove c being complex if you can't define a complex number

hasty mist
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Sloppy

rustic light
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So is it correct to say that the proof is trivial? That is basically what I want to know

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Following those definitions

vital crag
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Depends what you consider trivial

gritty drift
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I mean you can't wave your hand and say it's trivial lmao but it's not a super hard proof with the requisite tools

vital crag
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That's a subjective word

rustic light
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I have an uneasy feeling that I am missing something
since V is a vector space over the reals, then any eigenvalue of T:V->V must belong to the reals
But I was thinking about something like the 90ΒΊ rotation transformation from R^2 to R^2, doesn't that have complex eigenvalues?

gritty drift
#

You only guarentee real e-vals for a hermitian operator, otherwise its free game

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Here's the setup for the evals of a Hermitian are real proof (I gave this in a tutorial recently so I have it typed up nicely). Notice how we assume lambda is a complex number

vital crag
rustic light
# gritty drift You only guarentee real e-vals for a hermitian operator, otherwise its free game

Alright, so I tried writing this down:

<Tv, v>=<Ξ»v, v>=Ξ»<v,v>
then Ξ»=<Tv, v>/<v,v>
Since we're working with real inner product spaces then the numerator and denominator are both real, and <v,v> isn't 0 because v is not zero
This seems to imply that any transformation with a real inner product only has real eigenvalues, but that can't be true. So what is incorrect about this?
The fact that T is self adjoint should come into play somehow but I don't know how

gritty drift
#

Okay...

#

There's nothing stopping lambda from being a complex number, that's why the general case fails

#

Now if T is hermitian you can do the switcharoo <Tv, v> = <v, Tv>

gritty drift
#

This will imply Ξ» = Ξ»*...

rustic light
#

isn't that the definition of an eigenvalue? λ∈F is an eigenvalue of T if there exists v in V, vβ‰ 0, such that T(v)=Ξ»v

gritty drift
#

Who says V is a real VS?

rustic light
#

Are euclidean vector spaces not spaces over the reals?

gritty drift
#

Oh alright... that makes your question poorly phrased. Your prof (or you during transcription) probably misspoke/miswrote

#

Let V be an euclidean space with inner product <.,.> and T:V->V a linear operator
Show that if T is self-adjoint, then every eigenvalue Ξ» of T is real.

.... Assuming euclidean means "real VS" is an idempotent statement, it's like saying "If we get the real roots of any polynomial, they'll all be real"

rustic light
#

Yea thats why I asked if I could just say the proof is trivial lol

#

Sorry I might have not been explaining myself very clearly because I am a little confused about this

gritty drift
#

I mean in the way you state it sure, but I'm like 95% sure your prof meant:

Let V be ANY vector space with inner product <.,.> and T:V->V a linear operator
Show that if T is self-adjoint, then every eigenvalue Ξ» of T is real.

rustic light
#

Yes I see. Now I wanna go back to the other question that I had about the 90Β° transformation from R^2 to R^2

#

"A Euclidean vector space is a finite-dimensional inner product space over the real numbers." This is basically the definition of euclidean vector space that we are using

#

So R^2 is an euclidean vector space right?

rustic light
gritty drift
#

R^2 is a euclidean VS if you go by the word-for-word definition, but we usually work in C^2 under the hood

rustic light
#

I see. So if I'm working extrictly in R^n then that transformation does not have eigenvalues or eigenvectors yes?

gritty drift
#

Like your rotations and stuff all happen in C^2, we just typically chose matrices that happen to be R^2, so we don't notice

#

Exactly

#

You can't define them cause they're complex

#

But we usually want to define them, so we work in C^2 even if our matrices are all real

rustic light
#

Basically the trivial "question" could be rephrased to something like: if T has an eigenvalue then it is real.
So it does not fail because in this case it doesn't have an eigenvalue since we are in R2

gritty drift
#

Exactly

#

We don't even need T to be hermitian in that construction, it's like saying "all real numbers are real"

rustic light
#

Yes I see. Thank you.
Unfortunately this isn't the first mistake that I have encountered in this course, it isn't uncommon for this professor. Really makes the learning process way more confusing. Makes me a little sad

#

Thanks for the help

#

.close

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worthy radish
final saddleBOT
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Please don't occupy multiple help channels.

worthy radish
#

Do I have to do 1/3*3/2 etc?

tired walrus
#

if you are simplifying this by first turning it into $(a^{1/3})^{3/2} \cdot (b^{1/2})^{3/2}$ then yes, the exponents multiply together.

soft zealotBOT
worthy radish
#

Ok b

#

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soft pewter
#

Two devices, located at points A and B, pull with forces of 720 N and 810 N respectively in order to lift a load vertically to a height of 3.5 m.

If the work W (in J) is defined as the dot product of the force \vec{f} (in N) acting on an object and the displacement \vec{d} (in m) of that object, that is,

W = \vec{f} \cdot \vec{d},

what is the work done by the resultant force acting on the load?

soft pewter
#

cos 63 = a/810 = 367,63

#

sin 63 = b/810 = 721,71

#

(367,63;721,71)

#

cos 27 = a/720 = 641,52

#

sin 27 = b/720 = 326,87

#

(641,52;326,87)

#

do i multiply these components or do i add them

#

i dont understand why i have to add them when in my book it says when u want to do scalar product of composants u multiply them

#

<@&286206848099549185>

#

.close

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noble stone
#

sine of both to get the upwards components, since the side opposite (as opposed to adjacent with cosine) the angle is vertical
add them to get the total upwards force
work is force times displacement
i'm not french but it seems to be lifted by 3.5 meters?
so multiply the displacement by the sum of forces
i haven't done physics problems in a while but that's what i'd do

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distant scarab
#

if we have a prime number "q" that is 1024 bit and another large number "a" (1020-1024 bit) number that we want to check if its Quadratic residue , using Legendre symbole
we need to compute a ^ (p-1)/2 which is kinda impossbile , is there another way to find if our number is Quadratic residue

distant scarab
#

i.e q = 25081841204695904475894082974192007718642931811040324543182130088804239047149283334700530600468528298920930150221871666297194395061462592781551275161695411167049544771049769000895119729307495913024360169904315078028798025169985966732789207320203861858234048872508633514498384390497048416012928086480326832803

and
a = 45471765180330439060504647480621449634904192839383897212809808339619841633826534856109999027962620381874878086991125854247108359699799913776917227058286090426484548349388138935504299609200377899052716663351188664096302672712078508601311725863678223874157861163196340391008634419348573975841578359355931590555

trail mango
#

not claiming there isn’t a better way, but doesn’t seem impossible to compute that mod q

distant scarab
#

how would u compute it

trail mango
#

let me get on my computer for this one

hasty mist
#

Bruh

trail mango
#

do you have a way to check it?

#

i got 12198191382510180130171785779099635405775646886012417221562882673911806474606622930917413991202999512582284613332305654295896813876410078041259926827289489544738064234567425318685278617664636888180070131538546281599196217240157921967978943264140230808292994118880960193709071196232722730098178814120258104487

hasty mist
#

Hm one sec

trail mango
#

when you think it's impossible i think you are just underestimating how fast exponentiation can be

distant scarab
#

i mean it should be {0,1,-1}

trail mango
#

the value of a^(q-1)/2 (mod q)

distant scarab
hasty mist
#

I got 1

distant scarab
bleak jay
#

a = 45471765180330439060504647480621449634904192839383897212809808339619841633826534856109999027962620381874878086991125854247108359699799913776917227058286090426484548349388138935504299609200377899052716663351188664096302672712078508601311725863678223874157861163196340391008634419348573975841578359355931590555
q = 25081841204695904475894082974192007718642931811040324543182130088804239047149283334700530600468528298920930150221871666297194395061462592781551275161695411167049544771049769000895119729307495913024360169904315078028798025169985966732789207320203861858234048872508633514498384390497048416012928086480326832803

Calculate (q-1)/2

exp = (q - 1) // 2

Compute a^(exp) mod q using python's built-in modular expo.

result = pow(a, exp, q)

Output the result

print(result)

#

i ran this code on python

#

and it crashed

#

gg

trail mango
#

that's quite the code

bleak jay
#

i dont have python configured on this scrap

#

that's the issue

#

so

#

somebody run this

distant scarab
hasty mist
trail mango
bleak jay
#

yeah im gonna gts

hasty mist
bleak jay
#

goodnight 9993sob_damn

hasty mist
bleak jay
distant scarab
#

yeah id sleep too

hasty mist
bleak jay
candid hull
trail mango
#

is q prime

hasty mist
#

Bruh

trail mango
#

sagemath says it is not

hasty mist
#

It’s not

trail mango
hasty mist
#

Oh well

#

The code works

#

At the end of the day, it’s the end of the day.

trail mango
#

undeniable fact

hasty mist
#

Can we please get me helpful already

trail mango
#

same

hasty mist
#

I think OP is actually gone.

trail mango
#

anyway you can compute these pretty simply in sage.

a = 3
q = 7
R = Integers(q)
x = R(a)^((q-1)/2)```
#

it works fine with big boi numbers

#

exponentiation is FAST

#

there's even a built in legendre symbol function too

#

but just wanted to show exponentiation is fast

hasty mist
#

oily_flapjacks

candid hull
#

too much oil for oiler

hasty mist
trail mango
#

euler would not have been able to compute a ^ (q-1)/2 (mod q) here

hasty mist
#

only oily

#

@distant scarab

#

Does that answer your question?

final saddleBOT
#

@distant scarab Has your question been resolved?

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tranquil lake
#

even odd decomposition is pretty cool. but I want to understand how the equations get derived

I get the algebra basics of even vs odd, but I want to understand this follow up

bleak granite
# tranquil lake even odd decomposition is pretty cool. but I want to understand how the equation...

A function (f(x)) is called even" if and only if \(f(-x)=f(x)\iff f(x)-f(-x)=0\). Also a function \(f(x)\) is called odd" if and only if (f(-x)=-f(x)\iff f(x)+f(-x)=0).

In general if we have some function, take (f(x)) again, then we can construct another function (O(x)=\frac{f(x)-f(-x)}{2}) which will always be odd. This comes right from the idea that (f(x)-f(-x)) encodes oddness. Simiarly, define (E(x)=\frac{f(x)+f(-x)}{2}) which will always be even. If you add them then you get back the original function (f(x)=E(x)+O(x)).

As a side note, if (f(x)=e^x) we can actually get the functions (\sinh(x)) and (\cosh(x)) in this way, but that is by definition of those latter functions.

soft zealotBOT
#

Ξ Ξ±Ο³Ξ±ΞΌΞ±ΞœΞ±ΞΌΞ±Ξ›Ξ»Ξ±ΞΌΞ±

tranquil lake
#

so sinh(x) is the odd signal from e^x

bleak granite
#

oh whoops I flipped the order catgiggle but the idea still stands

formal trail
#

similarly you also get cos(x) and i sin(x) by applying to e^(ix)

tranquil lake
#

woah

#

Is there a calculus-y way for finding that E(x) = f(x) + f(-x) / 2

#

Like how did they get it in the first place

formal trail
#

you can think of it via the taylor series

#

taking f(-x) keeps all the even terms the same and flips the signs of all the odd terms

#

so taking the taylor series of f(x) + f(-x) , all the even terms add up (so now they are doubled) and all the odd terms cancel

tranquil lake
bleak granite
#

higher's taylor explanation is another good justification

formal trail
bleak granite
#

perhaps less ad hoc than mine

tranquil lake
#

I saw that
1/2 ( f(x) + f(-x)+ 1/2 (f(x) - f(-x)) easily simplifies to f(x)
since 1/2 f(-x) - 1/2 f(-x) = 0

#

and 1/2 (f(x) + 1/2 (f(x) = f(x)

tranquil lake
opaque ember
formal trail
#

,, e^x = \frac{x^0}{0!} + \frac{x^1}{1!} + \frac{x^2}{2!} + \frac{x^3}{3!} + \frac{x^4}{4!} + \frac{x^5}{5!} + \cdots \
e^{-x} = \frac{x^0}{0!} - \frac{x^1}{1!} + \frac{x^2}{2!} - \frac{x^3}{3!} + \frac{x^4}{4!} - \frac{x^5}{5!} + \cdots \
\cosh x = \frac{x^0}{0!} + \frac{x^2}{2!} + \frac{x^4}{4!} + \cdots \
\sinh x = \frac{x^1}{1!} + \frac{x^3}{3!} + \frac{x^5}{5!} + \cdots \
\begin{multlined}
e^x + e^{-x} = \ab(\frac{x^0}{0!} + \frac{x^1}{1!} + \frac{x^2}{2!} + \frac{x^3}{3!} + \frac{x^4}{4!} + \frac{x^5}{5!} + \cdots) \ + \ab (\frac{x^0}{0!} - \frac{x^1}{1!} + \frac{x^2}{2!} - \frac{x^3}{3!} + \frac{x^4}{4!} - \frac{x^5}{5!} + \cdots) \ = 2\frac{x^0}{0!} + 2\frac{x^2}{2!} + 2\frac{x^4}{4!} + \cdots = 2\cosh x
\end{multlined} \
\begin{multlined}
e^x - e^{-x} = \ab(\frac{x^0}{0!} + \frac{x^1}{1!} + \frac{x^2}{2!} + \frac{x^3}{3!} + \frac{x^4}{4!} + \frac{x^5}{5!} + \cdots) \- \ab(\frac{x^0}{0!} - \frac{x^1}{1!} + \frac{x^2}{2!} - \frac{x^3}{3!} + \frac{x^4}{4!} - \frac{x^5}{5!} + \cdots) \= 2\frac{x^1}{1!} + 2\frac{x^3}{3!} + 2\frac{x^5}{5!} + \cdots = 2\sinh x
\end{multlined}

soft zealotBOT
#

cloud ☁

opaque ember
#

big tex whiplash

formal trail
#

i just wrote out the algebra for e^x but the same arithmetic would apply to any taylor series

tranquil lake
#

oooh that makes it more clear

#

thank you both

hasty mist
#

Anytime

tranquil lake
#

(In the mean time I was watching 3b1b to remind myself of Taylor series since my calc class only briefly brought them up and I haven't used one in a few months)

#

.close thank you all!!

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late spoke
final saddleBOT
late spoke
#

CAN SOMEONE HELP ME WITH THIS MATH QUESTION PLZ?

proper dagger
#

,rccw

soft zealotBOT
late spoke
#

Huh....?

rugged merlin
proper dagger
late spoke
#

I really just don't understand

#

I don't know what it's asking if me

#

Of*

proper dagger
#

what is the topic being tested here

late spoke
#

Algebra

proper dagger
#

and what are the other questions like?

#

well yea it's algebra alright, but what topic in algebra? reasoning? modelling?

#

also, again, what are the other questions like?

late spoke
#

(don't mind the other stuff) but this is the rest of the paper

proper dagger
#

knowing how the other questions sound like can help us gauge the intention

#

,rcw

soft zealotBOT
proper dagger
#

so from my understanding you're being asked to say if it is a valid statement to make

late spoke
#

But like i don't get the equation

#

And I don't know what x is

rugged merlin
proper dagger
#

can you use algebra to find one value of x? are there any others?

late spoke
#

My teacher just started teaching us of algebra a week ago

#

but

#

I'll try the equation again

rugged merlin
#

An example might do you well here.

late spoke
#

No T w T

proper dagger
#

have you learnt about equation balancing then?

late spoke
#

No

proper dagger
#

right

#

suppose we have x + 5 = 7.

#

we wanna know what x is.

late spoke
#

X would be two then

proper dagger
#

good, but how did you get to that conclusion?

late spoke
#

Cuz 7 - 5 is 2

proper dagger
#

and what gave you the right to subtract 5?

#

the steps are more important than the answer here

rugged merlin
#

Take the equation [
3x - 5 = 10
]
Our first step is to isolate the $3x$ on one side of the equation. To do so, you can add 5 to both sides:
[
3x-5\0b{{}+5} =10 \0b{{}+5} \Implies 3x = 15
]

proper dagger
#

you missed a 10 somewhere

soft zealotBOT
rugged merlin
#

Yeah fixed

proper dagger
#

OP, pay attention to this very step

#

note that in algebra, if you do something to one side, you must do it to both

#

this is the step I was testing you about

late spoke
proper dagger
#

you are correct in this simple case

#

but suppose you have x + 5 = 6x instead

#

now you cannot simply eyeball a solution

#

this is where equation balancing (aka the "do to one side = do to both" principle) comes into play

late spoke
#

My teacher told me a method of finding an answer is guess and check

proper dagger
#

oh nonononono.

late spoke
#

I'm scared-

proper dagger
#

you don't have the luxury of taking 10 years per question

#

and come on. there IS a better method - algebra!

#

you learn algebra precisely so that you don't have to do it by trial and error

#

ok so the basic idea in all of algebra is equation balancing

late spoke
#

Okay

proper dagger
#

which I've been drilling over and over here

#

now, why is this so important, you might ask

proper dagger
#

maybe you can eyeball a solution directly. maybe you can't. but we don't care because we don't need to guess.

#

we can simply isolate x (that is, turn the equation into x = something)

#

the first step is already shown here (adding 5 to both sides)

#

but you now have 3x on the left instead of x

late spoke
#

But how do I turn x into something if that something is not what x is supposed to be-

proper dagger
#

in fact, not could, but must

late spoke
#

Ohh

#

WAIT

#

SO IF I JUST TAKE AWAY X

#

AND DO THE REST OF THE EQUATION

#

THEN I COULD POTENTIALLY FIND OUT EHAT X IS

proper dagger
#

hold up, what are you thinking

late spoke
#

X*

proper dagger
#

show an example please

late spoke
#

So the question I'm stuck on

proper dagger
#

mhm

late spoke
#

3x +4= 7x

#

If I take away the x

proper dagger
#

7x*

late spoke
#

Oh yeah

#

Thank u

#

Wait

#

But what does 7x mean

proper dagger
#

ok consider the equation being phrased like this

#

I have three packets of money

late spoke
#

Okay

proper dagger
#

now, you give me $4

late spoke
#

Okay

proper dagger
#

with your money, I have an amount of money equivalent to seven packets of money

#

so x here represents the amount in one such packet of money

#

now, to solve this one, you'll have to bring the two x's to the same side of the equation

#

this is most easily done by subtracting 3x from both sides of the equation.
can you see why that works?

#

if this is confusing we can go back to Lex's example

late spoke
#

X IS 1

#

Oh my god

proper dagger
#

as I've mentioned, the steps are more important than the answer

late spoke
#

X IS ONE

#

CUZ CUZ

#

OKAY SO THE QUESTION IS

proper dagger
#

and no, I will not accept guess and check as a method

late spoke
#

3x +4 = 7x

#

SO

#

YK THE +4

#

JUST DO THAT

#

BUT LIKE YOU MENTIONED

#

MOVE TO THE OTHER SIDE

#

AND THIS MADE ME THINK BACK

proper dagger
#

you can chill off the caps lock lolz

late spoke
#

TO SMTH MY TEACHER SAID

#

sorry

proper dagger
#

nw

late spoke
#

And she said

proper dagger
#

continue

late spoke
#

You have to turn the operation into its opposite when you are placing it on the other side

proper dagger
#

do you know why that is the case?

#

this is important.

late spoke
#

Cuz your doing the equation backwards right

proper dagger
#

not... exactly

late spoke
#

Cuz like

#

Actually

#

I don't know if I can explain this

proper dagger
late spoke
#

Okay

proper dagger
#

why is it that you use the inverse operation when you move an operator and its operand to the other side?

late spoke
#

It's cuz your like

#

Doing the equation backwards, like you would in like for your example earlier x + 5 = 7

#

Me doing

proper dagger
#

doing the equation backwards may explain why we need to move stuff to the other side

#

but it does not explain why we use inverse operations

#

for example

late spoke
#

HOW DO I EXPLAIINNNN

proper dagger
#

x + 5 = 7, right?
why can't we say x = 7 + 5? why must it be x = 7 - 5?

#

if you can answer this one question, you are set for most of algebra

late spoke
#

Uhhh

#

Cuz when you say x = 7+5 then the original equation wouldn't make sense

proper dagger
#

how so

late spoke
#

The original equation is x+5 = 7

#

If you do x=5+7 then that's above 7

proper dagger
#

not too bad of an explanation but unfortunately I was looking for something more specific

late spoke
#

The answer is to the equation is SUPPOSED to be 7

proper dagger
#

in fact, the answer I'm looking for is exactly what you're doing when you "move" terms from one side to the other

#

right, I think enough beating around the bush

late spoke
#

Since the answer to the equation is supposed to be seven you can't ADD to seven

#

Then that wouldn't be the answer

proper dagger
#

that still doesn't cut to the heart of the problem

late spoke
#

I'm sorry

proper dagger
#

but it's ok, that's why we're here

late spoke
#

I would type in caps but you told me to cut back on that

proper dagger
#

the answer as to why you flip the operations / use the inverse operations when moving from one side to the other is because you are doing the same thing to both sides

#

suppose you want to know the answer to x + 5 = 7

#

you don't know that x = 2 beforehand and you dw to guess and check

#

but you know that if you manipulate the equation to say x = something, then you have the value of x for which the original equation works

#

now, that +5 is getting in the way of that at the moment

#

we would really want to remove the +5 so that the x stands alone

#

and what do we do to remove the +5? we subtract 5.

late spoke
#

Ohhh

proper dagger
#

but wait! equations are like a pair of balancing scales. if you do one thing to one side, it will now become unbalanced

late spoke
#

Ooooohhh

proper dagger
#

therefore, you balance it by subtracting 5 from the other side as well

#

but let's see what happens after that

late spoke
#

OOOHHH

#

Okay

proper dagger
#

and this is precisely why we "flip" the operations when moving it over to the other side

#

we are not actually flipping the operations per se

#

we are just doing the inverse of those operations so that the original and inverse operations on our chosen side cancel to leave x alone

#

but by doing so we also need to rebalance the equation by doing the same to the other side

late spoke
#

BRO

#

Just imagine I'm typing in caps okay?

proper dagger
#

this concept holds until you get into and past uni

#

remember this well

late spoke
#

Your so helpful omfg

#

You are scary aswell

#

Thank you so much

proper dagger
late spoke
#

I owe you my first born if that's how it works

proper dagger
#

no thank you LMAO

late spoke
#

Also I'm writing down your explanation in my notes

#

Yoink

proper dagger
#

here, my personal notes

late spoke
#

I'm crying your so nice

proper dagger
#

nps

late spoke
#

You have to be like a college professor

#

Also

#

what do you mean it holds up will uni

#

Till*

#

does it change in uni?

proper dagger
#

until you get into and past uni

#

this is a universal concept

#

it does not change

late spoke
#

Ohh okay

#

Again, thank you so much

#

I CAN GO TO SLEEP NOW

proper dagger
#

have a nice rest

#

!done btw

final saddleBOT
#

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late spoke
#

.close

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untold wagon
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untold wagon
#

I know the E[X] = 1/p

#

with the PMF defined as P(X=k) = p^(k-1) * p

#

what's an approach to calculate the variance tho?

#

Maybe there's a formula? But not sure how to derive it

rugged merlin
#

Yk

#

,, \Var[X] = \vb E[X^2] -\vb E^2[X]

untold wagon
#

Yes I know this property

soft zealotBOT
untold wagon
#

We already have E[X]^2

#

But we need E[X^2]

atomic moon
rugged merlin
#

Calculating that directly is difficult probably

#

Try doing E[X(X-1)] instead

sonic crystal
#

yakuuuuuuuuuuu

rugged merlin
#

You can then recover it by [
\vb E[X^2] = \vb E[X(X-1)] + \vb E[X]
]

soft zealotBOT
untold wagon
#

ok let me try it

#

thanks

#

.close

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rugged merlin
#

Are you from mg

untold wagon
#

hm

#

maybe...?

rugged merlin
#

So youre that chris

untold wagon
#

hmm

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marble vale
#

So, expanding a number is easy

4Β² = 4*4 = 16
But what if I need to go back from 16 to 4 and I don't know that 4Β² = 16? Is there a formula for that?

rugged merlin
#

Its called the square root function

#

It is the "inverse" of the squaring operation

#

,align
4^2 &= 16 \
\3{16} &= 4

soft zealotBOT
rugged merlin
#

As you dee the first line starts from 4 and gives you 16, the second line starts from 16 and gives you 4

marble vale
#

Sure
But what if I don't know that 16 = 4Β²? Putting a sign wouldn't help me

rugged merlin
#

But I mean, that's why the square root function exists

#

You dont have to know (although you should)

#

For example 29929 = 173^2

#

You probably did not know that but you dont need to

#

,w sqrt(29929)

rugged merlin
#

The square root function just tells you

marble vale
rugged merlin
#

Like you are asking how to compute a square root then, I guess?

marble vale
rugged merlin
#

It comes from knowing your squares, yes

rugged merlin
#

Like yeah I wouldnt know that sqrt(29929) = 173 either

marble vale
#

x Γ— x = 16
x = ?

marble vale
rugged merlin
marble vale
marble vale
rugged merlin
#

Oops wrong reply

lilac moat
#

Generally, we would write xΒ² = 16 instead of x Γ— x = 16

marble vale
rugged merlin
#

Well $x^4$ is in reality $(x^2)^2$ so I can work it out from that

#

^5 I wouldn't know at a glance

#

Unless its a power of 10

soft zealotBOT
marble vale
#

28,561

#

Can you work this out?

rugged merlin
#

no lol

#

Idk what that is

marble vale
#

I picked a number from 1 to 20 and put it in (xΒ²)Β²

rugged merlin
#

No sane teacher would expect you to either

marble vale
#

So, I should

Β² - from 1 to 20
Β³ - from 1 to 10
And then just say that's enough?

ornate knot
#

to find the sqrt of 28561

rugged merlin
#

To do that you should probably memorise those yes

#

Otherwise youd need to do work by noting down the prime factors of the number

marble vale
#

I see
Thank you guys

#

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boreal smelt
#

What should I do in this question?

final saddleBOT
desert mantle
#

probably split (t^2+5)^(n+1) as (t^2+5)^n * (t^2+5) and use ibp

boreal smelt
#

okayy

#

but I got tan inverse term in the integration

#

won't it be a problem ?

desert mantle
#

yeah thats not nice

#

maybe make 5 into parameter and differentiate

boreal smelt
#

I was trying to solve for n=1

#

but how do I integrate $I_2 = \int_{0}^{x} \frac{1}{(t^2 + 5)^2}$

soft zealotBOT
#

Prathmesh

left echo
#

Integration by parts works fine

#

Differentiate 1/(t^2 + 5)^n and integrate 1

#

You'll end up with $I_n = \frac{x}{(x^2 + 5)^n} + 2n \int_0^x \frac{t^2}{(t^2 + 5)^{n+1}}\dd{t}$

soft zealotBOT
#

jewels!

boreal smelt
#

I see

#

that's nice

left echo
#

Inside the integral do a + 5 - 5 and after a bit of moving things around you'll have what you need

boreal smelt
#

okayyy

#

lemme try

#

okayy thankssss

#

got it

#

option 1

#

.close

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tiny kraken
final saddleBOT
tiny kraken
#

Okay so, the question here is not exactly what I want to ask

#

But a slightly different version of it, what if we're allowed move diagonally to the left

#

Then how would I do the problem

left echo
#

How did you do it originally?

tiny kraken
#

Using pascal' triangle

#

No not really

glossy zephyr
#

oh no right mb you end up with 3 options per

tiny kraken
#

smth like this

left echo
#

Hmm

#

I'd have started bottom-up

woven ledge
# tiny kraken

maybe fill in each letter with the number of ways to get to it

tiny kraken
#

Oh no recussive

#

hmmcat Hmm

woven ledge
bold turtle
tiny kraken
bold turtle
#

And also, you should recognise what pattern you end up with if you do what CherryMan is suggesting

woven ledge
tiny kraken
bold turtle
#

Ah

#

You can still do the same thing

desert mantle
bold turtle
#

You're not really doing anything more complicated than adding three numbers together at a time, in order to generate the structure

tiny kraken
#

okay thanks y'll

#

.close

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#
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tiny kraken
#

I would love a method that can get me answer in a single calculation

#

That was what I looking for lol

bold turtle
#

That requires overgeneralisation, to an extent that it's like the "Bill Gates with a massive ping pong paddle" meme

desert mantle
#

well there is a solution to the recursion

tiny kraken
#

.reopen

final saddleBOT
desert mantle
#

but thats just overcomplicated

tiny kraken
#

Oh

#

Can you roughly tell what it is

desert mantle
#

all linear recursions are solvable

tiny kraken
#

Wait, so just solve the recursions ?

tiny kraken
#

.close kannawave

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tiny kraken
#

It would be great if someone can check my working of this problem

tiny kraken
#

So took the base case when all the diagonals are drawn from a vertex to others

#

Then I generated other cases by rotating one diagonal at the time

#

After n-3 rotations, all the diagonals should be drawn from the next vertex to others

#

Repeat this process n times

chilly pollen
#

Notice that we always have to choose two consecutive sides, for two of the triangles

#

@tiny kraken The remaining triangles always contain only one side of the polygon for an n-gon

desert mantle
#

one problem with your approach is that

  • its not clear that you indeed get every option
  • its not clear that you get every option exactly once
pliant shore
#

that's two problems, mr can't count /j

desert mantle
#

I'm a mathematician, of course I cant count

pliant shore
#

yeah counting is hard

#

that's why I don't dare answer

tiny kraken
desert mantle
#

dunno about wrong. but those things are certainly problematic and without addressing those its definitely not right

tiny kraken
chilly pollen
#

mb. Looked combinatorial

tiny kraken
#

if it's possible

#

you're right it is wrong thonkzoom

#

I'll deal with this problem tomorrow then, it's late here

#

Thank you all

tiny kraken
#

.close

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tiny kraken
#

Combinations is the next chapter

icy tulip
#

its ez

tiny kraken
#

I don't want to rely too much on the technique

#

I meant rely on combinations if that makes sense lol

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steady vale
#

hello! i was wondering if this is legal math

steady vale
#

i just wanna confirm that the way i did it is okay to do

loud sundial
#

looks fine other than that

#

continuity

steady vale
#

thanks so much!!

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crisp spade
final saddleBOT
crisp spade
#

In the computation of the curvature of this curve, why is the absolute value of the denominator taken?

#

Stupid question

#

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quiet garden
final saddleBOT
quiet garden
#

What I do wrong for b

gleaming spear
quiet garden
gleaming spear
#

Well you're not really done yet, still 1 step to do

quiet garden
#

What step

gleaming spear
#

The answer should be a number, but you have x and y

quiet garden
gleaming spear
#

||The first line of the question||

quiet garden
#

I change it to sin(u+v)?

gleaming spear
#

Yeah, given it's =x

quiet garden
gleaming spear
#

Seems good to me

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#

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next wraith
#

alright i need help

final saddleBOT
glossy zephyr
#

!da2a

final saddleBOT
#

No need to ask β€œCan I ask…?” or β€œDoes anyone know about…?”—it’s faster for everyone if you just ask your question!

next wraith
#

im typing the instructions

#

theres a quadrilateral that can have a circle inside it, AD=a, AB=2a. then theres a line that divides ADC in half, and it intersects AC at point E: AE/CE=2/3. the perimeter is 84 and cosADC=1/16

plucky rover
#

Well the first step would be to draw a diagram

next wraith
#

and i need to find the radius of 2 circles, triangle ACD is inside circle 1 and triangle ABC is inside circle 2

#

its like that ig

#

so uh now idk, any clue would be helpful, im awful at geometry

plucky breach
#

i thinnk you could use incenter theorm for this

next wraith
#

incenter?

plucky breach
#

its the meeting point of 3 medians

#

its the same distance from all sides

#

so you could find incenter

#

then plug both incenter andd the point perpendicular to it on a line to find the radius

next wraith
#

can you walk me through it? im not familiar with it

plucky breach
#

sure

#

so first you have to find the median

#

which is the midpoint of a segment to the oopposite vertex