#help-49

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midnight plankBOT
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craggy owl
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need some help with this question

midnight plankBOT
craggy owl
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  1. im confused on how fxx (-1, 2) is not negative
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to me it looks like its going down?

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then up at a certain point but still down first

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  1. could someone explain how to do f xy? its change of slope but not sure how to see that from the graph
midnight plankBOT
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@craggy owl Has your question been resolved?

craggy owl
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<@&286206848099549185>

midnight plankBOT
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@craggy owl Has your question been resolved?

tall lintel
craggy owl
tall lintel
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If you look here, the point (-1, 2) seems to be on a concave up portion (i.e with respect to the x axis, since f_xx is the concavity of f by varing x).

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So it seems that f_xx is more positive rather than negative.

craggy owl
tall lintel
craggy owl
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sorry shift a little to the left/right in the y direction?

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im a bit slow

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we would be looking at the

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fy (-1,2) is negative

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and fx (-1, 2) also -

tall lintel
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This is the tangent line to the surface at (-1, 2), right?

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So here's the thing,

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fx is the slope of the tangent line (in the x direction).

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If we then take the derivative of this function (fx) with respect to y, what is this derivative doing?

craggy owl
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how the slope in x-dir changes as we move in y?

tall lintel
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So what that means is, we're still looking at the slope in the x direction, but we want to see how that slope changes.

tall lintel
# tall lintel

Imagine that the blue and yellow points are just teeny tiny nudges of the red point in the corresponding y direction. What do you think happens to the slope as it moves from the red point (specifically from the red to the yellow point, since one-variable derivatives follow the positive direction)? Does it increase or does it decrease?

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^ This is btw not a conceptual question, it's hard to tell from the graph.

craggy owl
tall lintel
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Ngl I think the slope ||increases. This is because the concavity (looking from the x direction) actually decreases significantly as you move in the y direction.||

tall lintel
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Yeah bum question. Interpreting a 3D question using a 2D frame of reference is not that great.

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I'm sure there's some arguments regarding saddle points that apply here or something.

tall lintel
craggy owl
tall lintel
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Hopefully so

craggy owl
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i will ask a TA about this too but its an online course so i had this to go from

craggy owl
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but thank you

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i'll suffer a bit more

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.close

midnight plankBOT
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twilit field
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I would like to prove this

midnight plankBOT
twilit field
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So I need to show $g \ker(\phi) g^{-1} \subseteq ker(\phi)$

grand pondBOT
twilit field
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Let $x \in \ker ( \phi)$. Then \phi(g x g^{-1}) = \phi(g) e_{\overline{G}} \phi(g^{-1})$

grand pondBOT
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wai
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

twilit field
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okay

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got it

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tq

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.close

midnight plankBOT
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frail carbon
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you're welcome?

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twilit field
midnight plankBOT
twilit field
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Kind of confused

pine wave
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what do you think is confusing here?

twilit field
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so firstly, every element of the range need to have a pre-image?

pine wave
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"onto", yeah, I believe so

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wait codomain

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range by definition, every element has a pre-image

twilit field
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In that case I need to find all those combinations of elements whose product is 30

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So the kernel would be 0,1, 2,3,5,15

subtle zinc
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Z_30 is an additive group btw

twilit field
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F

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right

subtle zinc
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try using 1st iso thm

spiral rock
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You have a surjective homomorphism

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Also in this case if it weren't surjective it would be the trivial homomorphism

twilit field
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Also, I believe the kernel has 6 elements

spiral rock
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Yes

subtle zinc
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take the order of both sides of the iso

twilit field
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Z_30 can be partitioned into 5 cosets

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As for why

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I think I'm forgetting some thoerm

subtle zinc
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ok so |G/ker(phi)| = |phi(G)|

restive sleet
subtle zinc
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cuz both groups are isomorphic (hence bijective)

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what's the |phi(G)|?

twilit field
subtle zinc
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no 5

twilit field
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right

subtle zinc
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it's the image group

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ok so |G/ker(phi)| = 5

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and we know |G| = 30

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do u know lagrange's thm

twilit field
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yea, I forgot that the converse is true for cylic groups

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The possible generators are

subtle zinc
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ok but we just need the orignal thm

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for now at least

twilit field
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why, to determine the elements of the kernel surely we want the cosets

safe remnant
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hello, im new here, im interested in math so i joined here

subtle zinc
safe remnant
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ok, ill wait

subtle zinc
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lagrange's thm says that |G/ker(phi)| = |G|/|ker(phi)|

subtle zinc
midnight plankBOT
safe remnant
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Omg i thought you were talking to me 🫠

twilit field
subtle zinc
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ehh

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u kinda need the fact that cosets all have the same size

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which u get kinda used to and is easy to prove but really that's lagrange's thm

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like lagrange's thm is kinda an easy thm

safe remnant
twilit field
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I didn't realise you were askig for that 😭

subtle zinc
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?

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ok so ker(phi) has 6 elements

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and it's a subgroup of a cyclic group so is cyclic

twilit field
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we know 0 is in the kernel

subtle zinc
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therefore it must have a generator of order 6

twilit field
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yea, so 6 works

subtle zinc
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what are the order 6 elements of Z_30

subtle zinc
twilit field
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this is only 5 elements though

twilit field
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each subgroup need to be of order 5

subtle zinc
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ah sorry i meant 5 is the only element of order 6

twilit field
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yea

subtle zinc
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cuz ker(phi) is a cyclic group of order 6

twilit field
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{0,5,10,15,20,25}

twilit field
subtle zinc
twilit field
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Any such function is one -one and onto, there's only 1

dreamy lichen
spiral rock
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There are at least 2

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Trivial + identity

twilit field
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yes

spiral rock
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Think what determines such a homomorphism uniquely

dreamy lichen
spiral rock
twilit field
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n!

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my bad

spiral rock
dreamy lichen
dreamy lichen
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or everything to itself?

spiral rock
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No, everything to itself

twilit field
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Is there any efficient way to do this

spiral rock
dreamy lichen
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and trivial means everything to identity?

subtle zinc
twilit field
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I basically need to solve f(x+y)=f(x)+ f(y) modulo n

dreamy lichen
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yes, but idt its useful to think about it like that

twilit field
dreamy lichen
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maybe it would be best to start by constructing few explicit examples

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can u find all the homomorphisms from Z4 to itself?

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or at least some?

twilit field
dreamy lichen
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so everything to 0, yeah, that works

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what else?

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can u find something less trivial

twilit field
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the identity is the other extreme

dreamy lichen
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yeah, thats also quite trivial though

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what else?

twilit field
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oh, as Z_4 is cyclic

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the set of outputs will have a genertor

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Z_4 can have cosets of order 1,2, or 4

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Phi(0)=0; phi(1)=2

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@spiral rock , "‼️ ". Is that wrong?

dreamy lichen
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no, u're going in the right direction now

twilit field
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there are 4 such functions

spiral rock
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Its ths key fact that makes this nice

twilit field
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I can't believe I forgot that , ( I've proven this too 😭 )

twilit field
# twilit field

Okay, so the number of functions would be given by $\sum_{i=1}^{n} \frac{n}{\phi(n)}$

grand pondBOT
spiral rock
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Why phi

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Its cyclic groups

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And remember you only need homomorphisms

twilit field
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*generators

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oh

twilit field
twilit field
misty gorge
twilit field
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1 has n-1 places to go to

misty gorge
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you should just be thinking

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it's not about computing things like an integral or whatever

twilit field
misty gorge
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you are in the wrong mindset

twilit field
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I just tracked where 1 gors

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This shouldn't have taken me so long 😔

misty gorge
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why? there is no reason why it should take you any particular amount of time to complete. you just have to get out of the mindset that "X problem should take me Y minutes" because that's not really how math works

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like you discovered something about groups today that allowed you to find this trick of tracking where 1 goes

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and the trick is simple but the discovery process is not

twilit field
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was solving a functional equation for an assignment

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took me 5 hours to realise a simple result would mean that no such function can exist

misty gorge
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i don't understand what your point is

twilit field
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I know that I leanr a lot by taking time is my point

misty gorge
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ah

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yeah

twilit field
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the sideroads can be more enlightening

misty gorge
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yeah. if you complete a problem in 30 seconds and it takes you no effort at all then that's more of a waste than your functional equation problem

midnight plankBOT
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@twilit field Has your question been resolved?

zealous schooner
misty gorge
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i didn't say or imply that

oak nymph
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The answer to the problem is a consequence of the above simple fact, which you should engrave into your mind

midnight plankBOT
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safe onyx
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Is my understanding of implies correct?
(Here X means don't care/irrelevant)

safe onyx
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(1 means true 0 means false for P / Q values)

midnight plankBOT
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@safe onyx Has your question been resolved?

midnight plankBOT
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@safe onyx Has your question been resolved?

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modern lynx
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does this function have a vertical assymptote at 0

modern lynx
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i mean it looks like it

dreamy lichen
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by the defn u mentioned earlier, it does

midnight plankBOT
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@modern lynx Has your question been resolved?

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keen harbor
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In this passage, is there a reason the author wrote one with brackets, and the other without?

sick fossil
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No, just to emphasize where the sides of the original equation were

keen harbor
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ok, thanks.

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.close

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modern lynx
midnight plankBOT
modern lynx
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should i find both the LHD and the RHD and make them equal or should i just try to find the limit definining the derivative

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(i already got past the continuity part of this Q)

sick fossil
modern lynx
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(as my reason)

sick fossil
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or something similar

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"...defined as this limit"

sick fossil
modern lynx
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okie

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,lose

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.close

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royal dirge
midnight plankBOT
royal dirge
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i used this fact

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AB:DA = 2:3

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then k:w = 4:9

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well, its wrong

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i think i assumed these are similar triangles

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when they are actually not

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but then i feel like they are similar

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they have that shared vertical angle

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anyways, im not really sure how else to approach this

shell wigeon
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Yeah they aren't similar

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ABCD being cyclic gives you BCD = DAE = BAF, ADC = ABF, and ABC = ADE

royal dirge
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cyclic means what? is that a synonym for inscribed in a circle?

shell wigeon
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Yes

royal dirge
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interesting, i've never seen that before

shell wigeon
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Opposite angles are supplementary (BCD+BAD = ABC+ADC = 180º)

royal dirge
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oh yeah, that makes sense

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because the circle adds to 360

vast anchor
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what's up guys i'm new here

fallow scarab
royal dirge
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how do i relate those angles to area though?

shell wigeon
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Well, there are similar triangles in the figure, find them

royal dirge
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if i cut the quad in half it forms two triangles

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but i dont think they are similar

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i make this cut

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but now i have no triangles that share two angles

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same with this cut

shell wigeon
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Here, this is to scale, maybe that will help you find the similarities

royal dirge
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ohhh

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CDF is similar to ABF

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and CBE to ADE

shell wigeon
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Yes

royal dirge
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that makes more sense

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ok allow me moment now

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ADE has sides 15, 3, 6 (out of order)
ABF has sides 2, (8/3), 2

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huh

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i got nonreal finding the area of ADE

shell wigeon
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No those side lengths are wrong

royal dirge
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oh no

shell wigeon
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I don't think you need them anyway

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I computed them to draw the figure but I don't think the question would require that

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(I haven't solved the question yet, just waiting for you)

royal dirge
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well, before we continue, can you explain why those sides are wrong

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what i did was

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BC/AD = EC/ED

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and so on

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to find each one

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does BC not correspond to AD?

shell wigeon
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It's not EC/ED since BC and AD are not parallel

royal dirge
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ah

shell wigeon
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Try imagining flipping the triangle ADE about the angle bisector from E

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Then D goes onto EB and A onto EC, and that new segment is parallel to BC

royal dirge
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oh

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so i can use my side length strategy, i just have the wrong sides being compared

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wait, i dont think that is possible though

shell wigeon
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Sure, but maybe thinking of areas is better

royal dirge
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i can relate the area of the big triangles to their smaller similar triangles

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like A_CBE:A_DAE = 16:9

shell wigeon
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Right

royal dirge
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A_CFD:A_ABF = 25:4

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now i need to relate these two pairs

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well A_CBA:A_CDA = 15:8

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thats not the triangles im looking at though

shell wigeon
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You don't need to cut the quadrilateral

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(that 15:8 is false anyway)

royal dirge
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oh lol

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how do i relate these two ratios then?

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sorry im kinda tired of math for today lol, maybe its obvious

shell wigeon
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Use r,g,b for the areas

royal dirge
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r+g:g = 16:9

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r+b:b= 25:4

shell wigeon
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Right

royal dirge
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let me write as fractions so its easier to see it

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$\frac{r+g}{g} = \frac{16}{9} \ \frac{r+b}{b} = \frac{25}{4}$

grand pondBOT
#

UCYT5040

royal dirge
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there we go

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i need to find b/g

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$g=\frac{r+g}{\frac{16}{9}} \ b=\frac{r+b}{\frac{25}{4}}$

grand pondBOT
#

UCYT5040

shell wigeon
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That looks complicated

royal dirge
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yeah am i overthinking it?

shell wigeon
#

You should isolate r instead, to use elimination

royal dirge
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$r=(\frac{16}{9}-1)g \ r=(\frac{25}{4}-1)b$

grand pondBOT
#

UCYT5040

shell wigeon
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Right

royal dirge
#

$\frac{7}{9}g=\frac{21}{4}b$

grand pondBOT
#

UCYT5040

royal dirge
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now i can just undo cross multiply

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hold on one sec

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ok sorry im back

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$\frac{7}{9}=\frac{21}{4}\frac{b}{g}$

grand pondBOT
#

UCYT5040

royal dirge
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i get 4:27

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answer key agrees!

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thank you so much for your help!

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this was the last problem i got wrong. and im not doing any more math for today lol

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again, thank you!

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.close

midnight plankBOT
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sly cape
#

What is the logic behind putting numbers in brackets and not actually an equation?

grim ferry
#

Well some countries use BODMAS, some use PEMDAS.

so you’d kind of do “Brackets” or “Parentheses” before u multiply

sly cape
#

but you cant do anything with a number in a bracket...

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like (-2) is just -2

burnt flame
grim ferry
grim ferry
#

Especially if you’re in exams and you get something like multiple negative signs..

sly cape
grim ferry
sly cape
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what about 3*(+2)

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does something like this exist

burnt flame
burnt flame
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-2 is negative 2

sly cape
#

kk

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.close

midnight plankBOT
#
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sly cape
#

try moosy and maddie

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ty*

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.reopen

midnight plankBOT
sly cape
#

but this −1(−1)

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its -1 times -1

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@burnt flame

grim ferry
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negative multiply by negative is positive

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-a * -b = +ab

sly cape
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so whenever something is near brackets, you multiply?

subtle blaze
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Some say subtraction isn’t real

sly cape
grim ferry
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Follow PEMDAS or BODMAS, whatever you’re taught

sly cape
subtle blaze
#

There’s only ever negative numbers

burnt flame
sly cape
grim ferry
subtle blaze
#

-2 is one symbol, it is the symbol such that when you add it to 2 you get 0

burnt flame
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in general when you have variables next to each other too, its multiplying them, or a variable next to a number

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2x=2*x

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xy=x*y

sly cape
burnt flame
#

-(-5+3)=-1*(-5+3)

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-x=-1*x

subtle blaze
#

It so happens that the -1 symbol is special and you can rewrite the -2 symbol as the multiplication 2 * -1

subtle blaze
#

- signs can’t exist on their own, whenever they are by themselves it implicitly means there’s a 1 after it

sly cape
#

so whenever theres a - or + i can add 1?

subtle blaze
#

Brackets are there so that we can package a whole symbol into a “box”

sly cape
#

but signs arent symbols

subtle blaze
burnt flame
subtle blaze
#
  • is a real thing (addition)
    - is a fake thing (subtraction)
burnt flame
#

-(-5+3) is the 'opposite' of -5+3

subtle blaze
burnt flame
#

when we add them together, we should get 0

subtle blaze
#

It’s just 2 disconnected parts

sly cape
burnt flame
quiet parcel
subtle blaze
#

The only 2 properties you know about -a is

  1. whenever you do -a + a or a + -a you get 0
  2. -a = a * -1 = -1 * a
sly cape
#

but if we had +(-5+3)

subtle blaze
sly cape
#

why is 1 and 0 so special numbers in math..

burnt flame
subtle blaze
sly cape
subtle blaze
quiet parcel
subtle blaze
#

$+2$ is as bad as $\frac{}{2}$

grand pondBOT
#

frosst

burnt flame
#

-something is just a quick way of writing -1*something

subtle blaze
subtle blaze
#

It’s true in a field at least (ignore this if you don’t understand it)

quiet parcel
#

and it's practically just a concept, hell I even had that straight thought once when I was trying to find out the proof for why zero is an integer, and why it's not just a concept, zero has a duality of being both real and complex, so many things make it special

burnt flame
grim ferry
#

No offence to anyone but I think we’re overcomplicating this for the poor op 😭

sly cape
subtle blaze
#

The - is attached to the (-2) object

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And the - in here is attached to the (2) object

burnt flame
#

subtraction is just adding negative numbers

subtle blaze
burnt flame
sly cape
subtle blaze
#

I wanted the intrigue and delving into that thought..

grim ferry
#

Okay, well I wrote this for someone just now

subtle blaze
grim ferry
#

Take a and b as any real number that you want. Then,

a + b = a + b. eg. 1 + 1 = 2.
a - b = a -b. eg 1-1 = 0
a + -b = a - b. eg. 1 + -1 = 1-1 =0.
a - +b = a-b. eg 1 - +1 = 0.
a * (-b) = -ab. eg 2 * (-2) = -4

subtle blaze
#

But -a + -b = -(a + b)

sly cape
burnt flame
quiet parcel
# sly cape yeah so 5-(-2) = 3

think of it like this, you have 5 apples, and you owe 2 so you're in debt of a 2 apples (debt is the subtraction), now if they tell you that you're no longer in that debt, you actually no longer owe those 2 so you actually gain them to yourself, and gaining is addition, so you'd have 7 now in total

subtle blaze
#

We pick our maths so that it’s true

#

It turns out to be useful if we require it to be true

#

It somehow models something the real world does, and that’s useful so we pick it to be so

subtle blaze
sly cape
subtle blaze
burnt flame
#

the brackets are grouping it together

sly cape
subtle blaze
#

But you can distribute

#

You shouldn’t think of it as removing the bracket

#

You should think of it as the distributive property

sly cape
#

so is it a single number?

subtle blaze
#

a*(b + c) = a*b + a*c

burnt flame
subtle blaze
#

This we take for granted

#

We just assume it is true

#

(Maths is based on a bunch of arbitrary assumptions that turn out to be useful)

sly cape
#

but is (a+b) a single number?

subtle blaze
#

Yes

sly cape
#

but a + b arent

subtle blaze
#

Yes

#

Well, you could say it is too, but now we’re being pedantic

sly cape
#

-(-a-b) how is this possible?

#

they are negative already

#

how can you already make them negative again?

#

like twiec

subtle blaze
#

That is a shorthand for -((-a) + (-b))

#

We know that -a and -b are numbers, in particular they are the numbers which when you add it to a and b respectively you get 0

#

So (-a) + (-b) is addition between two numbers which (we assume) is again a number

#

This number also (by assumption) has its negative version

sly cape
#

so is the minus glued to (-a-b) in -(-a-b)?

so if i wanted to add 5 i'd have to minus it with (-a-b)?

quiet parcel
# sly cape how can you already make them negative again?

i once heard of this one thing from reddit or somewhere...

imagine you're standing looking at something in the right (positive, +) direction and your task is to turn around in the opposite (negative, -) direction.

if you turn around from the right direction, you'll be facing the opposite (negative) direction, if you turn around again, you'll be facing the opposite direction again but this time it'll once again be your starting right direction

every "turn around' and "opposite direction" is a -
every "right direction" is a +

subtle blaze
#

You can somehow “unstuck” the - sign if you do -a = -1 * a

sly cape
subtle blaze
#

Yea

#

Technically it results in 5 + (a + b)

sly cape
subtle blaze
#

But for addition we also require (a + b) + c = a + (b + c) so it doesn’t matter if you have brackets or not

subtle blaze
#

It’s 5 + (-1 * (a + b))

#

There are a whole lot of brackets everywhere but we omit them for the convention of pedmas or whatever you learn it as

sly cape
#

kk

#

okay

#

but what is the difference between podmas and bemdas

#

i was taught this:

()
x^2
.* / :

  • / -
twilit jetty
#

for example 5 - 5 - 5 is seen as starting at 5, doing - 5, then doing - 5 again

#

5 * 5 / 5 does * 5 first then / 5

#

however, for 2^3^4, you start with 3^ then 2^

#

2^3^4 = 2^81

twilit jetty
#

you tell me, you typed it like that

#

try reading it slower

sly cape
#

you don't do specifically one thing...

twilit jetty
#

if you do 1 + 4^2,

#

do you do the ^ or the + first?

sly cape
#

differently

sly cape
twilit jetty
#

lets ignore pemdas for now

#

Im talking about you bro

#

if YOU do 1 + 4^2, do you do the ^ or the + first

sly cape
#

^

twilit jetty
#

so much for left-to-right

twilit jetty
sly cape
#

5 + 9 - 4

twilit jetty
#

yes, you view this as 5, then + 9, then - 4

#

each operation you can view is something that takes an input number, does something to it, then leaves an output number

#

commonly this is read as starting at 5, then doing + 9 to it to get 14

#

this is technically different than just viewing + and - as operations that take two numbers together

#

but its more in line with the usual left-to-right that people actually do

twilit jetty
sly cape
#

but what if this

5 * 9 : 2

twilit jetty
#

5, then * 9, then : 2

sly cape
#

,calc 45/2

grand pondBOT
#

Result:

22.5
sly cape
#

,calc 4.5*9

grand pondBOT
#

Result:

40.5
sly cape
#

not the same result

twilit jetty
#

4.5 * 5, no

#

be consistent with your inconsistency

#

also, this is an example where either way is correct

sly cape
twilit jetty
#

(5 * 9) / 2 = 5 * (9 / 2)

#

buddy pal you did it wrong

#

,calc 5 * (9 / 2)

grand pondBOT
#

Result:

22.5
twilit jetty
#

find a better example

#

for example, 6 / 2 * 3

sly cape
#

i think you're starting to get aggressive.

twilit jetty
#

I was just trying to mirror yours

twilit jetty
#

and you presented the example without even testing it first

#

Im trying to match your energy you know

#

as I was saying, theres a reason why PEMDAS or BODMAS isnt actually airtight

#

thats because of a common rule that usually people use to read the operations instead

#

the strongest operations go first,

lusty python
twilit jetty
#

and with operations of same strongness, they are read left-to-right if they do actions

sly cape
twilit jetty
#

they are, yes

#

as I was saying, same strongness

sly cape
twilit jetty
#

listen, please

sly cape
#

see how division and multiplication is different

#

different order

lusty python
twilit jetty
#

the word "or" is in there

#

that implies you can do one or the other

lusty python
#

yes

twilit jetty
#

you can also see theyre of the same color here

#

compare that witht he brackets, order, and addition/subtraction

sly cape
lusty python
twilit jetty
#

thats not what the "or" means

#

the "or" means neither of them are stronger than the other

#

the "or" means we have to use a different rule other than "multiplication first" or "division first"

#

the "or" is equivalent to using the same color background

#

it does not imply you can do them in any order

#

do not misunderstand the image to get 'extra points'

twilit jetty
# sly cape

no one image alone can explain how we do things, ok?

#

Im right here you know, let me tell you what the reason is

lusty python
# sly cape

if according to your logic, why does according to PEMDAS, you have to perform multiplication first?

#

that is what your logic is here

sly cape
#

6 / 2 * 3

but here.. doing in any order will get you different results

twilit jetty
#

yes, so heres the idea that we have

lusty python
twilit jetty
#

the idea is that we stick to one way of viewing things, and we stick to it hard for consistency

#

this way isnt for "correctness" as much as it is for "consistency"

#

this is a key idea in math that often gets overlooked

sly cape
twilit jetty
#

consistency is more important than correctness

lusty python
#

we can't directly 'prove' it

lusty python
twilit jetty
sly cape
#

so why don't bodmas and pemdas have the same order?

twilit jetty
#

oval,

#

are you aware different countries do things different ways?

#

you know theres a U in colour in british english?

#

theres no "special reason" the u has to be there

#

well for the U in there, there actually is a reason, but thats besides the point

sly cape
twilit jetty
#

more often or not, changes happen and theres no good intentional reason for them

#

PEMDAS and BODMAS both communicate the same idea

sly cape
twilit jetty
#

which is that multiplication and division arent done first

#

theyre just done left-to-right

twilit jetty
#

again, please dont misconstrue my words

#

accents are not an intentional choice

lusty python
twilit jetty
sly cape
twilit jetty
#

that is not supposed to communicate to you the correct order

lusty python
#

to tell you in simple terms

#

BODMAS

#

and PEMDAS

#

they all mean the same thing

#

the thing is that people call it differently

#

depending on their country

sly cape
twilit jetty
#

let me look at my exact wording

twilit jetty
lusty python
lusty python
sly cape
twilit jetty
lusty python
sly cape
lusty python
twilit jetty
#

common misconception: people cant read your mind, you have to tell us in more detail what the confusion is

sly cape
twilit jetty
#

oval thats not how you read that

#

the difference here could just be in how the same information is presented in two different ways

sly cape
sly cape
twilit jetty
#

for example, color and colour are spelled differently, but they both mean the same idea

#

are you sure?

lusty python
twilit jetty
# sly cape

this picture sure is saying the order doesnt matter

lusty python
#

BODMAS

#

or PEMDAS

twilit jetty
#

its not muliplication or division first thats the rule

lusty python
#

they said that parentheses should be calculated first

twilit jetty
#

its multiplication and division, left to right, which is the rule

#

parentheses and brackets are the same word in american and british english

lusty python
#

and since in the brackets, there was only a -2, so it means -2

twilit jetty
#

consider for example -2^2
we usually do the ^ first, so -4

if on the other hand, you want to enforce the -2 is the number being squared, so -2 * -2,
you place parentheses around the -2
so (-2)^2 is 4

lusty python
sly cape
#

ok but why cant it be bomdas and pemdas?

#

so the order is actually 'the same'?

twilit jetty
#

no reason, its just that BODMAS is a popular way of viewing it, and BOMDAS is less popular

#

you know "order" isnt common in america right

#

we call it exponentiation

#

we dont call them indices

#

you may as well ask why neighbor has a silent "gh"

#

its not math, its history

lusty python
#

or listen

#

has a silent sound t

twilit jetty
#

lets go by the usual rules

#

there are two operations here, ^ and -

sly cape
lusty python
twilit jetty
#

now -x has a similar operation that is short for "0 - x"

lusty python
twilit jetty
sly cape
twilit jetty
#

theres plenty of these around

twilit jetty
#

it is common to view -x^2 as -x * x instead of -x * -x

sly cape
twilit jetty
#

bold to ask

sly cape
#

okay can you explain with the brackets and exponents

twilit jetty
#

I just told you its common to view -x^2 as one instead of the other

#

shouldnt that be reason enough

#

-x^2 is more commonly viewed as -x * x

#

therefore -x^2 is consistently -x * x

#

this is a matter of convention, not correctness

#

do you know what convention means here? you seem to want to look for a right answer where there is only a consensus answer

#

if you want -x * -x, you do (-x)^2 to signify that the - sign goes first (called "negation" when used on a single number)

sly cape
twilit jetty
#

not true

#

^2 specifically means multiplying with itself

#

and in -x^2, whats being duplicated is x, since the negation operation - hasnt been done yet

#

-x^2

twilit jetty
#

(-x)(-x) and -x * -x are the same

lusty python
#

yes

twilit jetty
#

and they both mean x^2

sly cape
#

but why is -x^2 not -x * -x

twilit jetty
#

to remain consistent with the existing rules we already have

#

consider 0 - x^2 for example

subtle blaze
#

If you look at 2x-4^2(3-(x+y))

twilit jetty
#

would this really be (0 - x)^2?

#

what about 1 - x^2?

#

we view that -x should be the same as 0 - x

#

instead of being "the minus sign"

sly cape
twilit jetty
#

this is so common that even if its attached to the number, we still put in ()s around it

#

for example, if I want to square -4 with itself, Id write (-4)(-4) or (-4)^2

#

I cant write -4^2

#

you can see here an extra () has been used, to denote that the - cannot be done last

#

operations have context

#

you cannot "regular expression" your way out of this

#

you cannot "string replacement" your way out of this
when you see a -2, it does not need to mean -2, it only means 0 - 2

#

and so -2^2 is 0 - 2^2, which is 0 - 4 or -4

#

the alternative is messy

subtle blaze
twilit jetty
#

lets say we view -2^2 as -2 * -2

subtle blaze
#

But why have so many brackets when you can have a convention

sly cape
twilit jetty
#

now compare -x^2 with -(-x)^2

#

oval, look at what I am talking about right now

#

are you listening?

sly cape
#

multiplication first than minusing with 0

twilit jetty
#

you do realize that, right

twilit jetty
#

as I was saying

#

lets compare -x^2 with -(-x)^2

#

show me an example of -2^2 and -(-2)^2

#

how do you calculate the both of these?

sly cape
#

-2 * -2 and -(-2)(-2)

twilit jetty
#

so theyre different, youre saying?

#

lets go with that

sly cape
#

sure, because one is with a bracket

twilit jetty
#

now lets suppose x itself is -2

#

x^2 is?

sly cape
#

-2 * -2

twilit jetty
#

yep, thats correct

#

x is -2, x * x is 4

lusty python
#

now then what

#

is -x^2

twilit jetty
twilit jetty
#

x^2 is 4, so -x^2 is?

sly cape
#

-x * -x

twilit jetty
#

write it out

#

what is the value of -x^2?

lusty python
#

for x = -2

sly cape
#

wdym?

#

oh

lusty python
#

you just calculated that x^2 = 4 for x = -2

sly cape
#

-2 * -2

lusty python
sly cape
lusty python
twilit jetty
#

now consider this

sly cape
#

because two - is the same

twilit jetty
#

what is x^2 - x^2?

sly cape
#

you cant put like multiple signs like 5+++++++5

sly cape
lusty python
twilit jetty
#

well yes you can

lusty python
#

but it's redundant

twilit jetty
# sly cape 0

but we've just agreed that x^2 and -x^2 are both 4, didnt we

#

4 + 4 cant be 0

sly cape
#

sure buddy

twilit jetty
#

you wouldnt get an error if you used the negation symbol thats next to the enter key on the calculator

#

calculators only view a limited part of how we communicate math

twilit jetty
sly cape
#

x * x - x * x

twilit jetty
#

thats different

#

in this case, why would -x^2 not be -x * -x?

sly cape
twilit jetty
#

you wrote -x * x

#

not -x * -x

#

those are different

#

-2 * 2 is -4,
-2 * -2 is 4

sly cape
#

x * x - x * - x

twilit jetty
#

then, if x is 2?

sly cape
#

2 * 2 - 2 * -2

#

16

twilit jetty
#

that would be 8, not 16

#

try that again

#

unless

#

unless youre viewing it as (2 * 2)(-2 * -2)

#

what youve done here, by accident, is inserted an extra * in the middle of things

sly cape
#

that

twilit jetty
#

when previously the expression was x^2 - x^2

#

this is the main reason why we dont view -x^2 as -x * -x

burnt flame
sly cape
#

im lost..

twilit jetty
#

you tell me why you put that * in there

#

it wasnt there before

sly cape
#

x^2 - x^2

x^2 = x * x
-x^2 = -x * -x

sly cape
twilit jetty
#

4 * 4 is 16, 4 + 4 is 8

#

the x * x would just be 4
the -x * -x would be 4 again
if it was x * -x, thatd be -4

#

the other *s only get you 4s

#

so wheres the 16?

burnt flame
sly cape
twilit jetty
#

moosey we're currently trying out an idea where the negator has greater precedence than the exponentiation operator, which has greater precedence than the subtraction operator

burnt flame
#

o

sly cape
#

okay so can we get to the point?

twilit jetty
#

how did -2 * -2 turn to 4 + 4

sly cape
#

cause now we're making some extraordinary cofusing equations

sly cape
lusty python
#

I think I have to step in onto this one

#

Let me cook guys

sly cape
#

ok

twilit jetty
#

-2 * -2 would be 4, not 4 + 4

sly cape
lusty python
#

So expressions like -2 or -(4 + 3). Let's call it a unary expression

twilit jetty
#

whyd you write 4 + 4 then

sly cape
#

no you misunnderstood

lusty python
twilit jetty
#

oh thats disgusting, I see

#

well dont invent new ways to write math in the middle of me trying out your idea

lusty python
#

And to the left of it, it has no number, or at most operators

sly cape
#

-2 * -2 is FOUR
2 * 2 is FOUR

lusty python
sly cape
twilit jetty
#

this looks like 2 * 2 * 4 + 4

sly cape
#

it doesnt

#

the brackets show the results of multiplication

twilit jetty
#

if ou had to explain it, it isnt clear

sly cape
twilit jetty
#

in the middle of trying to be clear, youve used brackets, which are themselves a part of math

#

maybe you can say "which is"

#

2 * 2 (which is 4) + (which is also 4)

sly cape
lusty python
twilit jetty
#

if you just write 2 (4), thats short for 2 * 4

lusty python
sly cape
#

this time

twilit jetty
#

oval, yes I did, and its still your fault because that was an ambiguous statement

#

(2)(4) means 2 * 4, its another way to write down multiplication

lusty python
sly cape
twilit jetty
#

make the most of it

lusty python
lusty python
#

So let's define a unary expression as this

#

It has an operator of + or -

#

There's no expression to the left of it

#

And it's right expression is exponents or parentheses

sly cape
#

example?

lusty python
sly cape
#

okay thats negative 7

lusty python
#

Or +1

twilit jetty
#

yep, not "minus 7" since theres no 0 to the left of it

#

when you use - in this way, its called a negation

lusty python
#

-x^2 is also an example of a unary expression

sly cape
lusty python
#

We treat unary expression as a number

twilit jetty
#

well we dont see a 0 to the left of it, so - 7 and -7 are the same

lusty python
twilit jetty
#

youd need something on the left to see the difference: 0 - 7

#

0 - 7, 0 -7, and 0- 7 are also the same

lusty python
#

So for example: -2 * -2

#

Since we treat -2 as a number, then we perform multiplication on both sides

sly cape
#

okay

#

its 4

twilit jetty
#

yep, its 4

lusty python
#

Yep

#

Now try -2^2

sly cape
lusty python
sly cape
#

duplication of a number

hybrid rain
#

Can someone help me with cypher ?

twilit jetty
#

which order are we using, oval's version or the conventional version?

lusty python
lusty python
midnight plankBOT
sly cape
twilit jetty
#

thats not how you read the + symbol here

#

^2 does not mean duplication in that sense

#

for example, if I did (1 - 1)^2, which would be 0,

#

would you really be doing 1 - 11 - 1?

#

thats -11

lusty python
sly cape
twilit jetty
lusty python
sly cape
lusty python
#

And we treat unary as a number

#

So to calculate a unary

sly cape
#

idk what is unary

last slate
#

erm acktually

-2^2 = -(2 * 2)
if you wanted -2 * -2
it wld be (-2)^2 :3

lusty python
#

You have to calculate the right one first

lusty python
lusty python
sly cape
#

yeah so unary = - 7 and ary = - 7

lusty python
#

So to calculate -2^2

#

You have to calculate 2^2 first

#

Then change the sign of it

sly cape
#

but -2 is a NEGATIVE number!!!

twilit jetty
#

that doesnt really answer why you couldnt just do the -2 first, just that youre supposed to "not do that"

sly cape
#

negative and positive number

twilit jetty
#

I think I know what to answer this with

#

youre aware we are using two different kinds of - here

#

one for denoting a negative number

#

and another for subtraction

lusty python
twilit jetty
sly cape
#

okay but this is a negative 2

twilit jetty
#

oval, listen to me

sly cape
#

it isnt two and then subtract

twilit jetty
#

yes or no, you can see the two different operations?

#

one that takes in one number and considers it negative

sly cape
#

yea

twilit jetty
#

and another that takes in two numbers and finds the difference

sly cape
twilit jetty
#

no it isnt

sly cape
#

it is

twilit jetty
#

and its entirely for a reason you gave:

#

now so far, you are saying that because the - sign is part of the number, it shouldnt be that an 'outer' operator can just take out part of it

sly cape
#

okay add 5 and -5 together

#

i can do 5 + -5 = 5 - 5

lusty python
twilit jetty
lusty python
twilit jetty
#

however, by doing this, you are treating the - signs differently

#

consider -5 - 5 for example

sly cape
#

do you understand what i mean?

lusty python
twilit jetty
#

so tell me this

#

if I wanted to subtract -5 and -5 together, how would I write it

sly cape
#

-5 + -5

twilit jetty
#

if I wanted to multiply -5 and -5 together, how would I write it

sly cape
#

-5 * -5

twilit jetty
#

and if I wanted to add -5 and -5 together?

twilit jetty
sly cape
#

-5 - -5

twilit jetty
#

so adding no longer places a + sign between numbers now?

twilit jetty
#

wouldnt adding -5 and -5 be -5 + -5?

#

theyre both -5 and Im adding them

#

whats different here

sly cape
#

because the 2nd subject is a minus

lusty python
lusty python
sly cape
#

this isn't right

twilit jetty
#

it isnt, yes

#

thats because the way youre doing things isnt very good

#

we have a better way around this

sly cape
#

adding -2 and -2 is
-2 - -2

lusty python
twilit jetty
#

I think we've just stepped into a different kind of error that unary expressions arent going to solve

lusty python
lusty python
#

Avoid confusion

#

Add the parentheses first

#

Should be (-2) + (-2)

#

Good luck!

sly cape
#

since the second 2 is a minus

twilit jetty
#

ok Im going to show you something that you need to know beforehand

#

what do you think the + operator does?

sly cape
#

fine

sly cape
twilit jetty
#

you surely arent adding -2 and -2 here to get -4

#

youre turning the second number to always be positive then adding them

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so if I were to start at -2, and try adding various numbers, Id get:

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-2 + 5 = 3
-2 + 4 = 2
-2 + 3 = 1
-2 + 2 = 0
-2 + 1 = -1
-2 + 0 = -2
-2 + -1 = -3
-2 + -2 = -4
-2 + -3 = -5

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any time I use the + operator, that is called addition

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if the number we get is lower than before, it is still considered addition

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in this case, we notice that adding a negative number makes you lower than before

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does it simplify to subtraction? yes

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but the initial step has used the + sign

sly cape
twilit jetty
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not correct, oval

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using the + sign is all you need to call it addition

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signs do not care about the output of their result slanting a particular way

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-2 + -1 is considered adding -2 and -1
-2 and -1 add to -3
-2 and 1 subtract to -3

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-2 + -1 "negative 2 plus negative 1"
-2 - 1 "negative 2 minus 1"
-3 "negative 3"

sly cape
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and whats the point?

twilit jetty
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doesnt this go against what youre thinking

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youre saying -2 plus -1 should be -2 plus 1 instead

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even though thats not how the plus symbol is supposed to be interpreted as

twilit jetty
sly cape
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its -1 not plus 1

twilit jetty
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are you just saying -2 + -1 isnt considered addition because, when you simplify, theres a - sign?

sly cape
twilit jetty
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thats interesting, so whats the + sign doing there?