#help-13

1 messages · Page 272 of 1

cedar kilnBOT
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Please only use the <@&286206848099549185> ping once if your question has not been answered for 15 minutes. Please do not ping or DM individual users about your question.

hot crag
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my man

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please stop pinging us

solemn fern
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i only pinged once bro

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i waited 15 mins

hot crag
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...?

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a. it'd been 5 minutes since you posted when you pinged us the first time
b. it'd been 13 minutes since you posted when you pinged us the second time
c. the factoid states both wait 15m and ping ONCE

solemn fern
#

is it really that strict? 2 mins?

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if thats the case then sorry for the 2 mins

hot crag
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*sighs*
ykw leave it

solemn fern
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ok so are you the helper?

hot crag
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i help as per my discretion, sorry

solemn fern
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and what does that mean?

hot crag
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...?

solemn fern
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bro im new to this how do i get help

hot crag
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just wait okay

solemn fern
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alright

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<@&286206848099549185>

hot crag
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yep, good

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that works see

solemn fern
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omg u were there the whole time waiting for it

hot crag
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(now again i cant help, this is one of my weak points so im sorry)

solemn fern
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BRUH

hot crag
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sorry :(

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someone else will cm dw

solemn fern
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oh im sure they will

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i give up on life
who said humans are better than ai
i will ask an ai
and if it gets it wrong, at least i didnt lose half my brain cells waiting

cedar kilnBOT
#

Please do not trust ChatGPT or similar AI tools for mathematical tasks, as they often generate output which "sounds correct" but has numerous factual or logical errors. Use of these AI tools to answer other people's help questions is strictly against server rules (see #rules).

flint plinth
#

we have an understanding

cedar kilnBOT
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@solemn fern Has your question been resolved?

solemn fern
# flint plinth

Should Mhyd1427 wait for 30 mins and not get an answer tho😢

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I squeezed my brain and google and wolfram alpha to get an approximation 66 square units

flint plinth
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you're trying to calculate this?

solemn fern
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Im pretty sure

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But i think i mightve made a mistake forming it

flint plinth
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it doesn't look very friendly

solemn fern
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Really isnt

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Even wolfram alpha had to approximate it

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So this means that there was a mistake forming the integral

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But its the only way it seems

flint plinth
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the thing inside the square root is a perfect square

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but i don't know how much that helps

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$$x^8 + \frac{1}{2} + \frac{1}{16}x^{-8} = \left(x^4 + \frac{1}{4}x^{-4}\right)^2$$

wraith daggerBOT
solemn fern
#

Or maybe the question is assessing my ability to form integrals and use approximation methods maybe?

flint plinth
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possibly, what's the context, is this a calculus course or what

solemn fern
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I have the question posted i think here

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Here

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This was my attempt

cedar kilnBOT
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@solemn fern Has your question been resolved?

cedar kilnBOT
#
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burnt glacier
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hi! thers a way to solve this limit using euler?

cedar kilnBOT
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@burnt glacier Has your question been resolved?

cedar kilnBOT
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@burnt glacier Has your question been resolved?

versed siren
burnt glacier
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this one

upper ruin
wraith daggerBOT
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Alberto Z.

burnt glacier
versed siren
upper ruin
cedar kilnBOT
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@burnt glacier Has your question been resolved?

burnt glacier
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Youre right. I know its not ideal but i would like to figure this out

upper ruin
pastel vault
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Rather than trying to think you can apply one strategy to all of them

upper ruin
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I agree

cedar kilnBOT
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@burnt glacier Has your question been resolved?

burnt glacier
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i agree as well but my professor did somehow managed to solve it this way

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i tried to solve as he did but i only made it halfway

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this were i got stuck at

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he started like this but from this point im kinda stuck

pastel vault
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So he didn't take the logarithm of that

burnt glacier
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a crazy man do crazy things i guess lol

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but it did got me curious about it

burnt glacier
pastel vault
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Fair, your question is going to be sitting for a while though

burnt glacier
# raw gulch

Thanks. How did you managed to put lnx in the numerator?

burnt glacier
raw gulch
# burnt glacier this were i got stuck at

there is initial mistake here, so I'm not going to continue that, since: (1+x)^1/x --> e, when x->0, and in your case, x - 1 does not go to zero when x ->0, clear?

raw gulch
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you need this:

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but not what you wrote in your paper

raw gulch
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unless you figure out some sophisticated substitution of the variable

burnt glacier
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I “added zero” to the limit

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/doubled it by 1

raw gulch
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yes, but x - 1, must go to zero if x -->1

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and in your case

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x - 1 goes to -1

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so you cant replace it with e

burnt glacier
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oh so it only works if x—/—>0 ?

raw gulch
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your expression must go to zero,

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not mandatory x

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but all this expression behind 1

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you see ?

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x - 1, here, goes to zero

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i understand what you wanted to do, sure, but in your case, it failed

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do you know the oroginal answer ? if not i can tell you

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then you can verify your calculations

cedar kilnBOT
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@burnt glacier Has your question been resolved?

gentle pecan
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Are we permitted to use LHopitals Rule?

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If so, ths limit isn't too bad to find

cedar kilnBOT
#
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fresh loom
#

any help here?

cedar kilnBOT
#

@fresh loom Has your question been resolved?

fresh loom
#

.close

cedar kilnBOT
#
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cedar kilnBOT
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Show your work, and if possible, explain where you are stuck.
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naive ember
#

can someone explain wtf is happening here?

cedar kilnBOT
#

@naive ember Has your question been resolved?

cedar kilnBOT
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cedar kilnBOT
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Available help channel!

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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
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raw yoke
cedar kilnBOT
raw yoke
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minor problem; they never taught us how to do questions where you need to find the line of intersection

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I've got the cartesian equations for each

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-4Xx1-3Xx2-5Xx3-7=0

3Xx1+5Xx2+x3+8=0

cedar kilnBOT
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@raw yoke Has your question been resolved?

main needle
#

you want to eventually get to equations like x1= ... + ...*x3 and x2= ... + ...*x3

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just have to cancel out some rows in a matrix first

pastel vault
# raw yoke

Find the normal vectors of both planes using the cross product

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Then the line of intersection must be normal to the two normal vectors you get

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If you draw a diagram you can see why

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Oh right once you get your line, sub x, y, z into ax + by + cz = d for any one of the planes

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That's how you find a point the line passes through

cedar kilnBOT
#
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Show your work, and if possible, explain where you are stuck.
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crimson sedge
#

HI

cedar kilnBOT
crimson sedge
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i dont understand this,

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im new to sin / cos stuff

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if anyone could explain this, it would mean SO MUCH

tepid wraith
crimson sedge
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o..

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IM SORRY

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I DONT UNDERSTAND IT

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i dont know it

tepid wraith
crimson sedge
#

oh

tepid wraith
gusty forum
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probably meant P and Q
i can tell the underpaid teacher energy just from that ss

tepid wraith
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for P x is 0 because it's on y axis

crimson sedge
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okay

tepid wraith
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now plug in x=0 in y=x^2-4x+6

crimson sedge
#

so i sub in?

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oh okay

tepid wraith
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ye

crimson sedge
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0^2 - 4(0)+6

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like this?

tepid wraith
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yes

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what do you get

crimson sedge
#

so its 6

tepid wraith
crimson sedge
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P

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wait

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WAIT

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Y

tepid wraith
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yes

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y coordinate of P is 6

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now what would the point be

crimson sedge
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wait

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do i sub in the y?

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y = 6

tepid wraith
crimson sedge
#

oh okay

tepid wraith
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you got x and y

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for P

crimson sedge
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0, 6

tepid wraith
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yes!

crimson sedge
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(0 , 6)

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OH OKAY

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SO I KNOW THAT

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B AKA Q

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IS

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LIKE

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X = 5?

tepid wraith
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yes

crimson sedge
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omg okay

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wait

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5^2 - 4(5) + 6 = the y for q

tepid wraith
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please talk in a singular or few sentences

crimson sedge
#

okay sorry

tepid wraith
crimson sedge
#

25 - 20 + 6 = 11 ?

tepid wraith
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write coordinate

crimson sedge
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y = 11 therefore, coordinates for q is (5 , 11)

tepid wraith
#

now do you know integration?

crimson sedge
tepid wraith
tepid wraith
crimson sedge
tepid wraith
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or differentiation

tepid wraith
#

what's a definite integral used for

crimson sedge
tepid wraith
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it's used for area under curves

crimson sedge
#

okay let me write that down rq

tepid wraith
#

do you know how to integrate?

crimson sedge
#

not really.. T.T

tepid wraith
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for example $\int x^n dx=\frac{x^{n+1}}{n+1}+C$

wraith daggerBOT
#

The Prophet Of The Damned

crimson sedge
#

OH YEAH I KNOW THAT

tepid wraith
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great

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that's all you need

crimson sedge
#

when it goes to the opposite its like n-1 rightt?

pastel vault
pastel vault
tepid wraith
crimson sedge
tepid wraith
crimson sedge
tepid wraith
crimson sedge
#

okay

tepid wraith
crimson sedge
tepid wraith
tepid wraith
pastel vault
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Not x = 2

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Plug n = 2

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Very important difference

tepid wraith
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i forgo lmao

crimson sedge
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okay wait

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x^3/3 + c

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?

tepid wraith
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yep

crimson sedge
tepid wraith
#

now what's the integral of -4x

pastel vault
tepid wraith
pastel vault
#

Think about what the exponent is if you just have x

pastel vault
tepid wraith
pastel vault
pastel vault
tepid wraith
crimson sedge
pastel vault
#

Yeah basically cause you have x^0 = x^(2 - 2) for example
= x^2 / x^2 = 1

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You can have any other number instead of 2 and it will still cancel

tepid wraith
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kim why did you decide not to learn calc before trig

pastel vault
crimson sedge
tepid wraith
crimson sedge
tepid wraith
crimson sedge
tepid wraith
#

don't get distracted

crimson sedge
pastel vault
#

I need to check, anyways

pastel vault
crimson sedge
tepid wraith
tepid wraith
crimson sedge
tepid wraith
pastel vault
#

Honestly take your time

crimson sedge
tepid wraith
crimson sedge
tepid wraith
crimson sedge
tepid wraith
#

if i say $x^n=x^1$ what is the value of $n$?

wraith daggerBOT
#

The Prophet Of The Damned

crimson sedge
#

1

tepid wraith
#

yes

tepid wraith
crimson sedge
#

x^2/2 + c

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how do I tell from the question, when to plug in a number?

tepid wraith
tepid wraith
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replace 1 with the power that's given

crimson sedge
#

okay

tepid wraith
pastel vault
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I was helping someone else

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Yeah go ahead

tepid wraith
pastel vault
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Let's say the green function is f(x)

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And the blue function is k * f(x)

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So the area under the green function is the integral of f(x)

pastel vault
crimson sedge
tepid wraith
pastel vault
pastel vault
tepid wraith
crimson sedge
pastel vault
#

If the green function is f(x) and the blue function is k * f(x)

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How much larger is the area under the blue function compared to the green function?

crimson sedge
pastel vault
crimson sedge
#

yeah

pastel vault
#

We're just stretching that shape in the y-direction

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And we're increasing it by a factor of k

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k times larger

crimson sedge
#

k is constant?

pastel vault
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Yep k is a constant

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If we have k, we mean it's a constant

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Like if we have x, y, or z, we mean it's a variable

crimson sedge
#

how can we tell which one it is?

pastel vault
crimson sedge
#

okay

pastel vault
#

It's like how you get better at understanding the events in a book or how characters develop if you read more

crimson sedge
#

ooo yeah thats true

pastel vault
#

So because the integral is just the area under the graph

tepid wraith
#

definite integral*

pastel vault
#

The integral of k f(x) dx = the area under k f(x) = k * the area under f(x) = k * the integral under f(x)

pastel vault
#

$\int k f(x) \ dx = k \int f(x) \ dx$

wraith daggerBOT
pastel vault
#

You can have a variable such as x in your limits of integration

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And it's still true

pastel vault
tepid wraith
#

do you know sum rule for differentiation?

crimson sedge
pastel vault
tepid wraith
#

i think we need a transaltor

crimson sedge
pastel vault
#

You need patience

tepid wraith
#

oh god

tepid wraith
crimson sedge
#

sorry, at what age do people learn this usually.

tepid wraith
crimson sedge
tepid wraith
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south is in uni

tepid wraith
pastel vault
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Nahhhh man

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You can't trick me now

crimson sedge
#

im 15 and i dont know this...

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im SO DONE

tepid wraith
#

but in india it's 15-16

pastel vault
tepid wraith
crimson sedge
pastel vault
#

underage discord, sus

tepid wraith
tepid wraith
#

13 not against tos

pastel vault
tepid wraith
#

i turn 14 in may

tepid wraith
crimson sedge
#

wow man

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im actually envious of people that are hella good in maths like this

pastel vault
tepid wraith
#

get back to topic

pastel vault
#

I suck at drawing

pastel vault
#

Okay I might explain the next thing then

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So if you have f(x) + g(x)

crimson sedge
#

okay

pastel vault
#

The area under f(x) + g(x) is just the sum of very thin rectangles

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And the height is f(x) + g(x) ofc

tepid wraith
pastel vault
#

I'll pull up a picture

tepid wraith
#

practice does

pastel vault
tepid wraith
#

practice is a real one

pastel vault
#

Like these rectangles in practice would be so thin, their width would be pretty much 0

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So the area would be exact

tepid wraith
pastel vault
tepid wraith
#

but it's a jumpscare when limit of a sum

pastel vault
# pastel vault

Yeah the height of these rectangles is going to be f(x) for the particular x value

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If you let the rectangles have width almost-0

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Then every x will have a rectangle corresponding to it

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So the 'height' is just f(x)

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And the width we call dx, dx stands for a very small number on the x-axis

crimson sedge
#

is that for every qn

pastel vault
pastel vault
#

The height of a function is just f(x) for that value of x

crimson sedge
#

can you give an example question

pastel vault
crimson sedge
#

then explain the answer (u dont have to if its too yea)

wraith daggerBOT
pastel vault
#

The height of the function on the left is f(x) + g(x)

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And the height of the right hand side is also f(x) + g(x)

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And all the widths are the same

crimson sedge
pastel vault
#

So the combined area of all the rectangles is the same -> the integrals are the same

pastel vault
crimson sedge
pastel vault
#

You can always choose some points on the x-axis of f(x)

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And make those points the same for g(x)

crimson sedge
#

OH YEAH

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like any coordinates?

pastel vault
#

The assumption is that these are the areas from x = a to x = b, for both of them, sorry

tepid wraith
# wraith dagger **south**

this implies $\int af(x) + bg(x) \ dx = a\int f(x) \ dx +b\int g(x) \ dx$ when combined with the scaling example

wraith daggerBOT
#

The Prophet Of The Damned

pastel vault
wraith daggerBOT
pastel vault
#

Combining the two rules together

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Okay now we can do your question, the area of region A1 which is the region under the parabola

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That's $\int x^2 - 4x + 6 \ dx = \int x^2 \ dx + \int -4x \ dx + \int 6 \ dx$

wraith daggerBOT
pastel vault
#

Using the f(x) + g(x) rule for 3 functions

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Like (f(x) + g(x) + h(x)) = (f(x) + g(x)) + h(x), break it into 2 first

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And then break it again

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$= \int x^2 \ dx + (-4) \int x \ dx + 6 \int 1 \ dx$

wraith daggerBOT
pastel vault
#

Using the k f(x) scaling rule

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$= \frac{x^3}{3} + (-4) \frac{x^2}{2} + 6x$ plus a constant

wraith daggerBOT
pastel vault
#

(We add a constant cause if you differentiate an integral, you get the original function back)

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(So if you differentiate a constant, you get 0 and you get the original function back as well)

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With me so far? This is a lot I know

crimson sedge
#

if im quite honest, ive never been taught these formulas

pastel vault
#

True

tepid wraith
crimson sedge
pastel vault
#

We're almost there I promise: we can turn this into a number which tells us the area

crimson sedge
#

ive never been taught this in year 10

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idk why

pastel vault
#

Now we can actually just sub x = 5 in, that gives us a number we can call A
And sub x = 0 in, that gives us a number we can call B

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Then the integral from 0 to 5, or the area under the parabola is just B - A

tepid wraith
crimson sedge
pastel vault
#

Like I know we're subbing in individual numbers

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But the area from x = 0 to x = 5

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Is just (area from x = -1 to 5) - (area from x = -1 to 0)

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Or (area from x = -10000 to 5) - (area from x = -100000 to 0)

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You get the idea

crimson sedge
#

what im getting is that A1 is the integral of the graph? so we plug x=5 in the equation and A2 is area under PQ - A1 ?

pastel vault
#

In other words, the area under the line, minus the area under the parabola

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That's A2

pastel vault
#

But actually, if you notice, the area under a line is just a trapezoid

crimson sedge
#

can u highlight wheres the parabola

pastel vault
#

Let me scroll up

crimson sedge
#

okay

pastel vault
#

I highlighted the parabola in blue

pastel vault
tepid wraith
pastel vault
#

Yeah so of course the first thing would be to figure out the equation of the line

tepid wraith
pastel vault
#

So that we can minus the parabola and get a function

tepid wraith
tepid wraith
#

you can see its 5 units

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now delta y would be the difference of the y coordinates of p and q

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now remember what y coordinate of p and q are

crimson sedge
#

so

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6 and 11

tepid wraith
#

yez

#

the difference of 11 and 6 is?

crimson sedge
#

5

tepid wraith
#

so delta y is?

pastel vault
#

Or if you know the slope already, just tell us

crimson sedge
tepid wraith
crimson sedge
#

wait 6/11

tepid wraith
#

it would be the difference

crimson sedge
#

oh i thought changes in Y = Y1/Y2

crimson sedge
tepid wraith
crimson sedge
#

okay

tepid wraith
#

what was delta x

crimson sedge
#

5

tepid wraith
#

@crimson sedge

crimson sedge
#

then

#

minus a1 for the final answer?

tepid wraith
#

ok

crimson sedge
#

is it wrong.........

pastel vault
#

It's correct for when you have a line

crimson sedge
#

so uh

tepid wraith
tepid wraith
crimson sedge
#

this is so stressful 😭

tepid wraith
#

practice

#

gtg

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@pastel vault take

pastel vault
#

Like honestly just come back to this tmw

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And then you can practice more if you want to

crimson sedge
#

okay

#

thank you so much again

pastel vault
#

No worries

cedar kilnBOT
#

@crimson sedge Has your question been resolved?

#
Channel closed

Closed by @exotic mortar

Use .reopen if this was a mistake.

cedar kilnBOT
#
Available help channel!

Send your question here to claim the channel.

Remember:
Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
• Type the command .close to free the channel when you're done.
• Be polite and have a nice day!

Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

civic coral
cedar kilnBOT
civic coral
#

How do I tell whether the cross product of OA and OB is parallel to (1,-2,2,)

coral jewel
#

cross product of two vectors is the normal vector of the plane containing those 2 vectors

#

it doesnt make sense for a vector to br parallel to a point

civic coral
#

Emmm

#

(1,-2,2) is vector

carmine dock
#

If vectors u, v are parallel
then we can write u=kv where k is a scalar

cedar kilnBOT
#

@civic coral Has your question been resolved?

broken yoke
#

If you are asking about if 1i-2j+2k is a parallel to OA X OB then 1i-2j+2k=k(OA X OB) here k is a constant. In other terms if two vectors are parallel it means they are multiple of one-another.

cedar kilnBOT
#
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#
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oblique lynx
#

in my signals and systems class, one TA uses such notation

$$
\langle f(t),g(t) \rangle = \int_{-\infty}^{\infty}f(t)g^*(t)dt
$$

Is this property/notation possible to use only in Hilbert spaces? I thought that this notation is used for inner product.

wraith daggerBOT
#

konxmok

oblique lynx
#

also can somebody please help my understand, why is Hilber space so special? Why dont we use like some normal vector space. We touched it a bit in my quantum mech class but i dont se much why is it used (i dont have strong background in functional analysis since i study engineering)

crimson delta
#

well hilbert space is basically vector space + inner product

#

and yes thats precisely the notation for an inner product

crimson delta
oblique lynx
#

but isnt inner product also defined on normal vector space?

crimson delta
#

and together with that inner product they are a hilbert space

oblique lynx
#

also do you think that you may can point me to some literature that would help me understand the basics of spaces? I always had rather hard time with this topic and it will come handy for me

crimson delta
#

when we say something is a hilbert space, we say that it is a "normal" vector space and it has an inner product

#

basic of spaces?

crimson delta
#

not sure what thats supposed to mean

oblique lynx
#

sorry ofr the formulation, in lin alg we defined some abstract spaces, then here in physics and signals they throw hilbert spaces and i am just confused by the topics, so i thought that i will try to understand it more deeply (even when its not actually needed for any of my classes)

crimson delta
#

for vector spaces any linear algebra book should be good. for specifically banach/Hilbert spaces any functional analysis book should give some information

oblique lynx
#

as we are engineers, they dont really "explain it", they just say that it works good f.e. in the Hilbert space

oblique lynx
#

also i have one more question, i have to calcuate correlation functio R12 of these two signals

#

I know the cor. func. is defined as

$$
R_{12}(\tau) = \langle s_1(t+\tau),s_2(\tau) \rangle =\int_{-\infty}^{\infty}s_1(t+\tau)s^*_2(t)dt
$$ but i am not really sure how to construct the integral with the tau shift, can somebody help me construct it? (i am able to calculate it, just not to costruct it)

wraith daggerBOT
#

konxmok

oblique lynx
#

.close

cedar kilnBOT
#
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cedar kilnBOT
#
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somber juniper
#

i need help with upper and lower bounds theorem. i just learned that a polynomial can have multiple upper and lower bounds. when the question asks us the upper bound what we're supposed to tell?

somber juniper
#

like it makes 0 sense

#

i dont understand this theorem at all. i know this in general but everday i learn that i know smthn wrong abt this theorem

#
  1. how do i find the upper or lower bounds for a polynomial?
  2. also learned that the greatest value we find using rational root theorem is the upper bound and the lowest value we find is the lower bound. Is this True or False?
  3. i just learned that a polynomial can have multiple upper and lower bounds. when the question asks us the upper bound what we're supposed to tell?
  4. im so confused what this theorem even means. as i know upper bound mean we can have no roots greater than this and this works with the same (but in opposite) with the lower bound
#

these are my questions abt this theorem can someone pls hel me with these

idle tusk
somber juniper
#

hold on

crimson delta
#

well if for example -10 is a lower bound, then clearly -20 also is a lower bound

#

its a "worse" bound, but its still a bound

somber juniper
somber juniper
#

okay pls lets start from the beginning im abt to go crazy bc i've been trying to finish this damn lesson for the past 6 days

#

and i have been trying to find the stupid bounds of a polynomial for the past 3 hours

#

what is this theorem

#

i dont get it

carmine dock
#

Do you mean the bounds of the roots of the polynomial?

somber juniper
somber juniper
#

well yeah i guess

#

idk what the question is even asking okay

#

it says

Find integers that are upper and lower bounds for the real zeros for the polynomial

#

i got

$$x^3-3x^2+4$$ and i found -1 as lower bound and 4 as upper

wraith daggerBOT
somber juniper
#

i also got $$2x^3-3x^2-8x+12$$

wraith daggerBOT
somber juniper
#

i have been trying to find the upper and lower bounds of this one for 3 hours

somber juniper
#

which one im supposed to give as an answer

carmine dock
#

either one is fine i think

#

Do you know what is an upper/lower bound?

somber juniper
#

i knew it but im so confused that i forgot whats even that

somber juniper
carmine dock
#

Ok so consider a set A
If a real number p is greater than or equal to any elements of A
then p is a upper bound for A

somber juniper
#

then this means we got infinity numbers of upper bound?

carmine dock
#

yep

slate lintel
#

yeah technically 3552256783362 is an upper bound

#

butttt there's probably a specific answer they're looking for, maybe the lowest possible integer that works as one?

somber juniper
#

then we cant answer to the questions stating a specific upper/lower bound

carmine dock
#

Yeah maybe they are asking for the lowest upper bound

somber juniper
#

how do i find upper bound or lower bound? I use rational root theorem usually but this time it didnt work for the second polynomial

#

$$2x^3-3x^2-8x+12$$

wraith daggerBOT
somber juniper
#

this one

carmine dock
#

Can you show your work

somber juniper
#

alr wait a sec

#

here

#

12 is upper 6 is upper as well

#

so i just try each of these numbers and find the lowest ?

carmine dock
#

Maybe the question had specified
what is the original question

somber juniper
#

im doing question 78 atm

carmine dock
#

You can write any one of them in this case

somber juniper
#

okay so u see i wrote -1 as lower and 4 as upper

#

it says its incorrect

#

and it doesnt give answer to others

#

see

#

no 78

#

and the only one i did is incorrect

#

but -4 is also lowest here

#

like agh

#

-4 is the lowest lowest bound

carmine dock
#

Your answers are valid

somber juniper
#

it says -2

carmine dock
#

this is really weird

somber juniper
#

im redoing it and -4 is also a lowest bound

somber juniper
#

i've been dealing with this for the past 6 days

#

once it says A is correct and on the next page it says A is incorrect

carmine dock
#

For 77, the roots are -1,2,2
So even though 3,-2 is a possible answer
4,-1 should also be correct

somber juniper
#

is -4 also correct?

#

for 77

#

also someone said the highest value we got when we're dealing with rational root theorem is the upper bound and the lowest value is the lowest bound

carmine dock
#

if you are talking about lower bound, yes

somber juniper
#

is this correct

somber juniper
somber juniper
#

so basically the highest value is the upper bound?

#

<@&286206848099549185>

crimson sedge
#

What the problem

somber juniper
#

is the highest value we find using rrt the upper bound?

crimson sedge
#

?

somber juniper
crimson sedge
#

Ohh

cedar kilnBOT
#

@somber juniper Has your question been resolved?

somber juniper
#

.close

cedar kilnBOT
#
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cedar kilnBOT
#
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calm elm
#

i'm trying to draw something and my page is 24.6cm and that length is supposed to represent 31m

calm elm
#

i can't for the life of me figure out how to divide the length of the paper into meters or whatever

#

so when i draw a point on my paper that's supposed to be say 1.3m, i want to know how many cm or mm that is

stoic gale
#

Only use 20 cm of the page, each cm represents 2 meters or something along those lines

calm elm
#

that's a good idea, i'll do that

#

thanks

stoic gale
#

Nws

cedar kilnBOT
#

@calm elm Has your question been resolved?

cedar kilnBOT
#
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tired delta
cedar kilnBOT
tired delta
#

Anyoneee

nocturne reef
#

!status

cedar kilnBOT
#
What step are you on?
1. I don't know where to begin.
2. I have begun but got stuck midway.
3. I got an answer but I was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
nocturne reef
#

Sidenote, I wish my handwriting was as neat as yours lmao

tired delta
#

I don't know where to begin.

nocturne reef
#

Okie dokie, so do you know how to find extrema (maxima/minima) using the derivative?

tired delta
#

yess yess

nocturne reef
#

Okay, so how do we do that? ANd what do we get if we differentiate f(x)?

tired delta
#

by using power rule igg

nocturne reef
#

Yeah exactly, so give that a go and let me know what you get for f'(x)

tired delta
#

its 2x - 5

nocturne reef
#

Good, so what is 2x-5 equal to at a maximum/minimum?

tired delta
#

umm dont know 😭

nocturne reef
#

haha okay, so the rule is that your extrema are when f'(x) = 0

#

So 2x -5 = 0

#

So what's x?

tired delta
#

5/2

nocturne reef
#

Exactly, now they'll want it as a coordinate so we need to find the y value when x = 5/2

#

How do we do that?

tired delta
#

by puting the value of x

nocturne reef
#

Yeah you sub x back into f(x)

#

So what do we get for the y value when we sub x=5/2 in

tired delta
#

0

nocturne reef
#

I came out with -1/4 lol

#

$(\frac{5}{2})^2 -5 \cdot \frac{5}{2} + 6$

wraith daggerBOT
#

TayBee

nocturne reef
#

Don't substitute into f'(x) as we know that it equals 0 when x=5/2

#

Substitute it back into your original function, f(x)

tired delta
#

ohh ok ok

nocturne reef
#

Okay, so our extreme point is at (5/2, -1/4)

#

Now is it a maximum or a minimum?

tired delta
#

maxima igg

nocturne reef
#

What does a quadratic with a positive x^2 term look like?

tired delta
#

ax^2+2x+c=0 ??

nocturne reef
#

Yeah but I mean like if you draw it on a graph, what shape is it

tired delta
#

u maybee

nocturne reef
#

Yeah exactly a u

tired delta
#

yess yess

nocturne reef
#

So is the extreme point (at the bottom of th eu) a max or min\

tired delta
#

can u send a picc i cant get it

nocturne reef
#

Positive quadratic looks like that right?

#

So is the green dot the maximum or minimum value of the function

tired delta
#

yess

#

ig its the origin ??

nocturne reef
#

Origin is irrelevant here, it's the minimum - the line represents all the values the function can take right? So that green dot is the smallest value the function can ever take

#

This is your specific functiuon

tired delta
#

yess yess so its absolute minimaa

nocturne reef
#

Exactly

#

So that's the first question done, we have a minimum at (5/2, -1/4)

#

As a sidenote, we can also work out if something is a max or min with the second derivative, f''(x) - differentiate f(x) twice basically. Then substitute in the value you got for x when f'(x) = 0.

If f''(x) > 0 then it's a minimum and if f''(x) < 0 then it's a maximum.

#

But a quadratic is something we're all familiar with so I don't thinkkkk they would need you to do that here

#

If you did

#

f''(x) just equals 2

#

So it's always >0 therefore your extreme point is a minimum

#

But anyway

#

Part b

#

What do the words domain and range mean?

tired delta
#

set of input

#

igg

nocturne reef
#

Yeah so the domain is the input

#

The range is the output

tired delta
#

yess

nocturne reef
#

The domain is basically asking the question of are there any values of x that would make f(x) undefined if you put it in

#

So like if you had a fraction, it would be undefinied if the denominator was equal to 0, or if you had a square root, it would be undefined if what was inside the square root was negative

#

But here

#

Are there any values of x you could put in that would cause a problem?

tired delta
#

noo

nocturne reef
#

Good, so our domain is just $x \in \mathbb{R}$

#

Latex has failed me

#

X is a real number lmao

#

Or alternatively (-infinity, +infinity)

#

Depending on how you've been taught to write domains

tired delta
#

ohh ok ok

#

and wb rangee?

wraith daggerBOT
#

TayBee

nocturne reef
#

There we go XD

#

And range is what we get out

#

So what possible values can y be?

#

Think back to what we worked out re. the minimum and what the graph looks like

tired delta
#

2,1,0

nocturne reef
#

So our minimum y value is -1/4 remember?

tired delta
#

yess

nocturne reef
#

But as you can see it can be anything higher than that

#

So y is any number that is greater than or equal to -1/4

#

Does that make sense?

tired delta
#

yes yess

#

so it can be 0

#

ohh so 1?

nocturne reef
#

Ignore that I got muddled XD

#

We'll write our range as:

#

$y \ge -0.25$

tired delta
#

ohh ok

wraith daggerBOT
#

TayBee

nocturne reef
#

because if you look at the graph, the lowest y value we have is -0.25

#

And from there it just increases

tired delta
#

yess

nocturne reef
#

But it increases forever

#

To infinity

#

So that's our range

#

Does that make sense? Thats q b done lol

tired delta
#

so infiity is our range ??

nocturne reef
#

No our range is y >= -0.25

#

That's how we write a range

tired delta
#

ohh ok ok

nocturne reef
#

The range is just an inequality representing what values y can take

#

Using interval notation

#

You could write

#

[-0.25, +infinity)

tired delta
#

ohh ok ok

nocturne reef
#

So part c is just putting it all together

tired delta
#

wait a min i will be right back

nocturne reef
#

When you draw a function you should include

  1. x intercepts
  2. y intercepts
  3. extreme points/points of inflection
  4. asymptotes
  5. The general shape
nocturne reef
#

There are no asymptotes because it's just a quadratic, we know our extreme point (the minimum), we also know the general shape, so that's 3 4 and 5 done

#

All we now need to work out are the x and y intercepts

#

So how do we do that?

tired delta
#

now we can put the values

nocturne reef
#

Yeah, so our y intercept is when x=0 and our x intercepts are when y=0

#

So starting with the easy one, what's our y intercept?

tired delta
#

-1/4

nocturne reef
#

No that's our minimum

#

So we go back to our function

#

x^2 - 5x + 6

#

And we substitute in x=0

#

What do we get if we do that?

tired delta
#

oh yes

#

-1/2'

nocturne reef
#

$y = 0^2 -5(0) + 6 = 0 - 0 + 6$

wraith daggerBOT
#

TayBee

nocturne reef
#

What is 0-0+6 XD

tired delta
#

hmm?

nocturne reef
#

On your calculator, 0^2 - 5(0) + 6

#

Should just give you 6

#

So that's our y intercept

tired delta
#

yes yess

nocturne reef
#

You can see it labelled here

#

So now for our x intercepts

#

We substitute in y=0

#

$x^2 -5x + 6 = 0$

wraith daggerBOT
#

TayBee

nocturne reef
#

So solve that, and what values do we get for x

tired delta
#

2

#

?

nocturne reef
#

Yes good 2 is one

#

But there are two solutions

#

What's the other one?

tired delta
#

its 0

nocturne reef
#

Nope

#

Factorise the quadratic or use the quadratic formula

#

Or use the solver on your calculator if that's allowed lmao

tired delta
#

-2

nocturne reef
#

(x-2) is one of the brackets but that gives x=2 which you've already found

#

What's the other one

#

What two numbers multiply to +6 and add to -5

tired delta
#

2 times 3?

nocturne reef
#

-2 times -3

#

So your two brackets are (x-2)(x-3)

#

Which means x-2 = 0 or x-3 =0

#

So x = 2 or?

tired delta
#

yess yess

#

they an be both

#

can*

nocturne reef
#

Yes, x=2 is one solution

#

What's the second one?

tired delta
#

x=3

nocturne reef
#

So there's are your two x intercepts

#

(2,0) and (3,0)

#

So label everything on your graph and that's the question done

#

Good work haha

tired delta
#

thanks sir or friend

#

whichever u r

#

whats ur age btw?

cedar kilnBOT
#

@tired delta Has your question been resolved?

#
Channel closed

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#
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After 15 minutes, feel free to ping <@&286206848099549185>.
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summer lintel
#

A symmetric matrix $A$ is called positive definite if $0 < x^T Ax$.

\textbf{Lemma 6.37}

For a symmetric matrix $A$ of size $k \times k$, the following statements are equivalent:

\begin{enumerate}
\item $A$ is positive definite.
\item All eigenvalues are positive.
\item There exists a constant $C > 0$ such that $C \cdot \lVert x \rVert^2 \leq x^T Ax$ for all $x \in \mathbb{R}^k$.
\end{enumerate}

\textbf{Proof:}

First we show that (1) $\implies$ (2).

$\lambda \cdot \lVert v \rVert^2 = \lambda v^T v$ and $\lambda v^T v = v^T A v$ and $\lambda v^T v = v^T A v$.

Why is this true?

wraith daggerBOT
#

// 1800

pastel vault
wraith daggerBOT
pastel vault
#

You're just writing the first v as a row vector v^T

summer lintel
#

why is v*v = v^t v

pastel vault
#

And then $\lambda v^T v = v^T \lambda v = v^T A v$

wraith daggerBOT
pastel vault
#

Then the first entry of the row vector v^T is v1, which gets multiplied by the first entry v1 in the column vector

#

Similarly you get v2 * v2

#

So it's v1 * v1 + v2 * v2 + ... + vn * vn

summer lintel
#

so

pastel vault
#

Should be a row vector dot a column vector

#

You get the idea

summer lintel
#

dot product of v is v*v = v_1^2,v2^2,v3^3 etc

pastel vault
#

So it's just v_1^2 + v_2^2 + ... + v_n^2

summer lintel
#

yeah that is what i meant

#

you add them all uip

pastel vault
#

Cool

summer lintel
#

$|v| = \sqrt{v_1^2 + v_2^2 + \ldots + v_n^2}$. Squaring both sides of this equation gives us $|v|^2 = v_1^2 + v_2^2 + \ldots + v_n^2$.

wraith daggerBOT
#

// 1800

summer lintel
#

and the dot product of v with itself is equal to the v^t dot v?

summer lintel
#

what about the next step

pastel vault
summer lintel
#

yeah

pastel vault
#

So lambda is just a constant: we can order it anywhere

summer lintel
#

how does lambda turn in A

pastel vault
#

It's a definition

summer lintel
#

ok

pastel vault
#

So if $Av = \lambda v = \lambda I v$, multiplying by the identity matrix which does nothing

wraith daggerBOT
pastel vault
#

$Av - \lambda I v = 0 \implies (A - \lambda I) v = 0$

wraith daggerBOT
pastel vault
#

See where that comes from now?

summer lintel
#

but then we have a v too much

#

if lambda is equal to A v

pastel vault
#

lambda v = Av

summer lintel
#

so what is the definition of lambda

pastel vault
#

Such that lambda v = matrix A multiplied by vector v

#

And v is a special vector such that when you multiply it by matrix A, all it does is scale the vector along a line

#

And it doesn't move it away from that line

cedar kilnBOT
#

@summer lintel Has your question been resolved?

#
Channel closed

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split egret
cedar kilnBOT
split egret
#

Are they both 136

#

?

hot crag
#

theta, yes. gamma, not necessarily

#

mb: gamma, no

split egret
hot crag
#

i mean

#

it's fairly obvious, cointerior angles

split egret
hot crag
#

no...?

#

don't reply ping me

#

please

split egret
#

Ok sry

#

Wdym no...?

hot crag
#

is alr

split egret
#

?

hot crag
#

gamma is cointerior with 54 deg

#

what do cointerior angles sum to?

split egret
#

Yeah so it's 126

#

?

hot crag
#

yse

#

you said 124

#

126 is right

#

!done

cedar kilnBOT
#

If you are done with this channel, please mark your problem as solved by typing .close

hot crag
#

@split egret

split egret
#

Ok thanks bye

#

.close

cedar kilnBOT
#
Channel closed

Closed by @split egret

Use .reopen if this was a mistake.

cedar kilnBOT
#
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fathom star
cedar kilnBOT
fathom star
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I know the power reducing formula for cos^2x: 1+cos2x/2

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do the 2's turn into 3's for cubed?

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1+cos3x/3

buoyant latch
fathom star
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hm, maybe I missed something in the book then. Dont recall seeing this, but I have a example for sin^4x. 🤔

fathom star
# buoyant latch

Do you just have to remember each formula individually or is there a conversion for squard to another power?

buoyant latch
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I just google it

fathom star
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If only I could google during test 😅

crimson delta
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well cos^3=cos*cos^2 so you could use the one for ^2 twice

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would take longer obviously

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combined with double angle

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easier to just remember

fathom star
crimson delta
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forget it

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made a mistake in my head. would be even worse than I thought

fathom star
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would you do the power reducing for cos^2x then multiply the result by cosx?

crimson delta
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yes but then you have cosx*cos(2x) and then other stuff you have to worry about

fathom star
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Still not sure what im supposed to be doing then

crimson delta
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dw. just remember the formula for ^3

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😛

fathom star
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Not even sure why this is on the practice test based on what Im reading about it

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.close

cedar kilnBOT
#
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cedar kilnBOT
#
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modern prism
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Need help with this

cedar kilnBOT
pastel vault
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!status

cedar kilnBOT
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modern prism
cedar kilnBOT
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@modern prism Has your question been resolved?

cedar kilnBOT
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#
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sand meadow
cedar kilnBOT
sand meadow
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is any option right?

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i think for bijection null space should be 0

cedar kilnBOT
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@sand meadow Has your question been resolved?

cedar kilnBOT
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@sand meadow Has your question been resolved?

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cedar kilnBOT
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undone reef
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Pyramid SABCD base - rhombus. The length of the rhombus side is 15 cm, and the length of the larger diagonal is 24 cm. The side walls of the pyramid form an angle equal to 45 degrees with the base (Which is a rhombus). Prove that OE = 7.2cm (O - Base center, E base edge center)

cedar kilnBOT
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What step are you on?
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deft saddle
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try drawing it out first

undone reef
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I have the drawing it was given with the task

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but its in another language so i didnt do a photo, i rewrote it

deft saddle
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send anyway

undone reef
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i think im onto something but i dont know how to turn cos alpha = 3/5 into degree

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Photos quality really bad