#help-4

1 messages · Page 67 of 1

barren imp
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i⁷⁶= 1?

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Am I doing this correctly?

marble arch
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Yes, you're correct

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Both of them are

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Also 1/i you can multiply i on both sides

barren imp
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And i^(-22) is... -1?

marble arch
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$\frac{1}{i}$ = $\frac{1 . i}{i . i}$ = $\frac{i}{i^2}$ = $-1$

barren imp
barren imp
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?

marble arch
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Bloody hell, okay decimal means into

honest stone
#

$\frac{1}{i}$ = $\frac{1 \times i}{i \times i}$ = $\frac{i}{i^2}$ = $-1$

barren imp
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?

rocky lotusBOT
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𝙸𝚗𝚏𝚒𝚗𝚒𝚞𝚖³

#

doctorstrangejr

marble arch
barren imp
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Where did the other i's come from?

marble arch
barren imp
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Ok so what about...m

marble arch
barren imp
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$\frac{1}{i^(-11)}$

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...

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Not what I meant

rocky lotusBOT
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RainbowOcean

barren imp
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...

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Ok

marble arch
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Wait I get it

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1/1^(-11) yeah?

barren imp
barren imp
marble arch
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Well just make it i^11

barren imp
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So...

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Uh

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×1?...

marble arch
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Just keep the power positive, look for the multiple of 4 JUST before it, and count

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so it's i^8*i^3

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or 1*i^3

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or just i^3

barren imp
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Does the 1/a and - cancle eachother out?

marble arch
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Sorry I didn't get that

barren imp
#

So you have to... (whats the term Im looking for...)

barren imp
#

And you have a fraction withing a fraction do they cancle eachother out?

marble arch
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Yes

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Fraction within a fraction?

barren imp
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Yes

marble arch
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Can you give me an example of what you're trying to say?

barren imp
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So the 1/a`² is essentually 1/(1/a²)

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Would they cancel eachother out leaving you with a²?

marble arch
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No no, how did the two come out of the power

barren imp
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Oh

marble arch
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did you mean $\frac{1}{a^{-2}}$ = $\frac{1}{1/a^2}$

barren imp
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Yes

marble arch
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Okay yes

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it just becomes a^2

honest stone
marble arch
honest stone
#

did you mean $\frac{1}{a^{-2}}$ = $\frac{1}{1/a^2}$

rocky lotusBOT
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𝙸𝚗𝚏𝚒𝚗𝚒𝚞𝚖³

barren imp
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Yes!

rocky lotusBOT
#

doctorstrangejr

marble arch
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Peak stuff

barren imp
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You guys are pretty good with the commands

marble arch
#

Infinium is definitely better, I started using them rather recently

barren imp
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I can barely do basic server commands still💀

marble arch
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You'll soon learn toohappy

barren imp
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Thank you

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I have a feeling (unlike most my servers) I will be using this one very often especially when I jump back in Chemistry and physics

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So back to the fraction within a fraction

marble arch
marble arch
barren imp
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So... why are we doing it by sum

marble arch
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Sum, where?

barren imp
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The exponents.

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Off topic

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But where did I go wrong?

marble arch
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Where were you wrong again?

barren imp
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Here

marble arch
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Ahhhhhh

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Well it'd be -(16 + 1)

barren imp
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Yeah...

marble arch
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$(a+b)(a - b) = a^2 - b^2$

rocky lotusBOT
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doctorstrangejr

marble arch
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and $-i^2$ = $-(-1)$

rocky lotusBOT
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doctorstrangejr

marble arch
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which is +1

barren imp
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Yeah I got that

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Originally I put 17

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But then forgot the 16 is negative

marble arch
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Ahhhh that's fine man, we all make mistakes

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Let me show I would do it

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oh wait

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It's $(4 + i)(-4-i)$

rocky lotusBOT
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doctorstrangejr

marble arch
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That's $-16 - 4i - 4i - i^2$

rocky lotusBOT
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doctorstrangejr

marble arch
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or $-15 - 8i$

rocky lotusBOT
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doctorstrangejr

barren imp
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Ohhhhhh

marble arch
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me and you both completely missed it!

barren imp
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We did

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Ok check me if Im wrong here- for a different one

marble arch
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Alright sure

barren imp
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(8+9i)(8-9i)

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I got =145

marble arch
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It's correct!

barren imp
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Wait really?

marble arch
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Yup

barren imp
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That was fast

marble arch
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Yup, 64 + 81

barren imp
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Did you do it mentally?

marble arch
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Yup, I'm kinda decent at mental calculations

barren imp
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I used to but when you dont do math for a while you struggle with something basic like 6+8 or 9×7

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Im getting a bit better at it again

marble arch
barren imp
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But its taking some time

marble arch
barren imp
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Considering I have just started again last month Im having a bit more confidence

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But back to 1/i^(-11)

marble arch
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Alright then

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So send it up!

barren imp
marble arch
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Well, get the power positive

barren imp
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So you cant flip it to i¹¹ because of the fractions

marble arch
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Yup, but you can do so by sending it up

barren imp
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Eh...make it i⁸ +i³?

marble arch
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No wait see

barren imp
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Oh!

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Oh.

tawny moon
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,tex exp rules

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nvr mind i thought that was a guild preamble

barren imp
tawny moon
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but do you know what you can do whenever you see a negative exponent?

barren imp
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But its already a fraction

tawny moon
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aha. the rule works both ways

barren imp
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Its a fraction in a fraction

tawny moon
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ok how about this

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do you have a calculator?

barren imp
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I thought if I cross the numerators cancled out it would leave us with i¹¹

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But apparently thats not it

marble arch
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Well $a^2$ = $\frac{1}{a^{-2}}$ right?

tawny moon
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you are not done yet

tawny moon
barren imp
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I do but itz not adapt for complex numbers

rocky lotusBOT
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doctorstrangejr

marble arch
barren imp
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???

marble arch
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So it basically works the other way too

tawny moon
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anyway you got to the point of i^11

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now, I'm going to quote something a helper said to another helpee some time ago, if I may

marble arch
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Yeah sure!

barren imp
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So a'²= 1/a²
And
1/a` ²= a² ?

tawny moon
marble arch
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Oh god no I confused them, when you reciprocate fractions, the signs of the power change

barren imp
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I loath fractions

tawny moon
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as long as you remember one simple rule - that flipping a fraction flips the signs of all exponents in the numerator and denominator - you're good to go

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there's a reason why the button to flip a fraction on a calculator is x^-1

marble arch
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like $i^{11}$ = $\frac{1}{i^{-11}} $ and vice versa

rocky lotusBOT
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doctorstrangejr

tawny moon
# tawny moon

either way, when you're done pondering on that, this is your next step

barren imp
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Huh...

tawny moon
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take your calculator right now

barren imp
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No no I believe you

tawny moon
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type this in.
1/(3^-1)

marble arch
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No like if you still have doubts

barren imp
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Im just trying to figure out HOW its done if you dont get cancle out the fractions

marble arch
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then do what she's saying, just do it even if it's clear, would help it settle in

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Okay so you agree that $\frac{1}{i^{-11}}$ = $\frac{1}{1/i^{11}}$ right?

rocky lotusBOT
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doctorstrangejr

barren imp
tawny moon
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can you show what you typed?

barren imp
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Oh

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Theres no /

marble arch
# barren imp Yes

Okay, now can't we make $\frac{1}{1/i^{11}}$ as $i^{11}}$ by sending the $i^{11}$ up

tawny moon
# barren imp

don't actually type 3^-1 raw in calculators like these

barren imp
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💀👌

tawny moon
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either type 3^(-1), or type 3, followed by the x^-1 button

barren imp
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Ohhh so it flips essentially

tawny moon
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also, it's supposed to be 1**/**(3^(-1))

rocky lotusBOT
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doctorstrangejr
Compile Error! Click the errors reaction for more information.
(You may edit your message to recompile.)

hazy pivot
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Use \/

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Instead of /

barren imp
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If it was just i¹¹ it would stay the denominator:O

tawny moon
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yes, it would (or you can bring it up as a negative exponent too, depending on what you want to do with it)

marble arch
barren imp
tawny moon
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but here, we want the exponent to be positive, so as doctorstrange mentioned, we flip the fraction (formally called taking the reciprocal of the fraction)

tawny moon
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that's key

barren imp
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Either way

tawny moon
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not necessarily

barren imp
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Now I under- oh

tawny moon
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you can leave it as a negative exponent if you want to, depending on what you want to do with it

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but here we want the exponent to be positive

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so flip it is

marble arch
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But here, for simplicity, we make it positive

tawny moon
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now that our whole rodeo of burger fraction flipping is over

barren imp
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XD

tawny moon
barren imp
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Ok

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So -1² I thought its just 1?

marble arch
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Yes

tawny moon
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but now notice this.

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-1 is i^2, and (-1)^2 is 1.

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do you see where I'm going with this?

barren imp
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Yes

tawny moon
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so, what can we conclude?

barren imp
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i³=1

tawny moon
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is that a 3?

barren imp
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Wait-

tawny moon
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sure about that?

barren imp
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Ha... ok no I thought I saw where the direction was going

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I was wrong

marble arch
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Okay, well what would i^3 be (hint - i*i^2)

tawny moon
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i^2 = -1
(-1)^2 = 1
can you now draw the correct conclusion?

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(hint: make one substitution. your final conclusion should not have a -1 in it)

barren imp
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Oh- i² (-1) and i² (-1)
(-1) • (-1)=1
i² • i² = i⁴ =1

marble arch
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Nice!

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Okay, so tell me i, i^2, i^3 and i^4 now

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(well, you can exclude i xD)

barren imp
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Ok i² = (-1)
And i³= -i
And i⁴= 1

marble arch
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Bravo!

barren imp
tawny moon
#

I'm giving you the second part in advance because you more or less found it out

tawny moon
# tawny moon

this is the key part you were missing in your initial answer of i^11

marble arch
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Yup, check the multiple of 4 just before it

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basically values of i in powers repeat after every 4th power

barren imp
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Wait if i² is -1
Why is i > (-1)?

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Oh wait

tawny moon
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that is a pattern marker

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don't even think of complex inequalities

barren imp
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catthumbsup Im overthinking again

marble arch
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like i -> -1 -> -i -> 1

tawny moon
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we don't have (at least not at this stage) well-defined orderings for the complex field

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so don't try to compare two complex numbers

barren imp
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i is +
i² ends negative

barren imp
marble arch
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And this repeats for every 4th multiple of power

barren imp
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Ok but i¹¹= -i?

marble arch
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if I ask you i^5, i^6, i^7 and i^8, you'll have the same answer in this very order

marble arch
barren imp
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Yayyyy

marble arch
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Just use the multiple of 4 analogy, and remember that values of i repeat

barren imp
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Is it 3-8i?

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Or wait-

marble arch
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so $i^{4n}$ = 1, $i^{4n + 1}$ = i, $i^{4n + 2}$ = -1, $i^{4n + 3}$ = -1, if we write it more formally, (where n is a whole number)

barren imp
#

I see

rocky lotusBOT
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doctorstrangejr

marble arch
barren imp
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So in that case its its something like i^((4)(12) +3)= -i

barren imp
marble arch
#

Exactly, so $i^{(4*12)+3}$ = $i^{51}$ = $-i$

rocky lotusBOT
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doctorstrangejr

tawny moon
marble arch
barren imp
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Can you show an example?

marble arch
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Okay

barren imp
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For instance how does 3+8i ->3-8i

marble arch
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$(3 + 8i)(3 - 8i)$ = $(3^2 - (8i)^2)$

rocky lotusBOT
#

doctorstrangejr

marble arch
#

You get how right, the identity?

barren imp
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Yes

marble arch
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Okay

barren imp
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What happens to the ²s

marble arch
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Now i just gets squared, and the imaginary term is removed

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$(3^2 - (8i)^2)$ = $(9 - (-64))$ = $73$

rocky lotusBOT
#

doctorstrangejr

marble arch
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Notice how it gives only a real number (73) and no imaginary term

barren imp
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Uhhhh

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Yes

marble arch
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That's what a conjugate does basically, and we need the (a + b)(a - b) identity for that

barren imp
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How does that get it to 3-8i?

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Or is the complex congugate just a step

marble arch
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It is just a step

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You could say that

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like see

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$(3 + 8i)$ does the work of $(a + b)$

rocky lotusBOT
#

doctorstrangejr

marble arch
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now we need an (a - b) to get only a real number, and that term we call its conjugate

barren imp
#

What about $\frac{10}{-i}$

rocky lotusBOT
#

RainbowOcean

marble arch
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You got the previous one right?

barren imp
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I see so

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This is just a beginner step for later problems

marble arch
#

Alright

marble arch
barren imp
marble arch
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no no both sides, both the numerator and denominator

barren imp
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What would tjat look like

marble arch
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$\frac{10.i}{-i.i}$ where . is *

rocky lotusBOT
#

doctorstrangejr

tawny moon
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(brackets are a thing kek)

marble arch
#

Yeah I've tried but it doesn't help

barren imp
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So why wouldn't i cancle out the one above

marble arch
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Because we need it for simplification!

barren imp
#

Ah ...

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So -i (i) = i²=-1?

marble arch
#

-i^2 isn't it?

barren imp
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Oh!

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Your right

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THEN it turns to 1

marble arch
#

Yup!

barren imp
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Which leaves 10i

marble arch
#

Exactly

barren imp
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Ok ok now I get that one more

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So then... 1 + 7i/1 + i...

marble arch
#

Okay

barren imp
#

$\fract{1 + 7i}{1 + i}$

rocky lotusBOT
#

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

barren imp
#

...

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You get what I mean...

marble arch
#

Allow me

#

$\frac{1 + 7i}{1 + i}$

rocky lotusBOT
#

doctorstrangejr

barren imp
#

Yeah

marble arch
#

Okay, so what do we multiply both sides with (Hint : we want a real number in the denominator)

barren imp
#

1?

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Or 7

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Or i again?

marble arch
#

Well, what do you multiply a complex number with so that it only leaves a real number?

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what's the term?

barren imp
#

Its self?

marble arch
#

well, its conjugate

barren imp
#

i

marble arch
#

with (a - bi) for the (a + bi) we have

barren imp
#

Oh

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1 - i

marble arch
#

Yes

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Now multiply both sides with (1 - i)

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$\frac{(1 + 7i)(1 - i)}{(1 + i)(1 - i)}$

rocky lotusBOT
#

doctorstrangejr

barren imp
#

So then 1 + 7i²

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And 1 - i²

marble arch
#

oh god

barren imp
#

Wait

marble arch
#

my fault

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Just open the brackets and evaluate it

barren imp
#

Ok

marble arch
#

god I shouldn't have explained with the squaring

barren imp
#

So then

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2+6i

marble arch
barren imp
#

And 2

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Oh. 8?

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Where is the 8 from

marble arch
#

well -i*7i gives 7

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and there's already a +1

barren imp
#

Ohhh

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So we still foil

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Oh ok so then its 1-i+7i-7i²

marble arch
#

Sorry but I should sleep now, really sorry if I've confused you, there are people better than me here

barren imp
#

Its ok

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Thank you for helping

marble arch
#

Anytime man, and sorry again

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@tawny moon can you take over?

tawny moon
#

ah shucks, I just entered a channel

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ok, I'll try but Idk where you guys are at atm

barren imp
barren imp
barren imp
tawny moon
barren imp
#

Yes

tawny moon
#

what is the objective here?

barren imp
#

This

tawny moon
#

ah ok

visual remnant
#

Come on

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This mad easy

barren imp
#

💀

tawny moon
visual remnant
#

Ok sorry

tawny moon
#

anyway

tawny moon
barren imp
#

I just got back in to math after a WHILE I only have a few weeks under my belt give ke a breaksully

tawny moon
barren imp
#

And then below is

tawny moon
#

-6i?

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also, do something about that i^2

barren imp
#

Oh-

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1 + 6i -7 (-1)

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Which makes 1 + 6i +7
8 + 6i

tawny moon
#

now do the denom

barren imp
#

Then the bottom 1-i²

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Or

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1-(-1) = 2

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8+6i/2

tawny moon
#

now divide the numerator by the denom

barren imp
#

Ok

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That makes 4 + 3i

tawny moon
#

careful about bracketing: (8+6i)/2 is preferred

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and that's the final answer

barren imp
#

Oh

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Yayyy

#

And then the conjugate for -14i is
14i ?

barren imp
tawny moon
#

nps

barren imp
#

Ok then 11/-i

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Eh... 11i?

tawny moon
#

first, state the objective

barren imp
#

I need to put it in standard form

tawny moon
#

a + bi?

barren imp
#

Yes

tawny moon
#

well it's gonna be just bi here only since we don't have an a

barren imp
#

A is 0

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So its just 11i?

tawny moon
#

working?

#

or reasoning?

#

arguably more important than the answer itself that you know why it is correct

barren imp
#

Ok well if its 11/-i multiply both by i

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Leaving 11i

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A+ bi form is = 0 + 11i

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Technically

tawny moon
#

I was expecting a more thorough explanation of what happens in the denom, but I suppose this works

barren imp
#

Oh! Right the -i (i) = -i²

#

Which makes -(-1) = 1

tawny moon
#

excellent.

barren imp
#

So its not important

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I mean it is

tawny moon
#

can't say it's "not important", we just got lucky it simplified this way

barren imp
#

But it turns it to a whole number

tawny moon
#

specficially, it turns into 1, so we don't have to deal with it

tawny moon
barren imp
#

True

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Hmmm

tawny moon
#

anything else?

barren imp
#

Still working on the top

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Ok so far I have 64+32i+32i+16i²

#

Over 64+32i-32i-16i²

tawny moon
barren imp
#

Wai-

tawny moon
#

remember, we choose to mult by the conjugate of the denom precisely to create a diff of two squares situation

barren imp
#

I thought

#

I thought I need to foil

#

The denominator is (8-4i)(8+4i)

tawny moon
#

you do. but you have not simplified the denom

#

and here's a bit of a pro tip for you

#

since you know that you're creating a diff of two squares in the denom, you can directly write the denom as a diff of two squares

tawny moon
#

my bad

#

the extra i terms confused me - I was not expecting to see any i remaining

barren imp
#

Do the +4i/-4i cancel eachother out?

tawny moon
#

no

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wait what do you mean +4i/-4i

barren imp
#

Well 8/8 is 1?

#

Oh- the negative

tawny moon
#

ok let's take this again

tawny moon
tawny moon
barren imp
#

Ohhhh

#

I was just showing you as I was still in the process of working it out in case I made a mistake you saw me me

tawny moon
#

fair enough

#

appreciate the hard work

barren imp
#

Thank you:) So then so far. 64 + 64i +16(-1)
Over
64-16(-1)

tawny moon
#

continue

barren imp
#

Which then simplies further to 48 + 64i
Over
80

#

Ugh...

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That doesnt... seem right

tawny moon
#

fractions it is

#

it just so happens that 48, 64 and 80 share a very convenient common factor

barren imp
#

Ok so then... 8-

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No

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16

tawny moon
#

you will have a and b as fractions

barren imp
#

So then 3+4i/5

tawny moon
#

no, don't combine them

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(at least I don't think your site wants it that way)

barren imp
#

It says to divide

narrow arrow
#

i mean imaginary part 0*

barren imp
#

Wait...

#

The example is showing something different

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But I dont understand why we are reducing this one

narrow arrow
barren imp
narrow arrow
barren imp
#

This wasn't in my notes...

narrow arrow
#

you cant tell me you didnt see 5 as a common factor

#

brotherr 🙏

#

well you dont even really gotta factor out the five in the first step if you are okay with more calculation

tawny moon
#

hang on

#

where are we now

tawny moon
#

I just said that you should not leave your answer as $\frac{3 + 4i}{5}$

rocky lotusBOT
#

fox(x, y); ∂(fox)/∂x (Flower)

tawny moon
barren imp
#

Ok so then

tawny moon
#

split the two terms into their own fractions

barren imp
#

Do we make it 3/5 and 4i/5

tawny moon
#

I prefer $\frac{3}{5} + \frac{4}{5}i$

rocky lotusBOT
#

fox(x, y); ∂(fox)/∂x (Flower)

tawny moon
#

because then it's a direct comparison with a + bi

barren imp
#

Oooohh

#

I guess you can reduce it or jump to complex conjugates

#

Lets see

tawny moon
#

it's just rewriting the thing so that $\color{yellow}{\frac{3}{5}} + \color{red}{\frac{4}{5}}i$ can be compared with $\color{yellow}{a} + \color{red}{b}i$

barren imp
#

I see

rocky lotusBOT
#

fox(x, y); ∂(fox)/∂x (Flower)

tawny moon
#

so that no one can contest and say that "oh but you didn't write it in the correct form!!!"

barren imp
#

Thats so helpful!

tawny moon
#

yeah, this is a common trick some examiners love to use unfortunately

#

so I tend to give them what they want to the T

barren imp
#

I see

tawny moon
#

anything else?

barren imp
#

Ok yes

#

(-7+ 7i)(9 + i)

#

For the answer I got
56+ 56i

tawny moon
#

let's see

#

that 56 is defo wrong

#

the 56i is correct

barren imp
#

Oh-

tawny moon
#

-7 times 9 is so negative that no i^2 can save it

barren imp
#

Its... -70

#

So -70 + 56i

#

Uh.. ok this one Im a little unsure of

#

(-4+6i)²

#

It just says multipy

#

I think we still foil but Im a bit unsure

tawny moon
#

yes, foil as usual

barren imp
#

I got... -10?

#

Wait-

#

-20

tawny moon
#

what about the imaginary part? can't leave that hanging

barren imp
#

The imaginary- oh...

#

I see it is -48i

#

Thats where I went wrong

#

So its -20 -48i

tawny moon
#

good. anything else?

barren imp
#

There are things but I think its best to call it a night thanks for helping me again getting sleep last night helped alot

#

I will probably pick up and review before I retake something tomorrow

tawny moon
#

wise choice

#

oh wait it was you whom I told to sleep last night too

#

ok lol

barren imp
#

Yep

#

I was very out of it yesterday

#

But while it was a bit rocky today I think I am doing pretty decent

#

Anyway hope you have a good night:)

tawny moon
#

well it's afternoon for me

#

but yes, have a good rest

barren imp
#

Oh-

#

Right timezones

#

Anyway have a good day:) bye

tawny moon
#

aight

barren imp
#

.close

vale dockBOT
#
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vale dockBOT
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primal matrix
#

Hi, I'm starting with derivations, is this correct?

frozen ledge
#

you forgot the +

#

at the end for 3(-1)x^{-2}

primal matrix
#

Yess, ty

safe fulcrum
rocky lotusBOT
frozen ledge
#

that too

safe fulcrum
#

it's better to write it as $\sqrt{2} \sqrt{x}$, so its derivative will be $\sqrt{2} \frac{1}{2 \sqrt x}$

rocky lotusBOT
safe fulcrum
#

if you apply the power rule you do get 1/(2 sqrt(x))

primal matrix
#

Ok ty, is there any rule to derivate the sqrt?

safe fulcrum
lucid nimbus
#

I think it's easier the second way he wrote it

primal matrix
#

The rule is invert the sqrt + multiply it by 2?

safe fulcrum
rocky lotusBOT
safe fulcrum
#

cause what does $\frac{1}{2} x^{-\frac{1}{2}}$ simplify to?

rocky lotusBOT
primal matrix
#

Ok ty, i close the doubt

#

.close

vale dockBOT
#
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primal matrix
#

.reopen

vale dockBOT
primal matrix
#

Hi again, why the sqrt of 2 doesn't derivates?

stark wedge
#

what

stone verge
#

the sqrt of two is the coefficient of sqrt(x)

primal matrix
primal matrix
#

Ok

safe fulcrum
#

yeah, $\frac{d}{dx} (kf(x)) = k \frac{d}{dx} (f(x))$

rocky lotusBOT
safe fulcrum
#

then k = sqrt2

primal matrix
#

I have not studied d/dx yet

#

I will continue studying, ty everyione!

#

.close

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#
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chrome pond
vale dockBOT
chrome pond
#

how do you get the mark circled

woeful trench
#

If the examiner sees that you have a sum of the forms that you've circled, you would get that mark (so either exactly the LHS, or something "similar")

#

They'll also accept if you forget they mention there's no replacement (hence the "condone...")

#

Please don't advertise your server in here, and certainly not in the help channels catokay

chrome spruce
#

Sorry

vale dockBOT
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stone depot
#

One message removed from a suspended account.

stone depot
#

One message removed from a suspended account.

fierce vector
stone depot
#

One message removed from a suspended account.

fierce vector
#

free body diagram

stone depot
#

One message removed from a suspended account.

fierce vector
vale dockBOT
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jolly sorrel
vale dockBOT
jolly sorrel
#

I'm not sure if this is correct

#

Because when I plotted the functions and tbe tangent line it went through y1 at a point

#

But at (-1,2) they had a shared tangent line

#

I'm pretty sure my handwriting is readable

untold oxide
#

Hi, form what I see, you've done well. You should write what you've done in addition to the calculation itself.

jolly sorrel
#

Write what I did?

#

I dont follow

untold oxide
#

that is, first you've made sure both functions pass through the point (-1,2)

jolly sorrel
#

They do!

untold oxide
#

that's the top part of the page

#

I know they do, they do bc you've made sure of that, butyou need also to wrote it down, that's part of the answer

jolly sorrel
#

?!

#

I have to write even that

#

I forget😀

untold oxide
#

So, add it. It will make your text more readable.

jolly sorrel
#

Okay

#

Thanks

#

.close

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#
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leaden portal
#

03 - (ITA SP/2007)
Determine the quantities of 3-digit numbers that can be formed with the digits 1, 2, 3, 4, 5, 6, and 7, satisfying the following conditions: repeated digits are allowed, except when the number starts with 0; and no digit can appear more than once (even if it is the first digit). Assign the result obtained.
a) 204
b) 206
c) 208
d) 210
e) 212

leaden portal
#

hey guys! i've solved this exercise in a way i can't understand the logic behind it

ebon glade
#

repeated digits are allowed
no digit can appear more than once

dreamy scroll
#

I was thinking the same

leaden portal
#

the answer is correct

#

i just don't understand how

#

i missed something

#

its not subtraction under is multipication

#

2!.4!

signal void
#

it's not

#

okay

#

okay

leaden portal
tawny moon
#

so what exactly is your question?

signal void
#

i see

leaden portal
#

how is this working

tawny moon
leaden portal
#

the transation is poor too, let me re write the question

#

it can repeat but only whit 7

signal void
#

in here, can rerwithe into 7!/(2! * 4!)*2+2

leaden portal
#

and only when the first digit is 1 or 2

signal void
#

r u ok?

tawny moon
#

at this point

#

!original please

vale dockBOT
#

Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.

tawny moon
#

it's ok even if it's not English

leaden portal
#

1 second

signal void
#

very busy

dreamy scroll
leaden portal
#

no worries, hahah

#

gpt is having a hard time translating it

#

1 second

tawny moon
#

the original image will do.

leaden portal
#

03 - (ITA SP/2007)
Determine how many 3-digit numbers can be formed using 1, 2, 3, 4, 5, 6, and 7 that satisfy the following rule: The number cannot have repeated digits, except when it starts with 1 or 2, in which case 7 (and only 7) may appear more than once.
Mark the obtained result.

a) 204
b) 206
c) 208
d) 210
e) 212

signal void
#

we can rewrite into 7!/(2! * 4!)2+2
and then calculate the this:
7!/4! +2=7 * 6
5+2=210+2=212
r u ok? @leaden portal

leaden portal
#

but what is the logic behind it

#

why is this working

signal void
#

please "Add friend"
I can explain more detail

leaden portal
#

👀

tawny moon
leaden portal
#

i get this

signal void
#

evader? @tawny moon
u r evader

leaden portal
#

its like saying it gets to the answer

signal void
#

yeah

leaden portal
#

but how?

turbid valve
signal void
leaden portal
#

i used a repetition formula to solve an exercise that can't

signal void
#

what do u not understand?

dreamy scroll
signal void
#

hoho

#

haha

#

hi @tawny moon
u r from japan? im japan

leaden portal
woeful trench
leaden portal
turbid valve
leaden portal
#

😢

turbid valve
#

I've gotta go to work rl quick but very quickly: split it up into cases

#

One case where the number begins with 1

#

One where it begins 2

#

And one where it begins with any other number

leaden portal
#

177 and 277

#

this would lead to 7!/4! + 2

#

i get this

#

but why using a repetition formula on 2 brackets . 2 works?

leaden portal
#

i'm learnig this topic and it would help me understand

#

i've solved this one using a method i have not understand why is working

#

its not good

hardy coral
leaden portal
#

yes

#

🙂

hardy coral
#

Ok, here's how I would do it

leaden portal
hardy coral
#

There is no digit 0, so no problem with the number starting with 0 and not actually being 3 digits

#

The "except" part only adds two cases: 177 and 277

leaden portal
#

yes! it would lead to 7!/4!

hardy coral
#

The rest is just: 7 choices for the first digit, 6 for the second, 5 for the third

#

So yes, 7!/4!

#

To that you can just add 2 for the special cases

leaden portal
#

but i did not solve this way

hardy coral
#

What did you use then

leaden portal
#

i get it that it is the easy way

hardy coral
#

You are missing a parenthesis but alright, this is the same as 7!/4! + 2

#

I don't quite know how you came up with it though

leaden portal
#

repetition formula on 2 spaces

#

[!(N+(R-1))/N!.(R-N)!]

#

how this formula found the answer is hounting me 🤣

hardy coral
#

pandahmm That formula is incorrect, otherwise you wouldn't have a *2 at the end

leaden portal
#

2 is for the 2 lines

#

in the exam made sense

#

pure luck then

hardy coral
#

What 2 lines

leaden portal
#

to be fair i looked at the answers and saw that it was close to 200 something

#

and i multipyed by 2 to get closer thinking a got something wrong in the way

#

then added 2 of 277 and 177

#

at the alternatives

hardy coral
#

Without repetition: $\binom{n}{k} = \frac{n!}{k!(n-k)!}$ - with repetition: $\left(\binom{n}{k}\right) = \binom{n+k-1}{k} = \frac{(n+k-1)!}{k!(n-1)!}$

rocky lotusBOT
leaden portal
#

i looked at the alternatives no]t answer

#

let me get this formula

#

its not these 2

#

nevermind

#

it was

#

well, i won't wast more of your time

#

thanks a lot

#

.close

vale dockBOT
#
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vale dockBOT
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atomic mauve
vale dockBOT
atomic mauve
dreamy scroll
#

uh huh

#

what now

atomic mauve
midnight fractal
#

@atomic mauve !help

honest stone
#

You opened a help channel.

#

Do you have a question?

midnight fractal
#

.help

vale dockBOT
#

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midnight fractal
wraith heart
#

.close

vale dockBOT
#
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dreamy scroll
honest stone
#

no he has helpful perms

#

which means you can pin and use .close

honest stone
#

Being helpful.

#

also, why do you need it? hmmCat

dreamy scroll
honest stone
#

Looking_suspicious yeah probably not.

honest stone
vale dockBOT
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proper timber
#

@everyone

vale dockBOT
proper timber
#

I need help

#

@everyone @everyone @everyone @everyone @everyone @everyone

#

@everyone

#

v

#

@everyone

#

@everyone

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@everyone

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@everyone

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@everyone @everyone @everyone
@everyone

sharp whale
#

<@&268886789983436800> @proper timber

glass kelp
zealous pendant
#

Who are they even pinging lol

woeful trench
#

Seems like they're gone RooThink

#

.close

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#
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glass kelp
#

Deleted

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noble raft
#

Need help

vale dockBOT
noble raft
#

Here’s my failed attempt

#

<@&286206848099549185>

zealous pendant
#

!15m

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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.

zealous pendant
#

Oh nvm

#

Sorry I thought you’d just posted it

noble raft
#

it was 14mins cmon dawg

#

Failed attempt 2

#

At my wits end here

ivory valley
# noble raft

I think you can use anticommutative property and induce a minus, then it should cancel out, i think

noble raft
ivory valley
#

a x b = -(b x a)

noble raft
#

in which failed attempt should I do this

#

1 or 2

ivory valley
#

the one with the jeans

noble raft
#

okay I'll give that a go

#

dont disappear on me

#

then BAC-CAB again?

#

okay I tried that and wounded up with same answer

#

@ivory valley

ivory valley
#

yeah i realized

noble raft
#

Am I just cooked

ivory valley
#

let's not give up

noble raft
#

does the unit vector e_r have a derivative and I just have been doing it wrong

ivory valley
#

surely there is something small we overlooked

noble raft
#

idk I'm feeling like I coulda overlooked a lot of things, this is entirely new to me

ivory valley
#

I think differentiating the relation $\bm{r} = r\hat{\bm{e}}_r$ and substituting the derivatives of $r$ might help

rocky lotusBOT
noble raft
#

So e_r as r(vector)/r

#

?

ivory valley
#

yea

noble raft
#

Wait I’m lost

#

What is the derivative of e_r wrt t

ivory valley
#

well, $\hat{\bm{e}}_r(t) \coloneqq \f{\bm{r}(t)}{r(t)}$

noble raft
#

Oh does quotient rule apply

rocky lotusBOT
ivory valley
noble raft
#

Okay I’ll try this and get back

#

Nope still lost I fear

#

Having spent hours on this I’m giving up for today

#

If anyone has a solution I’d appreciate it smmm

#

Anyways thanks for the help

ivory valley
#

what did you get as derivatives

noble raft
#

I do not see this shit simplifying

#

There’s no m or k

#

In the derivative of e_r

ivory valley
#

i misread

noble raft
ivory valley
#

So we have $\dot{\bm{e}} = \f{1}{k}(\ddot{\bm{r}} \cross \bm{L}) - \dot{\hat{\bm{e}}}_r$

rocky lotusBOT
ivory valley
#

$m\ddot{\bm{r}} = \bm{F}$ and $\bm{F}(\bm{r}) = -\f{k}{r^2}\hat{\bm{e}}_r$ imply $\ddot{\bm{r}} = -\f{k}{m} \cdot \f{\hat{\bm{e}}_r}{r^2}$ \
and $\bm{L} \coloneqq m(\bm{r} \cross \dot{\bm{r}})$ from the textbook.

rocky lotusBOT
ivory valley
#

@noble raft

ivory valley
vale dockBOT
#

@noble raft Has your question been resolved?

ivory valley
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thick solar
vale dockBOT
thick solar
#

help

#

I dont quite understand

cobalt crow
#

interior angles of a triangle need to sum to wat

thick solar
#

can I just get the answer

dusky bison
#

!noans

vale dockBOT
#

The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.

#

@thick solar Has your question been resolved?

dense wyvern
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orchid thistle
#

what is simplest form of log5+logx-log4+logy

orchid thistle
#

I got log(5xy/4)

#

but got marked as wrong and saw that the answer was log(5x/4y)

honest stone
proud kestrel
#

is there parenthesis around the -

honest stone
#

that’s why parens are necessary.

orchid thistle
#

no

honest stone
#

maybe they changed it?

orchid thistle
#

no parenthesis

eternal osprey
#

The software is buggy. Ask your teacher

proud kestrel
#

then ur answer is right lol

honest stone
orchid thistle
#

kk tyall i was doubting myself

#

ill ask again

honest stone
orchid thistle
#

.close

vale dockBOT
#
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brazen cargo
#

yo

honest stone
#

hi

vale dockBOT
#
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wild token
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Im struggling with 3a- we did an example but i didnt really understand it. Can someone walk me thru it

eternal osprey
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I think you're supposed to do dimensional analysis here

wild token
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I learnt two ways of doing it

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one in my physics module and then one in my mathematical modelling module( thats where the q is from)

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the mathematical modelling module uses a technique im not comfortable w thats why i wanted osmoene to maybe explain to me

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i can send an example q if thats helpful

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from the lecture notes

eternal osprey
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Should be the same, right? It boils down to solving linear system.

wild token
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this isthe method used in my mathematical modelling module

eternal osprey
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I think much of the complexity of the mathematical modelling module is that we don't assume ũ to be linear.

wild token
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I get confused by the division part

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It’s just idk

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He didn’t really explain it properly

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Like here

eternal osprey
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You mean the $A = [p_0]$ part, or $\tilde{p}=\frac{p}{p_0}$ part?

rocky lotusBOT
wild token
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Idk why they done it

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And it actually means

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And why they r dividing p by p0

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Idk😭 man

eternal osprey
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I think that so they have a dimensionless variable $\tilde{p}$?

rocky lotusBOT
wild token
wild token
eternal osprey
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$\frac{h}{h_0}$ by convention.

rocky lotusBOT
wild token
vale dockBOT
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@wild token Has your question been resolved?

eternal osprey
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Well, you can look at the dimension of $\sigma$, $\rho$ and $g$

rocky lotusBOT
vale dockBOT
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torn herald