#help-49

1 messages · Page 58 of 1

strong lava
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Yes

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sinon, version courte,
t'as bien fini ta sup là ?

pulsar sun
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I think I understand

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so the condition is that the points are not "reversed"

strong lava
pulsar sun
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its not the unique condition ?

strong lava
pulsar sun
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?

strong lava
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t'es bien en sup dans une petite prépa?

pulsar sun
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oui je me débrouille bien en plus

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oui

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désolé mais je n'arrive pas à me l'imaginer quand je bute sur quelque chose j'ai l'impression juste quand je le code de toute façon je fais déjà une rotation

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donc forcément elle existe

strong lava
# strong lava sinon, version courte, t'as bien fini ta sup là ?

SL2(R) est naturellement isomorphe au groupe (R / (2piZ), +), lui même isomorphe à R / Z aussi connu comme S^1, le cercle
L'isomorphisme en question se base sur le fait qu'une rotation est définie par l'image de (1, 0)
Pour tout autre point, il existe un changement de base orthogonale (plus précisément la composée d'une homothétie et d'une rotation) qui l'envoie sur (1, 0). Donc une rotation est aussi définie par l'image d'un point fixé, en regardant où elle l'envoie sur le cercle du bon rayon.

Bref, une rotation centrée en l'origine est donc déterminée par l'image de n'importe quel point différent de 0, définissant ainsi une fonction f : R* x R -> SL2(R) U {pas de rotation} surjective
Il est alors naturel que pour une paire quelconque donnée, il est fort peu probable que f(x, x') = f(y, y') soit dans SL2(R)
Encore moins 3 points

pulsar sun
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le problème étant que quand je l'ai codé effectivement je connais tout les points avant la rotation forcément et j'applique une rotation d'angle theta aléatoire à ces points donc la rotation à déja bien lieu, le mieux serait alors plutot de prendre 3 points avant et après sachant que ceux après conservent la même distance par rapport à l'origine et les distances entre eux, il n'y aurait alors pas de rotation que quand il n'y a permutations de 2 points après

strong lava
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donc tu construits tes points de tel sorte que la rotation existe toujours

pulsar sun
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c'est le problème de mon programme je viens de me rendre compte

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c'est pour cela que je ne comprenais pas

strong lava
pulsar sun
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faudrait juste que je dise ok je conserve les distance par rapport à l'origine et entre eux et voyons voir si une tel rotation existe

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non si c'était vraiment aléatoire j'en aurais jamais des rotations

strong lava
pulsar sun
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pas vu encore

strong lava
pulsar sun
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c'est le dernier chapitre à voir cette année

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ok

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on conserve la norme dans les isométries ?

strong lava
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par définition tu préserve la distance

pulsar sun
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une isométrie directe

strong lava
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la notion de directe est arbitraire et inutile ici

pulsar sun
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ça conserve l'orientation de la figure si j'ai bien compris

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donc c'est plutot à partir de 2 points ou plus qu'on a pas forcément rotation

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pourquoi m'a t'il parlé de 3 points ou plus ? je n'en ai aucune idée

strong lava
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C'était ton idée ?

pulsar sun
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oui enfin c'est mon prof qui m'a dit qu'a partir de 3 point ou plus ça va poser des problèmes

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je lui demanderai ce qu'il voulait dire par là

strong lava
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La question est bc plus intéressante si tu considères des rotations de centre quelque

pulsar sun
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c'est ce que je voulais faire au début, pourquoi donc ?

strong lava
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Car c'est soudainement plus trivial

pulsar sun
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mon prof m'a juste dit que je devait rester avec l'origine car $f : x \mapsto xe^{i\theta}$ était une app linéaire

strong lava
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Oui sinon 0 n'est plus fixe

grand pondBOT
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phoestaclies

pulsar sun
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meme un isomorphisme ici

strong lava
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Mais les espaces affines c'est pas le diable
C'est juste hors programme

pulsar sun
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bon bah merci bien, j'éclaircirais tout ça demain avec mon prof. T'as fait prépa aussi alors ?

strong lava
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Comme tu le sais

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À moins qu'on n'ai pas parlé depuis 1 an car j'ai changé de pseudo ici

pulsar sun
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tu as déjà une école, enfin tu es peut etre meme déja beaucoup plus loin que ça

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nan je me rappelle pas de notre discussion

strong lava
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Non je finis la L3 là

pulsar sun
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juste de ton pseudo

strong lava
pulsar sun
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c'était il y a deja longtemps je pense, après j'ai la mémoire courte pour certain trucs

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tu était à llg et tu est allé à ulm c'est ça

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bonne fin de soirée, merci encore

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👍 je tacherais de ne pas oublier ce pseudo

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.close

midnight plankBOT
#
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midnight plankBOT
#
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spice prairie
midnight plankBOT
spice prairie
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could somebody explain how the 4/log2x-2 3 becomes log3 2x-2

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i dont understand how

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2x-2log3 becomes 4log3/ 4log2x-2 right

vagrant marlin
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do you know that log base a of b

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is log b over a

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@spice prairie

spice prairie
vagrant marlin
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yes

spice prairie
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so

vagrant marlin
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so do you know change of base formula

spice prairie
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alogb = clogb/cloga

vagrant marlin
spice prairie
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oh yea

vagrant marlin
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yeah

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so it becomes 1 / log3/log(2x-2)

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do you follow

spice prairie
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yeah

vagrant marlin
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so it reciprocal so we flip

spice prairie
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oh and thats log2x-2

vagrant marlin
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so log(2x-2)/log3

spice prairie
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/ log3

vagrant marlin
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yeah

spice prairie
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ohh

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aightt

vagrant marlin
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u get it now

spice prairie
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and then 3log3 is just 1

spice prairie
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i have one more question tho

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2sec

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actually 2 more steps that i dont understand

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first this

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why does the above become that

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and then just this

vagrant marlin
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because

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he exponentiated both sides with a base of 3

spice prairie
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can you just do that

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is it a rule or

vagrant marlin
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yes

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do you know the natural logarithm

spice prairie
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ln

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right

vagrant marlin
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yes

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so if you have lnx=2

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for example

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you exponentiate both sides with base e

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to get x = e^2

spice prairie
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doesnt it become e^lnx = e^2

vagrant marlin
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yeah

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do you know that

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b^log base b of a = a

spice prairie
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uhh

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wdym

vagrant marlin
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one sec

spice prairie
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😭sorry

vagrant marlin
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lemme write it out

spice prairie
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aight

vagrant marlin
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like this

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oh sh

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why is the left grey

spice prairie
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😭

vagrant marlin
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wait do you get it

spice prairie
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the left a at the top

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is the base right

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or

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no

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wait

vagrant marlin
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a is the base

spice prairie
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yeah

vagrant marlin
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and also the base of the logarithm

spice prairie
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ohhh

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omd

vagrant marlin
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its a to the power of log base a of b

spice prairie
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aighttt i understand

vagrant marlin
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yeah

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so thats what happened basically

spice prairie
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isnt there like another way to do that

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or do i have to apply that rule

vagrant marlin
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its easiest to apply that rule

spice prairie
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aight aight

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and one more

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the right side is making me trip

vagrant marlin
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log(a^b) = bloga

spice prairie
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yeah

vagrant marlin
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so sqrt x

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is x^1/2

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which they took out of the log

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and then they squared it

spice prairie
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why does it become 1/4 tho

vagrant marlin
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because they square it

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squared

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on the right

spice prairie
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for what

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😭

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ohh

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cuz it goes

vagrant marlin
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do you see that the expression is squared

spice prairie
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out of the parentheses

vagrant marlin
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yh

spice prairie
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oh aight

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so thats it basically

vagrant marlin
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yh

spice prairie
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i hate logs bro

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its mad confusing

midnight plankBOT
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@spice prairie Has your question been resolved?

midnight plankBOT
#
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mighty pelican
midnight plankBOT
mighty pelican
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is the radius 8.9?

tiny token
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CAN SOMEONE HELP ME WITH 1+1

sweet wing
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do you have it in the form (x-a)^2+(y-b)^2=r^2?

mighty pelican
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yes

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(x-4)^2 + (y-8)^2 = 16 +64=8

sweet wing
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from there you can directly read off the radius

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since the RHS is radius^2

deep vine
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let's back up for a second. are you sure it's 16+64?

mighty pelican
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let me redo it

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1

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sec

deep vine
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make sure you're accounting for the constant correctly

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what i suggest is that your first step is to move the constant to the other side of the equation:
x^2+y^2-8x+16y = -16

mighty pelican
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is the radius

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just

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8

deep vine
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yes

mighty pelican
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ok thx

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the 16 and -16 cancelled out

deep vine
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gj!

mighty pelican
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and everything else was right

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like the center and stuff

deep vine
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yep

mighty pelican
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is this correct

sweet wing
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looks right

mighty pelican
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thank u

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correct?

sweet wing
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submit and find out

mighty pelican
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that doesnt tel me if its right or not

sweet wing
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you dont ever get feedback?

mighty pelican
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No

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idk why she just doenst let us see our grade immediately

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to stop cheatin gig

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ig

sweet wing
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but you see it at the end?

mighty pelican
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No

sweet wing
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never?

mighty pelican
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it shows u after the due date

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liek

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if u submit

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u can see after the thing is due

sweet wing
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yes, so afterwards

mighty pelican
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i mean like

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so its due at midnight tonight

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i wouldnt be able to see it til it was midnight

sweet wing
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that makes sense

mighty pelican
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should

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i keep the

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^2

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on the 13

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or no

magic rampart
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yeh you have to

sweet wing
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go to the form (x-a)^2+(y-b)^2=r^2

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youve found a and b

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now if you plug in the other point

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you can find r

mighty pelican
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i have everything

runic yoke
runic yoke
mighty pelican
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yeha

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but its a tedt

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test

runic yoke
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exactly

mighty pelican
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where the questions r mainly diff for each person

runic yoke
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i mean you can still ask friends for help

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ah wait

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nvm that wouldn't work

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if the questions are diff then there is no point in hidiing the grade

mighty pelican
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i agree

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its also in a different order

sweet wing
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if you know the answer is right, then you know (almost certainly) that the method is correct

feral meadow
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hello, could anybody help me out with this question?: A store offers a one-day 10% discount on all cell phones. They also offer a warranty that costs either 5% of the discounted price or $35. Write an equation based on the original price that models each possibility for the warranty.

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(sorry if this isn't how asking questions is supposed to work I can delete my message if so)

sweet wing
feral meadow
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ahh ok sorry i should have read that first

sweet wing
#

find an open channel and ask your question

midnight plankBOT
#

@mighty pelican Has your question been resolved?

midnight plankBOT
#
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twilit field
#

Consider the following subset of the XY plane $S={|z-iz|,|z|^2:z \text { is a complex number}}$

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
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then which statment is correct

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  1. S denotes an ellipse but not a circle
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2)S is a parabola

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  1. s is a circle
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  1. S is a hyperbola
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so $|z-iz|= |x+iy-i(x+iy)|$

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
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whic is

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$\sqrt{(x+y)^2+(y-x)^2}$

grand pondBOT
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ƒ(Why am. I here)=I don't know

hard umbra
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can you give a geometric interpretation to |z - iz|

twilit field
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it feels like it should be a hyperbola

hard umbra
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geometrically, what is |z - iz|

twilit field
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so z and iz are perpendiular to one another, right?

hard umbra
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yes

twilit field
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so it should be a stright line?

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no an ellipse

hard umbra
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no tell me what |z - iz| is first

twilit field
hard umbra
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z and iz are perpendicular of the same length

twilit field
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yes

hard umbra
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not algebraically

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you can do this purely from the geometry

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what is |z - iz| then

twilit field
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I don't really know the equations of conics in $\C$

grand pondBOT
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ƒ(Why am. I here)=I don't know

hard umbra
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you don't need to

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this is all real stuff

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z and iz are perpendicular and of the same length
what is |z - iz|

twilit field
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hmm

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a circle

hard umbra
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no

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it's just a real number

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i want the value

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the distance between z and iz

twilit field
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$\sqrt{2|z|}$

hard umbra
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z is outside with a | |

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
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right

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my bad

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$\sqrt{2}|z|$

grand pondBOT
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ƒ(Why am. I here)=I don't know

hard umbra
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so the x coordinate is just sqrt(2)|z|

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and the y coordinate is |z|^2

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i think at this point it's obvious what S is

twilit field
#

a parabola

hard umbra
#

evidently

twilit field
#

thanks

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.close

midnight plankBOT
#
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twilit field
#

$let f \Q \rightarrow \Q$ be a function such that $f(x+y)=f(x)+f(y)$

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
#

where $x,y\in Q$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
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and f(1)=10

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prove the function is a bijection

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so to start

surreal moon
twilit field
#

f(2)=f(1)+f(1)...

misty gorge
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(this function happens to be Q-linear)

twilit field
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no idea what that means

misty gorge
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it's linear

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since it's a map from Q -> Q

twilit field
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this is supposed to be solved using HS level knowledge

misty gorge
#

yeah

twilit field
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makes sense

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If I redefined it to be a map from R to R

misty gorge
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don't

surreal moon
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Define $x$ as a ratio of two integers $x=\frac{p}{q}$

twilit field
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it's derivative will be constant

grand pondBOT
misty gorge
#

it's not linear if it's a map from R -> R

surreal moon
#

consider what you can do with that

misty gorge
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it might not be continuous

twilit field
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so this proves it's increasing on $[1, \infty)$( can be shown by induction)

misty gorge
#

what

grand pondBOT
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ƒ(Why am. I here)=I don't know

surreal moon
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I believe you are overthinking it

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Prove that $f(nx)=nf(x)$

grand pondBOT
twilit field
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can I present my method first please

surreal moon
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Then prove $f(\frac{x}{n})=\frac{1}{n}f(x)$

grand pondBOT
surreal moon
twilit field
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sorry

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$f(1-0)=f(1)-f(0)$

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
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this proves f(0)=0

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and similarly I can show It's odd about 0

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so this can be extended to prove surjectivity

misty gorge
#

how

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how do i use what you said to show that there's some x such that f(x) = 5

twilit field
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f(3)=f(2+1)

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f(4)=f(3+1)=f(3)+f(1)

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f(5)=f(4)+f(1)

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f(3)=f(2)+f(1)

surreal moon
misty gorge
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none of these yield an x such that f(x) = 5

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f(3) is 30 for example

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(which you CAN get from what you said, i agree, but surjectivity won't come from that)

twilit field
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for instance for $\Q^+$

grand pondBOT
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ƒ(Why am. I here)=I don't know

twilit field
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$f\left(n\right)=\sum_{i=1}^nnf\left(1\right)$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

misty gorge
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yes i agree, but that doesn't get me 1/2 * f(1)

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as an output

twilit field
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I'm not done

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$f\left(1\right)=2f\left(\frac{1}{2}\right)=4f\left(\frac{1}{4}\right).....$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

this isn't enought though

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I agree

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should probably just find a general formula for $f(n) , n\in Q$

grand pondBOT
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ƒ(Why am. I here)=I don't know

surreal moon
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any thoughts?

twilit field
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I'm thinking

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any rational can be expressed as the sum of an integer and a rational number

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I guess I use that?

surreal moon
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Probably not the best route imo

twilit field
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why not?

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$f(\frac{p}{q}) = f(floor(\frac{p}{q}))+f(frac(\frac{p}{q}))$

surreal moon
twilit field
#

hmmm

grand pondBOT
#

ƒ(Why am. I here)=I don't know

surreal moon
#

$f\left(\frac{p}{q}\right)=f\left(\floor{\frac{p}{q}}\right)+f\left(\floor{\frac{p}{q}}-\frac{p}{q}\right)$

grand pondBOT
surreal moon
#

Sorry that's not a hint. I was just writing out your tex

surreal moon
twilit field
surreal moon
twilit field
#

$f\left(\frac{p}{q}\right)=f\left(\left[\frac{p}{q}\right]\right)+f\left(\left[\frac{p}{q}\right]\right)-f\left(frac\left{\frac{p}{q}\right}\right)$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

surreal moon
twilit field
#

no?

grand pondBOT
#

ƒ(Why am. I here)=I don't know

surreal moon
twilit field
#

$f\left(nx\right)=f\left(\frac{n}{2}x\right)+f\left(\frac{n}{2}x\right)=2f\left(\frac{n}{4}x\right)+2f\left(\frac{n}{4}x\right).....$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

like this?

surreal moon
#

Not quite. No. You proved $f(nx)=2f\left(\frac{n}{2}x\right)$. I'm asking you to prove that $f(nx)=nf(x)$

grand pondBOT
twilit field
#

then I'm not sure

surreal moon
#

Hint: You'll need induction

twilit field
#

okay

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hmm

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f(2)=2f(x)

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I'm not sure honestly

surreal moon
twilit field
#

f(1)

surreal moon
#

Our base case is to prove that $f(1x)=1f(x)$

grand pondBOT
twilit field
#

yes

surreal moon
#

I'm huessing that doesn't take a lot of effort to prove

twilit field
#

isn't that trivially true

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1x=x

surreal moon
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Yes. Exactly.

twilit field
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do f(1x)=f(x)=1f(x)

surreal moon
#

Yes. Perfect

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Base case proven.

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Now, for induction, what do we need to assume is true and what do we need to prove is true from that assumption?

twilit field
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f(nx)=nf(x) is true

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and then prove that f((n+1)(x))=(n+1)f(x) is true

surreal moon
twilit field
#

that's trivially true too

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but why does induction work though

hard umbra
#

it's certainly not "trivially" true

surreal moon
hard umbra
#

even if it is "trivially" true, you should be even more so able to write a proof

twilit field
#

hmm

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okay

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so f((n+1)(x))= (n+1)f(x)

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which is nf(x)+f(x)

quaint aurora
#

Does anyone know about groups? I'm just looking for more information, nothing more (if you know Spanish better, the truth is, English is difficult for me xd)

midnight plankBOT
surreal moon
surreal moon
twilit field
#

(n+1)=t

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uh, I think i've spent too much time on this problem

surreal moon
#

Hint: $f((n+1)x)=f([nx]+[x])$

grand pondBOT
hard umbra
#

brackets catscream

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this is pretty unfortunate notation, since a lot of people use [] for the floor function

surreal moon
#

Hint: $f((n+1)x)=f((nx)+(x))$

twilit field
#

might aswell solve this later

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sorry

grand pondBOT
twilit field
#

i'll do this later

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sorry

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.close

midnight plankBOT
#
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last slate
#

I'm lost on part b. I tried plugging in 5 for x in the equation above.

knotty forge
#

Because that will get you a different answer.

strange zodiac
last slate
#

yess it was equal to o.05. Thank you that makes sense!!

#

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manic bison
midnight plankBOT
manic bison
#

How to solve this?

twilit field
#

you sum up each element individually if I'm recalling the notation right

manic bison
#

How tho

#

Like there is an inequality at the bottom

twilit field
#

can you re-write the question more clearly please

#

can't read it

manic bison
#

Alright wait

twilit field
#

or type it out

manic bison
#

This one

twilit field
#

,rotate

grand pondBOT
manic bison
#

The notation here is Sigma btw

twilit field
#

oh

#

so i<j

#

I'm not sure then

#

sorry

manic bison
#

It's fine dw

sinful river
#

you do it step wise
as in first j takes a value (subsequent sum of all is)
then j steps up by 1

last slate
#

But what happens when j takes the value of 1 ?

sinful river
#

so your final sum is like this (all iterations are wriiten as (i+j))
(j=1 nothing)
(j=2) = i =1
j=3 i =1 and i =2
j=4 ; i=1 i=2 and i=3
j=5 not possible

last slate
#

Oh

sinful river
last slate
#

Okay

last slate
#

Something that helps when the range is large

#

I struggle with these kind of problems too

sinful river
#

but if the value is large people generally arnt sadistic enough to make you do it by hand

manic bison
#

Will the answer be something like this then?

sinful river
#

i cant take 0

#

and its always 2 values

manic bison
#

What will i be there

sinful river
#

it will be like this
(1+2) + (1+3) + (2+3) + (1+4) + (2+4) + (3+4)

#

thats it

#

notice the ranges of i and j

#

minimum is 1 and i can never be equal to j as its strictly less than)

manic bison
#

Oh I see

manic bison
sinful river
#

yes

#

the easier method is to expand it into 2 summations

manic bison
sinful river
#

please excuse the handwriting

manic bison
#

Double Sigma?

sinful river
#

yep

manic bison
#

Won't it be multiplication here then

sinful river
#

the inner sigma is done first then the outer sigma

sinful river
manic bison
#

Ohhhh

sinful river
#

like c++ or java

#

its a nested loop

manic bison
#

This was done yesterday in my math olympiad preparation class

sinful river
# manic bison Nope ;-;

ohk so basically it is always summation but the step up for the outer sigma will happen once when the entire case of the inner sigma is evaluated

#

so j will increase by 1 after summing all possible i values in the range
if you have i<j<k then its 3 sigmas deep
so k will increase once when all of J finishes which it turn steps once when all of i finishes

#

but the internal function always remains same

manic bison
#

Ohhhh

#

Wait lemme try it

sinful river
manic bison
sinful river
manic bison
#

Alr

sinful river
#

same sigma
the condition is (2 <= i < j <= k < 10)

#

the function is (i+2j+k)

#

step 1 write down the ranges of each variable starting from the rightmost variable

manic bison
#

k will be [j,10)

sinful river
#

it takes everything from 2 to 10

#

cuz j can even be 2

manic bison
sinful river
#

the outermost variable has no issues

#

so you can blindly just put the exact range mentioned in the question

#

no comes the tricky part
try for j

manic bison
#

i not included

sinful river
#

the k is correct though

manic bison
#

I see

sinful river
#

basically the same reason works i can take values from 2

manic bison
#

Wait I get it now it's cuz 2<= i

sinful river
manic bison
#

Yea

sinful river
#

now i's range?

manic bison
#

2 to j

sinful river
#

equal to j?

manic bison
#

Nope

#

J not included

sinful river
#

Perfect

#

now step 2
expand the summation into n seperate summations and add the previous results

#

innermost variable is ?

manic bison
sinful river
manic bison
#

i + 2j +k?

sinful river
#

thats the function lmao

#

the innermost variable is i

#

outermost is k

manic bison
#

Mb I'm dumb af ;-;

sinful river
#

terminology only its fine

#

so write the summation with only

#

i

manic bison
#

Hmm ok wait

#

This maybe?

sinful river
#

Perfect

#

now add the j summation next to it

manic bison
#

Hmmm alr

last slate
grand pondBOT
sinful river
#

and you are done

manic bison
#

I see

sinful river
#

now simply just go summation by summation for each subsequent j and k value

#

again KEEPING THE FUNCTION THE SAME

#

the (i + 2j +k ) part

#

and you are set

manic bison
#

Like

#

I have to go one variable at a time?

sinful river
#

yea 😅

manic bison
#

Wait lemme try to solve it

#

@sinful river I'm clueless ;-;

#

Do I use n(n+1)/2 or something

sinful river
#

no expansion

#

start with k =2
no j or i possible

manic bison
#

Ohhhh

#

Wait brb

sinful river
#

then k =3 j = 3 and i will be 2

#

and so on

old storm
#

Isn't this just a nested for loop

sinful river
#

Basically

#

raged summations are nested for loops
the problem comes when you dont know what a for loop is XD

manic bison
#

TYSM

sinful river
manic bison
#

TYSMMMMM

#

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twilit field
midnight plankBOT
twilit field
#

so to start, I approximate sin(sin(kx)) as kx

#

so I get

#

$(kx+cos(x)+x)^{\frac{2}{x}}$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

which is in the form $1^{\infty}$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

so the limit is effectively

subtle blaze
#

well cos x is essentially 1

twilit field
#

$e^{\frac{2}{x}\left(kx+x^2+\cos\left(x\right)-1\right)}$

subtle blaze
grand pondBOT
#

ƒ(Why am. I here)=I don't know

subtle blaze
#

nah nah

twilit field
#

the limit of this at 0

subtle blaze
#

i'd rather try find a form of $\left(1+\frac{a}{n}\right)^n$

grand pondBOT
#

Frosst

twilit field
subtle blaze
#

which disapear in the limit

twilit field
#

yeah

subtle blaze
#

sort of

#

the top converges faster is the proper math

twilit field
#

$e^{\frac{2}{x}\left(kx+x^2+1-\frac{x^2}{2}-1\right)}$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

I just need the answer for now, have an exam in 2 weeks

#

I'll care about rigour later

subtle blaze
twilit field
#

so k=3

subtle blaze
#

then go $(1 + (k+1)x)^y$

grand pondBOT
#

Frosst

subtle blaze
#

then x = 2/y

twilit field
#

huh, okay

subtle blaze
#

$\left(1 + \frac{2(k+1)}{y}\right)^y$

grand pondBOT
#

Frosst

subtle blaze
#

take the limit you get $e^{2(k+1)}= e^6$

grand pondBOT
#

Frosst

subtle blaze
#

because x goes to 0, 2/x goes to inf

twilit field
#

so k=2

subtle blaze
#

yes

twilit field
#

wait

#

oh right

#

yeah, missed an x in my approximation

#

thanks

#

.close

midnight plankBOT
#
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subtle blaze
#

👍

twilit field
#

sorry for not caring about the rigour atm

subtle blaze
#

because you have e^6 as what you want to get to

twilit field
#

yeah, got it

#

thanks

midnight plankBOT
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undone pawn
#

Hi! Does anyone know what N is?

midnight plankBOT
junior flower
#

beats me

#

i really can’t think of what that could be. do you have a statement of the intermediate value theorem somewhere?

junior flower
#

loll

#

yea, i dunno then

undone pawn
#

funky

#

i'll ask my prof tmr

#

ty tho!

#

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jovial birch
#

Could someone help me determine what approach I should use when solving this? ie. u substitution, integration by parts

obsidian glen
#

(1-cos^2(x))sin(x) is your numerator

#

then split it

jovial birch
#

I don't see that identity on my sheet, which one are you taking that from?

obsidian glen
#

sin^2(x) + cos^2(x) = 1

jovial birch
#

ah ok

jovial birch
obsidian glen
#

split as in distribute

#

also this is wrong

#

I meant something like\ $\int \frac{(1- \cos^2(x)) \sin(x)}{\sqrt{\cos(x)}} \dd x = \int \frac{\sin(x)}{\sqrt{\cos(x)}} \dd x - \frac{\cos^2(x)\sin(x)}{\sqrt{\cos(x)}} \dd x$

grand pondBOT
obsidian glen
jovial birch
#

May I ask why the 'dx' gets placed next to both terms?

#

oh I guess it's just how you've written it

#

usually it is factored out: (a-b)dx

#

but you wrote it a(dx)-b(dx)

#

regardless, I am hitting a brick wall with the square root of cosx in the denominator

obsidian glen
#

how about a u substitution to get rid of that then

midnight plankBOT
#

@jovial birch Has your question been resolved?

jovial birch
#

.close

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twilit field
#

suppose $log_a(b)+log_b(a)=c$the smallest integral value of c $\forall a,b >1$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

so to start

last slate
#

x = log_a(b)

#

do this substitution

twilit field
#

$\frac{\ln\left(b\right)}{\ln\left(a\right)}+\frac{\ln\left(a\right)}{\ln\left(b\right)}$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

AM>GM?

last slate
#

u are overcomplicating

twilit field
#

oo

#

so I have to minmise $x+1/x$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

last slate
#

yes

#

find critical points

twilit field
#

cool, the min would be 2

#

thanks

last slate
#

you welcome

twilit field
#

.close

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#
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craggy yew
midnight plankBOT
#

Please don't occupy multiple help channels.

craggy yew
#

how is it a quadratic

twilit field
#

Try expanding the RHS

craggy yew
#

kk

#

got a cubic

#

(might be wrong)

twilit field
#

,w (n+2)(n+6)(n+20)

twilit field
#

so you have $n^3=n^3+28n^2+172n+240$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

craggy yew
#

yes

#

oh wait

#

the n^3s get cancelled

#

ohhhhhhh

#

i get it now

#

.close

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#
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craggy yew
#

.reopen

midnight plankBOT
#

craggy yew
craggy yew
twilit field
#

I don't know the context

craggy yew
craggy yew
#

solution

twilit field
# craggy yew

notice how the equations are in the from $a^3=2+abc$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

$b^3=6+abc$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

and $c^3=20+abc$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

do you follow so far?

craggy yew
#

...yes

craggy yew
twilit field
#

now we have $abc=n$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

craggy yew
#

yes

twilit field
#

so we solve for n, yes?

craggy yew
craggy yew
twilit field
#

now we have $a^3+b^3+c^3=28+3abc$

grand pondBOT
#

ƒ(Why am. I here)=I don't know

twilit field
#

I think you should get the right answer from here

#

remember abc=n

craggy yew
#

im confused

craggy yew
# craggy yew

i just wanna know why is the answer 151/7(i think i might have explained my question in a dumb way before so sorry)

twilit field
#

,w 28+3(-15/7)

twilit field
#

@craggy yew does this make any sense

craggy yew
#

ohhh

craggy yew
#

thanks!

twilit field
#

cool, what exam is this?

#

some undergrad entrane ?

craggy yew
#

im prepping for ioqm

#

olympiad

twilit field
#

ah

#

as in the indian olympiad ?

craggy yew
#

yes

twilit field
#

cool, good luck

craggy yew
#

someone recommended me this book which has american problems as practice sums so im usin it

twilit field
#

also solve past putman problems IMO

craggy yew
twilit field
#

google past putman papers

craggy yew
#

if i recall correctly isnt putman an undergrad math exam?

twilit field
#

yes

#

but solve papers from the 60s

#

1960s that is

craggy yew
#

yes ik

#

are they easier?

twilit field
#

some of them have appeared in jee advanced papers

#

so yes

craggy yew
#

and school math is useless for olys anyways

twilit field
#

hmm, ok

twilit field
#

this in the 30s

craggy yew
#

still tough for me cuz i dunno calculus

twilit field
#

but yeah, do calculus first

craggy yew
craggy yew
twilit field
craggy yew
#

lol i cant even understand the question

midnight plankBOT
#

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rare cloud
#

A uniform sphere of weight W and radius 5 cm is being held by a string as shown in the figure. The tension in the string will be

rare cloud
#

Why is it at vertical equilibrium and not at equlibrium on the side

#

like not in the direction of string?

sage helm
#

cuz it's not moving?

#

if you mean translational equilibrium

#

i mean tbf there's equilibrium in all directions

#

work with what you please

rare cloud
#

how do you do it in the direction of string?

#

like if you take the component of W in the direction of string

#

W_s = Wcosx

#

T = Wcosx

rare cloud
sage helm
#

Ah okay

#

It's not "incorrect" per se

#

thing is if you're balancing forces along the string then you need to consider the normal due to the wall as well

rare cloud
#

oh

rare cloud
#

right?

#

T = Wcosx + Nsinx

sage helm
#

Yeah it's kind of hard to

#

Better to just balance the vertical

#

Might be able to do it with torque

rare cloud
#

thanks

#

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gaunt nimbus
#

pls send help

midnight plankBOT
gaunt nimbus
#

i dont know how to read this in order

#

For all epsilon > 0, there is some N > 0 such that for all n in R, if N < n, then 1/n is less than epsilon.

#

I just don't see why must 1/n be less than epsilon

sweet wing
#

you can choose N

#

and it can be in terms on epsilon

gaunt nimbus
#

wait

sweet wing
#

so, if oyu choose $N=\frac{1}{\epsilon} \leftrightarrow \epsilon = \frac{1}{N} < \frac{1}{N}$

grand pondBOT
#

Flappie

gaunt nimbus
#

can i pick N to be 1/e

sweet wing
gaunt nimbus
#

c

#

oh

#

thx

sweet wing
#

if epislon and N were swapped, then thats not allowed

gaunt nimbus
#

they are both > 0

sweet wing
#

but epsilon is stated earlier, the terms after are allowed to be dependent on it

gaunt nimbus
#

ic ic

#

so if I have for all in front of there exists, the variable for there exists can depend on the for all in front of it

sweet wing
#

if the statement was: $\exists N>0, \forall \epsilon, \forall n$ then $N$ is just some number

grand pondBOT
#

Flappie

sweet wing
#

or if you have something like: $\exists x,\exists y,\exists z$ then z is allowed to depend on x and y, yis allowed to depend on x, and x isnt allowed to depend on anything (unless something else was stated earlier)

grand pondBOT
#

Flappie

gaunt nimbus
#

ic ic

#

got it now

#

.close

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#
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pale ravine
#

Hello! how to proof that this equation has only got solutions in real numbers when sin(omega) and sin(delta) are equal (didn't put /2 because sin is positive for all possible angles because they belong to first quarter)

grand pondBOT
#

𝚃𝚛𝚒𝚜𝚝𝚎
Compile Error! Click the errors reaction for more information.
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midnight plankBOT
#

@pale ravine Has your question been resolved?

midnight plankBOT
#

@pale ravine Has your question been resolved?

pale ravine
#

I've found only one solution which is close to the restriction which is pi/2. Are there 0 solutions if angles belong to (0; pi/2)?

split jetty
#

hey its you xdd

pale ravine
split jetty
#

btw $\omega$ and $\delta$ are supossed to /2?

grand pondBOT
#

clonesolopros

pale ravine
#

both angles and both half-angles are in the first quarter and both must be half-angles

split jetty
#

let $a=2x, b=2y, c=2\omega, d=2\delta \implies$
$sin(a+b)cos(c)=cos(a-b)sin(d),$ where $a,b,c,d \in (0,\pi)$

grand pondBOT
#

clonesolopros

midnight plankBOT
#

@pale ravine Has your question been resolved?

faint cairn
pale ravine
faint cairn
#

One counterexample is enough. x = y is simpler because the cos term on the RHS goes away.

pale ravine
#

I understand it. but what counterexample will there be in case if x cant be equal to y?

faint cairn
#

The same argument would probably work except now it's uglier and you have to check for the constraints.

#

You just need to prove that for some omega there is more than one choice of delta.

pale ravine
#

You gave me an idea and I tried to redraw graph in Desmos. What will be a solution here if we look at graph? Everything in this crossing area? Or another function that should cross this red line?

#

Nvm, I think I understood what I was missing in this task and probably fixed it. At least it looks like I've fixed. After your message, I wondered what I was missing out on. So I decided to draw a full graph, made some constrains also took some things from the exercise and probably got what I needed. Thanks!

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.close

midnight plankBOT
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Channel closed

Closed by @pale ravine

Use .reopen if this was a mistake.

midnight plankBOT
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abstract aurora
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The table shows 3 values of x and their corresponding values of y, where y=f(x) +4 and f is a quadratic function. What is the y-coordinate of the y-intercept of the graph of y =f(x) in the xy-plane?

sweet wing
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did you try to graph it?

abstract aurora
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No

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I was told I should find the inverse function

sweet wing
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do you know the standard formula for a quadratic?

abstract aurora
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And also told to put it in factored form then substitute from the values on the table

abstract aurora
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Lol

sweet wing
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can you write it out please?

abstract aurora
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AX^2+bx+c

sweet wing
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great, now what happens if you plug in the numbers that you are given?

abstract aurora
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I can't plug in the values

sweet wing
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why not?

abstract aurora
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I don't know a b and c

sweet wing
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you have x and y values

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doesnt matter if you dont know a b and c

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thats what we are solving for

abstract aurora
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Okay if I put the values

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What should I do next

sweet wing
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you should get a system of equations

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you have 3 equations

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and 3 unknowns

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that means you can solve for the unknowns

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do you know how to do that?

abstract aurora
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I am not sure what u mean

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Okay so I have 3 quad fn.

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I think you meant to say

sweet wing
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so, if you plug in the first point, you get $21^2a+21b+c=-8$

grand pondBOT
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Flappie

abstract aurora
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Okay

sweet wing
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and for the second one $23^2a+23b+c=8$

grand pondBOT
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Flappie

abstract aurora
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Okay

sweet wing
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and then also the third one

abstract aurora
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Okay

sweet wing
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you can solve this for a b and c

abstract aurora
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Okay

sweet wing
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if you do that, then you have a b and c for you quadratic equation

abstract aurora
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Okay

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Well I don't have a b and c 😅

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I think you stopped at substituting the x and y values from the table

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Sorry if there's a misunderstanding

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😅😅

sweet wing
abstract aurora
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Yea but i don't think I can find the a b and c

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Because they are unknown 😅

sweet wing
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you can also graph it

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,w scatterplot (21,-8),(23,8),(25,-8)

sweet wing
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what do you notice about these points

abstract aurora
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Okay, thank you.

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😊🙏

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I think I will close this ticket now 😅. Thank you sir 😊 @sweet wing

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.close

midnight plankBOT
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Channel closed

Closed by @abstract aurora

Use .reopen if this was a mistake.

analog saddle
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can i open a ticket?

abstract aurora
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Yes

analog saddle
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so do i just send a question here?

midnight plankBOT
#
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.

analog saddle
midnight plankBOT
analog saddle
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ah🙏thx

midnight plankBOT
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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
analog saddle
# analog saddle

i have finished 12i), i'm confused for the rest of the two parts. i have no idea at all on how to begin question 13, it looks horrific

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oa is y = x(x+3)
ob is y = x - 1/4x^2
ab is y = x^2 - 6x + 9

worthy kestrel
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coordinates would be at the point of intersection of the lines

analog saddle
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oh ok

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do i equate oa and ob?

worthy kestrel
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no

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doing that gets u the point of intersection which is 0,0 or point o

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u want to find a and b

analog saddle
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yhyh alrr

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would ab and ob work?

worthy kestrel
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yes

midnight plankBOT
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@analog saddle Has your question been resolved?

analog saddle
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do i sub it back into any equation to find y?

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2 x values means 2 points of intersection or am I confusing myself?

worthy kestrel
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yes

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they are the x values for a and b.

analog saddle
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how would i be able to work out the area under graph?

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i know its integration but not sure nhow

midnight plankBOT
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@analog saddle Has your question been resolved?

worthy kestrel
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u finished part 2?

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area = int oa+ab-ob

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with appropriate bounds

midnight plankBOT
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@analog saddle Has your question been resolved?