#help-26

1 messages · Page 222 of 1

sick hawk
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Here is the mark scheme for you

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no im off

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sorry 4P2

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6!/3!

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2! * 4P2 * 6!/3!

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.close

topaz sinewBOT
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topaz sinewBOT
#
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topaz sinewBOT
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topaz sinewBOT
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naive snow
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i have a conceptual doubt related to conic section
in conic section we have a directrix, so is it a random line or the line along which we cut the cone?
what exactly does the directrix define?

prisma mesa
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the cone is cut with a plane

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not a line

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directrix lies on that plane (since it must lie in the same plane as the conic section)

naive snow
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is the directrix just there to define eccentricity?

prisma mesa
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not really, im trying to find the graph to demonstrate it...

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there is a pretty interesting connection

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press the set alpha = beta for parabola button

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oh wait they are missing the cone

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ill edit it

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okay now this should work

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so we have a plane that cuts the cone parallel to the cones slope

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that results in a parabola

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now the neat thing is that when we put a ball into the cone, such that it touches the sides of cone and the plane (i.e. is tangent to all of them), it touches the plane exactly at the focus of the parabola

naive snow
prisma mesa
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then what happens is, those red lines are equal because they are both tangent to the sphere

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its kinda like this in 2D, the red lines here are equal

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and it can also be proved that the blue line equals the red line

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hence why its the directrix

prisma mesa
naive snow
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so can i say that the directrix is the line perpendicular to the point of intersection of the two tangents of sphere which also happens to intersect the plane along which the cone is cut?

hollow ginkgo
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Hii

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I need some help with bearings

prisma mesa
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tick the additional constructions box in the graph

naive snow
naive snow
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yes i ca see planes

prisma mesa
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this directrix lies in the horizontal plane at which the ball touches the cone

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now we will prove that the parabola property indeed holds, i.e. that these 2 lines are equal in length

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youve already seen that this red line is same as the other red line (because they are both tangents to the sphere)

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so it suffices to show that the other red line is equal to the blue line

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we can first move the other red line like this to the back of the cone. That doesnt change its length

prisma mesa
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now that blue line is same as this orange line (its actually drawn as blue in the graph)

prisma mesa
prisma mesa
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these are the intermediate steps of the move

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so by moving it like that, the length stays the same

prisma mesa
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and finally, these 2 blue lines are the same length

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so we've proved that the red line = the blue line

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i.e. the directrix property works

naive snow
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what does the other blue line signify

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the one passing through focus?

prisma mesa
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it doesnt have a name, it's there only as a part of the proof

prisma mesa
naive snow
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ohk

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and why did we choose a sphere ?

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was there like an specific reason

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?

prisma mesa
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because as it turns out, it works. It's called a "dandelin sphere"

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it works for ellipses and hyperbolas too

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I too wonder how it was discovered

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i guess we will never know

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pretty cool vid on similar topic btw, just ellipses

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it too uses the sphere

naive snow
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what about circle? it is too part of conic section

prisma mesa
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but for ellipses and hyperbolas, the dandelin spheres touch it at the focus points

naive snow
# prisma mesa

and so we can say the same for pair of intersecting lines too then.. from this one earlier

prisma mesa
# prisma mesa

this fact is unrelated to conic sections, it's just used a lot in the proofs

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that fact has more to do with symmetry / congruent triangles

naive snow
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like if we cut the cone straight down.. we have 2 lines?

prisma mesa
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yeah, thats true

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there actually is a connection between that picture and hyperbola

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but its too deep to be uncovered in discord chat

naive snow
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hmmm

prisma mesa
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A really cool book which includes a very interesting section on conic section is Measurement by Paul Lockhart

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probably my favorite math book

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if u wanna learn more about this and perhaps geometry in general, that book is really great

naive snow
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well thanks a lot, ive always preferred calculus over geometry
but this one was actutally really really cool and intresting to learn about.

naive snow
prisma mesa
naive snow
prisma mesa
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yeah

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and it probably offers one of the best takes on calculus ive ever seen

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it makes it look incredibly easy

naive snow
prisma mesa
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Yeah, its quite cool

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that vid was too inspired by the book

naive snow
prisma mesa
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You wont regret it if you enjoy math and getting your mind blown

naive snow
prisma mesa
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sure

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well, the main difference between that book and standard textbooks is that the book doesnt care about rigor. It only offers intuition. And instead of writting stuff like d / dx x^3 = 3x^2, it writes it like d(x^3) = 3x^2 dx

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and it has couple of advantages

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in general, d(f(x)) ~ f(x+dx) - f(x)

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here is a super quick derivation of the product rule:

d(xy) = (x+dx)(y+dy) - xy = (xy + xdy + ydx + dy dx) - xy = xdy + ydx + dy dx ~ xdy + ydx

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its literally just algebra. Unlike the standard way where you have to randomly add +f'(x)g(x) - f'(x)g(x) or sth like that

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and chain rule with this setup is literally so easy you dont even notice you are applying it

naive snow
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yeah, this is quite better than the standard proof and quite amazingly it is following all the properties too

prisma mesa
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d(u^2) = 2u du
d(u^3) = 3u^2 du
d((x^3)^2) = 2(x^3) d(x^3) = 2(x^3) * 3(x^2) dx = 6x^5 dx

I just applied chain rule (actually, i just did normal algebra with the d-operator)

prisma mesa
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if it was taught like this, maybe students would actually understand what theyre doing

naive snow
prisma mesa
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it actually only works on nice enough functions (but so does normal calculus)

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pretty much every rule of calculus breaks if applied on ugly enough function

naive snow
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maybe that's why 😅

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anyways thanks a bunch!

prisma mesa
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np, have a great day :)

naive snow
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now i just close it?

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idk im new

prisma mesa
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yeah, u can use .close

naive snow
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.close

topaz sinewBOT
#
Channel closed

Closed by @naive snow

Use .reopen if this was a mistake.

topaz sinewBOT
#
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weak kestrel
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My answer doesn't match even with options

topaz sinewBOT
drifting swift
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,rccw

thorny flameBOT
weak kestrel
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Shouldnt answer be cos(beta)

weak kestrel
drifting swift
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what does this say

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it's too mangled to read

weak kestrel
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I mean it can be an answer but it's not in options so it should be one of the option that I can't derive

wintry meteor
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,rotate 30

thorny flameBOT
weak kestrel
drifting swift
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ok, so it's meaningless. got it.

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from my perspective, it looks like there's no correct answer...

weak kestrel
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That's meaningless ig

radiant tapir
drifting swift
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ah wait no

weak kestrel
drifting swift
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yeah, ok, you have to go through 2(alpha+beta).

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turns out the question was not wrong

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but it is quite evil

weak kestrel
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Oh got it

drifting swift
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,rccw

thorny flameBOT
drifting swift
weak kestrel
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I mean it's npi/2

weak kestrel
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Oh I see it might become -ve(negative)

drifting swift
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npi/2 describes too much

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cot(x) = 0 when x is an odd multiple of pi/2 only

weak kestrel
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(2n+1)pi/2?

drifting swift
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npi/2 allows for n=38 which gives 19pi and cot(19pi) is undefined not 0, so your disappointment will be immeasurable and your day ruined

weak kestrel
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I have another doubt question no 60 wait it's on path
It's evil

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60
No idea where to begin

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,rccw

thorny flameBOT
drifting swift
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this reads less evil and more laborious unless you know dirty trickery

weak kestrel
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I hate laborious questions

drifting swift
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unfortunately i am not a JEE nut and so do not know the right trickery.

weak kestrel
weak kestrel
sharp pagoda
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so you have no idea?

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try to use sin^2(x)+cos^2(x)=1 to simplify the first and second equation

placid swift
sharp pagoda
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yea so its (a-b)(sin^2(x)+cos^2(x))=a-b

weak kestrel
sharp pagoda
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doesnt matter

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a can be b but then c is d so its just how you look at it

torpid trench
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@weak kestrel the answer at the back of the book turns out to be ||b||?

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i solved it rn

weak kestrel
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Oh solution

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Lemme check

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Idk

topaz sinewBOT
torpid trench
wintry meteor
topaz sinewBOT
# sharp pagoda !nosols

As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.

wintry meteor
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Not noans

torpid trench
weak kestrel
# sharp pagoda !nosols

Bro just don't use anything anywhere
Why was it made?
Paste it there, for what was it made

torpid trench
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if more help is needed on how we deduced the answer by helpee then i am free enough to give it without hesitation

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no issue there

sharp pagoda
weak kestrel
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Tho if u wanna confirm or verify answer then dm me

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.close

topaz sinewBOT
#
Channel closed

Closed by @weak kestrel

Use .reopen if this was a mistake.

torpid trench
topaz sinewBOT
#
Available help channel!

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Ask your math question in a clear, concise manner.
Show your work, and if possible, explain where you are stuck.
After 15 minutes, feel free to ping <@&286206848099549185>.
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royal sky
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hello, here i suffice to model the ODE. but i have no idea of what even to start from, since the weight would oscillate right?

loud oasis
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it would oscillate indeed

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the oscillation is a consequence of how the ODE is set up though, all you need to do for the set up is use Newton's second law

royal sky
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hmm so far i have the equation -ky = mg

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but i have no idea how to make this like

wintry meteor
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By y do you mean x

royal sky
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include the oscillation factor

royal sky
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x here

loud oasis
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Newton's second law is $\sum F = ma$

thorny flameBOT
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κλαουντ ☁ (cloud)

royal sky
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is

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yes

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but would be mg here no?

loud oasis
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no, g is not the acceleration here

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mg is the force of gravity

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in general though the acceleration is always the second derivative of position

wintry meteor
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Resultant force = mass * x’’(t)

royal sky
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wait im a bit confused here because why wouldnt we just put mg, since the only force acting on the cube downward is gravity

loud oasis
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there are two forces, gravity and spring

royal sky
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yes

loud oasis
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so a = g is a consequence of F = ma in the specific case when there is only one force, gravity. then you have ma = mg therefore a = g

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but that logic is untrue whenever you add any other forces

royal sky
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i thought earlier you were against me using mg instead of ma here

wintry meteor
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We want to find the total force right now

loud oasis
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so we have newton's second law is
[ \sum F = ma ]
the gravitational force $F_g = mg$ should appear on the left side as one of the forces being summed, it should not appear on the right side replacing the mass*acceleration term

thorny flameBOT
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κλαουντ ☁ (cloud)

royal sky
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okay so what youre trying to say is that i shouldnt replace ma with mg

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both should be included

loud oasis
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yes

royal sky
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ah sorry i misunderstood earlier

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uh

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okay so

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what force would ma even be

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if the only force here are the spring and mg

loud oasis
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ma isn't a force

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Newton's second law says that the sum of the forces on an object = that object's mass * its acceleration

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it relates cause (forces, on left) with effect (acceleration, on right)

royal sky
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okay yes i see, so uh yes

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okay im just a bit lost because

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i see what you mean but i fail to see the connection to the overall problem here

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like i cant make the link in my head yet

loud oasis
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well there are two parts to setting up a newton's second law problem:

  1. find which forces are acting on an object
  2. find the formula for each force
  3. add them up (this is the ΣF part)
  4. find the acceleration (from definition) and put that in the ma part
  5. set them equal and you're done
royal sky
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  1. there is the force of gravity, opposin the force of the spring's resistance 2. -kx and mg, okay yeah this is where im stuck, because i dont see where ma comes into play
loud oasis
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ma doesn't come into play until step 4

royal sky
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okay then 3. -kx = mg 4.

loud oasis
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for step 3 you should only be adding them, not setting them equal. this forms the left side (the ΣF part) of the ΣF = ma equation

royal sky
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ah okay so overall force F net would be mg - kx? im not too sure whether it should be mg + kx or mg - kx because they do exert their force in opposite directions

wintry meteor
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Minus although I only know that knowing the answer

loud oasis
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well we know that mg should be positive because downward is the positive direction

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and the spring force should be upward (in the negative direction) when x > 0

royal sky
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okay yeah so my logic is that Fnet = mg -kx because when the spring exerts force F net towards the positive direction would be less

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okay so here ma = mg-kx

loud oasis
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indeed

wintry meteor
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What is a in terms of x and t

royal sky
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second order

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x

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over dt

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oh yeah thing is

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im not too sure how i can incldue the oscillation here

wintry meteor
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Then solve the differential equation

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Oscillation comes out of it

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As the solution

loud oasis
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it doesn't need to be included explicitly in the setup

royal sky
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okay uh just a slight problem here so

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in the solution they gave here

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they kinda just disregarded g?

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was it another way they did or

loud oasis
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oh you can do that by a change of coordinates

royal sky
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change of coodinates?

loud oasis
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so given F_spring = kx, at what coordinate x would the sum of the spring force and gravity be 0?

royal sky
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exactly at x=0

loud oasis
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-k(0) + mg = 0?

royal sky
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i think so yes

loud oasis
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k(0) = 0

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so mg = 0??

royal sky
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oh wait jno

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uh

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okay you see how for them

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x= 0 is when the spring is at natural

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like balanced

loud oasis
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yes so we set up the problem in a coordinate system where x = 0 is the position of the unstretched spring, whereas they set up the problem where x = 0 is the position where spring force and gravity force cancel

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so let's revise our forces to match that coordinate system

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so we know that spring force = -k * (distance from unstretched position). using their coordinate system, what is that distance in therms of x?

royal sky
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it would be k * ( -x) until when it surpasses the equilibrium point where it then would be k*x

loud oasis
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no, because x is not the distance from the unstretched length point

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we know that s is the distance between the unstretched length and the equilibrium position, and that x is the displacement from the equilibrium position

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so in total, what is the total displacement of the mass from the unstretched point?

royal sky
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ah so x = k+s

loud oasis
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k isn't a length

royal sky
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sry i meant

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x = unstretched + s

loud oasis
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is it?

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if x = 0 then we should have (distance from unstretched position) = s

royal sky
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x-unstretched = s

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uh

loud oasis
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but if you plugged in x = 0 would you get (elongation of spring) = s ?

royal sky
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yea that wouldnt make any sense

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x - unstretched = s?

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wait no

loud oasis
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imagine the mass started out in the unstretched position and then moved to x = 0. then it would travel distance s. it then moved to some position x, which is the additional distance it travels beyond s

royal sky
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it would make sense if abs (s)

loud oasis
royal sky
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ohhh thats what you meant

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okay its just s + x the elongation

loud oasis
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yes, so the spring force = -k*elongation

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that's the only thing that really depended on where we place x = 0 in our ode

royal sky
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yeah i was calculating smt else i got confused

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okay so

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i basically replace my x before by x+s

loud oasis
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in the spring force specfically, yes

royal sky
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so now im at the step where i have ma = mg-k(x+s)

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and i ahve to make it in terms of displacement x over t

loud oasis
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so plug in the definition of acceleration

royal sky
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as in i put everything to second order?

loud oasis
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wdym?

royal sky
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oh no sorry like

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put the acceleration in terms of x

loud oasis
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yes

royal sky
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it would just be d^2(x) / (dt)^2 = (mg-k(x+s))/m

loud oasis
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it should be just dt^2 on the denominator but yes

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because it's meant to be read as (dt)^2 rather than d(t^2)

royal sky
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ah

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okay so

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what did they do different here

loud oasis
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you can simplify the right side

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using the fact that the sum of forces is 0 when x = 0

royal sky
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d^2(x) / (dt)^2 = (mg-k(x+s))/m im not too sure how to simplify from this

loud oasis
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just looking at the sum of forces mg - k(x+s)

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we know that when x = 0, this should be 0

royal sky
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okay lets put x=0, aka at equilibrium then (mg-k(x+s)) = 0, it just turns a = g

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which uhh

loud oasis
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where did the a = g come from

loud oasis
royal sky
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like assume this is a case where x = 0, so (mg-k(x+s)) = 0 then we are left with a = 0/m okay wait uh

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i think i got confused somehwere

royal sky
royal sky
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if x is 0

loud oasis
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we aren't plugging in x = 0 to our entire equation $\sum F = ma$, we are making a separate equation $\sum F(x = 0) = 0$

thorny flameBOT
#

κλαουντ ☁ (cloud)

royal sky
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and this seperate equation

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we assume it to be

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at equilibrium

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and not moving?

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since Fnet =0

loud oasis
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it's at the equilibrium position. it may or may not be moving since it says nothing about velocity

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if the velocity is 0 then it would stay there forever. if velocity is not zero then it just passes through and swings to the other side

royal sky
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okay uh well

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if its at eq

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then mg -ks = 0

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thing is

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im not too sure wehre im supposed to reach

loud oasis
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ok so we know that mg = ks. this information can be used to simplfy your ODE

fleet flax
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This is actually a very standard SHM question

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Sorry for interfering

royal sky
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okay if i determine a condition, or like simplify an equation from equilibrium, can i plug this equation back into my original equation where it is not in equilibrium

royal sky
fleet flax
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Rest is just Math, honestly.

royal sky
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cos if i can just take an equation from equilibrium

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and plug it back into my original eqaution

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i can just easily simplify it

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but idk if i can

fleet flax
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What's your equation

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(or equations)

loud oasis
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you can do that, it's completely valid

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remember that mg and ks are constant, they don't depend on position at all

royal sky
royal sky
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yeah its just that

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i just didnt know i could substitution an equation from eq into one that isnt at eq

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it feels kinda counter intuitive

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okay tytyty

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.close

topaz sinewBOT
#
Channel closed

Closed by @royal sky

Use .reopen if this was a mistake.

topaz sinewBOT
#
Available help channel!

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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>.
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royal sky
#

when they ask instantaneous velocity, is it acceleration?

topaz sinewBOT
#

@royal sky Has your question been resolved?

loud oasis
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instantaneous velocity means velocity

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i.e. dx/dt

royal sky
#

ok ty

#

.close

topaz sinewBOT
#
Channel closed

Closed by @royal sky

Use .reopen if this was a mistake.

#
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>.
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• 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.

twilit eagle
#

i need help with this because it is about WRITING EQUATIONS WITH VARIABLES ON BOTH SIDES

placid swift
#

Well, what would be the equation for Jaycie?

twilit eagle
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uh

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like the formula?

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if its the formala i think its y = mx + b

placid swift
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Yes

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wait what

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No, okay tell me

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how much would it cost Jaycie to watch a movie after buying a membership, like collectively

twilit eagle
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it woud cost like hmm

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let me solve it and put it into desmos

placid swift
#

Dude no

twilit eagle
#

oh

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well

placid swift
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Like imagine Jaycie's a rich gal

twilit eagle
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ok

placid swift
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So she brought the theatre membership

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It cost her $27

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Now to celebrate this, she decides to watch a movie, which costs her $6

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So how much did she spend collectively on that theatre?

twilit eagle
#

like 6.00m + 27

placid swift
#

Well, alright then, you've found your equation I see

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Now, what would be the equation for Claire?

twilit eagle
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like 8.25m because i cant seem to find another number or value to make like another mx + b

placid swift
#

Yes, because there is no starting value

twilit eagle
#

ohh

placid swift
#

Now you're asked when is 8.25m = 6m + 27, so just evaluate them, find the value of m, and that's your answer

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(Or just pop LHS and RHS on Desmos and the point where they intersect is your answer)

placid swift
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like input y = 8.25x

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and y = 6x + 27

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The x value of the point where they intersect is your answer

twilit eagle
placid swift
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Well, subtract 6m from both sides

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then divide the 27 with 2.25, that's your answer

twilit eagle
placid swift
#

Alright, 6.25m = 5m + 5

#

(Subtracting 5m from both sides)

#

1.25m = 5

#

m = 5/1.25

#

m = 4

#

Like that

topaz sinewBOT
#

@twilit eagle Has your question been resolved?

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delicate topaz
topaz sinewBOT
delicate topaz
#

i got to (k-x)/x^2 = -3/4

#

dont know what to do after

maiden plank
#

what's the original question? please take a screenshot with the instructions too

delicate topaz
#

sorry instructiions got cropped out

grand sierra
#

which question are you doing

mighty geyser
#

65

grand sierra
#

sorry I misread

delicate topaz
#

655

#

65

#

i got to (k-x)/x^2 = -3/4

grand sierra
#

do you know derivatives?

delicate topaz
#

i alr did that part

grand sierra
delicate topaz
#

i did d/dx = to the slope

grand sierra
#

is a k a function of x?

#

or is it a scalar?

delicate topaz
#

huh

#

k is a number

#

that i need to find

grand sierra
#

you do not need qoutient rule here

delicate topaz
#

k/x

#

take derivitave

grand sierra
#

= k(1/x)

delicate topaz
#

oh ig u can do that way aswell

grand sierra
#

d/dx(k/x) = k((d/dx)(1/x))

#

qoutient rule only works when you have two functions

mighty geyser
grand sierra
#

and even then it's just product rule in a slightly different form

delicate topaz
mighty geyser
#

yeah but its just more work for no reason

grand sierra
#

you can do (x)(1/(x^2)) if you really really wanted to i guess

delicate topaz
eager pasture
#

You can do quotient rule, but you'll find out a lot it cancels out to give k((d/dx)1/x))

delicate topaz
#

ok let me do the d/dx one more time to get the right answer

eager pasture
#

Since f(x)=k has f'(x)=0

grand sierra
#

use Power rule 👍

delicate topaz
#

-k/x^2

#

ok so

#

-k/x^2 = -3/4

#

now what

grand sierra
#

k/x = y = -3/4x + 3

#

to get x in terms of k

exotic nest
#

You’re c-cheating on me @delicate topaz!? who is this man?

delicate topaz
grand sierra
grand sierra
delicate topaz
#

why is k/x =y?

topaz sinewBOT
#

@delicate topaz Has your question been resolved?

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merry helm
topaz sinewBOT
merry helm
#

shouldn't this be A + (NOT(C) . NOT(A))

#

nvm

#

.close

topaz sinewBOT
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reef nest
#

How was this simplified

topaz sinewBOT
drifting swift
#

$V = \frac{4\pi}{3} \cdot \frac{(\sqrt{S})^3}{(\sqrt{4\pi})^3}$

thorny flameBOT
drifting swift
#

would you like further elaboration or do you think you can continue the simplification yourself from here

topaz sinewBOT
#

@reef nest Has your question been resolved?

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topaz sinewBOT
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fallow wharf
#

Guy help with this one

topaz sinewBOT
hoary burrow
#

Cuz like I can't read the handwriting man

fallow wharf
#

Sure

#

See 11

hoary burrow
#

Aight thanks

fallow wharf
#

I tried substituting, but the end answer was not satisfying at all

fallow wharf
#

X +4 = t

inland mica
#

If you're doing it this way, you should split the fraction into 2

fallow wharf
#

I got this in end

inland mica
#

Great

#

What is the issue here

fallow wharf
#

Bruh the ans didn’t match

hoary burrow
inland mica
#

Maybe mistakes in your calculations

fallow wharf
#

Yeah, and then use the chain rule, while differentiating

#

I don’t think that I made any mistake in calculation. Can you see the actual answer? Wait, let me send it.

#

See 11

#

Guys?

hoary burrow
#

Right so

#

I got the answer and checked it on desmos

#

And it's correct

fallow wharf
#

So is my answer wrong?

hoary burrow
#

You're not far off

#

I think you just made a mistake in subbing

#

Just look through your workings carefully again

#

After that you should be able to simplify to the answer in the answer key

fallow wharf
#

Wait, let me send my work to you

hoary burrow
#

Alright

fallow wharf
hoary burrow
#

Oh yea that's correct now

#

You were missing the ^1/2 in your first answer

#

@fallow wharf

fallow wharf
#

Oh yeah my bad

#

But still, the actual answer is something else

hoary burrow
#

They are equivalent

#

You just have to simplify

fallow wharf
#

Oo

hoary burrow
#

Although in exam I don't think they'd reject this form

#

But just to see how they're equivalent

#

Factorise 2/3√(x+4) out of the expression

fallow wharf
#

That let’s do a cubic expansion

fallow wharf
#

Something like this

hoary burrow
#

$(x+4)^{\frac{3}{2}}=(x+4)\cdot(x+4)^{\frac{1}{2}}$

thorny flameBOT
#

denzio321

hoary burrow
#

@fallow wharf

fallow wharf
#

Ooo

#

Got it

hoary burrow
#

Also should multiply 8 by 3/2

#

Since you factorise it out

fallow wharf
#

Yeahhh

#

Thanks, I got the answer

#

.close

topaz sinewBOT
#
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dry dragon
#

Hello, I'm kind of unsure what to do next. So far I have found length BC (arc length) to be 6pi. Could I get some hints on what to do next and how I should be using area?

drifting swift
#

find the radius of the small arc

#

call OA=r

#

express the areas of sectors OAD and OBC in terms of r, then take their difference and equate it to 209pi/5

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wooden kayak
topaz sinewBOT
wooden kayak
#

For Q1, how do I plug x into the original equation

#

do I need to make it in exponent form then sub it in?

chilly walrus
wooden kayak
#

but idts, question is asking to put it into original equaion

#

5,6

#

same as answer key

chilly walrus
#

yeah replace "x" in the original equation with "5"

#

and see if it still makes sense

#

$\log_a(5^2 + 30) = \log_a(11\cdot 5)$

thorny flameBOT
#

artemetra

wooden kayak
#

theres no "a" in my calculator

chilly walrus
#

😄 you don't need a calculator for this

#

simplify both lhs and rhs

wooden kayak
#

this calc im using

chilly walrus
#

simplify what's inside the log

wooden kayak
#

not simplify

chilly walrus
# wooden kayak

the whole point of this exercise is for you to check that after you solve the equation, you don't get something like log(-5) which is undefined

chilly walrus
#

and now you simplify to verify it

wooden kayak
#

I didnt sub it in

drifting swift
wooden kayak
#

yeah

#

I would

#

oh so I plug it in just x^2 +30

#

and in the rhs too

wooden kayak
topaz sinewBOT
#

@wooden kayak Has your question been resolved?

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zinc obsidian
topaz sinewBOT
zinc obsidian
#

.close

topaz sinewBOT
#
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karmic cloak
#

Is this correct?

topaz sinewBOT
ruby cove
karmic cloak
#

I think it may be the same one I did last night I forget tho

ruby cove
karmic cloak
maiden plank
#

think I've seen these questions before

ruby cove
karmic cloak
#

I’m est time zone so I went to bed and now I am at school and have a free

ruby cove
karmic cloak
#

Kk

#

I’m confused why the range of f(X) is [0,♾️) and not [1.7,♾️)

maiden plank
#

,rccw

thorny flameBOT
maiden plank
#

gdi

karmic cloak
#

?

maiden plank
#

look at your first image

karmic cloak
#

Yea

clear python
#

,rccw

thorny flameBOT
maiden plank
#

did you list two domains for f^-1

karmic cloak
#

No we only need to find the range

#

But I’m confused why google says the range is zero to infinity but I think it is 1.7 to infinity

maiden plank
#

so you want to find the range of f^-1

karmic cloak
#

Oh wait

vocal escarp
#

Domain of f^-1(x) is the range of f(x)

maiden plank
#

if this is the case neither range makes sense, because f^-1(0) = (0^2 - 8)/5 = (0-8) / 5 = -8/5

karmic cloak
#

Yea

vocal escarp
#

X^2 makes any number positive, so we're js going from 0 to inf

#

Since there's no real number that makes the function undefined

karmic cloak
maiden plank
#

that's why I'm asking if you're finding the range of f^-1 or f

#

this is the graph of f, not f^-1

vocal escarp
#

Lool

topaz sinewBOT
#

@karmic cloak Has your question been resolved?

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#
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rough furnace
#

In space, given 2 lines $l_1$ and $l_2$ with equations $l_1:\frac{x-3}{1}=\frac{y}{2}=\frac{z+1}{3}$ and $l_2:\frac{x+3}{3}=\frac{y-1}{1}=\frac{z+2}{2}$. Determine a plane equation (P) contain $l_1$ and maximize angle between that plane and $l_2$

thorny flameBOT
#

Alexis_Fx

rough furnace
#

This's the original question, after doing a bunch of thing now I have to maximize $\frac{3a+b+2c}{\sqrt{14(a^2+b^2+c^2)}}=\cos(\theta)$

thorny flameBOT
#

Alexis_Fx

rough furnace
#

$a+2b+3c=0$

thorny flameBOT
#

Alexis_Fx

rough furnace
#

this's the condition and also a,b,c can't all be 0 at the same time

#

Well I tried Cauchy-Schwarz but equality hold when a=b=c=0 which can't be true so

#

Should I just sub a=-2b-3c? that seems lengthy

#

and also 2 variables

#

maybe I could use AM-GM after I sub?

#

idk

thin girder
#

Im guessing theta is the angle between the plane and l2 right?

rough furnace
#

oh wait I can't use AM-GM cuz a,b,c can be negative bruhhh

marsh charm
#

hmm sounds very TSA-ey

rough furnace
ruby cove
#

I think cauchy schwarz can be applied

#

Can you send your work? @rough furnace

rough furnace
thorny flameBOT
#

Alexis_Fx

rough furnace
#

This's what you meant right?

#

Then it cancel out the numerator

#

But in this case equality hold when a=b=c=0 which can't be true

ruby cove
#

Have you tried converting it in vector form?

rough furnace
#

Vector is difficult to work with

ruby cove
rough furnace
ruby cove
#

I’ll try to solve myself and send the solution if you wont get any help

#

Im currently out rn

rough furnace
#

btw vector equation of that plane look disgusting

ruby cove
marsh charm
#

actually imagine this

rough furnace
marsh charm
#

your 2 lines I1 and I2 are seperated now right?

marsh charm
#

Imagine there's a line parallel to I2 and intersects I1

rough furnace
#

hmmm

#

okay

marsh charm
#

now when does the angle reaches the maximum?

#

you can try to visualize this with 2 pencils on your hand

rough furnace
#

okay...

marsh charm
#

have you imagined how it'd look like

rough furnace
#

okay đoạn đó thì hiể rr

#

Nhma bấm mt ntn

marsh charm
#

đc r

#

thế thì e có đồng ý là lúc đấy vector pháp tuyến n, vector chỉ phương u1, u2 nằm trên cùng mặt phẳng ko

rough furnace
#

cs

marsh charm
#

ok

#

nghĩa là n sẽ vuông góc với [u1, u2]

#

mà n còn vuông góc với cả u1 nx

rough furnace
#

à hiểu hiể

#

À tutu

marsh charm
#

nên ra công thức n = [u1, [u1, u2]]

rough furnace
#

hmmm

#

ohhhhh

marsh charm
#

bấm máy tính, xong

rough furnace
#

trường chuyên dạy xịn v

#

Hiểu

#

;-; Em nghĩ đến việc nếu 2 đường thẳng đó cắt nhau thì tìm hình góc như a

#

Nhma tính ra ko cắt nhau nên bỏ luôn ý tường, vl

marsh charm
#

má sách ngu

rough furnace
#

Xong còn nhìn gợi ý nx tr ơi

marsh charm
rough furnace
marsh charm
rough furnace
#

Cho e bt phát

marsh charm
#

I'm the better book

rough furnace
marsh charm
#

sáng thì ko đc hehe

rough furnace
#

e thật sự rất cần quyển nào hay về Oxyz bruh

marsh charm
#

a ko phải cái phao để e dùng đâu

rough furnace
#

Trường thường có dạy mấy cái này đâu tr🥀

marsh charm
#

chụp cho a xem cái cách trong sách

rough furnace
marsh charm
#

chụp hết cho a

#

a check body quyển sách

rough furnace
#

In mấy câu nhìn căng căng vs đáp án thôi

rough furnace
#

Nhìn cái đáp án kìa

#

sợ thật ;-;

marsh charm
#

ok chúng ta sẽ cùng check body cho quyển sách

rough furnace
#

còn 1 khúc nx mà chắc a ko cần đọc

marsh charm
#

úi zồi ôi

#

bộ trưởng bộ hoàng kim cốt đây r

rough furnace
#

Em ra giúng họ đó

#

Có mỗi k bt tính max

marsh charm
#

thế này quyển sách phải lọ 36 phát mới ra cái lời giải điên khùng này

rough furnace
#

đc rồi đi kiếm sách mới thôi opencry

#

Gợi ý gì k

marsh charm
#

tính max à e?

rough furnace
#

Đề nói v

#

oh wait

marsh charm
#

thì max là góc giữa u1 và u2?

rough furnace
#

hold on

#

Em cần 1-2p để load

#

Thông cảm, đang ốm

marsh charm
#

a cx hơi ốm

rough furnace
marsh charm
#

same

rough furnace
#

Um okay mọi thứ vẫn v

marsh charm
#

bão chó

rough furnace
#

Em cần sách mới AAAAAAAA

marsh charm
#

chắc ko cần

rough furnace
#

hồi đó anh ôn sách j

marsh charm
#

ko có sách j

rough furnace
#

aw

marsh charm
#

chỉ có tư duy mà làm

#

thầy giao đề, về nhà làm, xong

rough furnace
#

Đề trường chuyên nó khác....

#

Đề em đi tính max min MA^2+MB^2+MC^2

marsh charm
#

vcl

rough furnace
#

lol

marsh charm
#

thế này thua

rough furnace
#

Làm riết chán

marsh charm
#

làm 1 bài 10000 lần chả có tác dụng gì

#

luyện 1 võ 10000 lần ms có tác dụng

rough furnace
marsh charm
#

trường biến HS thành gà công nghiệp

rough furnace
marsh charm
#

có một đống đề hay đấy

#

chứ cách giải nhanh nhất thế nào thì...

rough furnace
marsh charm
#

tsu có thì cx hiếm lắm

rough furnace
marsh charm
#

thấy cái nào dài quá thì đem lên đây hỏi

#

hoặc DM anh

rough furnace
#

Hay ngồi luyện đề Trường Sở nhẻ

#

Căng quá k

marsh charm
#

ehh cx đc

#

mấy bài nào chán quá thì bỏ

rough furnace
#

Cảm ơn a nhá, em ốm nên đi ngủ trc đây

marsh charm
#

ok e

rough furnace
#

.close

topaz sinewBOT
#
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topaz sinewBOT
#
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neon iron
#

How do I solve absolute value functions?

topaz sinewBOT
sweet shard
#

,tex .abs def

thorny flameBOT
#

riemann

sweet shard
#

use ^

neon iron
#

Okay how to solve it on a graph with equation?

flat pike
neon iron
#

I'm confused by the signs

#

I've been struggling with this for a few days now

sweet shard
neon iron
#

Yes

sweet shard
neon iron
#

How do you know what direction to go?

sweet shard
#

,tex .transformation rules

thorny flameBOT
#

riemann

neon iron
#

Ohhh

#

That kinda makes sense

#

Thank you, I think I get it now

#

.close

topaz sinewBOT
#
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merry helm
topaz sinewBOT
merry helm
#

don't understand how to do this

#

the "less than" is confusing me

finite storm
#

why so

#

a quarter of 240 is 1/4 * 240 = 60

#

so less a quarter is less than 60, no?

merry helm
#

yes

#

but

#

it would be a range of answers, how can it be an exact number

oak skiff
#

Hello guys does anyone know comp sci servers that help with java

merry helm
#

so
let x < 60
day 1: x for $12 each, making $k total
day 2: 2x for $9 each, making $k + 342 total

finite storm
#

why k

#

cant u write k in terms of x

#

and perhaps use that to set up a rel

merry helm
#

so day 1 he made $12x and day 2 $(18x + 342)?

#

leaving him with < 80 spruggles (stock)

finite storm
#

ok so

#

we know that day 1 + 342 = day 2

finite storm
thin girder
#

Day 2 is 12x +342 and its also 2x×9

finite storm
#

wonderful gng

merry helm
finite storm
#

bruh

finite storm
merry helm
#

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#
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finite storm
#

what😭

finite storm
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merry helm
merry helm
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merry helm
topaz sinewBOT
merry helm
#

this is the most trippy question

#

why is it so hard to visualize

#

i would have to draw it out but the problem is i'm bad at drawing

thin girder
#

I mean i can visualize it quite well
The answer should be 5

#

Oh wiat

#

Ye im dumb my bad

merry helm
#

it's A - 1

#

it's like you have to look at it straight on, rotate it, visualize what numbers are behind what and which side is going to be touching the board

thin girder
#

Ye damn this is hard

torpid shard
#

Its pretty easy to visualize if you consider whats the number on top instead of the bottom

#

From the start point: you have 5 at the bottom, 4 on top
You move to P, 3 ends up tops, so 6 is on the bottom.

#

and mind you, the triangles on top and bottom have opposing directions

merry helm
#

the only way to get 6 touching P would be to flip the dice upside down (to fit into the triangle outline on the board)

#

then if you would push that forward, it would fall onto 5?

torpid shard
#

You get 3 tops in P, so moving to Q, you have 2 opposed, so ends up with 2 on top, 7 bottoms.

#

if im not going dumb

merry helm
#

ur right

#

why can i not see this brah

torpid shard
#

imma hardly try to draw this in paint

#

wish me luck for a sec

#

no yeah, theres no chance that i draw this and it makes sense

torpid shard
# merry helm

idk, you can kinda see how by rotating it from Start to P, the one side facing to you its the 2, per se, the opposing face.
Once you roll to Q, since you are rotating perpendicular to the 2, it has to end up tops.

#

And by determining tops, you can know the result in bottom

topaz sinewBOT
#

@merry helm Has your question been resolved?

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#
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blazing umbra
#

Hello.

topaz sinewBOT
blazing umbra
#

How does this make ANY SENSE

fallow igloo
blazing umbra
#

b* means anti-parallel

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no?

#

matter of fact on the right side he is writing b // b* which means b is parallel to b*

fallow heart
blazing umbra
fallow heart
#

Oh ok

blazing umbra
#

by negating the arguments (with multiplying -1)

fallow heart
#

Exactly, that's the meaning of antiparallel

blazing umbra
#

Dude this is my first day ever at uni and its already confusing

fallow heart
#

But I don't understand your doubt

blazing umbra
loud oasis
#

maybe he meant to write b = -2b* and write b* = (-1, 1)

blazing umbra
#

b* = 2 (-1,1)

loud oasis
#

well idk your notation so idk if b* is meant to be any antiparallel vector or specifically -b

fallow heart
blazing umbra
#

and he drew a and a* parallel even tho they are anti parallel

fallow heart
#

The only thing you have to know regarding this photo is that two vectors u and v are parallel if and only if u = k v (for some number k)
@blazing umbra

fallow heart
fallow heart
#

If two vectors are anti-parallel, they are parallel as well

blazing umbra
fallow heart
#

Anti-parallel means parallel with negative value of k

fallow heart
blazing umbra
fallow heart
blazing umbra
fallow heart
blazing umbra
#

but I get it doesnt matter

#

if thats the definition

#

the b = 2 b* is still stupid

#

hoping he just missed the -1

fallow heart
fallow heart
blazing umbra
#

so anti parallel just means if k < 0

#

when u = k v

fallow heart
#

Mmh I might remember a different definition

#

Let me check

fallow heart
blazing umbra
#

even tho its AI sounds true, no?

#

my teacher said anti parallel means negating by -1 which would mean magnitude is equal

#

so I was lowk confused

#

but alright gotta blame myself

fallow heart
blazing umbra
#

dude I should really start asking questions

#

I was already suspicious mid class ngl

#

Im just showing the stuff he wrote down meanwhile

#

whatever thanks alberto

#

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dusky ridge
#

If P(x) is a monic biquadratic polynomial with P(1) = 10, P(2) = 20 and P(3) = 30, find the value of (f(12) + f(-8))/10

dusky ridge
#

😭

#

pls help me do this question

quasi depot
#

there are 4 unknown coefficients

#

you have 3 linear equations

quasi depot
drifting swift
#

and also when you say biquadratic, do you just mean degree 4? or do you also mean no odd-power terms

dusky ridge
#

Note: f(x) = P(x) is true.

dusky ridge
drifting swift
#

linear term known absent?

dusky ridge
#

what

#

oh

#

my bad

drifting swift
#

aight so we call this a quartic.

#

or just "4th degree".

dusky ridge
#

We also call it a quartic, yes.

thin girder
#

4 unknowns and only 3 equations damn thats crazy

dusky ridge
#

maybe the variable parts cancel while calculating the sum f(12) + f(-8)

ruby tree
#

Yes, this apparently has a unique solution

ruby tree
#

Then take the three points, make a system of three equations and four variables, and solve it

#

You'll have a free variable, it's fine just keep it and calculate the answer

drifting swift
#

f(x)-10x has roots 1, 2, 3 and another unknown one. does that help us at all or no?

worthy flax
#

f(x) - 10x is a quartic, right?

#

a monic one, even

drifting swift
#

i mean yes but is the lack of knowledge of the 4th root an impediment

worthy flax
#

this is where i assume we'll get stuff cancelling

drifting swift
#

f(x) = 10x + (x-1)(x-2)(x-3)(x-r)

worthy flax
#

you can write f(x) - 10x = (x - 1)(x - 2)(x - 3)(x - a) for some unknown a

#

yeah

drifting swift
#

f(12) = 120+11×10×9×(12-r)
f(-8) = -80+(-9)×(-10)×(-11)×(-8-r)

worthy flax
#

yeah the r parts will cancel nozoomi

dusky ridge
#

yeah

drifting swift
#

@dusky ridge you can continue from here yourself, can't you?

dusky ridge
#

I can. Thank you very much.

#

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