#help-33

1 messages · Page 244 of 1

limber wigeon
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which entails just taking the highest possible value in the range instead of lowest

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then summing

wooden shard
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why wouldnt it be minimum

limber wigeon
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because the mean of A is larger than the mean of B

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and you are trying to find the smallest difference between them

wooden shard
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ok i see

limber wigeon
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they have the same frequencies, but B has them over the intervals with lower values

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so everything is smaller in B

wooden shard
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887/23

limber wigeon
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then the difference would be?

wooden shard
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1

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woah

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ok thanks

#

.close

marsh citrusBOT
#
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marsh citrusBOT
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gentle patrol
#

What the heck does (cf)(x) = cf(x) mean and how does that suffice to prove closure under scalar multiplication?

proud prism
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well, (cf) and f are both functions

gentle patrol
proud prism
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cf: D to R,

(cf) (x) := c* f(x)

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in the right side we have pointwise real multiplication

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and in the left it’s scalar multiplication to f not necessarily usual real number muliplication

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f itself should be viewed as a single object

gentle patrol
proud prism
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yes, the right side to should make sense

whole thorn
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but i think dotdoc meant f is not in R, so cf is not usual real number multiplication

proud prism
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if you just wrote

(cf)(x) = c* f(x), it completly depends on how you interpret.

A standard setting is c is in R, and f: D to R.

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the key distinction is right side the multiplication operation is pointwise on the values of f

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and in left it’s on f itself.

proud prism
gentle patrol
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{ f : I -> F }

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function spaces

proud prism
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What’s structure you have in T?

gentle patrol
proud prism
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right, so c should come crom F

proud prism
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cf should also be another object in the collection.

gentle patrol
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I don't get what (cf)(x) = c * f(x) really means

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Maybe I would like to start from knowing what (cf)(x) is

proud prism
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quick question,

How do you know check if two function f, g are the same?

delicate prairie
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given a function f and scalar c, this is the way to define another function cf, and (cf)(x) denotes cf evaluted at x

proud prism
gentle patrol
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Yes

proud prism
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equal and defined by

gentle patrol
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yeah

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It doesn't always work, am I right?

proud prism
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if F is a field you can always do this

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it’s matter of whether you can afford to define it

gentle patrol
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Okay

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Thank you

#

.close

marsh citrusBOT
#
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marsh citrusBOT
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coarse nova
#

Calc 2

  1. Find the length of the loop of the curve x=3t-t^3 y=3t^2

How I attempted to solve: I assumed the loop of the curve meant the length between 2 t values that both had the exact same (x,y) output. For the y output to be the same, t0=-t1. So I set x(t)=x(-t) and using a calculator found an intersection at sqrt(3) and 0. I assumed that the intersection at 0 didn't matter since it seemed more like obvious. So I did the integral from -sqrt(3) to sqrt(3) of sqrt((dx/dt)^2 - (dy/dt)^2)dt and got about 20.785

My main question is can the parametric go negative or should I have done the integral from just 0 to sqrt(3) instead. Or is there something else I'm missing.

marsh citrusBOT
#

@coarse nova Has your question been resolved?

wind hare
marsh citrusBOT
#

@coarse nova Has your question been resolved?

tight furnace
#

There's no intersection of the curve with itself at t=0

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You looked for pairs t, -t with the same x-value, since you identified that was required for the y-values to match

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all that getting t=0 told you was that the position is the same at t=0 as it is at t=0

coarse nova
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So t=0 is irrelevant

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Does that mean the limits of integration are just -sqrt(3) and sqrt(3) then?

tight furnace
#

Yeah

marsh citrusBOT
#

@coarse nova Has your question been resolved?

#
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spark halo
marsh citrusBOT
spark halo
#

by balancing the force along the tangent to the particle, i obtained the result $q=\frac{mg}{vB}$ . I didnt quite get what "force of interaction" essentially meant, i assumed it would be any normal reaction force. Intuitively along the radial direction, forces cannot be balanced because the particle has some centripetal acceleration so i chose the tangential direction. Now how do i find "r"?

elfin berryBOT
#

atharvxd

marsh citrusBOT
#

@spark halo Has your question been resolved?

spark halo
#

<@&286206848099549185>

marsh citrusBOT
#

@spark halo Has your question been resolved?

topaz escarp
#

I just woke up give me 1s

spark halo
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yeah sure

topaz escarp
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“no force of interaction”

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does not mean “no centripetal force”

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it means the ring should not need to push or pull on the particle at all

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means all forces needed for the particle’s motion must come from external fields only

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gravity + magnetic force

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you’re right about the tangential direction

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now how to get r

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don’t balance forces radially

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insteaduhh

spark halo
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yeah that doesnt work

topaz escarp
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the particle is moving in a circle of radius r right

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that means it needs centripetal force

spark halo
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even if i write the law of motion of the particle in the radial direction to equate to the centripetal force however the parameter for angular position cannot be eliminated

topaz escarp
spark halo
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thats correct

topaz escarp
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the magnetic force

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qvB

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so just set them equal

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can you do that rn

spark halo
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r=mv/qb

topaz escarp
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no bro

spark halo
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wait a min

topaz escarp
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my eyes deceived me

spark halo
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but

spark halo
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that is the correct answer

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however the problem is

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doesnt the particle also have a velocity as a consequence of pure rolling?

topaz escarp
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yes but not an extra velocity

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pure rolling determines how the direction of velocity changes not how big the velocity is

spark halo
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wont you write $\vec{v_p}= \vec{v}+ \vec{\omega} \cross \vec{r}$

elfin berryBOT
#

atharvxd

topaz escarp
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yes

spark halo
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so when writing lorentz force

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you missed writing the omega cross r term?

topaz escarp
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it doesn’t change the final force balance

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bc the magnetic force uses the total particle velocity

topaz escarp
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but treating those as separate physical speeds is no

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the mag force sees only the resultant speed

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that speed is constant

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so that’s valid

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but yeah write in full kinematics

spark halo
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the magnitude of the resultant velocity changes with angular position irght

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and im sorry the answer is not r=mv/qb

topaz escarp
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yes

spark halo
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its v^2/g

topaz escarp
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yes

spark halo
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so uh

topaz escarp
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tell me

topaz escarp
#

not wrong

spark halo
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yeah i got r=mv/qb

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the angular position parameter got eliminated

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i just realised i got r=mv/qb

topaz escarp
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nice you closed the loop now

spark halo
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ok yeah i got the answer to match

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but how did you predict by intuition that the angular component wont be involved in the lorentz force equation

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i didnt understand that

topaz escarp
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so

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if the only forces acting come from uniform fields

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and the system has no angular asymmetry

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then any angular parameter you introduce must cancel out

spark halo
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what does uniform field mean precisely?

topaz escarp
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its magnitude and direction are the same at every point in the region of motion

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a field is uniform if that checks

spark halo
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does this hold true for non conservative fields?

topaz escarp
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yess

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uniformity hasnothing to do with being conservative

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what matters is spacial uniformity

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not whether a potential exists

spark halo
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and uh

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i still didnt get how you equated qvb= mv^2/r

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now its true the net force acting on the particle is qvb

topaz escarp
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newton’s 2nd law

spark halo
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because of symmetry

topaz escarp
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in the normal direction

spark halo
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yes

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got it

topaz escarp
#

lorentz force magnitude: qvB

it (force) is perpendicular to velocity

perpendicular force = normal acceleration

normal acceleration for curved motion v^2/r

topaz escarp
spark halo
#

got it

#

i have another problem id like to ask

topaz escarp
spark halo
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ill attempt it once before tho

topaz escarp
#

okie dokie

spark halo
#

@topaz escarp

spark halo
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i solved it

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can you think of a shorter way to do it?

topaz escarp
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shortest way i can think of

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is to see what velocities matter for lorentz first

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then kill the w * r part

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using symmetry

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then take the motion

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and treat it like a charge particle with charge Q

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and ig then bring in rolling constraint if needed

spark halo
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the radius of the center of mass is to be found

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in the subsequent circular motion

topaz escarp
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nothing from rotation enters the radius

spark halo
#

wdym

topaz escarp
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yeah you’re right

spark halo
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????

topaz escarp
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like you’re right

topaz escarp
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and nothing from the rolling or angular motion changes the cm radius

spark halo
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the sphere would keep pure rolling while its center of mass performs uniform circular motion

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the radius wouldnt simply be mv/qb

topaz escarp
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yes

topaz escarp
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the center of mass is what moves in a circle

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the only net external force causing that curvature is the magnetic force

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so all rotational/rolling details affect torque, not the net force on the cm

spark halo
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the center of mass needs to move in a circle while the sphere rolls purely

topaz escarp
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friction does exist

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but it does not provide the centripetal force for the cm

spark halo
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i cant find a reason as to why it wont

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qvb-f=centripetal force

topaz escarp
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write newts law only for the center of mass

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static friction adjusts itself to satisfy the rolling constraint

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it is not fixed in direction or magnitude

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when the cm that starts curving:

the required torque to keep rolling changes

friction supplies that torque

but radial acceleration of the CM is already fixed by the magnetic force

there is no kinematic requirement that friction contribute to radial acceleration

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if it did, then the CM speed would change, or rolling would break

spark halo
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the torque equation can be written as $\frac{2}{5}MR^2 \omega \Omega = f.R + \frac{1}{5} QR^2 \omega B$ where $\Omega$ is the angular velocity of the circular motion of the center of mass and \omega is the angular velocity of pure rolling.

elfin berryBOT
#

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

topaz escarp
#

the torque equation only fixes the friction f needed to keep pure rolling. it does not alter the force balance on the CM, which is still

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‘’’QvB=\frac{mv^2}{r_{\text{CM}}};\Rightarrow; r_{\text{CM}}=\frac{mv}{QB}’’’

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can you copy paste this into here

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latex is mad at me

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we broke up last year apparently

spark halo
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$QvB=\frac{mv^2}{r{\text{CM}}};\Rightarrow; r{\text{CM}}=\frac{mv}{QB}$

elfin berryBOT
#

atharvxd

spark halo
#

the torque equation will fix friction but why will the friction not alter the motion of cm?

topaz escarp
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bc static friction only enforces the rolling constraint and its line of action passes through the instantaneous center of rotation

it contributes literally 0 net work and no required radial acceleration of the cm

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the only force that can curve the cm path is the magnetic force

so friction cannot change the cm motion

spark halo
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if friction passes through the instantaneous center of rotation then it should indeed be involved in the body's law of motion right?

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i get that it does no work because there is no displacement of the point of contact

topaz escarp
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because the static friction force is purely tangential to the cm trajectory, while only a radial force can change the cm’s circular path, friction cannot alter the cm motion or its radius

spark halo
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oh yeah ive assumed friction to be radially outward

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however

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if lorentz force acts radially inward there must be a force acting radially outward to keepthe center of instantaneous rotation static?

topaz escarp
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no no

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nothing needs to act radially outward

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the instantaneous center of rotation is a kinematic concept

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not a force balance point

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and the inward lorentz force by itself supplies the required centripetal acceleration of the cm

marsh citrusBOT
#

@spark halo Has your question been resolved?

marsh citrusBOT
#
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shadow field
#

I have a matrix in Unity called: localToWorldMatrix which describes the transformation from a local object space to a world space.

This matrix is represented by a basis (with each column describing the scaled right vector (x-axis), up vector (y-axis), and forward vector (z-axis)) and a position alongside a dummy 4th row to allow for correct multiplication:

 x  y  z
[1, 0, 0, pos.x]
[0, 1, 0, pos.y]
[0, 0, 1, pos.z]
[0, 0, 0, 1    ] (dummy 4th row)```
I am attempting to convert this to a *Transform3D* matrix in Godot, which is identical to the above except for the forward direction of the z axis being interpreted by the engine as opposite. In other words moving along the z-axis in the positive direction in Unity moves in the negative direction in Godot.

My first thought was to simply invert the x and y components of the z axis and the z position as follows: 

INVERT_Z =
[1, 0, 0, 0]
[0, 1, 0, 0]
[0, 0, -1, 0]
[0, 0, 0, 1]```

INVERTED_LOCAL_TO_WORLD_MATRIX = INVERT_Z * localToWorldMatrix * INVERT_Z

However this resulted in the weird phenomena where some rotations were off, the Euclidean representation of z-axis rotations seemed to show negative theta (degrees) instead of positive theta (degrees) and vice versa, but it seemed to be only in some cases, and it seemed to be in cases where the rotation was quite minimal, with other seemingly random cases being flipped along the y axis leading to the z-axis rotation being correct.

Would anyone have any idea why this might be happening and how I can correctly reverse the direction of the z-axis in this matrix?

frigid topaz
#

the sandwich multiplication is correct in principle

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the wrong rotations are probably an artifact of comparing euler angles across two engines that use different euler decomposition orders

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unity uses ZXY and Godot uses YXZ

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verify the basis vectors directly instead of comparing extracted angles

marsh citrusBOT
#

@shadow field Has your question been resolved?

shadow field
#

yeah one sec typing

#

okay so the transform in unity of some object A is:

[2.2311, 0.175,  0,      155.8315]
[-0.302, 1.1157, 0,      57.1153 ]
[0,      0,      0.7471, 2.1879  ]
[0,      0,      0,      1       ]```
in godot it is:

[2.231005, 0.17558391, 0, 155.8315]
[-0.09068846, 1.1523061, 0, 57.11531]
[0, 0, 0.7470923, -2.18791]
[0, 0, 0, 1 ]```
which is incorrect, the desired transform is:

[2.231005,    -0.17558391, 0,         155.8315]
[0.09068846,  1.1523061,   0,         57.11531]
[0,           0,           0.7470923, -2.18791]
[0,           0,           0,         1       ]```
#

or incorrect is probably the wrong word, but you get what i mean

#

<@&268886789983436800>

shadow field
#

I also noticed a bunch of transforms had their scales flip inside out.

#

These seemed to be the ones which had been rotated correctly.

marsh citrusBOT
#

@shadow field Has your question been resolved?

marsh citrusBOT
#

@shadow field Has your question been resolved?

bold ice
# shadow field okay so the transform in unity of some object A is: ``` [2.2311, 0.175, 0, ...

https://gamedev.stackexchange.com/questions/207641/how-do-i-create-a-localtoworldmatrix-and-worldtolocalmatrix-in-godot

I have no Idea about game development engines, and I also don't understand the description of the math involved. I tried reading documentation to understand your problem, but it didn't help much

bold ice
shadow field
still temple
#

hello there

shadow field
#

hi

marsh citrusBOT
#

@shadow field Has your question been resolved?

marsh citrusBOT
#

@shadow field Has your question been resolved?

marsh citrusBOT
#
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novel juniper
marsh citrusBOT
quaint elm
#

there are only eight possible outcomes for 3 coins this takes 30 seconds the bruteforce way

novel juniper
#

I know, just wanted to verify something

#

but figured it out

#

.close

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gentle patrol
#

Definition0.3.21. A relation R on a set 𝐴 is said to be
(i) Reflexiveif 𝑎 R 𝑎 for all 𝑎∈𝐴.
(ii) Symmetric if 𝑎 R 𝑏 implies 𝑏 R 𝑎.
(iii) Transitive if 𝑎 R 𝑏 and 𝑏 R 𝑐 implies 𝑎 R 𝑐.

Definition 0.3.23. Let 𝐴 be a set and R an equivalence relation. An equivalence class of
𝑎∈𝐴, oftendenotedby[𝑎],is the set {𝑥∈𝐴: 𝑎R 𝑥}.
For example, given the relation ‘★’ above, there are two equivalence classes, [1]=[2]=
{1,2} and [3]={3}.

Question:
What does a R a mean? a in A? How does that relate to "An equivalence class of
𝑎∈𝐴, often denoted by[𝑎],is the set {𝑥∈𝐴: 𝑎R 𝑥}."?
What really is an equivalence class?

stoic saddle
#

R is a binary relation

#

you can think of it informally as a "function" which takes two arguments from set A and returns a boolean

#

when we say "a R a" you can think of it as meaning "R(a,a) = TRUE"

gentle patrol
#

I see R as a subset of A x A

proud ice
elfin berryBOT
stoic saddle
#

then a R a means (a,a) ∈ R

proud ice
gentle patrol
stoic saddle
#

What really is an equivalence class?
an equivalence class is a subset of A in which all elements within are related to each other by R but nothing outside it is related by R to anything inside

gentle patrol
stoic saddle
#

i have... no idea what you're talking about.

#

a R b does not by itself imply that (∀c ∈ A \ {a,b})[not(a R c) and not (b R c)] .

gentle patrol
#

I am sorry

#

I used tuples instead of sets

#

they are subsets of A sully

#

Thanks, I get it now

#

.close

marsh citrusBOT
#
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echo scaffold
#

Could somebody check these for me since my teacher did not post an answer key since it’s optional

marsh citrusBOT
#

@echo scaffold Has your question been resolved?

marsh citrusBOT
#
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shy harness
marsh citrusBOT
shy harness
#

how do i solve this??

noble geyser
#

!status

marsh citrusBOT
#
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
shy harness
#

i got the circum for both circles

#

now im stuck

knotty trellis
#

<@&268886789983436800>

shy harness
#

<@&286206848099549185>

whole sleet
#

Both circles travel the same amount of "circumference distance", if that makes any sense

ionic ferry
#

yeah I guess it's just the ratio of circumferences, but the distance between circles has a factor too

#

eh or does it though, something tells me the distance between them doesn't matter, not sure though

marsh citrusBOT
#

@shy harness Has your question been resolved?

shy harness
#

.close

marsh citrusBOT
#
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marsh citrusBOT
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marsh citrusBOT
#

Please don't occupy multiple help channels.

devout mauve
#

<@&268886789983436800>

marsh citrusBOT
#
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#
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elfin badger
marsh citrusBOT
elfin badger
#

wHy wouldn't it be the bit in red?

main idol
#

why do you think you can't do it your way in red?

elfin badger
#

becus its done in a different way but I guess my way would work

main idol
#

if you get the same answer then it's unlikely that it's wrong

marsh citrusBOT
#

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untold spruce
#

How is $G(x) -\alpha A(x)$ concave?

marsh citrusBOT
elfin berryBOT
untold spruce
#

Are they using first order condition/test?

main idol
#

there's probably multiple ways to prove G(x) - alpha * A(x) is concave. you can try using the definition on f(x) = G(x) - alpha * A(x) directly since G(x) is concave and A(x) is linear

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white rivet
#

If you have thirteen items that each have a 50/50 of being true or false, and their outcomes are irrespective of each other is 13 trues equally likely as 6 trues and 7 falses?

white rivet
#

Personal question, not for school

devout mauve
#

13 trues is equally likely as eg "the first 6 are true, the rest is false"

#

however, if you just say "6 are true, 7 are false", then those can be distributed in lots of different ways

#

which gives you way more options

obtuse umbra
#

We use uhm

devout mauve
#

then you have your answer

obtuse umbra
elfin berryBOT
#

1 divided by 0 equals Infinity

devout mauve
#

(this is called a binomial distribution if you want to look it up)

obtuse umbra
#

And there are only 1 case where there are 13 trues

obtuse umbra
white rivet
#

Thanks

#

how do I end?

#

!close

obtuse umbra
marsh citrusBOT
devout mauve
#

.close

marsh citrusBOT
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fickle nova
#

Suppose we have a sum S_n = 1 - 2 + 3 - 4 - 5 + 6 - 7 - 8 - 9
where between every positive term there's k negative ones, and k increases by 1 every time
Calculate S_435

fickle nova
#

Just had an exam with this and i thought i was a genius and wanted to know if i did it right

polar dew
#

Start with +1

Then 1 negative

Then +3

Then 2 negatives

Then +6

Then 3 negatives

Then +10

Then 4 negatives

etc.

So:

• The positive terms are
1, 3, 6, 10, 15, 21, ...
These are triangular numbers.

The m-th positive term is:
𝑇𝑚=𝑚(𝑚+1)2Tm

=
2
m(m+1)

Now look at how many terms are used up to the m-th positive block.

Each stage contributes:

1 positive

m negatives

So total terms after m blocks
1+(1+1)+(1+2)+(1+3)+⋯+(1+𝑚)
1+(1+1)+(1+2)+(1+3)+⋯+(1+m)

#

idk how to make the T and V signs in here

fickle nova
#

i had a different approach

polar dew
#

What did u use?

fickle nova
#

I noticed that the positive terms all follow the same pattern where it's (n n+2) (binomial distribution)

#

So i converted the entire sum into:
$2 \cdot \sum_{i=0}^m \binom {n + 2}{n} - \sum_{i=1}^n i$

elfin berryBOT
#

Saarker

fickle nova
#

where n is 435

#

and m is the number of these terms

#

which you find by verifying whether 435 itself is one of them

#

by solving $435 = \frac{m \cdot (m + 1)}{2}$

elfin berryBOT
#

Saarker

fickle nova
#

then you verify if the m is an integer and if it is it means that the last term of the sum is positive

#

$2 \cdot \sum{i=0}^m \binom {n + 2}{n} = \sum_{i=1}^m (i^2 + i)$

elfin berryBOT
#

Saarker

polar dew
#

Yeah i see what you did

fickle nova
#

wait wrong

#

So like

#

is it right

#

i wanna know the numerical result

polar dew
#

im not sure beacuse i didnt do it like that

jagged relic
fickle nova
#

$2 \cdot \sum_{i=0}^m \binom {n + 2}{n} = \sum_{i=1}^m (i^2 + i)$

fickle nova
elfin berryBOT
#

Saarker

jagged relic
#

,, \binom{n+2}{n} = \binom{n+2}{2} = \frac{(n+1)(n+2)}{2} = T_{n+1}

elfin berryBOT
fickle nova
#

i cant trust what i wrote down

#

but i think the result was right

#

i got -85600 or something along that

#

worst case scenario i just forgot to change up some indexes or whatever so its a bit off

jagged relic
#

S_n = -T_n + 2U where U is the sum of the positive terms

fickle nova
#

yup thats what i did

jagged relic
#

The terms in U are in T_n, and 435 is a triangular number

fickle nova
#

but U has a different index

fickle nova
#

which is like 29

jagged relic
#

,calc 29*30/2

elfin berryBOT
#

Result:

435
jagged relic
#

Right

fickle nova
#

could this mean i got the hardest question on the exam right

jagged relic
#

So you can just take the sum of T_n from 1 to 29

fickle nova
#

🥹

#

let me plug in the numbers

fickle nova
jagged relic
#

Not sure what you mean by that

#

,, 2U = 2 \sum_{n=1}^{29} \frac{n(n+1)}{2} = \sum_{n=1}^{29} n(n+1)

elfin berryBOT
fickle nova
#

originally i didnt have n = 1

#

i had n = 0 because i was referring to the binomial coefficient

#

so i made n = 1 so it would be n(n+1)

jagged relic
#

Ok sure

fickle nova
#

i expanded it and it was like $\sum_{i=1}^m (i^2 + i) = \frac{m(m+1)(2m+1)}{6} + \frac{m(m+1)}{2}$

elfin berryBOT
#

Saarker

fickle nova
#

please render right

#

yuppers

#

i cant believe i got this right

#

damn

jagged relic
fickle nova
#

thanks a lot for the help

#

cant wait to get the results back

jagged relic
#

Right so that's m(m+1)(m+2)/3

fickle nova
#

yup

#

well i kinda just plugged in everything

jagged relic
fickle nova
#

awesomesauce

jagged relic
#

,calc 435436/2 - 2930*31/3

elfin berryBOT
#

Result:

85840
fickle nova
#

wait THATS WHAT I GOTTT

#

tysmmm

#

do i close the chat now?

jagged relic
#

If you don't have any more question, sure

fickle nova
#

perfect

#

.close

marsh citrusBOT
#
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vague jay
marsh citrusBOT
tight furnace
#

Have you done <= yet?

vague jay
#

Suppose $\alpha = p(\lambda)$ for some eigenvalue $\lambda$ of $T$. We know that there exists a nonzero $v \in V: Tv = \lambda v$. Thus, $p(T)v = p(\lambda)v = \alpha v$, showing that $\alpha$ is an eigenvalue of $p(T)$.

elfin berryBOT
#

holo_morph

vague jay
#

This idea was already mentioned in LADR but the $p(T)v = p(\lambda)v$ equivalence follows from the fact that $T^kv = \lambda^k v$

elfin berryBOT
#

holo_morph

tight furnace
#

Nice

vague jay
#

yeah but I need the other direction 😭

tight furnace
#

Well you might suspect this already but it has to do with the field being specifically C

#

You might have a guess as to which property of C is needed here

vague jay
#

Conversely, suppose $\alpha$ is an eigenvalue of $p(T)$. Then for some nonzero $v \in V$,
\begin{align*}
&p(T)v = \alpha v\
&\Rightarrow (p(T) - \alpha)v = 0
\end{align*}
By the fundamental theorem of algebra, we have that
\begin{align*}
&p(z)-\alpha = c(z-\lambda_1)\cdots(z-\lambda_m)\
&\Rightarrow p(T)-\alpha = c(T-\lambda_1)\cdots(T-\lambda_m)\
&\Rightarrow (p(T)-\alpha)v = c(T-\lambda_1)\cdots(T-\lambda_m)v = 0.
\end{align*}
The above equation implies that some $\lambda_j$ is an eigenvalue of $T$, and since $\lambda_j$ is a root of $p(z) - \alpha$, we have that $p(\lambda_j) - \alpha = 0 \implies \alpha = p(\lambda_j)$, as desired.

elfin berryBOT
#

holo_morph

tight furnace
#

yayyy

#

that was how I did it too

vague jay
#

did u do all of ladr?

tight furnace
#

nah

#

I feel like Ive seen this problem before

#

But probably like posted in a discord server before lol

#

Actually my first instinct was to nuke it with Jordan normal form lol

#

but that's not the LADR way kekw

#

Well also ig we don't have finite dimensionality lol

marsh citrusBOT
#

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steady fjord
#

\textbf{Axiom - Pairing Axiom:} $\forall x\forall y \exists z \forall w ( w \in z \iff (w = x$ or $w = y))$

This means "for any sets x and y, there exists a set z such that the elements of z is either x or y

elfin berryBOT
steady fjord
#

or im trying to understand this axiom

#

so its just saying theres some set z that contains either x or y or both?

fervent rampart
#

it means "w is an element of z if and only if it is equal to either x or y" (i.e. the elements of z are x and y)

#

so it's saying that given x and y exist, z = {x,y} is a set that also exists

steady fjord
#

so i am curious

#

why cant the axiom just be given x exists, z = {x} is a set that also exists?

#

i think you can prove it from the pairing axiom

#

but why cant we just set z = {x} as an axiom itself? is it just hard to proof stuff with just this?

fervent rampart
#

this allows for constructions other than just that, for example constructing the ordered pair/tuple (x,y) = {{x},{x,y}}

steady fjord
#

ah okay

#

ty!

steady fjord
#

why do we say (x,y) = {{x}{x,y}} and not {{x},{y}}?

fervent rampart
#

tuples (x,y) is ordered, so you need to be able to tell which element is first and which element is second, but sets are not ordered, so {{x},{y}} = {{y},{x}}, which would mean (x,y) = (y,x) using that definition, whereas {{x},{x,y}} = {{x,y},{x}} retains the information about which element is first (the one in the singleton) in both orders

steady fjord
#

tysm!!!!

#

this makes alot of sense

#

.close

marsh citrusBOT
#
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vague jay
marsh citrusBOT
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stuck tendon
#

help i dont know how to do it

marsh citrusBOT
stuck tendon
#

so far i found derivative or slope of the first equation

serene bramble
#

Can you then find the tangent at (4, -4)?

stuck tendon
#

the tangent is when i plug in x = 4 into my derivative equation right?

serene bramble
#

(I mean, this is a two-parter question, the first part literally asking you to find the equation of the tangent — so I'd think to do that in any case)

serene bramble
#

[important to get that conceptual phrasing down correctly]

stuck tendon
#

ok i got y = -x

stuck tendon
serene bramble
#

yes - but I'm pointing out that "gradient" != "tangent"

stuck tendon
#

oh yeah

serene bramble
#

"gradient" is the value that represents the rise-over-run

#

"tangent" is a line

#

So they're different objects, hence the need to make the wording a little clearer there

stuck tendon
#

ok i see

#

so so far i found the

#

gradient

exotic valley
#

some people actually think that the first derivative's equation is the equation of the tangent

stuck tendon
#

but thats not the equation of the tanggent

exotic valley
#

so yeah best to clarify

stuck tendon
exotic valley
#

I'm saying it's a common mistake

stuck tendon
#

oh yeah

opaque agate
#

Yes i clicked on the channel because of the name

exotic valley
#

hence the "some people actually think"

#

but if you know that then cool!

stuck tendon
#

ok

exotic valley
#

sorry to interrupt

stuck tendon
#

i was just wondering

#

if i was right

#

so im sorry

#

but anyways

#

to find the equation

#

i will

serene bramble
#

The first derivative gives you a function to find the gradient of a tangent at a point which you can plug in, yh

stuck tendon
#

just plug in for y= mx + b?:

serene bramble
stuck tendon
#

ok good

serene bramble
#

Now what's the second part of the question asking?

stuck tendon
#

find the coordinate of the tangent where it meets again

#

wait but are we done the first part of the qustion?

#

is it just y = - x

serene bramble
#

ye

stuck tendon
#

ok thanks

#

.close

marsh citrusBOT
#
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vivid beacon
#

how to do this

marsh citrusBOT
sharp vigil
#

hint: ||factor theorem||

exotic valley
#

heh they give you space to type working? wow

vivid beacon
exotic valley
#

if a is a root of a poly, (x-a) is a factor of said poly

#

hope that would be clear

vivid beacon
#

what is a poly

exotic valley
#

polynomial

#

sorry, a bit too lazy to fully type it out

vivid beacon
#

so how do we do it

#

i was thinking complete the square

#

but seems wrong

#

or qudratic formula

knotty trellis
#

That's unnecessarily complicated

sharp vigil
#

or vieta

knotty trellis
#

Either write it in the factorized form, or use vieta's

vivid beacon
#

idk what vieta is

vivid beacon
exotic valley
#

you have the two roots and thus the two factors!

vivid beacon
#

but idk wht the numbers p and q are

#

i need to find them

distant turtle
#

one simple way is forming 2 linear equations in 2 variables by plugging in 5 - (3)^1/2 and then 5 + (3)^1/2

#

u can then solve the linear equations

#

to find p and q

vivid beacon
#

subtituating the soluton into the equation for both + and minus?

jagged relic
#

There is really no reason to form a system of equations

exotic valley
#

that's the most straightforward way

#

that I can think of at least

jagged relic
#

If a polynomial $ax^2 + bx + c$ has roots $r_1$ and $r_2$, then it equals $a(x-r_1)(x-r_2)$

elfin berryBOT
jagged relic
#

That's basically the factor theorem (for quadratics)

#

You need to internalize that

vivid beacon
#

i got i just had to use the qudratic formula

#

.close

marsh citrusBOT
#
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warm pebble
#

Let $R=\mathbb{R}/\mathbb{Z}$ denote the ring of real numbers mod $1$. Given an integer matrix $A$ with non-zero determinant and vector $b\in R^n$, I want to show that $Ax=b$ has exactly $|\det(A)|$ solutions in $R^n$. It is easy to see when $A$ is diagonal, as $0, 1/k, 2/k, ..., (k-1)/k$ all vanish in $R$ when multiplied by $k$. Also, I know that the number of solutions is invariant with left-multiplication by an invertible integer matrix

elfin berryBOT
marsh citrusBOT
#

@warm pebble Has your question been resolved?

marsh citrusBOT
#

@warm pebble Has your question been resolved?

marsh citrusBOT
#

@warm pebble Has your question been resolved?

night relic
# warm pebble Let $R=\mathbb{R}/\mathbb{Z}$ denote the ring of real numbers mod $1$. Given an ...

Have you considered decomposing the matrix so that you can get a diagonal matrix and some left multiplication of invertible matrices? ||LUP decomposition of the form PA = LU|| seems promising (||start with A, argue that left-multiplication with P is invariant on solutions, then examine LU instead||); of course, you would have to prove that everything required for this decomposition works under R/Z.
The other one that sprang to mind is ||diagonalizing,|| but i'm not 100% you can do that without right-multiplication. (you'd have ||AP = PD||, the LHS could cause problems)
Try those and see what you get?

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#

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stone fulcrum
#

Can someone please explain this to me?

marsh citrusBOT
stone fulcrum
#

I was doing a bunch of problems where you do up forces=down forces, f=ma and it was about splitting things into components, but the model answer for this question shows barely any working

paper kelp
#

Which part would you like help understanding?

stone fulcrum
#

Why didn’t we need to find theta and divide it into components? Ty

wispy jungle
#

It was originally in equalibrium

high pine
#

since these three forces cause the point to be in equilibrium, it means that each force balances the other two, in particular the force of 35 N balances the other two

stone fulcrum
#

I think I somewhat understood? So if i were to find the resultant force between 12 and 37 it would also be 35?

high pine
#

Exactly

stone fulcrum
#

Ohh ok thank you to all of u 🙂

#

.close

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#
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high pine
#

Of course you will have to apply it in the opposite direction to achieve balance

#

But the magnitude would be the same

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compact flower
marsh citrusBOT
wintry gale
#

is bro casually flexing the happy valentine's day gift?

compact flower
exotic valley
#

for future helpers, might wanna briefly explain what you've tried and where you're stuck on!

obtuse umbra
compact flower
#

I’m stuck on it conceptually, and how I can actually use any of 9.12 to show this

#

Conceptually, it’s really simple, but I can’t figure out the starting step even though I did 9.12

#

I currently have |a^n+1/a^n| < epsilon

#

And even then I don’t think that’s a good starting point

obtuse umbra
marsh citrusBOT
exotic valley
obtuse umbra
wintry gale
#

mb

obtuse umbra
marsh citrusBOT
knotty trellis
#

out of the 3 cases

compact flower
knotty trellis
#

So if |a| <= 1, we need to bound |a^n / n^p - 0|. How did you even get this to the |a^n + 1/a^n| < epsilon?

#

I'd just bound it by |a^n / n^p| <= |1 / n^p| and then make that < epsilon

compact flower
#

Ok now the 2nd

#

I actually just got the first

#

Can I assume n/(n+1) converges to 1

knotty trellis
#

n/(n+1) = 1 - 1/(n+1)

#

so if you have proved some theorems about arithmetic of limits and that 1/n -> 0, then you should be fine

compact flower
#

Alright

#

I’ll do it very quickly to be safe

knotty trellis
compact flower
#

That was the hardest part for me so I think I have the q down now, thank you

#

Like figuring out the setup and cancelling things

#

.close

marsh citrusBOT
#
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gaunt lynx
#

hello, can you somehow determine if a extreme point is a minima or maxima without pluging it into the 2nd derivative? my teacher does it somehow but i lowkey dont listen and i forgot how he did it

devout mauve
#

you can plug nearby points into f(x)

knotty trellis
#

or inspect the derivative to see if it's negative -> 0 -> positive or positive -> 0 -> negative

devout mauve
#

left of the extreme point its negative, at the extreme point its zero, right of the point its positive

gaunt lynx
#

yeah

#

i remmeber now

#

he said something like

#

like after a minimum there must be a maximum yk

#

but generally its always better to plug it into f''(x)?

gritty schooner
gaunt lynx
gritty schooner
gaunt lynx
#

okay also

#

this is another topic but

#

How do i know if i have to do a case thingy when parameters are involved?

#

its so confusing , sometimes you have to do it, and sometimes you dont

stuck tendon
#

lots and lots of practice and you will see differently

#

you will find trends and patterns at an instant of a glance

gaunt lynx
#

damn alright

#

so theres no trick

stuck tendon
#

that is why it is called intuition

gaunt lynx
#

for telling when?

stuck tendon
#

well it becomes unconventional

#

make your life easier by just practicing

gaunt lynx
#

yeah i will thanks

stuck tendon
marsh citrusBOT
#

@gaunt lynx Has your question been resolved?

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tulip galleon
marsh citrusBOT
wintry gale
#

Leibniz Integral Rule

#

probably

tulip galleon
#

yeah i tried using that

#

just leads to a mess

main idol
#

why is g(x) not a function of x

#

and why is a a function of x instead of a constant

dire basalt
#

Fr smth feels off innit

marsh citrusBOT
#

@tulip galleon Has your question been resolved?

wind root
#

prove f'(x)=x

marsh citrusBOT
#
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tulip galleon
marsh citrusBOT
tulip galleon
#

a is an integral and g(x) is an integral with the upper bound as an integral...

#

if that makes sense

lavish pelican
tulip galleon
#

ts is jee advanced btw

lavish pelican
#

Okay

#

Coming back to the question

#

That f'(x) is kinda throwing me off

marsh citrusBOT
#

@tulip galleon Has your question been resolved?

marsh citrusBOT
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oak marsh
#

hi

marsh citrusBOT
oak marsh
#

Hello

#

Salutations

#

I ran into a small error. For some reason it keeps saying i'm wrong but I checked with desmos and it has the same points

cunning fiber
#

(In the future, please make the first message you send the actual question since that's what the bot pins. This saves us the effort of having to change the pin manually.)

cunning fiber
#

try taking out the +0

oak marsh
cunning fiber
#

hm

oak marsh
#

maybe my math is wrong?

#

The answer is simplified

cunning fiber
#

wait a minute

#

why is the 1/4 there

#

the graphs don't match

jagged relic
#

it has the same points
No it doesn't

oak marsh
#

...

#

I must've overlooked

cunning fiber
#

rip

marsh citrusBOT
#

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

oak marsh
#

wait

#

AHH

#

I see it

#

thank you!, ill be back is an issue comes up

#

.close

marsh citrusBOT
#
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oak marsh
#

Question, How do I sketch this graph, more so. Where do I start?

oak marsh
lethal kite
#

ig a good starting point is to find the vertex

#

and figure out which way it is pointing

oak marsh
#

downward

#

Would I write this in vertex form?

lethal kite
#

u could if u want but it wont be rly usefull. Just notice that the max of -3x^2 is 0, so what can we say about the vertex?

oak marsh
#

It has an x value of zero

#

Since we can't complete the square?

lethal kite
#

the maximum is at 0, right?

#

because x^2>=0

oak marsh
#

I'm not understanding, could you elaborate a bit more please

lethal kite
#

so we know that x^2>=0, right

oak marsh
#

yes

lethal kite
#

so -3x^2 is negative snce x^2 is greater than 0, right?

#

or -3x^2 could also be 0

oak marsh
#

yes

#

would I just plug in zero?

lethal kite
#

yes

#

so the minimum of the function would be 0-2=-2

oak marsh
#

So the vertex would be (0, -2)?

lethal kite
#

yes

oak marsh
#

And I owuld just plug in random number till I find a second point with whole numbers?

lethal kite
#

well if you plug in a whole number for x the output is also a whole number, right?

oak marsh
#

yes

lethal kite
#

so ig you could do that..

#

but theres a better way

#

do you know parabola tranformations?

#

if not its ok

oak marsh
#

No, but i am interested in learning it if thats ok with you

#

Maybe i do, might not ring a bell

lethal kite
#

u know what x^2 looks like, right?

#

wait ill give you a screen shot

oak marsh
#

Yeah, its where the vertex is (0, 0)

lethal kite
#

notice that 3x^2 is "compressed" and thinner than x^2

oak marsh
#

OHHHH, its where the graph has a stetcha dn yeah, now it rings a bell

lethal kite
#

so in general ax^2 is "thinner" that x^2

oak marsh
#

ohhh, that makes sense now

oak marsh
#

Oh yes, my favorite tool

lethal kite
#

i reccomend you play around wih the graphing calculator with parabolas to get a fell on how much it "thins"

oak marsh
#

Got it

#

thank you very much!

lethal kite
#

np!

oak marsh
#

.close

marsh citrusBOT
#
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lethal kite
#

wait a sec

#

just a quick tip

#

if you were to graph it on paper, i would reccomend you to plot points because it is more accurate, and the transformation if only good for a rough sketch of more complicated polynominals

#

but yea nice job

#

!

marsh citrusBOT
#
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gaunt lynx
#

hello did i do this correctly

marsh citrusBOT
gaunt lynx
#

im have to calculate the multiplicity of zeropoints

#

but idk

marsh citrusBOT
#

@gaunt lynx Has your question been resolved?

gaunt lynx
#

yeah its correc

marsh citrusBOT
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marsh citrusBOT
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slim lark
#

two externally disjoint circles o1 and o2. find locus of centers of circles that at orthogonal to o1 and externally tangent to o2

slim lark
#

i think it might be a parabola but i tave no idea how to prove it

marsh citrusBOT
#

@slim lark Has your question been resolved?

frail obsidian
#

have you made any progress yet

slim lark
#

i havent

frail obsidian
slim lark
frail obsidian
#

wait, I'll show you where to start

#

you can have a go

slim lark
#

do you have full solution? english isnt my first language and especially in math it makes learning harder

frail obsidian
#

well yeah, but we're not supposed to share full solutions in this channel

slim lark
#

is it okay with rules for me to ask you to send me that in dm?

#

im gonna translate it and analyse it step by step

frail obsidian
#

oh that sort of full proof 😭

#

I'm sorry, don't have my phone on me rn

#

the proof is quite messy the way I have it

slim lark
#

ive just started learning bout elipses and parabolas and ummm its not going well

slim lark
frail obsidian
#

yeah definitely

#

essentially, this is orthogonality yeah?

slim lark
#

i think

frail obsidian
#

so by pythagorean theorem, (distance between centers)^2 = (radius 1)^2 + (radius 2)^2

#

that's your first equation

slim lark
#

in my lannguage its caled perpendicular circles 😭

frail obsidian
#

orthogonality is js fancy math speech for perpendicularity 💀

#

2nd equation comes from condition for tangency

#

distance between centers = sum of radii

frail obsidian
slim lark
frail obsidian
#

let radius of O1 be r1

#

radius of O2 be r2

#

radius of the locus circle would be equal in both equations right?

#

let that be r

#

so you rewrite both equations as r = something 1, r = something 2

#

set those somethings equal

#

and you'll have your locus

slim lark
#

i did and i still dont get that

#

i need to find the focus and the directrix

frail obsidian
#

ok, I'll type out a specific proof here, you can try generalizing it for arbitrary disjoint circles ok?

slim lark
#

ok

#

is o1 the focus? do i look in the right place?

#

the centre of o1

frail obsidian
#

you'll straight up get the equation of the curve

#

give me a few mins to latex

slim lark
frail obsidian
#

no like you can extract those details too

#

I'm js saying that its not required for the solution itself

slim lark
#

ok i get that

#

ill try to extract them

frail obsidian
#

Let the two circles be:

  1. $O_1:$ Center $C_1$ = (-a,0), radius $r_1\n$
  2. $O_2:$ Center $C_2$ = (+a,0), radius $r_2\n$
  3. Locus point P(x,y) (center of third circle having radius r\n)

Condition 1: Orthogonality to $O_1\n$
Distance between centers squared is same as sum of squares of radii$\n$
$(x+a)^2 + y^2 = r^2 + r_1^2\n$
i.e $r^2 = (x+a)^2 + y^2 - r_1^2\n$

Condition 2: External tangent to $O_2\n$
Distance between centers is sum of radii $\n$
$\sqrt{(x-a)^2 + y^2} = r+r_2\n$
i.e $r = \sqrt{(x-a)^2+y^2}-r_2\n$

Substitute eqn 2 to eqn 1 $\n$
$(x+a)^2 + y^2 - r_1^2 = (\sqrt{(x-a)^2+y^2}-r_2)^2\n$
$(x+a)^2 + y^2 - r_1^2 = (x-a)^2 + y^2 + r_2^2 -2r_2\sqrt{(x-a)^2+y^2}\n$
$\frac{r_1^2+r_2^2-4ax}{2r_2}=\sqrt{(x-a)^2+y^2}\n$

square both sides

#

oh my god

#

how do you format this 😭

elfin berryBOT
#

donkey
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marsh citrusBOT
#

@slim lark Has your question been resolved?

#
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tulip galleon
#

uh

marsh citrusBOT
tulip galleon
#

where did my doubt go

knotty trellis
marsh citrusBOT
#

@tulip galleon Has your question been resolved?

tulip galleon
#

this is pre university calculus btw

#

im in the 12th grade

marsh citrusBOT
#

@tulip galleon Has your question been resolved?

marsh citrusBOT
#
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shell tulip
#

I've big issues i don't understand what's limited development and what's his goal?

azure ivy
#

!xy

marsh citrusBOT
#

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

sinful thistle
#

what lol

shell tulip
#

"Hey! I'm struggling to understand the concept of Taylor expansion at infinity (limit development). Could someone explain how the change of variable $X = 1/x$ works and what's the point of it? Thanks!"

elfin berryBOT
#

tintinnono

shell tulip
#

.close

marsh citrusBOT
#
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marsh citrusBOT
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gaunt lynx
marsh citrusBOT
gaunt lynx
#

Determine, for each extremum and for each inflection point of the function, the coordinates as functions of the parameter and the equation of its locus.

#

hello what did i do wrong

marsh citrusBOT
#

@gaunt lynx Has your question been resolved?

gaunt lynx
#

<@&286206848099549185>

void pine
gaunt lynx
#

im basically stuck

#

thats what i meant to say

void pine
#

Oh ok

#

So what was your strategy here

gaunt lynx
#

so uhh

void pine
#

Why did you calculate the derivative

gaunt lynx
#

bascially use the pq formula

gaunt lynx
void pine
#

Ok yes how do you link extrema with the derivative

gaunt lynx
void pine
#

Yeah the extrema are zero points of the derivative

#

So i see you've calculated the zeros of the derivative

gaunt lynx
#

i havent really

#

im stuck

void pine
#

Do you have any idea what to do next

gaunt lynx
#

i did something wrong i think

void pine
# gaunt lynx

Don't you zgree that x1/2 are zeros of thederivative

gaunt lynx
#

it seems too much

#

like

void pine
#

You think you lessed up that

#

Ok lemme check

#

Did you calculat ethe discriminant?

#

I mean

#

Whatever you call it

#

Delta

gaunt lynx
#

no?

#

because ive got 2t +- the root

#

does that work with discriminant

void pine
#

Wdym

#

The discriminant always exists

#

Its square root might not

gaunt lynx
#

yes btu

#

i thikn i have an idea

#

wait can i simplify something here

void pine
#

So you did multiply by 2t before and this works okay

gaunt lynx
#

yeah

#

i think i can simplfiy osmething ther tho

void pine
#

And it does give a different result for the discriminant but the solution should be the same at the end

gaunt lynx
#

oh

#

okay

#

so uhh

void pine
#

Because now you changed your a, b, c coefficient of your pilynomial

#

So you have to use the new values for the formula

gaunt lynx
#

so wait my discriminant is 4t-3t^2 right

#

or wdym

void pine
#

No

gaunt lynx
#

the stuff inside the root isnt D?

void pine
#

This is the formula

#

It is tye stuff inside the root, i just think you got the formula wrong

gaunt lynx
#

what formula

#

this is the formula

void pine
#

So it would give 16t²-12t²

void pine
#

So p and q arethe2 last coefficients right?

gaunt lynx
#

yes

#

p is 4tx

void pine
#

So what is p

gaunt lynx
#

and q is 3t

void pine
#

No

#

q is 3t²

gaunt lynx
#

yeah

void pine
#

So you just miscalculated the stuff by forgetting a square i think

void pine
#

You forgot to suqare the p/2

#

In the root

#

I think

gaunt lynx
#

-4/2^2

#

is 4

void pine
#

Okay i see the problem

#

Again what is p

#

p is 4t not just 4

#

T is a coefficient

#

You're not solving for t

#

You're solving for x

#

Because it's f(x), not f(t)

gaunt lynx
#

so 4

#

4t

#

i wrote it down here

void pine
#

(4t/2)²=4t² not 4t

#

You see?

gaunt lynx
#

ohhhhhhhhhhhhhhhhhhhhhhhhhhhh

#

myyy hod

void pine
#

Happens

gaunt lynx
#

wait so we can just pull the root now ? it cancels the ^2?

void pine
#

So yeah your problem seems to be a small calculation but your overall strategy is going in the right direction

void pine
gaunt lynx
#

it isnt

#

always

void pine
#

Root of square turns everything inside positive

gaunt lynx
#

so its better to do a case differentiaation here?

void pine
#

For exemple root of square of -1 is 1 not -1

gaunt lynx
#

it doesnt work

void pine
#

Yes you have to do a case differentiation