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1 messages · Page 168 of 1

thorn tapir
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Yeah

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This is 100%

steady basin
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what about the 0 column

thorn tapir
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Try your own method on the RREF

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RREF means Row Reduced Echelon Form

steady basin
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yh ive done that

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what im saying is

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u said

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no of columns is 4

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but what about the 0 column

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shouldnt number of columns be 5

thorn tapir
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That is not part of the original matrix lmao

thorn tapir
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the number of column is basically of the original matrix B

steady basin
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ok

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but when u do RREF

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do u consider

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the inhomeginity

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as well

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ie the added column

thorn tapir
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You don't have to always add the 0 column to do RREF, it can be done on any matrix anywhere

steady basin
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ie the RHS of the augmented matrix

thorn tapir
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When you augment the b vector and then do RREF, then you're doing something called Gaussian Elimination of System of Linear Equations

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You're removing variables by making their coefficients 0

steady basin
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okok

thorn tapir
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When you do row operations it's technically adding equations to each other

steady basin
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ok

thorn tapir
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Essentially the elimination method of solving equations

steady basin
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i think we r come

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chartbit has also given me their agreement as well

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thanks mate

thorn tapir
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You're welcome

lone heartBOT
#

@steady basin Has your question been resolved?

lone heartBOT
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gray walrus
#

A pound of coffee beans makes 50 cups of coffee when brewed according to the instructions (4 cups = 1 qt). How many liters of coffee can one kilogram of coffee beans produce?

lunar palm
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do you know the unit conversions required for this question?

gray walrus
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L/kg

lunar palm
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more specifically you'll need the conversion formulas from
pound --> kilogram
&
cup --> litre

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do you know them?

gray walrus
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yes yes

lunar palm
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convert the 1:50 ratio with those formulas

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i.e 1 pound in kg:50 cups in liters

gray walrus
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okok got it

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thank you thank you

#

.close

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alpine sable
lone heartBOT
alpine sable
#

I'm messing up somewhere in the second iteration. If someone could help me please

lone heartBOT
#

@alpine sable Has your question been resolved?

alpine sable
#

.close

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chrome depot
#

Let x1, x2 be solutions to:
(5-x) : (x+1) = (x-1) : (x+a)

chrome depot
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I have to find parameter a such that x1^2 + x2^2 = 26

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How do I go about this?

weary wyvern
lone heartBOT
#

@chrome depot Has your question been resolved?

chrome depot
#

Here is the solution:

weary wyvern
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Didn't ask

chrome depot
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Kind of rude but okay

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.close

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plain hill
lone heartBOT
plain hill
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about this

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i find the sin(alpha)

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because i do that sin^2(a) = 1/1+ cot^2 (a)

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and i find that sin^2(a) = +/- 1/16

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and after i do that this was equal at -1/16

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and so sin(a)= -1/4

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but about cos(a)

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what i should do??

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<@&286206848099549185>

exotic belfry
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sin²+cos²=1

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or cot = cos/sin

lone heartBOT
#

@plain hill Has your question been resolved?

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somber spade
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2x + 3y = 45
x + 4y = 35

lone heartBOT
somber spade
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whats the best way of doing this?

sharp thorn
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Multiply the second equation by 2

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And subtranct

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2x+3y=45
2x+8y=70

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Solve from here

somber spade
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okay that actually was really easy

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is there other methods to do when you cant multiply?

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or divide

sharp thorn
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Draw lines and take the intersection

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Don't worry there won't be much cases without the elimination mehod

somber spade
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how would i draw lines and take intersection?

sharp thorn
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Graphing calculato

somber spade
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ah right

sharp thorn
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You enter both equations

somber spade
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is there another way which you can do on paper(

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😅

sharp thorn
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Idk any other methods sorry

modern sedge
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2x+3y=45
2x=45-3y
x=(45-3y)/2

x + 4y = 35
x=35-4y

x=x
35-4y=(45-3y)/2
And solve for y

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or the substitution

sharp thorn
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Oh yeah I substitution

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You have to convert x in terms of y and substitute or vice versa

modern sedge
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x+4y=35
x=35-4y

2x+3y=45
2(35-4y)+3y=45 and solve for y

sharp thorn
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Yep

somber spade
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not really understanding any of this 😅

sharp thorn
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Try my method

somber spade
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i was able to do your first method easily

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but i want to learn at least 2 methods on paper in case of a test

modern sedge
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The first method always works for the equations in form of ax+by=c

sharp thorn
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The two equations are
2x+8y=70
2x+3y=45

After subtract
5y=25
So y is 5

Then take the value of y and substitute it in any of the equation you'll get x

somber spade
somber spade
modern sedge
sharp thorn
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It's substitution method

modern sedge
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the one I posted earlier is a bit worse

sharp thorn
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It's very hard to teach in chat .. maybe contact your teacher or smtg

somber spade
modern sedge
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x+4y=35, that's first equation
x=35-4y by subtracting 4y from both sides

2x+3y=45 that's the second equation
2(35-4y)+3y=45 since x=35-4y we can replace it with it

sharp thorn
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MY English sucks already and I'm in phone so that's the maximum i can do

modern sedge
somber spade
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after the second equation

modern sedge
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Since x=35-4y is the result from first equation. This means that x is SAME as 35-4y, and since it's same you can replace x with 35-4y and you can also replace 35-4y with x

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equal means same

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If a=b and b=c, then a=c

somber spade
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right let me try and do it

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alright i understood it this fae

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far

somber spade
modern sedge
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2(35-4y)+3y=45

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this has just one variable so it can be solved trivially

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once you solve it you can plug it's value e.g. to x+4y=35 and get x

somber spade
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uh

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i didnt understand a thing about that

sharp thorn
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We are converting x in terms of y

somber spade
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could someone draw it on paper?

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and explain whats being done step by step?

sharp thorn
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After conversion we get
x=35-4y

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We take this value of x and substitute in one of the equations

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That's it

somber spade
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yes i understood that

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but how do i go from that

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to x=5

sharp thorn
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Im sorry I don't have paper now

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So wait

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Send me the 2 equations once sgn

somber spade
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2x + 3y = 45
x + 4y = 35

sharp thorn
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Okay so

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Acknowledge me with every step ok,

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Let me take the second equation

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x+4y=35

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Now let me take the 4y to the other side

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So
X=35-4y

somber spade
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yes

sharp thorn
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Understand?

somber spade
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yup

sharp thorn
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Now we have a value for y

somber spade
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x*

sharp thorn
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Sorry for x

somber spade
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yeah i understood this far

sharp thorn
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That is x=35-4y

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So let's take the first equation again

somber spade
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yeah

sharp thorn
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X+4y=35

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Or wait ig I have to take the other equation

somber spade
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first equation is 2x+3y= 45

sharp thorn
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Yeah this

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So we have a x in this equation right?

somber spade
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yeah sp 2(35-4y) +3y = 45

sharp thorn
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Yes exactly

somber spade
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yes so after this i need assistanse

sharp thorn
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Multiply 2 inside

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And tell me

somber spade
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what do you mean?

sharp thorn
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After multiplication 2(35-4y) is 70-8y

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This you got?

somber spade
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yes

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yeahyeah

sharp thorn
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So mpput this into the equation

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70-8y+4y=45

somber spade
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70-8y+3y=45?

sharp thorn
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Yes sry

somber spade
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its fine

sharp thorn
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So 70-5y=45

somber spade
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so 70-5y=45

sharp thorn
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Got it?

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Yes

somber spade
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yup

sharp thorn
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Now subtract 70 on both sides

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-5y=-25

somber spade
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-5y = -25

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yes

sharp thorn
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Negative cancels negative

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5y=25

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Y=5

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Got it?

somber spade
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negative cancels negative?

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i thought that was only in multiplication

sharp thorn
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For your understanding let me put it this way

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You multiply by(-1) on both the sidds

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Sidds

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Sides

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Got it?

somber spade
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yes

sharp thorn
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Yea that's it

somber spade
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but does thst happen automatically when its negative on both sides of equal?

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or do you actually have to do (-1)

sharp thorn
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Yes it does

somber spade
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ohh

sharp thorn
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You don't have to

somber spade
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ohh thank you learnt something new

sharp thorn
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You can just straight away cancel two negative signs in equality considering there is no addition or subtraction

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for example -ax=-c
Also means that
ax=c

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You can substitute any values for a x and c to check this yourself

somber spade
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makes sense but also doesnt make sense to me

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but yeah

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i understand it

sharp thorn
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Just cancel 2 negatives that's it

somber spade
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yeah thanks

sharp thorn
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Not an overkill

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You're welcome

somber spade
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wanted to learn 2 methods of doing it so i can double check my answers on my tests

sharp thorn
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Yes

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For double checking

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You will get x and y nah

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Just substitute those values in all the equations and make sure all of them end up true

somber spade
#

.close

lone heartBOT
#
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native temple
#

How to deal with earworms? I want quiet in my heart yet my mind thinks of a song I like even when I want quiet…

native temple
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This is about studying though

calm plank
#

Bro what

sharp thorn
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Not maths

spring plover
#

Take it to other channels on this server meant for discussion that isn't math help.

calm plank
modern sedge
#

.close

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alpine sable
#

hey, im not really sure how to do hypotenuse leg proofs, would this be the right way to go about it? i dont know if theres anything specific that i need to do special to them or whatnot

alpine sable
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(and then obviously do the triangle proof and stuff saying that the triangles are congruent)

calm plank
#

what is your question exactly?

alpine sable
#

is this the proper way to prove congruent triangles using HL

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i thought there was some special angle stuff you need to do or something but im not sure

gusty gorge
#

can you state the HL theorem?

lone heartBOT
#

@alpine sable Has your question been resolved?

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lofty flame
#

Summation (I=15, n=29+5, k = i^2 + 5i +4 )

Can anyone check if the answer is correct and tell me please how can I verify it

lone heartBOT
#

@lofty flame Has your question been resolved?

lofty flame
#

<@&286206848099549185>

vestal quail
#

Tips on how to actually become good at math😭😭

tacit bobcat
lofty flame
#

I want to verify the whole summation I need to redact the solution

tacit bobcat
#

,calc sum(map(range(1,5), f(x) = 7*x-3))

ocean sealBOT
#

Result:

90
lone heartBOT
#

@lofty flame Has your question been resolved?

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quartz panther
lone heartBOT
quartz panther
#

,rccw

ocean sealBOT
quartz panther
#

how do i find the missing side?

fringe sleet
#

pythagoras

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but first you need to find this length

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so look for something symmetries so you can find it

quartz panther
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2+5x - 2+x?

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so @fringe sleet its just 3x

tacit arch
#

the red line?

quartz panther
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the answer

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for the missing side

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coz sqrt(3x^2 + 6x^2) = 3x

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right?

tacit arch
#

show your full work

quartz panther
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yeah ive done something wrong i think

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so c

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  • sqrt of a^2 plus b^2
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and the missing side is 6x

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i think

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coz $2+5x-(2+x) = 4x$

ocean sealBOT
#

MathematicsPractice

quartz panther
#

@tacit arch

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sorry for ping im real desperate

tacit arch
#

oh you fixed it

quartz panther
#

the answer for the perimeter is somehow 14x + 4

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i dont understand how that is the perimeter

tacit arch
quartz panther
#

huh?

tacit arch
quartz panther
#

i messed up the working before sorry

tacit arch
#

or are you calculating something else

quartz panther
#

the red line is 4x

tacit arch
#

then where's your missing side/

quartz panther
#

sqrt 3x + 4x

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sqrt 3x^2 + 4x^2

tacit arch
quartz panther
#

9x^2 + 16x^2

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sqrt

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is 5x

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cool

#

.close

lone heartBOT
#
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quartz panther
#

.close

lone heartBOT
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peak mist
#

Hello what do I do to complete the ratio test'

peak mist
#

.flip

lament forge
#

,rotate

ocean sealBOT
peak mist
lament forge
#

well it looks like you should be able to simplify this expression quite a bit

high rapids
#

Radius of convergence is 1/ lim -> infinity |a_n+1/a_n| right?

peak mist
#

does this simplify it completley

peak mist
#

just need to know if the above simplification is correct

high rapids
#

Hmm what happened to the 5^n?

peak mist
#

its clear my simplifying is my weak point

#

would you mind walking me through how you owuld simplify it

high rapids
#

You could write 5^(n+1) as 5^n * 5

peak mist
#

got it

#

thanks

#

.clsoe

#

.close

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thin dagger
#

ok so do you guys know how to solve this?

high rapids
#

!status

lone heartBOT
#
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'm told it's wrong
4. I got an answer and would like my work checked
5. I have a question about someone else's worked solution
6. None of the above
thin dagger
#

1

high rapids
#

So which point is the relative maximum?

thin dagger
#

the top left point is the maximum

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ik that but

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you have to write it a weird way

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and Im very scared of getting it wrong

#

its not interval notation or anything but

#

I think you write an ordered pair then the x

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but idk which

lone heartBOT
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warped topaz
warped topaz
#

I got that b = 4

#

But idk how to get a

spring flower
#

how do i ask for help?

tacit arch
lone heartBOT
warped topaz
#

Btw in this question that 2 means log to the base 2

#

its written weird

serene junco
#

Find a point on the graph whose coordinates are integers

warped topaz
#

(-3,0)

serene junco
#

well yeah, I'm guessing that's how you found b=4, right?

warped topaz
#

Yeye

serene junco
#

See if you can find another one, without any 0 coordinates

warped topaz
#

(-2,6)

serene junco
#

then since you have b already, you should be able to use that to find a

warped topaz
#

Ok 1 moment I think I can get it

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A = 6?

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That's all I had to do?

serene junco
#

yep 👍

warped topaz
#

Oh damn

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Oke thank you!!

#

❤️

serene junco
#

np

warped topaz
#

. close

serene junco
#

❤️

warped topaz
#

.close

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#
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thick depot
#

prove $(a + b)^2 − (a − b)^2 = 4ab$

lone heartBOT
ocean sealBOT
#

Timsaay

calm plank
#

what have you tried so far?

thick depot
calm plank
#

you made a mistake in your algebra

thick depot
#

where?

calm plank
#

when expanding (a-b)^2

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remember that the minus sig applies to the whole expansion of (a-b)^2

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not just the first term

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if you put parenthesis around the expansion it should do the trick

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but you still have to fix a bit

thick depot
#

You mean $-(a-b)^2 = -(a-b)-(a-b)$

ocean sealBOT
#

Timsaay

thick depot
#

?

calm plank
#

not quite

#

so when you expand -(a-b)^2

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it should be $-(a^2-ab-ab+b^2)=-a^2+2ab-b^2$

ocean sealBOT
calm plank
#

get it?

thick depot
#

so the - is actually -1 multiplying it?

calm plank
#

yup that's the same thing

thick depot
#

Okay that makes sense

#

thank you

calm plank
#

no problem

#

now the rest of the proof should be easy

thick depot
#

Does this look better?

#

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ornate ginkgo
lone heartBOT
ornate ginkgo
#

Why the 1/2

worn fox
#

Differentiate tan(x/2) and see

ornate ginkgo
#

If i do that way it makes sense due to chain rule

#

So i just add the coefficient to the denominator whenever i see stuff like this?

worn fox
#

Yeah you want to undo the chain rule so to speak

ornate ginkgo
#

The reverse process is kinda hard to PROCESS.

worn fox
#

(This is just what you do when you u sub in an integral)

ornate ginkgo
#

Thank you tho

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misty sparrow
#

Hello, what is the trick when knowing if 8 is divisible by a large number? (for ex. 460) Because it will consume too much time if I'm going to add 8 manually.

amber obsidian
misty sparrow
#

Okay, got it! Thank you very much! I was thinking the same thing though I just want to make sure. closing this thread.

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alpine sable
#

huh

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alpine sable
lone heartBOT
alpine sable
#

idk where to start

calm plank
#

well start by looking at the graphs

#

so immediately you can see that there are 2 different kinds

#

the ones trending more and more upwards, and the ones becoming more and more flat

alpine sable
#

ok through pattern recognition i'd say

  1. A
  2. y
  3. c
  4. D
calm plank
#

not exactly

#

try plugging in some values

#

so for example in 50

alpine sable
#

ok

calm plank
#

try plugging in 2

alpine sable
#

for x ?

#

where did you get 2

calm plank
#

wait actually plug in 4

#

it doesn't matter what you plug in

#

but choosing something easy to calculate is preferrable

#

so sqrt(4) is much easier than sqrt(6) for example

#

because sqrt(4) is just 2

#

now if only 1 graph has f(4)=2, then that must be sqrt(x)

alpine sable
#

can you show the work

calm plank
#

i haven't really done any work

#

i just concluded that if f(4) is not 2, then the function cannot be sqrt(x)

#

because sqrt(4) is 2

alpine sable
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sinful field
lone heartBOT
sinful field
#

somebody help

wet nest
#

1600 ohm

sinful field
#

how come

wet nest
#

V=IR
12=IR
I=12/R
I_2 = 60/R
Req. = 400R/400+R
V=I_2Req
12= 60/R × 400R/400+R
Solve it to get R

sinful field
#

why not I=12/400

#

and I_2=5I

wet nest
#

Bruh, it is connected in parallel, voltage remains same, current gets divided
I_2=5I is true but I=12/400 is false

#

Req. = R1R2/R1+R2

sinful field
#

ohh right

#

i see

lone heartBOT
sinful field
#

okay thank you

#

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torpid storm
#

Hello guys

lone heartBOT
torpid storm
#

Just a bit confused and need help

#

Doing this exercise on finding the limits of function by their graph

#

Here’s my answers, but apparently I got one wrong.

#

Which one tho? And why?

limpid turret
#

Let's start at the first

#

What is the value of f(-4)?

torpid storm
#

Of wait is it at -5 instead??

limpid turret
#

Something seems off here

limpid turret
torpid storm
#

I didn’t see the graph is wrong?

#

Ooohhh

limpid turret
#

Yeah that's weird

#

you got tricked

torpid storm
#

Man I only have one more attempt for the quiz

#

I thought I did something wrong, I mean I did, but I didn’t expect it like this lol

#

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sinful field
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sinful field
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.close

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unkempt dew
#

find exponentiation

lone heartBOT
#

@unkempt dew Has your question been resolved?

unkempt dew
#

no

lone heartBOT
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@unkempt dew Has your question been resolved?

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unborn stag
lone heartBOT
unborn stag
#

unsure how to convert the theta portion to polar coords

#

cuz i get r = 3

raven rover
#

Try drawing A on the plane

#

That’ll probably help you visualize your bounds

unborn stag
#

i have drawn a circle of radius 3 with a line 3x going through it. they intersect at (3/sqrt(10), 9/sqrt(10))

raven rover
#

Great

#

So how can you get the angle this line makes with the horizontal

unborn stag
#

i was thinking tan(y/x) --> tan(3) but i don't feel very confident about it

hidden heart
#

surely it intersects at negative (x,y) and positive (x,y)

unborn stag
#

i formatted it wrong

raven rover
unborn stag
#

i was only talking abt the positive coord

raven rover
#

Careful with how the problem cuts off the region in a particular area in the plane

raven rover
hidden heart
#

a circle with the lines y=3x and y = 0

raven rover
#

Yes great

#

So it’s a sector, right?

hidden heart
raven rover
#

It’s a slice of a pie

unborn stag
#

yeah

raven rover
#

Great, so using polar cords, you know you have r going from 0 to 3, right?

unborn stag
#

yeah

#

i have that

#

i was stuck on theta

raven rover
#

You want to get every point from those close to the center to those on the edge

#

I see

#

So for θ

#

You want to find the θ which describes the line y = 3x

#

Then you go from where y = 0 (θ = what here?), to this y = 3x line

#

You want to describe both such lines using one value of θ Hera for each, these θ values will be your bounds

#

Think of them like where you make your pie slice

unborn stag
raven rover
#

Try drawing that triangle 🙂

unborn stag
#

alright, will try it now

#

yeah, i mean i keep getting tan(3)

#

which doesn't feel correct

#

im forgetting that its inverse tan right?

#

should be going from 0 to arctan(3)?

hidden heart
raven rover
unborn stag
#

im going to try integrating now

raven rover
#

👍

#

Something like this I think is what you’re looking at

unborn stag
#

yeah, i did that but integrated r first, i got 27.3375 as a final answer which im going to check rn

#

i got it

raven rover
#

Nice

unborn stag
#

thank you so much for the help

raven rover
#

Of course man

unborn stag
#

it was very concise

raven rover
#

👍❤️

unborn stag
#

much appreciated!

raven rover
#

I try my best 🙂

raven rover
unborn stag
#

you too!

raven rover
#

Good luck with multivar

#

👍👍

unborn stag
#

.close

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nimble trail
#

how do heaviside functions with coffiecients work?

nimble trail
#

i.e. H(3x-5)

#

like when do they start and so forth

lone heartBOT
#

@nimble trail Has your question been resolved?

raven rover
#

Well you’ll have to split up this function by case, one for when the input is positive/negative

unkempt dew
#

.reopen

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steady swallow
#

Two angles of a triangle are equal and the third angle is greater than each of those angles by 30 degrees. Determine all the angles of the triangle

steady swallow
#

nope

#

wait

#

imma draw

wraith robin
#

how to find x

hidden heart
lone heartBOT
steady swallow
#

nvm

#

its 3x + 30 = 180

hidden heart
#

yeah

#

always draw diagrams when its a shapes problem

#

it helps a lot

steady swallow
#

ok

#

sure

#

.close

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median oar
lone heartBOT
median oar
#

ok how does this P(X=i) and P(X=x) relate to each other?

#

(1-p)^x is the probability of x fails (x because we have P(X=x))

#

p^k is the probability of k successes

#

what's that binomial at the front?

#

i feel like it has to do with the ordering of each of the k independent geometric distributions

#

but im not sure why it's k+x-1 choose k-1

merry depot
#

the number of ways for the successes to appear in the k+x-1 trials (the last trial is always a success, so it's fixed there)

median oar
#

so like if i had 4 successes, last one is a success, and we want to find the probability we failed 5 times to get the 4th success

#

it'll be like

#

F F F F F S S S S
F F F F S F S S S
F F F S F F S S S
etc

#

but the last S is always a success so it doens't matter

#

so from k-1 successes

#

OH

#

k+x is the number of total trials

#

-1 because that last one is always a success

#

and we choose k-1 success because the last one is always a success

#

aha thank you very much

merry depot
#

np\

median oar
#

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rose raven
#

Is this sufficient

lone heartBOT
tacit arch
#

Yes that looks fine. Limit test is a little faster

lone heartBOT
#

@rose raven Has your question been resolved?

rose raven
#

This is the ambiguous case of the ratio test for this given question

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thorn tapir
#

A continuous injective map f exists such that f : [0,1] -> [0,1]^2.

Prove that f([0,1]) is nowhere dense in [0,1]^2.

thorn tapir
#

What I proved is this map isn't bijective, as no homomorphism can exist between these two spaces.

#

Now, for me to show it is nowhere dense, we have to show for any point in f([0,1]), there exists a epsilon > 0 such that B(epsilon, x) is not contained in f([0,1]).

#

This is because the definition of nowhere densebess says interior of closure is empty

#

f([0,1]) is compact and hence closed

#

So basically none of the points in the image are interior points

#

How do I approach this

lone heartBOT
#

@thorn tapir Has your question been resolved?

thorn tapir
#

<@&286206848099549185>

thorn tapir
#

.close

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#
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raven haven
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bronze bone
#

can someone help me? the answer key is 1999+ 1999/2000

spring plover
#

Can you write the general term of this series?

bronze bone
#

<@&286206848099549185>

flint pecan
#

try writing the general term for sqrt(1+1/1^2+1/2^2), sqrt(1+1/2^2+1/3^2),....

bronze bone
#

can u help ?

wild trail
#

As in what would a general term look like?

#

or say what would the kth term be?

flint pecan
#

or the nth term (whatever you're used to)

bronze bone
#

like this ?

lone heartBOT
#

@bronze bone Has your question been resolved?

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#
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bronze bone
#

.reopen

lone heartBOT
#

bronze bone
#

<@&286206848099549185> pls help me 😭

vital kite
raven dagger
spring plover
# bronze bone like this ?

One small mistake, your upper limit should be 1999.
Also, now we need to get rid of this square root to proceed further. So try and create a perfect square inside the square root.

astral briar
astral briar
lone heartBOT
#

@bronze bone Has your question been resolved?

exotic belfry
#

$\sum_{i=1}^{1999}\sqrt{1+\frac{1}{k^2}+\frac{1}{(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{k^2(k+1)^2+(k+1)^2+k^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k)^2+k^2+2k+1+k^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k)^2+2(k^2+k)+1}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k+1)^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\frac{(k^2+k+1)}{k(k+1)}=\
\sum_{i=1}^{1999}(1+\frac{1}{k(k+1)})=\
1999+\sum_{i=1}^{1999}\frac{1}{k(k+1)}=\
the\ rest\ is\ yours.$

ocean sealBOT
astral briar
#

yes

lone heartBOT
#
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coarse trail
lone heartBOT
coarse trail
#

Idk how part a works

minor needle
#

hint:
300p - 10p(16 - p)

coarse trail
#

Oh bro I'm stupid thanks

#

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visual scaffold
#

I need help to calculate the fourier trigonometrical series

visual scaffold
#

Also the exponential and armonic series but for now the trigonometric series

naive valley
#

how far did you get?

visual scaffold
#

Pretty much at the start, I think it's an even signal so the sine terms are 0

naive valley
#

it can't be even, otherwise the value at say 0.001 would have to be the same as at -0.001

#

but they have opposite signs

visual scaffold
#

Then it's odd?

naive valley
#

(or replace 0.001 with some small number that is less than tau/2)

#

yea, it's odd, you can check

visual scaffold
#

well in that case I need to find the sine terms

#

right?

naive valley
#

yep

#

so start by writing out the integral

visual scaffold
#

2/T integral from 0 to T/2 x(t)sin(kwot) dt

naive valley
#

looks mostly right, isn't it just sin(wt)?

visual scaffold
#

I'm not sure on the interval

naive valley
#

not sure what kwot signifies

#

oh wait we're doing fourier series not transforms

visual scaffold
#

yea

naive valley
#

$2\pi k t / T$ isn't it?

ocean sealBOT
naive valley
#

if i recall correctly

#

maybe your wo means $\omega_0$ and that equals $2\pi / T$?

ocean sealBOT
visual scaffold
#

yes

naive valley
#

cool

#

ok agree then

#

so now consider what the value of x(t) is

#

it's a piecewise function so you probably will break into two integrals

#

one for the part with t < 0 and the other for the part with t >= 0

visual scaffold
#

On the graph, there's also a tau constant

naive valley
#

yea

#

that will give you one of the endpoints for each integral

#

i.e. instead of integrating all the way to T/2, you will only go to tau/2

#

since x(t) is zero beyond that

visual scaffold
#

alright, give me a minute

#

so it's 2/T * [ integral from 0 to tau/2 of x(t)sin(....)dt + integral from tau/2 to T/2 of x(t)...]

#

actually, shouldn't the interval be from -tau/2 to tau/2?

#

in which case I break it into 2 from -tau/2 to 0 and 0 to tau/2

#

@naive valley

lone heartBOT
#

@visual scaffold Has your question been resolved?

visual scaffold
#

There is also a gap before the signal repeats itself, should I include that in the integral?

gusty gorge
#

that's not a gap; that's part of the signal

visual scaffold
#

hm so the integral goes from -T+tau/2 to T-tau/2?

gusty gorge
#

you can pick any integration bounds, as long as they cover one period of the function

visual scaffold
#

i don't really understand

#

could you give me an example of some valid bounds for that signal

lone heartBOT
#

@visual scaffold Has your question been resolved?

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#
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obtuse basin
#

I need help with this question part b)

lone heartBOT
obtuse basin
#

Could anyone help with part b). Im new

lone heartBOT
#

Commands:
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modern sedge
#

Distance is area under graph of velocity

obtuse basin
#

ik but

#

im stuck

heady pollen
#

the shape that we have is a triangle

modern sedge
#

What was your result in part a)?

obtuse basin
#

my answer for part a is 20m/s

gray isle
#

split the shape into two triangles by drawing a vertical line at t=60

obtuse basin
#

k then what next?

gray isle
#

you can determine the area and hence distance value you seek from doing (area) addition/subtraction

modern sedge
obtuse basin
#

Im still confused. I started off by calculating the area of the triangle ( part a) and got 20m/s as V when t = 90s so i used the same formula and tried t = 60s and my answer was 600m but the textbook says the answer is 750m i dont know how to arrive at that answer

modern sedge
#

You know that the whole area is 900 units, so if you subtract the area of violet triangle you should get the area between t=0 and t=60

modern sedge
gray isle
#

using t=60 gives you the area of at triangle with base 60s,
which the shape you want is not

obtuse basin
#

i used vt/2 (1/2 x b x h)

gray isle
#

the figure with the red border is not a triangle

obtuse basin
#

ohhhhhh

#

my bad

modern sedge
gray isle
#

you should at some stage determine the v at that blue point

lone heartBOT
#

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cloud scroll
#

So I'm trying to work with a measure theory claim that if a function $f: \mathbb{R} \to \mathbb{R}$ such that the set $f^{-1}(\lambda) = {x \in \mathbb{R}: f(x) = \lambda}$ for any $\lambda \in \mathbb{R}$ is measurable, then $f$ is measurable.
Right now I think this statement is false because if I want $f$ to be measurable, then I need to show that the set $f^{-1}([-\infty, a))$ is measurable for all $a \in \mathbb{R}$. The interval $[-\infty, a)$ has uncountably many points, so if I want to construct this interval, I need to take an uncountable union that looks like
$$\bigcup_{\lambda \in [-\infty, a)}f^{-1}(\lambda)$$

ocean sealBOT
#

_Cluster

cloud scroll
#

This is an uncountable union

#

so surely it can't be measurable can it?

mossy laurel
#

The problem here is that you cannot prove it general, you need a counterexample

cloud scroll
#

that's right

#

could I please have a hint to point me in the right direction?

mossy laurel
#

It's really hard to build a function or set that is not measurable

#

So you might suppose that the exists a set that is not measurable (which is true)

#

And you might try to build a counterexample using the indicator function of that set

cloud scroll
#

when you mean "there exists a set that is not measurable", are you talking about $f^{-1}([-\infty, a))$?

ocean sealBOT
#

_Cluster

cloud scroll
#

otherwise what set are you referring to?

mossy laurel
#

You do not start with a function f, you build it

#

So first you take a set that is not measurable

#

And you build f from that set

cloud scroll
#

is there an example where I can see this?

mossy laurel
#

Vitali sets for instance

cloud scroll
#

I've never heard of those, so I guess I have to search them up

#

okay, here's my idea. I'm going to define f such that

$$f(x) = \begin{cases}0 & x \notin [0,1]\text{ or } x \notin V\
1 & x \in V\end{cases}$$

where $V$ is the Vitali set over $[0,1]$, referenced in the stack exchange post above.

#

I'm going to be very dumb and guess this first

ocean sealBOT
#

_Cluster

cloud scroll
#

@mossy laurel

#

sorry for the double ping, tex bot doesn't properly render pings

#

I claim that f is not measurable

#

oh, but the set $f^{-1}(1)$ violates the assumption of the claim since $f^{-1}(1) = V$

ocean sealBOT
#

_Cluster

mortal trellis
#

you have to use (un)countability somewhere

#

that if you union uncountably many measurably sets you dont necessarily get a measurable set again

cloud scroll
mortal trellis
#

I am gonna write a trivial union. $X = \bigcup_{x\in X} {x}$

ocean sealBOT
#

Denascite

cloud scroll
#

okay, but how is $X$ not measurable? It could be an interval from the borel set

ocean sealBOT
#

_Cluster

mortal trellis
#

it could be

#

but it could also not be

#

I said nothing about X

cloud scroll
#

you're right

#

how about the rationals then? they are measurable with measure 0, my bad

lone heartBOT
#

@cloud scroll Has your question been resolved?

cloud scroll
# mortal trellis I said nothing about X

Can I please have another hint? I'm having trouble figuring out what you're suggesting with X. Also I'm not sure how to use vitali's set to resolve the $f^{-1}(1)$ issue

ocean sealBOT
#

_Cluster

mortal trellis
#

what if you instead managed to make it so that f^{-1}([0,1]) = V

#

but so that all elements in [0,1] are only hit once

cloud scroll
#

hang on, so are you suggesting that I define $f$ as follows:
$$\begin{cases}
0 & x \notin V\
x & x \in V
\end{cases}$$

ocean sealBOT
#

_Cluster

mortal trellis
#

0 would not be good here cause that is contained in [0,1]

cloud scroll
#

you're right

#

maybe a different output would be better

#

like 2

mortal trellis
#

actually no you still run into some problems with that

cloud scroll
#

yeah, because I think $f^{-1}(2) = \mathbb{R} - V$

ocean sealBOT
#

_Cluster

mortal trellis
#

yes

cloud scroll
#

hmm, what if I did the following instead

#

$$\begin{cases}
2x & x \notin V\
x & x \in V
\end{cases}$$

ocean sealBOT
#

_Cluster

cloud scroll
#

oh, I need to account for the non-representative elements as well

#

$$\begin{cases}
2x & x \notin V \text{ and }x \notin [0,1]\
x & x \in V\
x + 1 & x \in [0,1] - V
\end{cases}$$

ocean sealBOT
#

_Cluster

cloud scroll
#

scuffed but the idea is that

#

$f^{-1}(\lambda)$ for any $\lambda$ results in a singleton set which is measurable and has measure 0

ocean sealBOT
#

_Cluster

cloud scroll
#

and $V \subseteq [0,1]$. So if we do $f^{-1}([0,1])$ we get $V \cup ([1,2] - (V + 1))$ which is clearly not measurable because both sets are disjoint and $V$ is not measurable.

ocean sealBOT
#

_Cluster

cloud scroll
#

@mortal trellis could I please have your opinion on this?

mortal trellis
#

well scuffed is a word

#

give me a min

cloud scroll
#

sure thing mate

mortal trellis
#

ok I think it works

#

not what I had in mind tho

cloud scroll
#

what did you have in mind?

mortal trellis
#

take a bijection V->[0,1] and R\V ->R\[0,1]

cloud scroll
#

you can do that?

mortal trellis
#

why not

#

oh right you can probably run into CH problems

cloud scroll
#

it's harder for me to understand because I think of V as being smaller than [0,1]

mortal trellis
#

didnt actually think about that

cloud scroll
#

yeah, continuum hypothesis

mortal trellis
#

well still uncountable

#

but yes good point

#

ok then mine just doesnt work

cloud scroll
#

that's okay, it was still interesting to think about

#

and thanks for sticking with me

#

hope to talk with you again sometime

#

.close

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fallow rampart
#

can anyone teach me how to solve these kind of stuff

lunar palm
#

squaring both sides is usually a start

#

your aim is to get every x out of a square root

fallow rampart
#

yeah

lunar palm
#

to do that for equations like this, you need to:
-square each current root (to get x-3 out of sqrt(x-3) for example)

#

and
-only be left with square roots involving a quadratic equation at the very least

#

if you have sqrt(x^2 +2x +4) you could say = sqrt((x+2)^2) = x+2, for example
or in the form sqrt(quadratic) = f(x), you could just square both sides for a polynomial with no square roots.

the idea is when squaring you'll instead only have one term of sqrt( ) which is handier for algebraically simplifying

#

squaring both sides will allow you to do this

#

give it a shot

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lilac stratus
#

Could anyone help me with this question? I'm not sure how to proceed

echo socket
#

Is it me or you can simply deduce the general formula a_n = 1/2 + 1/4 + ... + 1/2^n from that?

#

And so the limit is basically an infinite geometric sum

lilac stratus
#

yeah right, as soon as I posted it I tested it and yeah that's it lol, thanks anyway

#

.close

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rotund laurel
#

prove (x+y)(x-y)= (x-y) is x=y

lone heartBOT
rotund laurel
#

i cant under stand this image

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#

@rotund laurel Has your question been resolved?

nimble fern
rotund laurel
#

@nimble fern

nimble fern
#

i see

#

do you know what is factorization?

lone heartBOT
#

@rotund laurel Has your question been resolved?

nimble fern
#

hello there!
where are you stuck?

lone heartBOT
#

@rotund laurel Has your question been resolved?

rotund laurel
#

.close

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nimble fern
#

nice! good

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fading loom
lone heartBOT
fading loom
#

hello

echo socket
#

Let's say the side of the square WXYZ is some number a

#

Then AD = BC = a, right?

fading loom
#

yes

echo socket
#

Also, AB = DC = 13 + 8 - a

#

This information is enough to solve for the perimeter

fading loom
#

hm

echo socket
#

And DC = DZ + ZY + YC = 8 - a + a + 13 - a = 13 + 8 - a

fading loom
#

huh

echo socket
#

Which bit is confusing you?

echo socket
#

We can break the side length DC into three segments

#

DZ, ZY, YC

#

Clearly, DC is the sum of those segments

#

So DC = DZ + ZY + YC

fading loom
#

ohh

echo socket
#

And, like I said, DZ = 8 - a and YC = 13 - a, meaning we can plug those in

#

And get DC = 8 - a + a + 13 - a

#

-a and +a cancel out, leaving us with DC = 8 + 13 - a

fading loom
#

uhuh

echo socket
#

Okay, let's now solve for the perimeter

#

Perimeter is just the sum of the lengths, so, in this case, it's a + a + 21 - a + 21 - a

#

As you can see, all of the a's cancel out

#

So the perimeter is just 42

fading loom
#

OHHH

#

OKAYY THANK U SO MUCH

#

I GET IT NOW

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#

@fading loom Has your question been resolved?

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marsh trout
#

How can I show that there is a C > 0 such that :

marsh trout
#

$\mathbb{E}(X \mathbf{1}_{{X<C}}) > 0$

alpine sable
#

(\mathbf for bold face)

marsh trout
#

thx

ocean sealBOT
mortal trellis
#

what do you know about X?

marsh trout
#

it's a random variable

#

nothing more

mortal trellis
#

then this doesnt seem true

marsh trout
#

why ?

#

btw C is a constant

mortal trellis
#

X=-3

marsh trout
#

oh no

#

sorry

#

I forgot something

#

$E[X] > 0$

ocean sealBOT
marsh trout
#

in fact what bothers me is to calculate the expectation of a random variable multiplied by an indicator

mortal trellis
#

well for an integral you would essentially cut off the part corresponding to above the line y=C here

cunning locust
last ether
#

What the fuck

marsh trout
#

I didn't understand what you two said to me

mortal trellis
#

I would probably just do a proof by contradiction

#

assuming you have something like monotone convergence theorem or something?

marsh trout
#

yes i have

#

but here i didn't have sequence of variables that converges

mortal trellis
#

make one up

#

always good to think about the sequence 1,2,3,4,...

lone heartBOT
#

@marsh trout Has your question been resolved?

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@marsh trout Has your question been resolved?

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lone heartBOT
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@silent sage Has your question been resolved?

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@silent sage Has your question been resolved?

spice eagle
#

a2 + b2 =????????????

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slate monolith
#

1/chance

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cinder spindle
#

question d?

lone heartBOT