#help-10
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do you know the unit for the answer?
Miles
the car travels 220 miles in 5s? O.o
that's better
but your final answer will be in miles, but no where near 220
so are you sure you're looking for miles travelled?
The book says 220 without units.
seems to be 220 feet
We have to convert miles to ft?
miles/hr to ft/s
a(t) = 12t? That doesn't look right to me
rectifying that now
Why cant we do mi/s in 5 seconds?
you can if you'd prefer, just convert to feet eventually
where did the 300 come from?
yup, that'll be acceleration in mi/s^2
So a(t) = 17.6t, where t is in seconds?
acceleration is constant, right?
Oh right so just 17.6?
Alright thanks!
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Hello,
For this problem, the transition matrix that I came up with is
|.65 .35|
|.28 .72|
though I'm not sure where to go from here to get the "distribution of customers" tomorrow, day after tomorrow, or 3 weeks from now
KurtDee
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
KurtDee
KurtDee
what would x0 be? it says 50% of the lunchtime crowd ate at each of the two restaurants today, would it just be <0.5, 0.5>?
how would one know x0=<50,50> from the information given
Oh can we just use it to represent the percentages
Ah ok. Past problems of this type actually gave us the number of people in the crowd
what is T?
does my transition matrix look right?
looks right
I decided that
Me & ollie's is state 1
Green bean is state 2
p_ij = probability of going from state i to state j
awesome
thanks guys @spiral maple @true rain
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comparing to this example
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what was the formulae to find area of paralleogram again?
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A box open at the top has a rectangular base 200mmx300mm and an
altitude of 150mm. If the base and the sides are 10mm thick, find the total
surface area of the box.
It said that the base and the sides are 10 mm thick so am I supposed to add 10mm on the altitude and also add 20mm on both 200 and 300mm?
Yeah sounds good
And it said the top is open so I am going to subtract the area of the rectangle at the top in the total surface area?
Yeah
am i overthinking this, or do you ned to count like the interior of the box area also?
Dont overthink please
This is probably not even highschool or atmost 1st year
I have suffered a lot through overthinking basic questions back in those days
sounds good haha
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the answer for this is 9.28 degrees, but how do you work it out?
can you use trigonometry?
normally, yeah, but multiple triangles makes it kind of confusing for me
see the above angle = 42-x
so appplying law of sines we get
8/sin(42-x) = 11/sin(48)
solve for x
if it makes it easier you can also entirely forget about the smaller triangle for a bit, solve the angle you need in the first triangle then subtract it from 42
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Let $s_n$ be a sequence that converges. Show that if $s_n \ge a$ for all but finitely many $n$, then $\lim{s_n} \ge a$
dulg
I looked over the hint for this question, but I want someone to walk me thru this question
The hint goes like this
It's 8.9)a)
But I do not understand why s < a in the hint?
I understand having a finite set $N_0$ $\in \bN$ which leads to $s_n \ge a$ for $n > N_0$ but I do not get why we assume $s < a$??
dulg
Am I supposed to set up a contradiction? And I don't understand how showing $s_n < a$ is supposed to help answer the question, especially since it seems contradictory
dulg
help would be really appreciated
yes, you are going to set up a contradiciton
contradiction*
assume the limit of the sequence exists and is less than a
since lim s_n = s, we know that for every ε > 0 some tail of our sequence will be entirely contained in (s-ε, s+ε)
take ε = (a-s)/2 and observe that (s-ε, s+ε) lies entirely below a
hence our tail has to consist entirely of points which are less than a
why is this impossible?
ah
man this makes so much sense
because we defined s_n >= a, for finitely many n
no
we are given that s_n ≥ a is true for ALL BUT finitely many n
consider that it is in general not possible to remove a word from a mathematical statement and have it still mean the same thing
i think i have a very vague notion that limits are concerned with infinite amount of "n", and so s_n >= a is satisfied
you're overthinking it.
hence our tail has to consist entirely of points which are less than a
why is this impossible?
the correct answer to this is ||because this would imply there are infinitely many such points, which is known not to be the case||
why would it imply infinitely many points?
you know what a tail of a sequence is, right
then why the fuck did you not say it the first time i mentioned the word
chill
a tail is what you get when you start the sequence at some term other than the 1st
i.e. it is a sequence in its own right
a sequence like $(s_k, s_{k+1}, s_{k+2}, \dots)$
Ann
other than the 1st term?
do you object to me saying "at some term other than the 1st" as opposed to "at some term other than the 1st term"?
no i am just asking for a clarification
i mean
what else could "1st" possibly refer to if not "1st term"
i'm confused at where you could possibly be confused with my wording
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can anyone help?
What does the expression approach when t gets veey large?
but like idk how that translates to C and k
Ok what does $-ke^{-0.25t}$ approach as t gets large
Calm Mango
Yes
If k find from where ya
The second statement
then
after that?
ohh then done?
Find the time when growth reaches 2m/y
Dude calculate it yourself
42?
Oh you did
yepp
I am eating
AHAHAHAHHAHA
Waut 5 min
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No prob
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Let $a$ and $b$ be real numbers, where $a < b$, and let $A = (a,a^2)$ and $B = (b,b^2)$. The line $\overline{AB}$ (meaning the unique line that contains the point $A$ and the point $B$) has $x$-intercept $(-3/2,0)$ and $y$-intercept $(0,3)$. Find $a$ and $b$. Express your answer as the ordered pair $(a,b)$.
i need help
crabbo
pls
what have you tried
@timid silo have you worked with equations of straight lines before at all
i have
yes
okay
are you able to write down the equation of line AB in terms of a and b?
in any form you like
i usually do slope-point form
ok then point-slope form it is
this may take me some time
ping me when you're done
i just need to know
which point is (x_1, y_1) and which is (y_2, y_2)
i know the order matters
@royal basin
yes
no, it doesn't matter.
if you don't screw anything up you will get the same result either way
crabbo
i chose to use the y-intercept
this can be greatly simplified
(b^2 - a^2)/(b - a) can and should be simplified unless you're willing to down in a sea of algebra
and drown you WILL
is there a way to simplify it?
Ann just said there was..
i dont see it
Look harder then
do you know of any algebraic identities involving two squares being subtracted
H
let me simplify
$y-3=(b+a)(x)$
crabbo
okay good
so you have the equation of your line
y = (a+b)x + 3
you know three things here:
(i) this line passes through (a, a^2)
(ii) this line passes through (b, b^2)
(iii) this line passes through (-3/2, 0)
each can yield an equation in a and b
it also passes through (0,3)
you have already made use of this information
oh right
trying to use it again will just give you 0=0
a.k.a. an equation that is true but useless
i may be mistaken here, but (i) and (ii) should turn out to be equivalent, giving you two equations in two unknowns as opposed to the initial appearance of three
we just need to find a and b
which should i choose to use
all of them
or, if you wish to minimize your workload, pick either (i) and (iii), or (ii) and (iii)
but turning them all into equations will not hurt.
@timid silo Has your question been resolved?
(i) -3=ba
(iii) $a=\frac{-3b+6}{3}$
crabbo
@royal basin
(iii) seems more complicated than it needs to be, but is otherwise correct
let me simplify it
a=-b+2
does a=0, b=2 satisfy ab = -3?
oh no
a+b-ab=-5
oh well
i dont know
😦
have you worked with quadratic equations before
ah yes
+5 not -5
right
but it isnt a quadratic
you can construct a quadratic equation of which a and b will be the roots
you know their sum and product and hence know the coefficients
what do you mean
i'm trying to hint at ||making use of vieta's formulas||
and i don't really see what you're getting at with a^2 + b^2 - ab @subtle quartz
what I mean to say is, that if it was a² - b² - ab we could consider it a quadratic equation
it has a name
this guys theorem
but that vieta's formula thingy seems to involve heavy algebra
yes
and there must be a better way
vietas is simple
I think maybe you could square both sides of a + b = 2
and then add/subtract eqns
and form a quadratic out of that?
oh wow I already kinda got a rough sol in my head
you both are overthinkingit
i would have two squares
y'all please stop
i think i got the sol yeah
you're severely overthinking it
god help us
treat a and b as the roots of a quadratic
i'll use t as the variable of the quadratic so as not to clash with previous notations
(t-a)(t-b) = 0
(x-a)(x-b)
@timid silo we had x in the problem before so i don't want to reuse it
i got sniped
my solution was this
you beat me to it again
and by construction the roots will be a and b
t=-1 nor t=3
flip a coin?
both
you know something about a and b that can and should allow you to disambiguate
go back to the original problem and read it carefully
they are real numbers?
go back to the original problem and read it carefully
"they are real numbers" says precisely nothing
we've been working with nothing but real numbers
let me repost your original problem statement
Let $a$ and $b$ be real numbers, where $a < b$, and let $A = (a,a^2)$ and $B = (b,b^2)$. The line $\overline{AB}$ (meaning the unique line that contains the point $A$ and the point $B$) has $x$-intercept $(-3/2,0)$ and $y$-intercept $(0,3)$. Find $a$ and $b$. Express your answer as the ordered pair $(a,b)$.
Ann
Let a and b be real numbers, where a < b, ...
how can i use that tho
you know one of a and b is -1 and the other is 3
which of -1 and 3 is the lesser of the two?
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lickkle confused about flipping inequality signs
you flip the sign here because.. why?
say you did
$x < \log_{\frac{1}{2}}{4}$
obviously this is incorrect
because i didn't flip the sign
The Torrent
yh so like uhhhhhhhhhhhh why do i flip the sign
1/2^x = 2^-x
its way easier than that smh
yessss it is
but what answers my question anyway
uhh you got it?
i mean
i know that you flip the sign
my question is about the sign
not how to do it
how to know when logging both sides
if your meant to flip the sign or not
i understand you flip the sign if you multiply by a negative
if you are multiplying or dividing -ve, then the sign would flip
but how do you know if logging both sides in base whatever is gonna be multiplying by -1
x < y
log(some base)(x) < log(some base)(y)
wait a moment
for what values of 'some base' is what i just wrote true
no you dont, so you cant do that
why not
you mean log? yes you can as we know that both the x are +ve
but
why cant u here
also
theres only 1 x (in my example)
so like
idk what u mean at all
bruh
bruh
shall i start all over
explaining my question
yeah
x > y
lol
$x > y$
\$log_{z}(x) > log_{z}(y)$ for what values of z
theres my question
The Torrent
z>0
thats not right
becauseee
see here
if you log in base 1/2 both sides
$x < log_{\frac{1}{2}}(4)$ FALSE
The Torrent
but z is greater than 0, as you just said so?????
have you even learnt log? :/
CAREFULLY
yes?
wheres the fault in what i just did?
apply indices here instead of log
but whats wrong with what i just did? i dont understand?
i dont wanna find a different method, i wanna understand flipping the sign with logs
you cant as you dont know the sign of x here!!!!!!!!!
like if i say
you cant use logs
if you dont know the sign of x?
no 🙂
what has mark scheme done then?
x^2 is always positive 🙂
wheres x^2
oh i see they just test value
is there no other way
Is ur question why the sign flipped?
yes but also the conditions for which the sign flips
Log(1/2) is negative
the 2nd method
I presume here that by log they mean log base 10
i maybe? understand this? uhhhhhhhh
but its not like your multiplying both sides by x or anything?
but igg
The 2nd method requires finding which value of x equals 4 and then (since the less the power the greater the product for numbers less than 0) the inequality is true for all values greater than the value you find
The 2nd method is great for questions like these since it’s just two numbers
You can just apply this @timid silo
Also the sign doesn’t flip here so I don’t understand what you find wrong with method 2
Also this is a pretty intuitive method I wouldn’t have thought of

why should we take log if we can solve this more easily :/
Maybe it's in their curriculum but this is some simple playing with indices stuff
also how can i get the helpers role?
how does this testing thing work
i dont understand how they determine which way the sign is in method 2
Just go to a general chat and ask, if it's taking too long @ a random staff
well itts just like mathematical induction, it wont be helping you in complex solving though
but
how determine x bigger
its just like general sense of sensing the range of x
o
i just understood it nevermind
if they tried number smaller than -2
it would be false
yeah
like x-6 should be +ve
so its common sense that x must be greater than 6 to make it positive @timid silo
thanks!! 🙂
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The largest dimension of a rectangle exceeds the triple of the smallest by 3.8 dm. Calculate the area of the rectangle knowing that the half perimeter is 45.4 dm.
Fun question, what do you have so far?
idk 
Ok, no worries. So first let's find the lengths of each side since we know that the sum of all sides is 90.8 (since the problem says 'half perimeter is 45.4')
yes
The small side is unknown, so we will call it "x" and the other side is "triple of the smallest" and "exceeds..by 3.8" so that will be 3x+3.8
okay okayy
So the parameter will be: x + x + 3x+3.8 + 3x+3.8 (add all sides) and half of that is 45.4
(1/2) (x+x+3x+3x+3.8+3.8) = 45.4
{math}
8x+7.6 = 90.8
x = 10.4
So now that you know the smaller side is 10.4, the larger side is 3*(10.4)+3.8
And the area would just be the multiple of the two
yes
Did you get ||364||?
yes
Awesome, that should do it!
you too
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can the radius of a circumscribed circle be equal to one of the side of triangle?
im not sure on this
but visualize a right angled triangle ABC. C is the right angle
AB is the diameter
Visualize moving point C
now surely somewhere along the way AC is equal to the radius
it varies between 0 and 2r
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come in #math-discussion
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83
Bc i accidentally put the wrong screen shot
Exactly number x 100 / percent
Oh ok
😂
i love ur question btw
Oh ok
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can someone help me confirm my answer for this question, and maybe clarify the difference between a unique solution, no solution and infinite solutions?
Are you in linear algebra? Or have access to solving linear systems with matrices?
For infinite solution, equations must be multiplication of each other
Like this
2x+3y=9
4x+6y=18
X and y have infiniy solutiın here
Because they cancel out
And the only equation remains first one
Im in HL math in IB so we havent done matrices(or maybe not yet). I have cancelled out the variables of x from these equations, and eventually y too. I got to the point where 4m(m-1)z= -2m*2 -12m -4
The second one is just two times the first equation, so it doesn't give another info
I don't think I understand
I don't think the second equation is two times the first equation
I gave another example for ininifte many solution
This is something different than your question
ohhh yea I understand what you mean
I understand the basis of the difference between infinite and no solution, but what im having trouble with is the unique solution
like I know (m-2)x=0, if m=2, there is infinite solutions, but if (m-2)x=5(or any other number besides 0), and m=2, there is no solution
Uhmm
Consider unique solution a situation which is not infinite solution or no solution
so in this equation I just wrote, m = anything besides 2?
When you put m=2 what happens?
the lefthand side = 0, which means there will be either infinite or no solutions
<@&286206848099549185>
Man I looked at the question again. The only possibility for the system not to have a solution is when m=1 because if you look at 2nd and 3rd equations, the left side are the same but 2nd one is equal to 2 whereas 3rd equals to -3. This is impossible, so m=1 makes the system no solution. There is also no root for m to make the system infinite solution (you know the conditions.). Summary, any value other than 1 for m makes this system unique solution. Does this make sense?
@smoky wraith
yea I got that if m=1, no unique solution. But I also got that if m=0, no unqiue solution either
<@&286206848099549185>, I got m=1, and m=0 will not give a unique solution. But I also got that if m=(1/2), there will be a unique solution. How do I phrase my answer because I am uncertain when it comes to "parameters"
I was multiplying the 3 equations, and then adding and subtracting them until I got to a point where there was only one variable left which was 4m(m-1)z= something
so if m=0, then the entire left hand side is 0 which does not give a unique solution
Why do you say m=0 and m=1 no unique, how does that help you? M can be any real number
You can’t just check numbers 1 by 1
There are an infinite amount
nah I didn't guess, I was multiplying the equations and then adding them up to get rid of x and eventually y. For examples, I multiplied the second equation by 2, and subtracted the first equation by that.
At that point, I got that (1-2m)y - z=-m-2, so I did not have x anymore
“I got m=1 and m=0 no unique… but m=1/2 there will be”
You are aware there are gonna be an inf amount of m where there will be an unique solution, right?
yea so my final equation was that 4m(m-1)z = -2m^2 - 12m +4
yes I realize that, but in the book it the answer just says m=1, m=0 & m=0.5 so I got very confused by it, and wanted some clarification
like I understand how they got to these values as I do too, but they say m=1 and m=0, but if m=1 or 0, there is no unique solution
Then the answer is wrong
Right so the answer would just be that "m can not = 1 or 0."?
as it is asking the parameters of m so the system has unique solutions
Yes
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|x-2|=2x-1
Solve for x?
modulus yeah
You can sqaure both the sides
To remove modulus
Or take 2 cases (x-2) and (2-x) after removing modulus
Just sqaure both sides
(x-2)^2. =(2x-1)^2
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Hi guys, can you help me out with this limit? Thanks
what have you tried..?
Initially this reminded me of a notable limit (the one elevated to alpha which in this case is 1/2) but I don't have the "+1" and trying to rearrange it seems to mess things even more
have you tried rationalizing?
Yes
And even if the numerator has a better look
The denominator still has that 4*x which gives 0...
$\frac{(x+9)-9}{4x(\sqrt{x+9}+3)}$
Mosh
after rationalizing
Exatcly but won't the denominator still be 0?
what's x+9-9?
x?
and what's x/x?
I'm literally blind for the love of god
20 mins on this stupid exercise...
Thanks a lot man
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suppose there are three number a , b , c
And if they're in AP , than (a+c) must be always even right ??
My Proof
Since ,(a+c)=2*b. Hence, proved ,**(a+c)must be always even**
Actually I'm solving a problem and I've used above assertion so just confirming .
So, please reply even if you think it's too obvious
yes
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any clue?
do you know what f(x) will look like
no?
ok
ok so f(x)
the numbers from -100 to 100
are roots, unless the power is 0
at each root you need to worry about if the function changes sign or not
You know when that happens?
Shuri2060
would you know how to sketch this curve?
parabola at x-1
i mistyped
and cross from 1
it touches the axis at x = 1
and crosses at x = -1
but yes
they want you to consider same idea
The important thing is whether the exponent of the root is odd or even
you only care about the parity, remember
odd or even
yes. you see why from the recursive formula?
yes. so now you have the pattern about how the function switches or not
and then
You have all the info you need?
the function is negative to the left of -100
and then you need to figure out what % of it is positive between x = -100 and x = 100
if the exponent of a root is even
the sign does not change
if it is odd, it changes
If you're stuck, try drawing a picture for the first few roots
from x = 100
so what I need to do is count the positive exponenent?
no
you need to try to find a pattern
the exponent just tells you the function changes sign or not
of f(x) is pos or neg
start from x = 100
try sketch the graph
for the first few roots
x = 99, 98, ...
yes
so from this you should be able to work out pattern
and figure out how much is positive
51?
then double check 🙂
I am still confuse
more reliable than me trying in head
draw a new diagram
so we have odd odd even odd odd even ...
and maybe do a few more than 5 roots so the pattern is obvious
yes
so roughly 2/3 should be positive
your answer should be roughly 2/3, but this is discrete
so you have to carefully check the ends
just double check the pattern isnt cut short
at -100
(im not sure myself)
uhh 100 is 1 mod 3
-100 is 2 mod 3
so i think there will be an extra bit
So i think you can consider -98 to 100
as one section
then consider -98 to -100
or you can do -100 to 98
and do 98 to 100
if you see what i mean
so we have 198 gaps, 2/3 are positive
132
- then an extra one. so the answer should be 129/200 probability.
I might have made mistake
nice
how about this problem
I got the explicitly form of the sequence
but how inductive proof
whats the formula
a_n = 2^n-1
check the base case
you write that 2^1-1 = 1 = a_1
so base case is good
then you assume your formula is true for k
a_k = 2^n -1
You use this to show it is true for a_{k+1}
(use the recursive formula)
have you seen how a proof by induction works?
no
oh ok, you need to know that
it goes like this
You have a statement P(n) you want to prove for all natural n
so P(1), P(2), ...
uhhh thinking of an example
ok
lets say P(n) is '3n + 3 is divisible by 3'
To do a proof by induction, first you prove the base case
that is P(0) or P(1) depending on if you include 0
so 3*1+3 = 6 which is divisible by 3
so P(1) is true
make sense so far?
yes
Next you prove that P(k) implies P(k+1) for all k
If you manage to prove this, it proves the statement for all natural numbers
because P(1) => P(2) => P(3) => ...
if that makes sense?
kind of
so in this example i would do it like this
Assume P(k) is true
So we assume 3k+3 is divisible by 3
now, 3k+3+3 is also divisible by 3
(some number theory property)
oh
therefore 3(k+1) + 3 is divisible by 3
so we have proven P(k) => P(k+1)
that completes the induction step
so we assume a_n-1 is 2^n-1-1
usually the letter you use is k to be clear
because you want to prove P(n) for all natural n
usually you prove
P(1) and
for all k, P(k) => P(k+1)
By induction, since P(1) is true, and P(k) => P(k+1) for all k >= 1,
P(n) is true for all n >= 1
Something like that
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Average rate of change over 0 <= x <= 3 is 1 right
Because from 0 to 2 its 2
From 2 to 3 its -1
Or does that make it 1/2 since (2 + -1)/2 = 1/2?
neither
no
average speed = total distance / total time
even if not a distance time graph, same principle applies
average rate of change = total change in y / total change in x
So 0
O right
not from 0 to 4
👌
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Given a graph of f(x), how do i find the x coordinates of each POI?
I know a POI exists when f''(x) = 0 and has a sign change
its just the opposite
B7rmObB1pPjqAAAAAElFTkSuQmCC.bin
stolen from somewhere
a curve changes between concave and convex at a point of inflection. Can you figure out why?
@timid silo
no
f'' is 0
this means that the gradient f'
reaches a maximum or minimum
say f' is increasing
Oh so it changes
that means the gradient is getting steeper and steeper
f'' changes signs yes
Yes and the slope on f' changes from positive to negative
no
At that point
oh yes
yes
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How do i find area of a trapizoid that has a right angle
Is it still the same for any kind of trapizoid?
a trapezoid with a right angle is still a trapezoid
but there might be a shortcut
do you mean a trapezium?
split it into a rectangle and triangle. that could help speed things up
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how do u solve number 4
u can’t determine the equation just from the graph
it’s a quadratic one
not y=mx+b
i’m pretty sure independent
big hmmmm from me
when the graph doesnt have units on it
are you meant to assume each grid square is 1 by 1
That graph isn't quadratic, just FYI
o
decimal x ???
i mean just looking at the points, x’s are decimal

