#help-0
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the number of terms isn't n-1
oh i see then
just like how the number of integers from
1 to 100 (inclusive) isn't 100-1 = 99
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How do I find qtp
what have you tried?
Pythagoras. If I couldn’t find qt or pt
I also tried looking for equilateral triangle
Or like any dif side length
apply TQS is a sector of a circle with centre T
R*theta?
QT is 15
yes
@fossil mason Has your question been resolved?
What do i do now?
determine your angle
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How are they rewriting this
doesnt 4/100 = .04 and 25/100 = .25, where are they getting the 5 and 2 squared for a and b
ohhhh
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$-4\sqrt{2}=81-b^2$
bababeeboo
subtracting 81 from both sides gets me -86.66, and then dividing both sides by -1 gets me 86.66, and then sqrting both sides gets me b = 9.31
im finding b to be able to get the co-vertex for this question
but the covertices (9.31), (-9.31) obv arent right since a has to be > b
so im not sure what im doing wrong
@gilded kiln Has your question been resolved?
<@&286206848099549185>
a calculator said the co-vertices are (7, 0) and (-7, 0) but I have no clue how they got that
<@&286206848099549185> ?
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A bit of an abstract question, but does anyone have any idea how I could normalise these results?
For example, I would be able to say that if x_0 - x_c < 0 , the equilibrium is "skewed" toward the left, if it's > 0 towards the right and if it's = 0 then it's perfectly balanced
but how could I quantify how much the skew really amounts to?
Say, on a scale from 0 to 1 ?
because x_0 - x_c is unbounded on both sides
does x_0 - x_c / max(x_0, x_c) seem reasonable ?
I'm unsure
yea I think it does
@alpine sable Has your question been resolved?
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what does the c underbar math symbol means
this
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Can someone elucidate me on what I've done wrong here?
Retraced my steps but can't figure out how I'm screwing up at the signs.
i'm not sure why you made the 14 negative when you had it positive on your last step
also how'd you get 7 for your denominator
I didn't make it negative, I'm pointing out that that's the answer given as the solution in the end of the book.
Multiplied the complex rational expression by the reciprocal of the denominator.
are you sure the answer doesn't say -(x-14)
oh wait that entire thing is over 7/(x^2-4)
which shouldn't change the sign of the 14 but makes sense how you get 7 in the denominator lol
I'm gonna sue this publisher for not using parentheses, it's messing me up
You're absolutely right
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t=3.4
is there a question somewhere?
.26
the refrence number
thank you for that information
9 (2/2 Points) DETAILS PREVIOUS ANSWERS
very bad, possibly
why it’s hw?

💀💀
we don't know
i can show
extraordinary
i would definitely subtract pi in that case
the pi is a lie
why
I dunno
no one can answer the question if there is no question
Yeah for real
t=3.4
.26
🧠
Amazing solution
❌
?
extraordinary
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<@&286206848099549185>
@reef trout Has your question been resolved?
@reef trout Has your question been resolved?
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The integral is the area under the curve, does that help?
I'm aware
but i don't know how to get that from a quarter circle
wait
so that area is 9pi/4, the quarter circle
so... maybe subtract 9 (3*3) from that..? but thats a negative number
ah
9 - that number
kek
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@bright hedge its because they lie on the unit circle
@rich basin close your session lol
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Why is dividing an amount by 0.5 = same as multiplying by 2 and vice versa (multiplying an amount by 0.5 the same as dividing by 2)?
Yeah, good question
So
When you divide by half, you're asking the question "how many halves fit into this?"
For example, when we do 1/0.5, how many halves go into 1?
@viscid dew
Four.
6 halfs.
Ye
So you'll notice that
When we divide by 0.5, it results in doubling the dividend
This is also explained by the fraction rule where:
$\frac{a}{\frac{b}{c}} = \frac{ac}{b}$
Umbraleviathan
"What is half of this?"
Multiplying by 0.5 is "what is half of this?"
Dividing by 0.5 is "how many halves fit into this?"
Well
Better question is
What is 0.5 of this?
I came up with this one: "how much [number] is fit in the sum"?
Because after all, the number could be anything.
Isn't sum (summary) = amount?
I'm partly using a translator because I'm not native English-speaker.
Uh
Sum is like
Well
In a colloquial context, I guess
Although mathematically, not really
Regardless, if you're using "sum" colloquially, then it could work
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Hi, can someone help me with span?
I didn't understand from where did the span {1,1} come from
on the first example
have you tried solving for x1 and x2 normally?
Yes
what did you get
You should try solving it in row echelon form
But that is the result when I solve it with REF
Yes they are identical now
So using gaussian elim. the second row is all zeros
yes
leaving you with just x1-x2=1
x1 =1
x1=1-x2
x2 can be any number
it is not necessarily 0
so x2=k
k is any number
okkk
x1=1-k
x2=k
write it in vector form
(x1, x2)=(1, 0)+k(-1 1)
if k can be any number then the solution includes the span of (1, 1)
aaa Okay I see, what if the solution is not any number
The span would be the vectors
that we found
@ancient fjord Has your question been resolved?
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If I pick seven random digits and arrange them as a number, what's the chance the two last digits are equal? So from 0000000 to 9999999 (which has the last two numbers equal), what's the chance?
I thought we could isolate the first five digits and think of the last two separately. There are 10 possible combinations for equal digits (00, 11, 22, etc), so I thought maybe one in each (10^5)*(10^2), which is one every 10^7, is that right?
I forgot the properties on exponents, so I'm not sure if we add the exponent or multiply them.
But multiplying is in nested exponents, so I thought my best bet would be adding them.
Because for the 00 ending we have 10^5 possible numbers, for the 11 ending it's the same, all the way up to 99. So it's actually 10*(10^5), leaving me with 10^6 since 10=10^1, right?
One in each 10^6 numbers have the last two digits equal.
you are right in your approach by ignoring the first 5 digits and making the last 2 same
however I didnt understand how you arrived at this conclusion?
the total numbers in your sample space is 0 to 9999999 which is 10^8 if I'm not wrong
and the total numbers with last 2 digits same is 10^6 as calculated by yourself
OOH yeah, that's right
My objective is to find the probability that if I pick a random number with 7 digits, the last two are equal, as I've said. So it'd be fair to say that one every 10^6 seven digits numbers would have the last two digits equal, right?
Wait so would 0 be included then?
coz that technically isn't 7 digits but ok
Just fill it till it's 7
yeah got it
12 would be 0000012
yeah but i still don't understand this tho
Your probability would be 10^6/10^8 right?
Meaning $\frac{10^{6}}{10^{8}}=10^{-2}$, right?
3317
3317
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Closed due to the original message being deleted
What's your progress so far?
Yeah that's some weird wording you've got there.
You're looking for the domain in which the values increase.
Ok so looking at a graph how can you determine if it's increasing decreasing?
if it’s going up from to right ?
up to right
Generally just up will do.
okay
with increasing x this is correct
so
You go from left to right in x
yep ok
If the graph goes up its increasing
okay and how do i find the domain doinf that
because the answer doesn’t make sense to me
(0, infinity)
i dont see where the 0 came from
Before zero is the graph increasing or decreasing?
Note that in 0 the function doesn't increase nor decrease.
Just in 0.
on thé x axis??
ohh wait i think i see
so for part ii) is is (0,-infinity)???
because the answer says (-infinity,0)
whys infinity in the x slot
Nah, it's an interval, the greater number should be on the right.
oh so it doesn’t matter about the x and y??
Not sure I get what you're asking.
It does matter.
Question is: To which range of x, y increases if x increases?
yeah no for part ii) i mean sorry
it’s asking about the decreasing
so before x= 0 the graph decreases from forever
y being -infinity
so isn’t it (0,-infinity)
3317
Now it's correct.
yeah i’m confused why that is sorry
why the infinity is at the front
because that’s the y value is it not??
Because it's lesser than 0.
or is infinity the x value when decreasing
Lesser on the left, greater on the right, that's how intervals work.
If you invert the order you just get the null set.
No, y approaches negative infinity as x approaches negative infinity.
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Question regarding coefficient of determination within linear regression, does it simply mean how strong the linear regression in predicting future datapoints?
not future datapoints, no
It's more about proportion of change in 1 that can be predicted by the other varibale
As opposed to extrapolation
As far as I remember
Isn't that the slope?
The slope would surely just be change in y/change in x
This is to do with how much variation in a variable is because of the change in the other
I'm not rlly sure how best to word it sorry
Coefficient means the slope of the mx+c linear regression the m there is the coefficient not the accuary of the model
no it means the R^2 value
and as I said it doesn't mean strength of predicting future datapoints
Did u meant coefficient = r^2 value?
They said coefficient of determination =r^2
So what does it mean?
how much of the variation in respone is explained by the explanatory variables
is one way to view it
R^2 does indicate the performance of the model ig
I asked someone about this chart and they said that the R2 is equivalent to a "magnet" to the datapoints on the chart
R2 = 0.314 (31.4%) means that the "magnet" of the blackline is that powerful, if it had 100% then all the datapoints would be on the black line itself and if it had 0% then it would scatter all over the chart, is that accurate explanation?
R2 is a measure of the goodness of fit of a model. In regression, the R2 coefficient of determination is a statistical measure of how well the regression predictions approximate the real data points. An R2 of 1 indicates that the regression predictions perfectly fit the data.
It's written directly on wiki ig
magnet wtf
yeah its supposedly an analogy to explain it better to me haha
Lol like the line is a magnet attraticing the data points
yeah
so like given that its 0.314, thats considered "weak" relatively
but if it was say 0.7 that would be considered 70% powerful
From what I learned in machine learning
Ya
R2 is indeed the performance of a model
and 100% would mean that all datapoints is right on the line itself
Ig the magnet analogy works
Tho u just need to make it clear in the exam that its to do with variables
As opposed to the line being a magnet lol
Dude can I just ask if I understand the question correctly did u meant if r^2 is the measure of how good the line of best fit is
Or how well it will perform on unseen data
basically I'm trying to understand what R2 means and how we can benefit from it in future data
Can it be used as a predictor for future datapoints?
Or is it completely useless in that?
The model being the line itself, yeah?
And the line itself says "in a perfect case scenario, the datapoint should be on this line"
And that "perfect case scenario" is represented with R2 at 1.0 (or 100%)
yeah
So summing it all up R2 atleast in the field where I worked in is used more of a metric to evaluate the performance of a linear regression model
So I'm asking that because another friend was arguing against the person that explained the analogy... And said that 0.5 R2 means that there is no relation
so I got confused 😂
I'm receiving two opposite explanation and didn't know what to believe
I don't think so
about what @oblique spire said? 🤔
R2 is a measure of the goodness of fit of a model. In regression, the R2 coefficient of determination is a statistical measure of how well the regression predictions approximate the real data points. An R2 of 1 indicates that the regression predictions perfectly fit the data
It's written on wikipedia ig
Unless u meant something called overfitting
Well as I said it's one metric
We still have stuff like RSS
They are different metrics
yeah quality is a bit weak hard to read numbers
Did
so clearly R^2 doesn't say anything about how good your model is in itself
It is saying in one way
U have to generalize
Between other metrics
LIKE rss
Such that it works well on almost all
It's just one of the many metrics
Yeah I mean I assume there are exceptions to R2 right? but would you say it works in 99% of situations?
wdym work?
as in the model is "predicting" the datapoints
Well I have seen machine learning engineers use r2 to evaluate linear regression models
All the time
Maybe it's applications are a bit different in normal stats
You can fit a linear regression with a R^2 very low just fine
as long as assumptions are met
No?
Ah
all this means is your confidence intervals will be bigger
yes you can
the assumption that variance is the same at all points and they are independent
only asusmption needed for linear regression
I think what @noble sinew means is that the data has to be:
1- homoskedastic
2- linear
3- independent
4- normality in observations
is that it?
I mean a good model can have a bad R^2 but a model with good R^2 will generally be a good model
yes
That doesn't make my statement
Wrong
Ig
That high r^2 is good
But low r^2 isn't bad either
you said the higher the better
Oh right mb
step 1 before fitting linear regression is plotting your data (assuming the dimensions actually allow you to look at your data)
but assuming assumptions met then all higher R^2 does is make your length of conf interval shorter
that is all it does
okay one more question, i know that R2 is calculated using different formulas and I've seen many websites calculate R2 by simply multiply correlation by itself...
Was just wondering if R2 can always be calculated by simply multiplying correlation by itself? Because that seems like a very simple formula to calculate something that is supposedly complex with a lot of assumptions in it...
if you mean Pearsons correlation coefficient then yes
Isn't R2 coefficient of determination? 🤔
which is persons correlation coefficient squared?
That is what I'm asking
Can it always be calculated by multiplying correlation by itself?
yes there are many (pearsons is the standard one)
So if I want to calculate R2 I can only use pearson
but if I used another correlation?
It would give a wrong R2 ?
I always thought correlation is -1 to 1 and assumed that it is always the same number
@noble sinew
Because they are defined differently yes ofc you get another number
Thank you for your help everyone @noble sinew @oblique spire @hybrid zenith
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.. don't ping helpers right away
@thick lynx Has your question been resolved?
Depends on the questions. Typically competition math doesn’t have a lot to do with standard syllabus
Depends on the questions you call hard
hard school maths is not really comparable to competition math
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I’ve gotten 48
Wrong question
Closed due to the original message being deleted
Help with c
ive gotten 48
but since 48 is in the group 200<w<400 i dont know how to deal with it
its in between the 3rd and 4th group
im getting confused
how to comment on if hes correct
ping me if anyone comes to help me
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d
randomlyly closed
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The Exercise: ABC a non-isosceles right triangle at A. I is the midpoint of [BC] and [AH] is its height from A. Show that: cos IAH = 2AB*AC/BC²
I didn't understand how to show it , I consider your help thank you
Have you drawn it out?
Cos of I can't read it?
IAH
Ig
Lemme try
@uneven wing Has your question been resolved?
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I just want to check I did it right... in the blue pen
@frigid verge Has your question been resolved?
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Hello , im having trouble understanding shanon entropy , i need to find out for example how the entropy is for a password consisting of 4 numbers ( 0-9 so 10 posibilities)
So i calculated -sum k=1 to 2 ( 1/10)*log2(1/10) but the answer seems wrong
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so this problem is assigned to me by my teacher
and I answered with this, but I'm not confident with my answer, so I would like to ask anyone if this is correct?
I'm asking because I have very little knowledge on limits and continuities and I just watched some videos about it and tried to answer based on my understanding
Okay so you have the right idea, but not quite
When checking for continuity within [-1, 1]
Check to see if the area to the left of -1 would be equal to the area right of -1
Aka, check a = -1
And a = 1
@native kite Has your question been resolved?
<@&286206848099549185>
help
,rotate
so I tried something like this, both a=1 and a=-1 aren't equal
so it's discontinuous?
it's not continuous on the interval [-1,1]
which you have shown
by showing that the function has a jump
from -8 to -3
okay got it
but what about this?
im referring to this
yeah this is the problem
meaning the limits from the left and the right are the same and equal to the value at that point
from the left you used the wrong part
you used the first part of the function but you should've used the second part
because we're looking at x = 1
also 3 isn't correct if i remember correctly
how do I do that?
the reasoning as to why it is discontinuous is incorrect
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How do you approach this
First multiply both sides by x-1
Then discriminat
Done
Assume x ≠ 1
I simplified it
lett me show you
where i got to
x^2-2x(m^1/2)+2(m)^1/2((m)^(1/2) + 1)) -3 = 0
since it has no real roots
but how do i do the discriminant from here onforth
whats the a, b , c
No
wait what
It’s equal to zero
You’ve confused the equation with the discriminant
Just get coefficients of x^2, x, and a constant term
Those are your ‘a’, ‘b’, and ‘c’
No
is it 2sqrtm?
Nope
hmm
ax^2 + bx + c = 0
what
2sqrt(m)(sqrt(m)+1) is a constant
2sqrt(m)(sqrt(m)+1) - 3 ?
Yep
-2sqrt(m)
Yea
oo
(-2sqrt(m)^2-4(1)(2sqrt(m))(sqrt(m)+1)-3))<0
shouldnt m be greater than or equal to 0
im actually lost
@rotund plank sorry for the tag
could you elaborate on how i'd go about solving it now
It’s okay
Yes it should
Just expand it
@slender girder Has your question been resolved?
I did
I got -10m -8sqrtm I think
-10 m - 8 sqrt(m) - 3<0
how ?
<@&286206848099549185>
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I don’t even know where to start with these two questions
dP/dt = Kt?
P=Ce^(kt)
For the first one
Is that correct
apparently, you do
@fossil valley Has your question been resolved?
think about what it means to increase at a constant rate
@fossil valley Has your question been resolved?
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The speed of sound at sea level is 760 mph (mach 1.0) what is the speed in mph of a bullet traveling at mach 0.7?
I subtracted 0.7 from 1.0 and got a 0.3 difference. Do I then divide 760 by 3?
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For b, get the second, fourth, and eighth terms of the arithmetic sequence.
Use those as the second, third and fourth terms of the affine sequence.
Use the formula and fill in values you know.
You should get two equations from that.
And you have two variables to solve for.
@slender girder
I tried
To do that
so u2 =8
u4 = 18
u8 = 38
in the original arithmetic sequece
they're telling us u2= ru_3 + s and u4= ru_2 + s ?
So, in the affine sequence,
u₂ = 8
u₃ = 18
u₄ = 38
u₃ = ru₂ + s
u₄ = ru₃ + s
You got the indexes mixed up.
The larger one is on the left of =.
Yes, and fill in u₂ and u₃ there.
18 = 8r + s
38 = 18r + s
Now it's just simultaneous equations.
Yeah r in terms of s.
r=2
18 = 8r + s
38 = 18r + s
18 = 8(2) + (2)
38 = 18(2) + (2)
If those are truly equal, you got the right answer.
For C, I'd guess you use induction.
On m.
Well, you start with m = 1.
You show that the formula given in part C is equal to the equivalent from just before B.
lemme send you the reworded q
OK.
Show that the mth term of the affine sequence equals the 2^(m-1)th term of the arithmetic sequence.
That's C part ii.
For C part i, induction.
proof by induction ?
Yes.
uₘ₊₁ = ruₘ + s
uₘ₊₁ = rᵐu₁ + s((rᵐ - 1)/(r - 1))
No, you leave r and s as variables.
It's asking you to show it for all r and s.
So, r and s can't take on any particular value when you're proving it, or else you've only proven it for those values.
No, but start with m = 1.
What will be u₁?
u_(m+1)
No, m = 1 means m + 1 = 2.
oh itll be u_2
But we don't exactly need that.
okay so u_2=r*u_2 + s
uₘ₊₁ = ruₘ + s
uₘ₊₁ = rᵐu₁ + s((rᵐ - 1)/(r - 1))
So,
ruₘ + s = rᵐu₁ + s((rᵐ - 1)/(r - 1))
okay sure
So, prove that for m = 1.
They're both u_m+1
Right, so they're both equal to each other.
No, it's not.
The form of the thing on the left and right aren't the same.
you want me to manipulate it?
It's not immediately apparent that they're actually equal.
You need to prove that, unlike with 1 = 1.
Yes.
and show that they're equal?
Right.
I mean
I got to
U_2=r^1 * u_1 + s(r^1-1)/(r-1)
dont they cancel
the r-1/r-1
No, m = 1, not 2.
Yes, (r - 1)/(r - 1) cancels.
No.
They give you two formulas for the sequence.
One is known to be correct.
The one above part B.
It's a recursive formula.
One isn't.
It's a more direct formula.
No, it's the formula above question B.
Oh
The recursive formula.
In C part i, they give you the closed form version.
Where you don't have to go through each and every previous item in the sequence like with the recursive version.
right
The recursive formula is correct, but the closed formula might not be.
So, you set the formulas equal to each other and then you use induction to show that they are indeed equal for any m.
the thing is
if we used 1
in the closed formula
we'd get u_2 = r * u1 + s
after cancelling the r-1's
Well, fill in the ms.
So, the formulas are the same for m = 1.
That's the base case.
Now we do the inductive case.
Let's say it works for a certain m. Does it then definitely work for m + 1?
ruₘ + s = rᵐu₁ + s((rᵐ - 1)/(r - 1))
I suppose so?
We want to prove that.
And the inductive hypothesis is that it worked for the previous m.
ruₘ₋₁ + s = rᵐ⁻¹ u₁ + s((rᵐ⁻¹ - 1)/(r - 1))
The previous m worked, so we know for sure that that equation is correct.
How can we transform that equation into ruₘ + s = rᵐu₁ + s((rᵐ - 1)/(r - 1))?
m-1 ?
Yes, with induction, you have the base case, and we did that with m = 1.
You also have the inductive case, where you assume it worked for the previous number and show it works for this number.
The assumption is called the inductive hypothesis.
Inductive hypothesis:
ruₘ₋₁ + s = rᵐ⁻¹ u₁ + s((rᵐ⁻¹ - 1)/(r - 1))
Oh, an adult, but I don't want to get more specific than that.
No.
The base case has the a particular value for m.
The inductive case doesn't.
Here's how induction works.
You show it works for one number.
You show that if it works for a number, it works for the next number.
So, if it works for m = 1, then it will work for m = 2.
Then, if it works for m = 2, it will work for m = 3.
we want to know if it works when m = 0 now ?
How does it work?
for every natural number
No.
With induction, we prove that it works for one number. It could be 53.
Then, we prove that if it works for one number, it works for the next.
The inductive step in a proof by induction is to show that for any choice of k, if P(k) is true, then P(k+1) is true.
Yes, that's what I said.
So we showed that P(k) is true
No.
bruh
That is definitely not it.
We assume P(k) worked.
We don't prove it.
We assume it without proof.
Let's forget the mathematical notation for a bit.
Could we go onto another question, and get back to this one
in a little while?
a much easier question
I simplified this
as much as I could
Now I'm struggling to find the values of m that satisfy the equation if it has no roots
I knew that the discriminant must be <0
i.e. b^2-4ac <0
Please show your work.
You didn't distribute the 4 to the - 3.
Yes, there are other errors there, too.
Oh really
Right.
8m + 8 ?
.
-8sqrt(m) * sqrt(m) + 1 would be -8m - 8sqrtm
Right.
How did you get -4m?
Ahh, OK.
so 12m?
No, it's 4m for the b²
So, 4m - 8m - 8 sqrt(m) + 12
okay
-4m - 8 sqrt(m) + 12
OK, so:
-4m - 8 sqrt(m) + 12 < 0
m + 2 sqrt(m) - 3 > 0
Now, we can take sqrt(m) as the value we find via quadratic formula.
a = 1, b = 2, c = -3 will give us what sqrt(m) can be at the boundary between where -4m - 8 sqrt(m) + 12 goes from greater than or equal to 0 to being less than 0.
Does that make sense?
yeah
You can also do a = -4, b = -8, c = 12.
Right, and sqrt(m) can't be negative.
Now, since the x² coefficient is positive, we know it points up.
The U of the quadratic does.
So, > 0 is on the outside of the roots.
m ≥ 1 is almost correct.
Right.
so m>1 ?
yeah lets
-4m - 8 sqrt(m) + 12
x^2-1/x-1
-4(1) - 8 sqrt(1) + 12 = -4 - 8 + 12 = 0.
So, that's a good sign.
The discriminant is 0 exactly at m = 1.
Sure, but we have m > 1, which doesn't include m = 1.
However, we want to check m = 1 to make sure it's 0.
Ahh
The discriminant is continuous, so when it goes negative, it was just at 0.
Makes sense
Then we try with m = 2.
-4(2) - 8 sqrt(2) + 12 = 8 - 8 sqrt(2) < 0.
So, that's good.
And that's all we really need to check.
No problem.
You're really well versed in maths
Well, at the calculus and below parts.
No, it's not that I like it, it's just about as far as I remember from school.
Ahh
I remember some linear algebra as well and some abstract algebra.
Do you remember distributions?
Not really.
No, it's been too long.
Ahh I see
Let's go over induction right quick.
You prove it works for a number, like 53.
Then you prove that if it works for one number, it works for the next.
No we didnt
You don't prove that it works for that number.
We assume it does
You assume that it works for that number without proof.
