#help-10
1 messages · Page 69 of 1
kk
answers 1/2
ya
bro me when i forgor sqrt(b) = b^1/2
It's just power rule
ye!
damn bruh i got 1 more
me when calculator 
@drowsy nest tyvm for the help
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need help with some grade 9 maths
might seem a lil stupid to some of you older ones but
ask away
don't understand fractional indices
what do you not understand about them
ok so 9 to the power of 1/2 is = 2 root to the square of 9 =3
lemme get a photo probably
Here is a photo
...
wrote this down during class
I don't go to the best school teacher doesn't help just makes us go through a powerpoint and sits on her phone or laptop
The second line under fractional indices
9 to the power of 1/2 and so on
@merry peak
ping me if you reply
or whoever replys
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can someone pls help me evaluate sin(75) with a sum identity
notice that $75 = 30 + 45$. So then do $sin(30 + 45) = sin(30)cos(45) + cos(30)sin(45)$
MellowDramaLlama
is it fine if i did sin(45+30) instead
yeah same thing
I think you might've goofed up the angles somewhere
yeah i think i goofed up on a denominator
you should get $\left(\frac{1}{2}\right)\left(\frac{\sqrt{2}}{2}\right) + \left(\frac{\sqrt{3}}{2}\right)\left(\frac{\sqrt{2}}{2}\right)$
no it needs to be simplified
MellowDramaLlama
sqrt 6+ sqrt2 / 4
yep perfect!
wow tysm
you can also write it as $\frac{\sqrt{2}(1 + \sqrt{3})}{4}$ but both are correct
MellowDramaLlama
yep np 🙂
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what am I supposed to do here?
do I just subsititute for 2?
I dont understand how im supposed to use the given formula to solve this
differentiate
what
y = f(x)
slope = gradient = tangent
gradient/slope of y at x=2 = value of dy/dx at x = 2
.
im kinda lost
do u k wat the q is asking u to find
yes the slope
what is slope?
do i estimate it here or find it here
y2-y2/x2-x1
this only works for?
a linear function
yes
is the equaiton in the q a linear function?
but we make space between the points so small its basically a linear function
uh no
or u can do that
im confused
how am i supposed to solve for it without estimating it
hav u learned differentiation?
it seems no is the answer
hence do one thing
let a = 2
let h = a very small value larger than a
and then use the formula ig
kinda ridiculous but ig shd be
larger than a?
shouldnt it be as close to 0 as possible?
we want the gap to be as close as to 0
not the value
shud be close to a
so it would be like a = 2
h = 2.00001
but h is the size of the gap
thats just making the gap bigger
i want to get another say in this
<@&286206848099549185>
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write this in terms of sine and cosine
now what
do you know your double angle formulas?
yes
then join the fractions and use your double angle formulas
what is it
2sin^2x
really?
omg
sorry
that was a dumb question
i got tanx as the solution
pretty sure its right
thx for helping
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Did i do t(x) correctly?
I used the formula
y = f(c) + f’(c)(x-c)
y = f’(c)(x-c) + f(c)
I changed it to this but the equation still marked wrong
<@&286206848099549185>
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Alright
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if x = e^y, let y = t and find what x(t) would be
yeah, but more simply x=e^t
oh doesn't really help with the integral does it
instead let y = ln(t)
so set x = t
yep
okay so how would I find the bounds, im confused about this arc thing
if x = t, you're going from t = 1 to t=e^8
look at the endpoints they gave you for the arc
so i have to use the equation of arc length??
yes
ohh so you can use either bounds of x and y to solve for the bounds of t
yes
sqrt(t^2 + (ln(t)^2) doesnt look fun
that's not the arc length
oh yeah i need teh derivative
\sqrt{1^2+\left(\frac{1}{t}\right)^2}
how doyou show equations..
mathbot
$\sqrt{1+\frac{1}{t^2}}$
maximo
your integral is then $\int_1^{e^8}t^2\sqrt{1+\frac{1}{t^2}},dt$
$\sqrt{1^2+\left(\frac{1}{t}\right)^2}$
okay thanks, that wansn't that bad just need to know how to deal with paramatrics...
that isnt a fun integral to do either
maximo
it's a simple u sub
u = t^2?
u = 1+t^2
you altered the square root?
wdym
how did you end up with that integrand
$t^2\sqrt{1+\frac{1}{t^2}}$?
maximo
wouldn't this require ingration by parts or something
no
cuz subbing 1/t^2 would make 1/t^3
$t^2\sqrt{1+\frac{1}{t^2}}=t\sqrt{t^2+t^2\cdot\frac{1}{t^2}}$
maximo
oh you brought a "t" back inside
well i just symbolabed that intregral and its wrong apparently
what did you write as the answer
$\frac{\left(e^{16}+1\right)^{\frac{3}{2}}-2\sqrt{2}}{3}$
Whunder
okay i noticed that the original equation has a dx, and no DS
its a partial derivative?
which one
so you just integrate x?
no
so the dx makes it much easier but let's finish up with the parametrization
we now have x = t and y = ln(t)
then the integrand becomes te^ln(t) = t^2
and dx/dt = d/dt (t) = 1
so then dx = dt
so we just get the integral from 1 to e^8 of t^2 dt
did you follow that?
so dx goes away and becomes 1
maximo
so your integral becomes $\int_1 ^{e^8}t^2, dt$
maximo
yeah i sort of followed along. basically solves for dt which is equal to dx
yes
and allows you to sub
it just allows us to take the integral wrt to t instead of finding t as a function of x
(which is actually just t = x)
so
if we just went with the x's from the start, we'd get the same thing
notice that x = e^y -> y = ln(x)
so the integrand is truly just x * e^ln(x) = x^2
the whole parametrization spiel was because i though it was ds instead of dx
okay i hope i willl be able to apply these to the rest of the questions tmr, this session was insightful.
didn't need to parameterize but it worked anyways
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bed time haha
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30% of 80% plus 25% of 20%
You can just assume total no. Of PPL in the department is 100
Or ig this
You might get fractional people lol
ok thanks im done with that one
LOL
this one now pls
Set variables and equations
wdym
nah this isnt my homework
this is my elder brothers
i dont understand any of this
im tryna do it for him
@smoky slate
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@kindred swift next time get your brother to post here himself.
hes doing his SHL exam and im tryna help him
Swedish Hockey League
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Hi, does anyone know about saddle points and stable games?
Like here how do I know if this game is stable or not
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hey, i know this channel is supposed to answer math questions but may i post a c++ question
some c++ questions are math but not all
it’s about consecutive numbers
you can't post a non math c++ question
but consecutive numbers counts as math right
so basically i had to write a code that checks if 2 numbers, x and y, are consecutive
my idea was
int x,y;
cin >> x >> y;
if ((x>y && x=y+1))||(y>x && y=x+1)) {
cout << “yes”;
}
else {
cout << “no”;
}
yeah that shuold work, you have to use == for equality
Can't you just do (y == x + 1 || x == y + 1)?
I mean, why are you testing whether x > y or y > x?
numbers can overflow into negative
Oh, true.
the test deals with it
#include<iostream>
using namespace std;
int main()
{
int x,y;
cin >> x >> y;
if ((x>y && x==y+1)||(y>x && y==x+1)) {
cout << "yes";
}
return 0;
}
you were right i got some errors
i needed to use == and delete one bracket from the if
thanks for the help guys
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How do I solve
$\lim{x\to{1}} x^\frac{1}{x-1}$
Without using l'hospital rule?
Nex ex Umbra
$L = \lim_{x\to{1}}x^\frac{1}{x-1} \$
$\ln{L} = \lim_{x\to{1}}\frac{\ln{x}}{x - 1}$
A Lonely Bean
Does the fraction on the right remind of you of anything?
Ah and then factor the x?
Not really
Idk, I just see 0/0 and then I jump to using l'hop 😅
$\frac{\ln{x}}{x - 1} = \frac{\ln{x} - 0}{x - 1} = \frac{\ln{x} - \ln{1}}{x - 1}$
A Lonely Bean
Does it look familiar now?
Not really, sorry Idk what I'm supposed to see
That's the derivative of lnx at 1
There's actually another way of doing this but I can't seem to remember it so what comes to my mind is this lol
Ah sorry, I'm also trying to solve it without derivatives
Ah
Okay one moment let me remember
But you can use the limit definition of e, right?
Let u = x - 1
Then you have (1 + u)^1/u as u approaches 0
By definition this is equal to e
Or you could substitute u = 1/(x - 1) to get (1 + 1/u)^u as u approaches infinity
The same thing
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how do i find the integer values of x in this equation:
6−x<4−2x≤28+2x
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What impact should unit conversion have on the relationship between standard deviation and variance?
For example, when the units are kilograms, the sd is 3.156 kg , and the variance is 9.96 kg which is the sd^2.
However, when we convert this to grams, the sd is 3,156 g (the equivalent of 3.156 kg) but the variance is 9,963,829 g (the equivalent of 9,963.829 kg).
the variance is 9.96 kg^2 actually.
9,963,829 g^2
and there's no contradiction there
1 kg^2 = 1000^2 g^2
though units of squared mass have somewhat dubious physical significance, i admit
so for instance,
if the standard deviation is 2 hour
if u were to convert this to variance in minutes --> would it be 240 minutes or 14400 minutes
ah
the units for variance are the SQUARE of those for the original variable and its mean and sd
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Why is this true?
If G is isomorphic to H, then G is abelian if and only if H is abelian.
Uhh, because G is isomorphic to H, they are practically indistinguishable as groups
Yeah just prove it yourself
Try to show it yourself, it's not hard
damn alr
@supple epoch Has your question been resolved?
i think it uses the fact that the inverse of an isomorphism is an isomorphism
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The Cartesian product F x ... x F m times
An element of it is a tuple (a_1, ..., a_m) with a_i in F for all i
Oh I see thanks
I’m quite confused here
Why are they choosing two linear independent subsets of S denoted as T and T’? Why can’t they just compare S and T’
they are choosing a linearly independent set T such that all other linearly independent sets T' have size less than or equal to that of T
Could T be S here?
no, because S need not be linearly independent
S is just a finite spanning set
they are showing that the linearly independent subset of S that has maximum size is a linearly independent spanning set (hence a basis)
@toxic hollow Has your question been resolved?
So the proposition is claiming there is a maximum L.I subset of S which means that in any finite spanning set there’s a L.I spanning set?
Essentially what I mean is that any spanning set Z must have a maximum finite L.I subset which actually causes the set Z to be spanning?
@toxic hollow Has your question been resolved?
the proposition is claiming that every finite spanning set contains a linearly independent spanning set, and that specific linearly independent spanning set happens to be the linearly independent subset of maximum size
they prove that every finite spanning set contains a linearly independent spanning set by presenting one, namely the linearly independent set with max cardinality
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what can i do next?
u can integrate it nicely without a sub
you're supposed to substitute x = tan(theta), not x = sec(theta)
ah crap
mb
the question asks to use x = tantehta
ah ok
before your last step, use the identity $1 + \tan^2 \theta = \sec^2 \theta$
tushar
follows from the identity for sin and cos
so i get tan^2 / sec^2
never done that before
Differentiating under the integral by introducing a parameter
Alright then
the questions asks anyway to use sub x = tantheta
which is sin^2
or rewrite it in terms of cos(2 theta) if it's easier to integrate
wait so tan^2 / sec ^2 = tan^2cos^2?
yes
yeah the reciprocal of cos is sec
got this so far
but i assume i gotta change the limits right?
to match the sub
i forgot to
so can i just do it now?
before i integrate
yes
this correct?
your first line here is wrong
which first line
the first line in your picture
you have the identity wrong
also you must take the limit after evaluating the integral, not before
is the limits just arctan b and 0?
the bounds, yes
the integrand is wrong though
the identity is: $\cos 2\theta = 1 - 2\sin^2 \theta$
tushar
^^
nice
maths is beautiful
i find integration so cool
especially subsitiution
like u can substitute something in for something else and u get to the same answer
Like bruh why
when i started it i hated out
Actually same
icl its taken me months to get my head round it and get better at it
I was very close to hating calculus in general
But someone showed me the derivative of x^x^x^x^x^x^x... and it really interested me
One video by one YouTuber potentially picked my major in college
dang
BPRP btw
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Help please
We have this equation where a, b, c and x are all positive real numbers. We search for all possible x values that satifies this equations.
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How do i proof this
So basically I should prove it by integral estimation?
How do you mean
we know that $1<=k<=40$
Yes
Mehdi_Moulati
So I should take integral of 1 over sqrt x with the bonds 1 to 40?
so 1 <= sqrt(k)<= sqrt(40)
I haven’t solved this type of problem before so I am basically no clue, but I think I can start by integrating 1/sqrt (k) with the range 1 to 40. Am I thinking right?
isnt k up to 400?
you need to know 1/sqrt(k) between what's
so you should start from k
surely that was a mis ping @tardy epoch srry
so $1<=\sqrt{k}<= \sqrt{40}$
But do u mean 1/sqrt k or just k
Mehdi_Moulati
square root
Yea I agree
then $\frac{1}{\sqrt{40}}<=\frac{1}{\sqrt{k}}<= 1$
.reopen
What do u mean
I can’t see anything
TeXit bot will translate it
Oh okay
but it's to slow
tex bot doesn't like space between 1 and $
thanks
i was never mad at you?
oh ok
So is that the answer
Mehdi_Moulati
from here will do the sum of each of them
sum of 1 from 1 to 40 is 1* 40
Do u mean some integral
$\sum_1^{40} \frac{1}{\sqrt{40}}<=\sum_{k=1}^{40} \frac{1}{\sqrt{k}}<= \sum_1^{40} 1$
Oh okay take the sum of each thing
yeah
right
Thank you so much @spiral knot
Mehdi_Moulati
am i blind or didnt youssef want to bound
$$\sum_{k=1}^{400} \frac{1}{\sqrt{k}}$$
Why did you multiply everything with 40?
nvx
Yea it was too 400
Well it’s
no its 400
up to 40 the sum is 11.something
The range is between 35 and 40
No it’s 400 in sigma notation
This is from the booj
And the question is: (show with estimating integral that)
<= 40 is easy, just calculate the integral from 0 to 400 of 1/sqrt(x)
But I think u thought right
which is always larger than the sum
Wait how do u mean
$\sum_{k=1}^{400} \frac{1}{\sqrt{k}} \leq \int_0^{400} \frac{1}{\sqrt{x}} \dd{x}$
nvx
Oh just like that?
yes
yes
right
yes
Thank u so much @gloomy valve
we want lower & upper bounds only
So we want also 35?
i think you can do better than 35
a lower bound is:
,w integral 0 to 400 1/sqrt(x+1)
similar to your upper bound idea
So I add 1 inside the sqrt
But why did u just add 1 inside the square root why not 2
Is it because k is equal to 1 @elfin burrow ?
the blue boxes are the sum, so it's bounded between the integral of the function in red and the integral of the function in black
Oh okay that’s makes sense
But that x+1 is hard to integrate right?
not at all
you just calculated an identical integral
u = x + 1
yeah
2(sqrt(401) - 1) = 2sqrt(401) - 2 > 2sqrt(400) - 2 = 38 > 35
neat visual argument, not sure how it can be argued formally though
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Guys sorry to interrupt u, but I struggled a lot with this question also, so I thought I would take the integral of 1/sqrt(x)(x+1) with the bonds 0 to infinity. And then change 0 to B where B approchaes 0+?
not sure why taking the integral would help here?
unless you know how to bound the difference between the series and the integral
,w integral from 1 to inf 1/(sqrt(x)(x+1))
oh that's convenient. maybe that is all you have to do then
Why didn’t u take the bonds zero to infinity?
k=1
Hmmm
So wouldn’t that work if we took 1 to 400 in this problem
It would right
Then u just changing 1 to a B where b is approaching 0+
sure? you can redo the proof if you want
I mean if we take 1 to 400 we would get improper integral
So we would have to do the change
And then we would definitely get same answer
Anyway thank you @tardy epoch!
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Closed by @uneven night
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,w integral from 0 to inf 1/(sqrt(x)(x+1))
.reopen
✅
Why u take zero to infinity
oops
Wait what
Hahahaha
No problem
But I have a question
Why did u take integral of 0 to 400
Why don’t u take 1 to 400
because the first blue box extends to 0
so to obtain an overestimate, i integrated the function in black from 0
but you can just use riemann's method here
first term is 1/2
How did u know
all the terms from n = 2 to infinity you can bound above by this integral
so an upper bound is 1/2 + pi/2 = (pi + 1) / 2
just substitute k = 1 into the sum
Oh sry I looked at the wrong problem
Yes so if I plug in 1
I get 1/2
That’s right
I see
finally
tushar
I didn’t understand why u added 1 inside the sqrt @elfin burrow
Can you please explain it to me
to obtain an underestimate for the blue boxes
i shifted the function to the left
so that the area under the curve is always less than the area of the blue boxes
that way the integral will be an underestimate
And because k =1?
the boxes have width = 1 and height = f(x) = 1/sqrt(x) and area = 1/sqrt(x), so they are just the terms of your sum
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Hello, in my lecture of verifying trigonometric identities the professor showed an example of a step that I didn't understand.
cosx-cosx(sin^2x)
cosx(1-sin^2x)
I don't understand how this factoring works...
A-AB = A(1-B)
Any help?
Which part are you confused on?
Does it have a name?
I see the leap now....
If I reverse the identity
A(1-B) = A-AB
I was about to say try expanding it out to see if that helps?
$\text{cos}x - \text{cos}x(\text{sin}^2x)=\text{cos}x\cdot 1 - \text{cos}x \cdot (\text{sin}^2x) = \text{cos}x(1-\text{sin}^2x)$
ta
I see, I don't know why I couldn't immediately grasp it but now it makes sense, thank you
🙂
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What trigonometric identities do I need for trigonometric substitution in integrals and how do I do it?
for trig sub? just sin^2 + cos^2 = 1 and tan^1 + 1 = sec^2
do u have an example question
$\frac{\pi}{\sqrt{8-2x^2}}$
kangaroo rat
ok notice we have a^2 - x^2
Yes
Sin x+cos x=1
yes so rearrange that and we get
1 - cos(theta) = sin(theta)
so lets make x = asin(theta)
Why???
Ye
its gonna be really hard to intergrate that expression because of the square root
Yes
so the idea of trig sub is to use trig identities to remove that square root
lets think more broadly.
so assume we have
$\sqrt{8-2x^2}$
Other slash
ty
Np
wait wrong expression lol
Lol
$\sqrt{a^2 - x^2}$
cantprogram
ok assume we let $x = asin(\theta)$
god damn ur a latex pro
cantprogram
There
ok lemme rewrite everything
K
if we are integrating $\sqrt{a^2 - x^2}$
cantprogram
we need to get rid of the square root so to do this lets assume we let $x = asin(\theta)$
cantprogram
if we plug in $x = asin(\theta)$ we get
cantprogram
$\sqrt{a^2 - (asin(\theta))^2}$
cantprogram
cantprogram
and we can factor out $a^2$
cantprogram
$\sqrt{a^2(1-sin^2(\theta))}$
cantprogram
and notice the trig identity
sooo
we can rewrite this as
$\sqrt{a^2cos^2(\theta)}$
cantprogram
cantprogram
and see we removed the square root
Why $x=asin(\theta)$
kangaroo rat
and made the integration wayyyy easier
Ye
because when we plug in asin(theta) we can factor out the a^2 and be left with a trig identity
But what trig identity did u use
we are manipulating our substitution to remove the squareroot
depends on the intergral
if its a^2 - x^2 well you can use sin^2 + cos^2 = 1
if its x^2 - a^2 we can use tan^2 + 1 = sec^2
etc
actually this should be the absolute value of acos(theta) but we can remove absolute value bec of the domain of cosine
just a note
So how does sin^2+cos^2=1 make u want to make x=asin(theta )
Ohhhhhhhhhh
I’m getting it
yeah its honestly just practice
but fundamentally its a technique typically used to get rid of the square root
Anything else?
if we make x= sin then after the manipulation we will just have cos^2 and not a^2 - cos^2
Yes
you need to replace dx with d theta
no worries
Can I dm you later if I want help with a problem, or ping you in server?
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im looking for help to determine the probability of getting n unique digits after selecting m digits
likle one example would be
probability of getting
8 unique digits
out of 10 total digits selected (0-9)
well getting 8 unique results would just be the combination (10/10 x 9/10 x ... 2/10) wouldn't it? since the first "draw" would restrict the choices of the second number to only have nine possible positive choices out of 10. next number would only have 8 out of 10 and so on
i might be missing something in your question tho.
oh ok maybe digits isnt a good choice
uhh
lets say 5 digits
and 3 unique
wait
for this you are saying we do 10!/2!/10^8 * 8/10 * 8/10?
i understand that part
but
i think that is incorrect
yes? well to be more precise $\frac{10!}{10^8 \cdot 2(!)}$
Winus
no no need that is fulfilled in the fact that we can choose 10 diffrent numbers for the first number than 9 and so on. we basically cheack all the ways we can choose 8 unique numbers out of 10
then we divide it but the total amount of ways to choose 8 numbers out of 10 which is 10^8 cuz we have to choose 8 times where we have 10 choices
yes
ohh wait i get what you are asking now
i thought it was the simpler version where you ask what is the probability that you choose only unique choices not where you allow a certain amount of repetes
mhm im a bit confused i tried
quite alot of things but im doing something wrong and im not sure where
i know the combiniations is
(10!/3! + 10!/2!/2!)
right?
but then i dont know the probability
OH wait
mmm nvm i still dont have it
becuase theres one scenario where your repeated digit is the same
and then another scenario where they are different
^ this is for the 2 repeat scenario
i wish i had the answer ontop of my head but statistics are ridiculous confusing
yaaaaaaaa... i used to know this when i was in my probability class but
now its slipping away
found this, might be something tho they choose from 0 to k rather than only 0 to 9
the formula in there seems pretty promising
yes the formula does seem to work
however i do not understand TT
seems to be inclusion exclusion of some sort
yeah if i understand it correct the sum basically asks what's the probability to get n unique in n choices. then it asks for n unique in n+1 choices. continuing like this until you reach the desired m ways. alternating adding and removing to avoid counting any ways multiple times. but then again half of the statistics field is just pure magic anyways
@modern dragon Has your question been resolved?
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how many relations are reflexive?
not exactly
for reflexive its when the matrix diagonals are all 1s right?
yeah
not the diagonals, just the main one
so how many possibilities for such matrices?
when i = j?
for each non diagonal entry you have two possibilities
n * 2 choose 1
you have n²-n of those entries
so 2 possibilities ffor the first
2 for the second
and so on
n²-n times
i already said too much probably
for each index you have 2 choose 1 possibilities
because the main diagonal ones
are set
we dont count the possibilities
theres only 1
all 1s on the main diagonal
the rest are free to switch about
isn't a matrix only reflexive when the main diagonal is all 1s
of course
why would status of non main diagonals matter
so we're not allowed to touch those, because it will stop working if we do
it doesn't
i thought we were looking ways main diagonal can be 1
think im misunderstanding question
we're not exactly looking for a ratio of two numbers
yes, we're looking for what you said
"a way" is the entire matrix
every one of n×n numbers is known, that's 1 way
consider your whole matrix, we know there are 1s on the diagonal, now you have many choices for all the other coefficients (those not on the main diagonal) we are counting the possibilities for them
n^2 - n * (2 choose 1)
why?
everything besides the diagonal how many ways can they be different
if the diagonal can only be reflexive when they are all 1, then that leaves n^2 - n entries to choose 0 or 1?
if you can go by train or by car to Paris or to Cape Town tomorrow or today
you have 3 choices, 2 choose 1
total is not 6 choices, but 8
2^3?
is it 2^(n^2 - n)
yeah
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why so urgent
Ah okay, if ACB is 90 and DCB is 126, DCA = 126-90 = 36. Since DCE is 90, ACE = 90-36
Did I make a mistake bo
pretty direct lmao
thanks
lmao
Wait what did I do
yeah its correct
i think
how u solve it
90-36?
that's why you don't just give the answer
give them a hint
and then let them come to it
all good
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ecb = dcb - dce and ace = dce - ecb
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I really need help i dont understand how to do this at all
I would say try to understand the definitions of the terms at least. For example, is JM perpendicular to KL? We don't know that because we don't have the lengths of JK and JL, we only know that M evenly divides KL, so JM is (maybe) not a perpendicular bisector of KL...
Here is an explanation for altitude and medians: https://byjus.com/maths/altitude-median-triangle/
i understand the definitions
then you must understand how to match the definitions the the triangle given, for example an altitude is a line that starts from one angle must intersect the opposite length of the triangle at 90 degrees...
I would also say that unless you are explicitly told, don't assume lengths or angles by observation. For example, the 2nd image looks like a right triangle, but it doesn't have the red square as in the 3rd, so I would not make that assumption.
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Lim x -> a x-a /( lnx - lna)
l'Hospital allowed?
yes
the question is l hospital question
but I forgot how to do it on the test
so gonna ask and see if I did it right
but I have a feeling I am wrong because the answer I got was 0
take derivative of both the numerator and the denominator
