#help-0
1 messages · Page 168 of 1
what about the 0 column
yh ive done that
what im saying is
u said
no of columns is 4
but what about the 0 column
shouldnt number of columns be 5
That is not part of the original matrix lmao
No
the number of column is basically of the original matrix B
ok
but when u do RREF
do u consider
the inhomeginity
as well
ie the added column
You don't have to always add the 0 column to do RREF, it can be done on any matrix anywhere
ie the RHS of the augmented matrix
When you augment the b vector and then do RREF, then you're doing something called Gaussian Elimination of System of Linear Equations
You're removing variables by making their coefficients 0
okok
When you do row operations it's technically adding equations to each other
ok
Essentially the elimination method of solving equations
ight kl
i think we r come
chartbit has also given me their agreement as well
thanks mate
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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?
do you know the unit conversions required for this question?
L/kg
more specifically you'll need the conversion formulas from
pound --> kilogram
&
cup --> litre
do you know them?
yes yes
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@alpine sable Has your question been resolved?
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Let x1, x2 be solutions to:
(5-x) : (x+1) = (x-1) : (x+a)
Write it as fractions then cross multiply
@chrome depot Has your question been resolved?
I have managed to solve it myself in the mean time
Here is the solution:
Didn't ask
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about this
i find the sin(alpha)
because i do that sin^2(a) = 1/1+ cot^2 (a)
and i find that sin^2(a) = +/- 1/16
and after i do that this was equal at -1/16
and so sin(a)= -1/4
but about cos(a)
what i should do??
<@&286206848099549185>
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2x + 3y = 45
x + 4y = 35
whats the best way of doing this?
Multiply the second equation by 2
And subtranct
2x+3y=45
2x+8y=70
Solve from here
okay that actually was really easy
is there other methods to do when you cant multiply?
or divide
Draw lines and take the intersection
Don't worry there won't be much cases without the elimination mehod
how would i draw lines and take intersection?
Graphing calculato
ah right
You enter both equations
Idk any other methods sorry
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
or the substitution
Oh yeah I substitution
You have to convert x in terms of y and substitute or vice versa
x+4y=35
x=35-4y
2x+3y=45
2(35-4y)+3y=45 and solve for y
Yep
not really understanding any of this 😅
Try my method
i was able to do your first method easily
but i want to learn at least 2 methods on paper in case of a test
The first method always works for the equations in form of ax+by=c
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
yeah this was easy to understand
this is what i didnt understand
Try this method instead
It's substitution method
the one I posted earlier is a bit worse
It's very hard to teach in chat .. maybe contact your teacher or smtg
cant understand this either
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
MY English sucks already and I'm in phone so that's the maximum i can do
Which line dont you understand?
after the second equation
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
equal means same
If a=b and b=c, then a=c
how do i find the value of x and y from this??
2(35-4y)+3y=45
this has just one variable so it can be solved trivially
once you solve it you can plug it's value e.g. to x+4y=35 and get x
We are converting x in terms of y
After conversion we get
x=35-4y
We take this value of x and substitute in one of the equations
That's it
2x + 3y = 45
x + 4y = 35
Okay so
Acknowledge me with every step ok,
Let me take the second equation
x+4y=35
Now let me take the 4y to the other side
So
X=35-4y
yes
Understand?
yup
Now we have a value for y
x*
Sorry for x
yeah i understood this far
yeah
first equation is 2x+3y= 45
yeah sp 2(35-4y) +3y = 45
Yes exactly
yes so after this i need assistanse
what do you mean?
70-8y+3y=45?
Yes sry
its fine
So 70-5y=45
so 70-5y=45
yup
For your understanding let me put it this way
You multiply by(-1) on both the sidds
Sidds
Sides
Got it?
yes
Yea that's it
but does thst happen automatically when its negative on both sides of equal?
or do you actually have to do (-1)
Yes it does
ohh
You don't have to
ohh thank you learnt something new
You can just straight away cancel two negative signs in equality considering there is no addition or subtraction
for example -ax=-c
Also means that
ax=c
You can substitute any values for a x and c to check this yourself
Just cancel 2 negatives that's it
yeah thanks
wanted to learn 2 methods of doing it so i can double check my answers on my tests
Yes
For double checking
You will get x and y nah
Just substitute those values in all the equations and make sure all of them end up true
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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…
Wrong server/ channel.
This is about studying though
Bro what
Not maths
Does not belong here.
Take it to other channels on this server meant for discussion that isn't math help.
But close this question first tho
.close
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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
(and then obviously do the triangle proof and stuff saying that the triangles are congruent)
what is your question exactly?
is this the proper way to prove congruent triangles using HL
i thought there was some special angle stuff you need to do or something but im not sure
can you state the HL theorem?
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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
@lofty flame Has your question been resolved?
<@&286206848099549185>
Tips on how to actually become good at math😭😭
You can verify it with calculators
I want to verify the whole summation I need to redact the solution
First example the first summation is verified this way:
,calc sum(map(range(1,5), f(x) = 7*x-3))
Result:
90
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,rccw
how do i find the missing side?
pythagoras
but first you need to find this length
so look for something symmetries so you can find it
show your full work
yeah ive done something wrong i think
so c
- sqrt of a^2 plus b^2
and the missing side is 6x
i think
coz $2+5x-(2+x) = 4x$
MathematicsPractice
the answer for the perimeter is somehow 14x + 4
i dont understand how that is the perimeter
where are you plugging in 4x here?
huh?
this is the red line
i messed up the working before sorry
or are you calculating something else
the red line is 4x
then where's your missing side/
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Hello what do I do to complete the ratio test'
,rotate
well it looks like you should be able to simplify this expression quite a bit
Radius of convergence is 1/ lim -> infinity |a_n+1/a_n| right?
yes that is correct i did that
just need to know if the above simplification is correct
Hmm what happened to the 5^n?
its clear my simplifying is my weak point
would you mind walking me through how you owuld simplify it
You could write 5^(n+1) as 5^n * 5
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!status
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
1
So which point is the relative maximum?
the top left point is the maximum
ik that but
you have to write it a weird way
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
but idk which
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how do i ask for help?
!help
Please read #❓how-to-get-help
Find a point on the graph whose coordinates are integers
(-3,0)
well yeah, I'm guessing that's how you found b=4, right?
Yeye
See if you can find another one, without any 0 coordinates
(-2,6)
then since you have b already, you should be able to use that to find a
yep 👍
np
. close
❤️
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prove $(a + b)^2 − (a − b)^2 = 4ab$
Timsaay
what have you tried so far?
you made a mistake in your algebra
where?
when expanding (a-b)^2
remember that the minus sig applies to the whole expansion of (a-b)^2
not just the first term
if you put parenthesis around the expansion it should do the trick
but you still have to fix a bit
You mean $-(a-b)^2 = -(a-b)-(a-b)$
Timsaay
?
Browi
get it?
so the - is actually -1 multiplying it?
yup that's the same thing
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Why the 1/2
Differentiate tan(x/2) and see
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?
Yeah you want to undo the chain rule so to speak
The reverse process is kinda hard to PROCESS.
(This is just what you do when you u sub in an integral)
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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.
Divide the large number by 8. If there is NO remainder, then the larger number is divisible by 8.
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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huh
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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
ok
try plugging in 2
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)
?
can you show the work
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
ok
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somebody help
1600 ohm
how come
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
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
As a helper, please do not give out answers that could be copied as a homework solution. Have the student work through the problem themselves and guide them along the way.
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Hello guys
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?
Sorry late reply but my answer for that is 5
Of wait is it at -5 instead??
Something seems off here
yes
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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find exponentiation
no
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i have drawn a circle of radius 3 with a line 3x going through it. they intersect at (3/sqrt(10), 9/sqrt(10))
i was thinking tan(y/x) --> tan(3) but i don't feel very confident about it
how does it intersect at 2 positive points
surely it intersects at negative (x,y) and positive (x,y)
i formatted it wrong
True, but what exactly is A as drawn in the plane?
i was only talking abt the positive coord
Careful with how the problem cuts off the region in a particular area in the plane
Yup
a circle with the lines y=3x and y = 0
my b i read it as the x coordinates are lmao
It’s a slice of a pie
yeah
Great, so using polar cords, you know you have r going from 0 to 3, right?
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
at y = 0 theta would be 0, but how would i describe y = 3x with theta, would i use trig?
Yup!
Try drawing that triangle 🙂
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)?
i believe so since tan(theta) = 3 so theta = atan(3)
I think so 👍
im going to try integrating now
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
Nice
thank you so much for the help
Of course man
it was very concise
👍❤️
much appreciated!
I try my best 🙂
Take care my friend
you too!
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how do heaviside functions with coffiecients work?
@nimble trail Has your question been resolved?
Well you’ll have to split up this function by case, one for when the input is positive/negative
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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
have you drawn a diagram
how to find x
open ur own channel
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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
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)
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
np\
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Is this sufficient
Yes that looks fine. Limit test is a little faster
@rose raven Has your question been resolved?
Cheers. I also have a limit test proof, but lecture content only covered ratio test and partial sums
This is the ambiguous case of the ratio test for this given question
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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.
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
@thorn tapir Has your question been resolved?
<@&286206848099549185>
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can someone help me? the answer key is 1999+ 1999/2000
Can you write the general term of this series?
what series do you mean?
<@&286206848099549185>
try writing the general term for sqrt(1+1/1^2+1/2^2), sqrt(1+1/2^2+1/3^2),....
how ? i don't know what the general term of it
can u help ?
or the nth term (whatever you're used to)
like this ?
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✅
<@&286206848099549185> pls help me 😭
what's the matter?
K doesn't go to 2000
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.
hmmm
expand the inside
@bronze bone Has your question been resolved?
$\sum_{i=1}^{1999}\sqrt{1+\frac{1}{k^2}+\frac{1}{(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{k^2(k+1)^2+(k+1)^2+k^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k)^2+k^2+2k+1+k^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k)^2+2(k^2+k)+1}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\sqrt{\frac{(k^2+k+1)^2}{k^2(k+1)^2}}=\
\sum_{i=1}^{1999}\frac{(k^2+k+1)}{k(k+1)}=\
\sum_{i=1}^{1999}(1+\frac{1}{k(k+1)})=\
1999+\sum_{i=1}^{1999}\frac{1}{k(k+1)}=\
the\ rest\ is\ yours.$
ThM
yes
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Idk how part a works
hint:
300p - 10p(16 - p)
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I need help to calculate the fourier trigonometrical series
Also the exponential and armonic series but for now the trigonometric series
how far did you get?
Pretty much at the start, I think it's an even signal so the sine terms are 0
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
Then it's odd?
(or replace 0.001 with some small number that is less than tau/2)
yea, it's odd, you can check
2/T integral from 0 to T/2 x(t)sin(kwot) dt
looks mostly right, isn't it just sin(wt)?
I'm not sure on the interval
yea
$2\pi k t / T$ isn't it?
Bungo
Bungo
yes
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
On the graph, there's also a tau constant
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
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
@visual scaffold Has your question been resolved?
There is also a gap before the signal repeats itself, should I include that in the integral?
that's not a gap; that's part of the signal
hm so the integral goes from -T+tau/2 to T-tau/2?
you can pick any integration bounds, as long as they cover one period of the function
i don't really understand
could you give me an example of some valid bounds for that signal
thanks a lot
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I need help with this question part b)
Could anyone help with part b). Im new
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Distance is area under graph of velocity
the shape that we have is a triangle
What was your result in part a)?
my answer for part a is 20m/s
split the shape into two triangles by drawing a vertical line at t=60
k then what next?
you can determine the area and hence distance value you seek from doing (area) addition/subtraction
Will it be just 2 triangles?
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
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
Show your work, idk what formula did you use so I cant tell why your answer is incorrect
using t=60 gives you the area of at triangle with base 60s,
which the shape you want is not
i used vt/2 (1/2 x b x h)
the figure with the red border is not a triangle
Try this trick it seems easiest to me
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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
$$\bigcup_{\lambda \in [-\infty, a)}f^{-1}(\lambda)$$
_Cluster
The problem here is that you cannot prove it general, you need a counterexample
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
when you mean "there exists a set that is not measurable", are you talking about $f^{-1}([-\infty, a))$?
_Cluster
otherwise what set are you referring to?
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
is there an example where I can see this?
Vitali sets for instance
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
_Cluster
@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 $f^{-1}(1) = V$
_Cluster
you have to use (un)countability somewhere
that if you union uncountably many measurably sets you dont necessarily get a measurable set again
you're right, but I am still a noob at measure theory so do you have any examples of this?
I am gonna write a trivial union. $X = \bigcup_{x\in X} {x}$
Denascite
okay, but how is $X$ not measurable? It could be an interval from the borel set
_Cluster
you're right
how about the rationals then? they are measurable with measure 0, my bad
@cloud scroll Has your question been resolved?
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
_Cluster
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
hang on, so are you suggesting that I define $f$ as follows:
$$\begin{cases}
0 & x \notin V\
x & x \in V
\end{cases}$$
_Cluster
0 would not be good here cause that is contained in [0,1]
actually no you still run into some problems with that
yeah, because I think $f^{-1}(2) = \mathbb{R} - V$
_Cluster
yes
hmm, what if I did the following instead
$$\begin{cases}
2x & x \notin V\
x & x \in V
\end{cases}$$
_Cluster
oh, I need to account for the non-representative elements as well
$$\begin{cases}
2x & x \notin V \text{ and }x \notin [0,1]\
x & x \in V\
x + 1 & x \in [0,1] - V
\end{cases}$$
_Cluster
scuffed but the idea is that
$f^{-1}(\lambda)$ for any $\lambda$ results in a singleton set which is measurable and has measure 0
_Cluster
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.
_Cluster
@mortal trellis could I please have your opinion on this?
sure thing mate
what did you have in mind?
take a bijection V->[0,1] and R\V ->R\[0,1]
you can do that?
it's harder for me to understand because I think of V as being smaller than [0,1]
didnt actually think about that
yeah, continuum hypothesis
that's okay, it was still interesting to think about
and thanks for sticking with me
hope to talk with you again sometime
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can anyone teach me how to solve these kind of stuff
squaring both sides is usually a start
your aim is to get every x out of a square root
yeah
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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Could anyone help me with this question? I'm not sure how to proceed
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
yeah right, as soon as I posted it I tested it and yeah that's it lol, thanks anyway
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prove (x+y)(x-y)= (x-y) is x=y
@rotund laurel Has your question been resolved?
which part of the image?
@rotund laurel Has your question been resolved?
hello there!
where are you stuck?
@rotund laurel Has your question been resolved?
hey i figured it out
ever seen a reply this fast ?
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nice! good
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hello
yes
hm
This is true because DZ is simply 8 - a and YC is 13 - a
And DC = DZ + ZY + YC = 8 - a + a + 13 - a = 13 + 8 - a
huh
Which bit is confusing you?
this
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
ohh
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
uhuh
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
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How can I show that there is a C > 0 such that :
$\mathbb{E}(X \mathbf{1}_{{X<C}}) > 0$
(\mathbf for bold face)
thx
Hmz
what do you know about X?
then this doesnt seem true
X=-3
Hmz
in fact what bothers me is to calculate the expectation of a random variable multiplied by an indicator
well for an integral you would essentially cut off the part corresponding to above the line y=C here
e * x = unresolved daddy issues and prob std's. you dodged a bullet there
What the fuck
I didn't understand what you two said to me
and how am i doing here ?
I would probably just do a proof by contradiction
assuming you have something like monotone convergence theorem or something?
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@silent sage Has your question been resolved?
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a2 + b2 =????????????
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1/chance
@dense flare Has your question been resolved?
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question d?



