#help-10
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because you are helpful : )
🫂
Alright thank you !!
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5 cards are dealt from a standard shuffled deck, what is the probability that all are from the same suit
Is my answer correct?
Total ways of choosing 5 cards is 52 choose 5
There’s 4 suits to choose from
After choosing what suit you get, there’s 12 remaining cards in the suit and you would need to choose 4 of them
Just confirming: there are 52 cards on the deck, 4 suits(Spade,Heart etc) I think. You have to pick 5 cards each of the same suit and it is random?
If it is like that then it becomes ```
P(Suit1 and Suit1 and Suit1 and Suit1 and Suit1) or P(suit2 or suit2 or suit2 or suit2 or suit2) ...
It becomes p(13/52 * 12/51 * 11/50 * 10/49 * 9/48) * 4 --> This is due to the suitn being equal in probablility
Hence the solution of chosing from the same suit is p(33/66640) * 4 --> 33/16660. That is the probability of chosing 5 cards from the standard shuffled deck of the same suit
Just following the laws of probability is all
@toxic hollow Has your question been resolved?
I do get your method, and I think I’ve realised where I’ve gone wrong
The numerator should 4 choose 1 multiplied by 13 choose 5
However I still can’t wrap my head fully around why my initial attempt was wrong
I dont even think I understand your method. It seems new but thats how i learnt probability if you think you are in the scenario. It also helps.
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Kind of lost on this
I did the following
so for the angles, i presume just convert everything to polar
but for the radius?
how did you get -19x on the LHS?
i completed the square i guess
13x to 19x?
oh sorry
mistyped it, it is 19x
the question just auto-generates
so the numbers rotated
completing the square gives (x - 6.5)^2 + y^2 = 6.5^2 i believe
okay, so circle with radius 6.5 centered at (6.5, 0)
right
for a given value of theta, you want the intersection of the line y = tan(theta) x and the circle (x - 6.5)^2 + y^2 = 6.5^2
[
\tan(\theta) \cdot x
]?
♡LexQa♡
alright
also does my preamble reset or something? @trail portal 
where is fleqn
nvm im blind lmao
where are you actually struggling? (x-a)^2 + (y-b)^2 = r^2 where r is the radius
actually no i think that's correct
i am trying to find the minimum and maximum values r and theta could take
as my question asks
No
oh ok i see
the circle is like this
r goes from 0 to 13/2
r is the length of a chord starting at the origin drawn t some point on the circle
right
they are seeking a parameterization from the origin
i.e. at theta = 0, r must range from 0 to 13
yeah
theta must vary from -pi/2 to pi/2
yes
wait wait, i am very rusty in my polar coordinates
how can you ascertain that?
just check whenever r = 0? i suppose?
pick any point on the circle
and draw a line from the origin to that point
the length of this line is r
and the angle it makes with +ve x direction is theta
write an equation relating theta and r
?
and also state the range of values theta and r are alloewd to vary through

that's just 0 to the boundary everywhere
as u vary this red point, that blue angle varies thru -pi/2 and pi/2 right
how did we figure that out btw?
what i said?
I assume you were explaining the process of how to find r above, and before that you said it must vary from -pi/2 to pi/2
I didn't quite get that i guess, sorry if i missed something in what you said
yeah this seems correct
well i guess u do understand frm the picture that the angle must vary through -pi/2 and pi/2
yes for some given theta
which is what they want, right?
yeah ig
are u allowed to type theta in those boxes
i did it by substituting y = tan(theta)x
i did it like that
prettier
r = 2 * 13/2 * costheta
imagine a ray from the origin making an angle theta with respect to the positive x-axis
for an arbitrary ray, the question asks you to provide a lower bound and upper bound for the length along that ray that you should travel so that you will trace out the given region as you vary over all rays
only rays in the first and fourth quadrants should be considered, as only those intersect the required region
hence you want to restrict theta from -pi/2 to pi/2
0 thru \pi also works. I usually think about these manually. Not quite sure if there is an analytic way people do these
i recommend finding r using silver's method
you can trivially shift to any interval [a,b] everything once you obtain one parameterization
(cos is periodic afterall, shifting around doesn’t matter indeed)
connect the red dot to the point (13,0)
then the angle at the red dot must be 90 (because of circle theorems)
so you can easily see that r = 13cos(theta)
that's probably the cleanest way to solve this problem
@timid silo see this
yep that
yes nicer
i wish Mac had a MS paint equivalent
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Hey guys could anyone help with this ? I have to prove whether or not this integral converges
I most certainly need to use the absolute value
And i managed to prove that the integral converges from 0 to 1/2
Now i’m stuck from 1/2 to 1
is it not symmetric around 1/2
and its all positive so you dont need any absolute values
The other question asked the same question but with bounds from 0 to 1/2
And i proved that it converges so that’s done
But i have a problem in 1 now
And can’t use taylor’s "expansion" i think it’s called in english ?
No i don’t think it is
Ln(1-x) with x between 1/2 and 1 is a negative number
Because value is <1
You said it isn’t though ?
I see
i think it should be symmetric around 1/2
How though ?
show that f(1/2-x) = f(1/2+x) for 0 <= x < 1/2
Damn never used this kind of reasoning i love it ! I’ll try
Ans yeah if i prove it’s symmetrical i can just conclude it converges right ?
exactly
Yep
no it shouldnt be symmetric
since the powers are different
if it were both 1.5 it would be symmetric
Yeah
$\int_0^1 \frac{\ln (x) \ln (1-x)}{x^{1.8}(1-x)^{1.5}} \dd x$
Gijs
this is the problem right
and youve proven its convergent for 0 to 1/2 right
Result:
0.28717458874926
No i mean when x —> 1
But as you pointes out i don’t need to take the absolute value
I know that the integral converges everywhere for 0 <= x < 1
So we just need to study the problem when x approches 1
But that doesn’t help us much
yeah okay fair
i guess try bound it by something
I’m open to suggestions 😂
how did you manage from 0 to 1/2?
I’ll send it to you
I managed using taylor expansion
But now that x —> 1 i can’t use it
I tried considering u = ln(x) so that when x —> 1, u —> 0 but i don’t think that works
@next wagon Has your question been resolved?
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I forgot how to do it
what have you done so far?
<D is 85 and <C is 61
AD bisects <CAB so it divides it into two congruent angles
so next to 34 is also 34?
<DAB
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<@&286206848099549185>
I can't even find a 5 step path that ends with a banana fickle
i don't understand how to do it
CHOOSE ONE OF THEM BELOW
1. don't know to add, subtract and multiply
2. don't know english
3. don't know math
4. don't know your name
5. i'm dumb
6. all of the above
7. none of these
8. write custom range between 1 to 7
can you write your question then I can solve
8
@limber eagle
an error occured
@limber eagle Has your question been resolved?
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Is the last part with the 45º the angle between a and b?
Multiply out the dot product
Remember the relationships between dot product, angle and lengths of vectors
a^2 doesn't make sense when a is a vector
Where is the cos term from
You don't multiply the whole thing by cos(45)
Also it's not a^2
You don't square vectors
@light brook understand the significance of a•a and b•b
And look specifically what the 45° is between
I saw that...
Mehdi_Moulati
cos(45) = sqrt(2)/2
Mehdi_Moulati
@light brook Has your question been resolved?
@light brook Has your question been resolved?
,w calc 3(4) - 3(3) - 10(2)(\sqrt(3)) cos(150 deg)
Ha I'm blind
,w calc 3(4) -3(3) - 8(2 sqrt(3)) cos(150 deg)
I get 27 still
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Hi there, the unit I am working on is Transformations of Functions.
See below the 2 examples that I was working on.
In part b, I am asked to sketch the original function with a reflection across the x-axis.
I do understand that both the A and the C value ( af[k(x-d)]+C ) would have to be negative in order to make this reflection.
However , I dont quite understand why the positive 2 was grouped together inside the brackets when C values are outside the brackets in the general formula af[k(x-d)] + c, for when there is a negative outside f(x), due to a reflection across the X-axis.
Originally, I thought the equation for r(x) should be r(x) = -√x + 2
Is someone able to explain the reasoning behind this to me, is it wrong to think of this in terms of the general formula? Or am I just totally off...
that sure is very pretty
The reflection turns f(x) into -f(x)
Since f(x) = √(x) + 2, that means -f(x) = -(√(x) + 2)
OH Shoot
ohhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh the whoel thing
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why cant you work this out using turning points
How would you use turning points?
because quadratics are symmetrical, wouldnt the turning point be the midpoint?
It would be, only if the arrow is landing at the same height as the archer (which it is)
Nvm
It is not
i know its wrong, but i cant quite visualize why
Consider if the archer was on a trillion story building
ok
The arrow would reach the turning point WAYYYYY before it hits the ground
Not at the midpoint
If you found the turning point, then doubled it, you'd get the time it'd take for the arrow to become level with the archer
But it still has a trillion stories to fall before hitting the ground
wait il re read the question and the chat
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This is what im thinking? Idk how to go on from here
πr²h is volume, not area
im so dumb
yes
area is 2 * pi * r *h right?
you mean weight
See if u can go from there
Same thing
so the weight is a force?
What area is acting on the surface?
Yes
Not rlly
the area of the circle
What's the area of the circle?
Thats A
mass*acceleration (of some sort, like gravitational constant)
why do I need to include density tho
How else will u get to mass
i gotta divide density by weight then?
nvm
Im tripping badly
U figured it out?
no
What are u stuck on
finding the numerator 😢
density * volume = mass
ah
Stephen
Correct?
yep
And what is A = ?
pi * r^2
you multiply it to get the area of the entire cylinder
Stephen
This is what we have now right?^
yes
Ok and the problem wants us to show that $p_c = (\rho)(g)(h)$
Stephen
And we have $p_c = (\rho)(g)* V/[\pi* r^2]$
h is multiplied
Stephen
to get the full area of the cylinder
Yep
Stephen
its just h
Stephen
Not sure, been a while since I’ve done fluids, gas laws
I’d recommend opening up a new channel and closing this one
It looks like it’s just PV = nRT
With 0.190 = h so A * h = V
thats what im thinking
But I’m not sure how to manipulate to get the addition of those densities so I still recommend opening a new channel sorry
kk
@dry egret Has your question been resolved?
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.rotate
,rotate 180
Yeah so how do I do it w/o the a^4 + b^4 identity
If you do that it's easy but since its something from school I'm pretty sure you aren't supposed to use that
I've tried everything i can btw, substituted the cosec^2 and sec^2, but i don't see much approach other than simplify and identity

Initial thoughts would be on those 1 + tan^2 and the 1 + cot^2 ...
i alr substituted those and did stuff, what happens is u get (a^4 + b^4)/ab (a = sin, b= cos) and from there if you use the identity for a^4 + b^4 it works out but im pretty sure thats not necessary
@tawny compass Has your question been resolved?
Ah yeah I see, there doesn't seem to be a simple way directly - easier though would be to convert both into this form you mentioned, which is easily doable...
Converting the RHS to that form just involves common denominator, multiple uses of the sin^2 + cos^2 = 1 identity, and splitting that -2(...) that you'd get into two separate bits
oh so you found a way? please share it, i dont get how splitting the 2sincos term helps
Right let me typeset what I did for you
oh got
i see it
a^2 - b^2 then substitute in for sin^2 + cos^2 right
wait that doesnt work lmao
$$
\begin{aligned}
\sec(\theta) \csc(\theta) - 2\sin(\theta) \cos(\theta) &= \frac{1 - 2\sin^{2}(\theta) \cos^{2}(\theta)}{\sin(\theta)\cos(\theta)} \
&= \frac{\sin^{2}(\theta) + \cos^{2}(\theta) - 2\sin^{2}(\theta) \cos^{2}(\theta)}{\sin(\theta)\cos(\theta)} \
&= \frac{\sin^{2}(\theta) - \sin^{2}(\theta) \cos^{2}(\theta) + \cos^{2}(\theta) - \sin^{2}(\theta) \cos^{2}(\theta)}{\sin(\theta)\cos(\theta)} \
\end{aligned}
$$
uhm ur thing failed to render
sorry for pinging i thought u forgot and thought it rendered or something
(yeah still typesetting it haha)
😬
chartbit
Final line converts to this, therefore you've manipulated both the left and right hand sides into the same thing
It's often an easier way to prove identities, get the same thing on manipulating both
i thought about splitting it to use (a+b)^2 but then dismissed that line of thought too quickly i guess 😭
very nice thank you!!
yea i tried to do that, dont know whats wrong with me, this is clearly what we were supposed to do
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Im supposed to prove that the complex numbers C are not a total ordered field using the assumption that either 0<i or i<0. i know you can show that in both cases this implies that 0<-1 but isnt this only a contradiction in the standard order we're used to in R?
For example if we take the order relation to be that the standerd order on the radius of a point to 0 (so the radius of -1 is 1) then -1>0 makes sense
And isnt that a total order since then every z can be compared?
I know im wrong but idk where i went wrong lol
0<-1 implies 0<-1*-1=1 implies -1<0
oh lol okey that makes more sense
what about this? I dont see how that counterexample shows up in this order relation
since then -1 = 1 > 0
well its easy to define an order on C
but you also want this to play well with addition and multiplication
any set has an order is equivalent to choice: https://en.wikipedia.org/wiki/Well-ordering_theorem
so it doesnt act orderly in terms of addition and multiplication? And thats makes it like not a well defined order on C?
So it is an order on the set C but not an order on the group C?
well any set having a well-order is equivalent. just having some order surely is weaker
not sure why you want to call it group now
idk what that means haha 😅
i ment field sorry
mixing up my words
yes
So its not a well defined order on the field C but it is on the set C?
get away from this well-defined stuff
the order is well-defined, there is absolutely nothing wrong with that
but it just doesn't have the properties that would make C with it a totally ordered field
But you cant define that order on the field C or am i missunderstanding
because its not compatible with the field axioms or whatever (addition/multiplication)
you can define whatever order you want on the set C or on the field C
but with whatever order you define, you do not get an ordered field
"ordered field" is a new thing, it does not just mean order defined on a field
Stealing from wikipedia:
oh thats exactly how my book introduces it tho. "In general we introduce a totally ordered field (F,+,.,<=) as a field (F,+,.) provided with a total order <= so that it satisfies the following properties : ....
isnt that what im saying tho?
the order isnt compatible with the field operations
so it cant be defined on that field
that quote says that "ordered field" is more than just field+order
it's field+order+properties
it can still be defined
it just doesn't satisfy the properties
OHHHH
i thought defining the order on the field "breaks" the addition on the field and therefor its not a field anymore
i think i got what you mean now
still a bit confusing but i think i got you?
yeah I think you do. I am being overly precise but there is a difference between not being able to define certain stuff and being able to define stuff but it not having properties you want
So if i define this order on the field, is it an ordered field, just not a totaly ordered field?
no
Okey so if i define that order on the field then its just a field with some order that isnt compatible with the field
sorry having trouble making it click
brb tho libraries closing haha
yes
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How would a toroidal planet core's magnetic field? Basically, if the Earth was torus shaped, it would have a toroidal core inside, and I'd like to figure out how would the magnetic field look like, mainly to know in what direction would a compass point if it was on it's surface
#old-network for physics
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I believe there is multiple interpretations that all work
If you know about this dm me
Also, why is the channel still occupied? I already closed it
It will close soon no worries
Although considering howww the magnetic field is ‘generated’ and assuming planets are held together with voodoo, you would have weird horizontal field lines as well
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Mention of decimals suggests quadratic formula (or completing the square)
From those y values, match them with the corresponding x values
im not sure how to go about doing that though
do you know the quadratic formula?
no
substituting/eliminating x gets you the equation in part a)
apply the quadratic formula to that equation to get the values of y
possible*
wdym
you said you knew part a)
so supposedly you already eliminated x to get
3y^2 - 24y - 47 = 0
this is the equation you want to solve atm
and this is a quadratic equation
which can be solved using the quadratic formula
so 9.6 and -1.6
sounds about right
it means there are (potentially) two possible values for y
and each will give you a respective value for x
so subsitute each in one?
for y
x = 67.6 y = 9.6 x = 0.4 y = -1.6 ?
cos i tried that and it didnt work
when determining x,
you should use the exact/unrounded values of y
how are you getting 19.8 for x
yeh
tyvm
@dire nexus Has your question been resolved?
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idrk how to start, I know its moved to the right by 5, stretched by sf 3 and moved down by 2
yup you nailed it
moved to the right by 5
So a moves right by 5, then becomes a/2
im kinda lost by what the point is
What does stretching do
@dark stirrup what does stretching do
I’ve never understood that properly
How does it affect a point
it says the answer is a = -10, b=1 or b=2
idk how to get to the answer from this tho
You do those operations on the point (a,b)
For example moving it to the right 5 units would get you to (a+5,b)
@muted delta, you can stretch both vertically or horizontally. y=a*f(x) will scale vertically by a factor of a. y=f(b*x) will scale horizontally by a factor of b
That makes a lot of sense
@warm wadi, you deduced that the graph shifts to the right by 5
That is, whatever the x coordinate was originally, it'll be 5 units to the right now
im lost
how do I find the possible values of it so if its a+5,b then the point it does (a+5)/2 how does it equal -10
You were told that the original x-coordinate was a
im so dumb
When you shift a 5 units to the right, it says the new x-coordinate is a/2
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Post your work
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Translate the parabola y=3x^2 + 1 along the vector v = (2, -1) what is the new function?
What have you tried
should I just sub them into the original parabola equation?
Yes
ok
I have another problem
which I can't solve
I have to show that for all foci and for all horizontal lines y=k (with k in R) there exists a parabola with focus F and directrix d:y=k
no idea how to do this
<@&286206848099549185>
The choice of F is arbitrary?
@mossy spear Do you know what a parabola is?
Like, geometrically I mean
this actually isn't completely true, there's a bit of an edge case if F is on y=k
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✅
yes
all the points in a parabola are equidistant to the focus and the directrix
Yeah, exactly
so put that in an equation
(distance from (x,y) to focus) = (distance from (x,y) to directrix)
ok one sec
|y-k|=sqrt((x_f - x)^2 + (y_f - y)^2)
where x_f is the focus x value and y_f is the y value
|y-k| is the distance from the point (x,y) to the directrix
Yeah
Notice if you square both sides, the y^2 terms cancel out
leaving you with something you can rearrange into
a form like y = ax^2 + bx + c
the weird edge case is when y_f = k
kinda falls apart there
uhh
don't worry too much about that part
so after I square both sides, I cancel out the y^2
I am left with something of this sort
and I showed this?
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is there a way to prove that $f_n (x) = x^n - x - 1$ is always increasing, if $n \geqslant 2$ integer and $f: [1, +\infty [ \mapsto \mathbb{R}$; without using derivatives?

how so
lilisworld
I guess you can prove it using reasoning
so it basically means comparing f(x) and f(x+1)
Since x varies from 1 to infinity
ah yes
Well you can just mention the fact that x^n will outweigh -x-1
And thus will give you a net increase over all the values of x between 1 and infinity
that

seems kinda 


Maybe I missed something
you need to prove that x^n - x is increasing for x>1

couldn't you use the same reasoning to extend it to f: (0,infty) to R?
which doesn't work
Is the \parens a packet thing
Maybe
no its a me thing
$\parens{x+2^x}$
Umbraleviathan
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
Package moment
VulcanOne
you could also just take any bounded from below function that's not increasing and use the same reasoning and say it will outweigh it's lower bound
Hmm
sorry i'm beating this reasoning to a pulp

Well I haven't done reasoning in a while
Civil Engineering moment
Beat it all you want
your a civil engineer?
Yeah
wow is it hard
Student still
Nah
Needs a
A bit of imagination and some uhh
Future thinking
You know
Like thinking ahead
do you mostly study calc
No
Which is why I hate undergrad studying for Civil
Masters and PhD uses calc a lot
.close
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Let's go to #discussion for more chats
okay
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how do you do the last question
@wild orbit Has your question been resolved?
where do you find those questions
a and b are correct
for c you know that rula buys 4 more sacks than paul
so let r be the number of sacks rula buys and p the number of sacks paul buys
r=p+4
because rula buys the same amount of paul's sacks but gets 4 more
so now from this substitute what r and p are using the previous equations
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thx
i got it
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So I know the 1/x^p is equal to x^-p
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has anyone here completed Schaums Outlines of Advanced Calculus
@marsh sand Has your question been resolved?
I need someone who has completed the book to help me.
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is there any trick to reform this easier than multiplying all out ?
n+2 choose 2 squared
@sullen tusk Has your question been resolved?
i thought about getting (n+1)^3 to (n+1)^2 , so i could get it into the first brackets and already have the ^2 for the result but not working yet
@sullen tusk Has your question been resolved?
((n+2)!/2n!)² is ¼n²(n+1)². the original expression is (n+1)²(¼n²+n+1)... If I didn't do anything wrong, they are completely different
$\binom{n+2}{2}^2 = \left(\frac{(n+2)!}{2!n!}\right)^2 = \left(\frac{(n+2)(n+1)}{2}\right)^2 = \frac{(n+2)^2(n+1)^2}{4}$
Denascite
Thats currently what i am aiming for but i couldnt be able to get to that
thank you, I'm slowly getting stupid writing math on my phone
Totally relatable. its freaking hard to read plain text math
My idea was to get the (n+1)^2 in the first brackets and then continue but i havent had an idea how to do this
pull the (n+1)^2 out of both terms
Oh
$(n+1)^2 \left[ \frac{n^2}{4} + (n+1)\right]$
Denascite
can you finish it from there?
ill give it a try. but should be able to. i think the hardest part is done
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I know the vector 3 over 1 is orthogonal to the line and passes through zero
but idk how to get the intersection point
@karmic hedge Has your question been resolved?
Vectors aren't lines, they don't pass through zero
if vector <a,b> is orthogonal to the line and <3,1> is orthogonal to the line then how can you relate <a,b> with <3,1>
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help
which one do u need help with
mind zooming the image pls
8、9
plss
pls help me



@supple apex
Don't ping specific people
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what have you tried?
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you know how when we mean 65432*1 we call it 6 factorial (6!)
so whats it called when we mean:
6+5+4+3+2+1
6th triangular number
pretty cool, thx
you can write a closed form for such an expression
like?
1 + ... + n = n(n+1)/2
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Did I set this up correctly?
The word problem is really confusing me lol
But if I did it correctly then I assume I would use sine
yup
solve for x yes
I got a weird number tho
i got 18.663
How did you put it in your calculator
alr
Did I set this one up correctly
250sin(18.663)=80
yes
okay yeah I got a a totally different answer idk why my calculator is being weird but Ty for ur help
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doing a past paper rn
no, e^(sqrt(2)x)
e^((sqrt(2)*x))
What's a past paper?
past exam
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Sorry i didn't see it
dw dw man
(You can always use l'hopital if you are already familiar with it)
No need tho - it should be easy to spot what the limit would be with an appropriate sub
indeed
or you can use the definition of the derivation
Mehdi_Moulati
forgot the limit, but yes
What's wrong with it
i said :
$\lim_{x \to 0} \frac{e^x - 1}{x} = 1$
Mehdi_Moulati
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What mistake have i made in sketching this graph
where did 8x^3 came from ?
the inside derivative
$$g(x) = x²e^{-2x}$$
$$g'(x) = 2xe^{-2x} -2 x² e^{-2x}$$
Mehdi_Moulati
x is powered to 4
ohh ,t hat make sense
Mehdi_Moulati
I cant upload my actual pic of my graph because discord is ruining it
but that looks similar to what i have posted which isnt entirely correct
x=1/sqrt(2)
you just missed x= -1/sqrt(2)
you can say that g(x) is even function :
because g(x) = g(-x)
you need just to check one side
Mehdi_Moulati
since e^{-2x} is always positive
anytime
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If the determinant of a matrix is equal to 3, is the determinant of its second power equal to 9?
det(AB) = det(A) det(B)
It follows for any integer n (including negative if A is invertible) det(A^n) = det(A)^n
Taking n = 2 and det(A) = 3 answers your question
Seems to be 9
If we change the order of columns in a regular matrix, the determinant of the matrix will always..."
change sign
none of the other answers are correct
remain the same
Its the “none of the other…” right?
Cuz it can get multplied by either 1 and -1
Since there is the always
Yes. Changing sign can hardly be interpreted as not changing sign
@strange fiber Has your question been resolved?
The number of odd permutations on a five-element set is equal to..."
25
5
60
120
It is 60, correct?
Half are odd
Half are even
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is this right
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what i had done recreated in paint
as you can see i have found the inequalities
but apparently there is a third inequality x<-
x<-5
where did that come from
yes but how does that count as an inequality in defining the region
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