#help-10
1 messages · Page 11 of 1
My bad, I didn't notice you were doing the exercise 50
so you could think of it as going zero steps away
when it touches
but the same rule applies
^^
hmm
close
the bottom left of the og rectangle
should be to the left of the reflection line
do you have an actual mirror?
no
or a piece of glass like a smartphone?
yes
you can put that against the line and maybe visualize what the other side should look like
to build some intuition
i get what u mean but i dont get it
it's ok
let's do it numerically then
take the bottom left of the og rectangle
you see how it's down one from the line?
yea
.
think of down turning into left and up turning into right
this is so hard to explain in text lol
better done visually
So I could be thinking of this wrong since I'm not doing it on paper, but here's what you could try. Put your pencil, on a grid point, that is on the shape, move your pencil to dotted line and count how many squares it takes, then go perpendicular, on the other side(empty side of the line), that many spaces
?
Almost, because you need to do the bottom part too
wdym
The bottom part isn't reflected properly
ohh this might help
turn your paper so that the dotted line is straight up and down
then use your finger for the original and match it with your pencil for the reflection that you're drawing
hmm
Same idea, put your pencil on a grid square, say the bottom left corner of the rectangle, move up to the dotted line, counting how many squares it took, then go perpendicular, to the left, that many squares
idek why this is so complicated for somn so easy
i wouldve been able to do in seconds
last year
it's more like we can't just point to the same sheet of paper over the internet lol
I'm telling you what you should do. It's not complicated
idk i understand/dont
if ur on phone u can like screenshot and edit it and draw on it
Put your pencil, on the bottom left corner of the rectangle
done
Move your pencil up to the dotted line, counting the number of grid spaces it took
Then go perpendicular, to the left that many spaces
What do you have now?
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is there a particular way that you're taught on how to do this?
This was in a test so no
i have a manual way of doing it but idk how to prove it
Can I see your manual way?
Because it was on a test, I would think you were given a way to do it haha
yeah exactly
Well more so a competition
can you factor out a six
then manually do some of it and find the pattern when you put the six back in
Taking mod 9, gives the sum of digits, mod 9.
But that's obviously not enough by itself
wait.. do you add the sum again if it has more than 1 digit?
I'm honestly not sure how to do this question
no right?
I don't think so
oh ok
I got 999 but I'm not sure it's right
that's what i got too
so 1026 * 111...1 with variable numbers of ones looks like 113999...999886 with variable numbers of nines
999 is the answer no?
i think 111 ones will have 108 nines
care to explain?
It has to be lower than 1000 due to the only option being a 3 digit number
yeah, i think that's the answer
I used a computer to solve it, it said 999 aswell, thank you :)
you can do it by hand
i just.... multiply 171 by 6 to get 1026
add the numbers together
1 + 0 + 2 + 6 = 9
and since there is 111 sixes
111 * 9 = 999
this is my work
I did the same way originally
can you do the digit sum out of order like that?
But I just needed to double check
I think so
Anyhow I got the answer thank you
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with f(x) = (2^x)(cos x) and the interval 0 ≤ 𝑥 ≤ π, find the critical points and state the nature of the critical point
So I found f’(x) which is
2^x[(ln2)(cos(x)) - sin(x)]
I set it equal to zero, cancel out the 2^x but then I’m stuck with (ln2)(cos(x)) = sin(x)
Anyone got any idea how to solve this ?
make tangent?
cosine is never zero in the domain that's the only thing to be careful of
lool nw that took me a minute also
Still not really possible to get x by hand tho
And wait
How would I know the nature of the critical point
Without second derivatives?
But x = arctan(ln(2))
I think we can use calculators
It’s a practice question for an assignment we are getting
Why can't you second derivative?
We technically didn’t learn it yet
But I kinda sped up and learnt most of the course on my own
But I’m not sure how she expects us to do it
Without using concacvity
And second derivatives
Well, okay. You can always check points near your point, to see if the curve is increasing or decreasing
f(arctan(ln(2)) is not really doable by hand though haha
Then check something like f(0) to see if that's a minimum or maximum
Right right
Okok thanks
Wait sorry
Another QUESTUIN
Question*
So I got 0.61 rads right
But when I graph it on desmos
WAITTTTTTTT
I’m an idiot nvm
Hold up mb
Actual question now
So I got x = 0.61 rads right when making f’(x) = 0
@ivory pilot Has your question been resolved?
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Should I try to rewrite the left side using the Taylor series of cos(x)?
-(cos(x)-1) times the infinite series of [(-1)^n * 2^(2n+2)] = 1/2
Does the divergence of the the series of powers of 2 mean anything for solving for x?
@marsh sedge Has your question been resolved?
$1/2 = \ -{(cos(x) -1)} * \sum_{k=0}^{+infinity} \ (-1)^n 2^{2n+2}$
theworstbesttourist_20
Your series doesn't even converge
Oh this is the question
This isn't a helpful expansion. Try to get something that converges
I'm lost, the sum looks like an alternating series
ln(1+x), sin(x), cos(x)
Maybe arctan(x)
Wait got it!
Thanks @tardy epoch
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he
Simplifying equation
cos a cos (b - a) - sin a sin (b-a)
I just need help figuring out how to simplify it
what rules do you know
Not many my brains been off due to me being extremely sick and I’m just trying to get little bits done
do you have a picture or note?
i did a and b in schoo and went home 
not sure what i can use here
look at your note for $\cos(\vartheta+\phi)$
jswatj
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Help
@static shoal Has your question been resolved?
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could i get some help on this question
1/(xy)=(5-x^3)/(4x^3)
mmmhm
ive done till that part
subbing the value of y in terms of x
but what do i do next
So try to write this expression as a function of X = 1/x^3
oook
You have to get an affine function and then youll be able to find the value of k and h
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[Linear Algebra, Similar Matrices]
I don't understand the point of similar matrices in an exercise.
If I have
1] the linear operator T:V->V
2] The base B1 for both space vectors
3] an associated Matrix A1 with B1 as starting and ending point
4] a base B2 for both space vectors
And I want to find a matrix A2 why would I use the concept of similar matrices?
Can't I just find A2 through the use of B2 and T?
@upbeat yacht Has your question been resolved?
<@&286206848099549185> I need your help por favor
@upbeat yacht Has your question been resolved?
you will find that A2 is similar to A1 if you do that
in particular the basis change matrix from B1 to B2 will be the relevant invertible matrix
so it might be easier to compute that basis change matrix and then calculating A2 from A1 using it instead of starting new at T
Yeah it might
But I'm not so sure about that
By that I mean that calculating from T could actually be wrong.
I tried the classic method and what I got was a different value compared to the one with similar matrices
The exercise in question: (without the values needed to craft the similar matrix]
T: V -> V, B2 is a base for both Vs
T([x y z]) = [x + y - z, y + z, 2x]
B2 = { [1, 1, 0], [-1, 0, 1], [1, 1, 1] }
Actually I'll create a new help for this
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how to simplify 4a(x+y)+2b(x+y)
$4a(x+y)+2b(x+y)$
Master Oogway
oh
you cant simplify it further
yes
do i still exaand?
no
oh
x+y
ok
so how do we write it?
just x+y?
?
2(x+y)?
no
oh
good
ok
do the same
)
yes
oh
$4a\cdot x + 2b\cdot x = x(4a+2b)$
Master Oogway
no
oh
oh
nothing
oh
get rid of it
ah
alright then ig im doing a revision ws without revising
so i might have some probelms
but thanks for the help:)
np
do i close or
if you're done yes]
i might have other qns not rlly sure tbh
bye
.close
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did u find f'(0) by lebinitz rule? im getting f'0=1
cos0 / 0^2 + 1
what about f'(0) and f''(0)
how did u get 0?
cos0 is 1 isnt it?
what did u meant by integral is always 0/0
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this is a question from an Oxford course( available on the website i am just doing this to improve my understanding)
I am not sure about what the question is asking
what i understand so far is that it's asking me to divide the given polynomial by the given quadratic and give the quotient and remainder
now i tried a particular example and i can obtain the coefficients by matching coefficient on both sides it gives me a triangular system in that case
but what does it mean by deriving a method that uses nested multiplication
i know that it has something to do with Horner's method but that's all
Also this is numerical analysis
@river plank Has your question been resolved?
@jaunty stream
@river plank Has your question been resolved?
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could you give me an example
Asagao 朝顔
you can simplify them
so to get them on a common denominator you can do
$\frac{2x+1}{(4x+3)(2x+1)}+\frac{2(4x+3)}{(2x+1)(4x+3)}$
Asagao 朝顔
and they have the same denominator
so like this rule? (a/b) +- (c/d) -> (ad+-bc)/(bd) ?
so there's an easy way to get them on a common denominator
(1-x) times what gives you (1-x)^3
(1-x)^2
yeah
so multiply top and bottom of the fraction by (1-x)^2
$\frac{x^3}{(1-x)^3}-\frac{4x(1-x)^2}{(1-x)(1-x)^2}+1$
Asagao 朝顔
like so
and now you can just combine like terms after you expand
also you can do the same thing with that 1
at the end
you can write 1 with the common denominator as well
since
anything divided by itself is 1
@timid silo Has your question been resolved?
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This is the question. I tried to get an equation with just one variable and got z^4 - 14z^2 - 96z + 301 = 0. I can't factorize this so I am not sure what to do.
Please could anyone give a clue as to how to approach this?
are you familiar with matrices?
k
3 equations, 3 unknowns. the tedious part is to solve for one variable in one equation, then plug it into the second and repeat for 3rd
e.g. solve for y in the first, plug into 2nd, solve for z and plug into 3rd
I have tried that, but i have ended up with z^4 - 14z^2 - 96z + 301 = 0, and i am not sure how to factorise it
btw, i have put the functions into a program, and it looks like to me that there are no such x,y,z
,w solve z^4 - 14z^2 - 96z + 301 = 0
pretty
lol
i am unable to use a calculator/any other sites for this as it is from an olympiad paper
yea it doesn't look like two of those parabola sheets intersect
which 2 are they martin?
oh the axes are labeled i'm blind
so there are no solutions?
the one with x^2 and the one with y^2
yea if you plot these two, they don't intersect
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wait does that make sense
kinda
there are no solutions right?
cause no value of x corresponds to any value of y to make the equations true
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@royal shard can you double check the graph? why would two sheets be in the same plane ?
can you plug one of these z values in for y and x and see if they satisfy your equations approximately?
.reopen
the second one should by 6z
oooohhh
trial and error
Sorry what's the question here
Have u tried bbc bitesize
lol
somewhere here 🙂
z^4 - 14z^2 - 96z + 301 = 0
probably messed up some algebra there then
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@tardy epoch
i use mathcha.io for those
it is really easy to use supports latex is free and looks cool
i don't think you realize how lazy i am
mathcha op for tikz
like if i can't do it from here or python console, i just won't
for anyone interested, in matchcha you press "alt" and "enter" and then type something in, like mathbb{R} and it shows you what you could have meant
Lol you even run python here
so it is usfull if you dont know all the latex names
what
,python print('hello world')
f
that would be too amazing
i meant i just alt tab to terminal
I tried putting sage in my preamble, but they said no
I swear you did it the other day
Oh ig you just copied from your terminal
You counted the number of words in something i sent
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.close
lol

my phraseexpander is misbehaving
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can you only refer to perimeter to two-dimensional shapes?
ahhh okay so to find the distance around a 3d shape, i would have to calculate the surface area right
Sure yeah, not sure distance around is the right word though
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thank you!
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hi
can someone help me with this
the first thing i tried was studing the sign for the numerator
making x-2 = -1/3 gives the solution x=3/2
for which x<3/2 make the inequality x-2>-1/3x not true and x>3/2 prove it
idk if i'm correct until here
@exotic ledge Has your question been resolved?
<@&286206848099549185>
i suggest splitting this into cases since we have the absolute value
consider x >= -1/2 and x < -1/2 separately
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Is the answer sqrt(50,000) km?
,calc 200^2+100^2
Result:
50000
yes
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how is this true?
jswatj
@fiery raptor Has your question been resolved?
I would bet that the "previous equation" mentioned is more or less this
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Hello, is this correct??
hmm
no
divding by 3 x gives x=15
So, this is incorrect
ig he is trying to solve an equation thats
$45x=3x^2$
Normal Zeta
?
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I have no idea what to do, I think 200 is the hypotenuse and that 100 a side?
yes, that's pretty logical, and that is the only way of doing the question
I just don't know how to find the angle
That's also assuming that the ground is flat and parallel to the horizon
start by drawing a diagram
no, next year
I need the angle where the string and horizontal meet right?
show is your diagram
ok
ideally sufficiently labelled
what counts as sufficent?
well I would want to see a triangle
the given info
and indication of the angle you're trying to find
ok
and labels for the position of the kite and person flying it
I'm stupid
I remember now
so, how do I find the angle?
I know the horizontal is sqrt30,000
what is a special triangle
30-60-90,
45-45-90
look up ratios of special triangles
what exactly are you looking at
note that here the ratio of a leg to hyp is 100/200 = 1/2,
and if you're looking at the correct stuff you should see something related to that
but that isn't the case for this triangle
what
I don't see what your issue is
check the pin
?
I said what the issue is in the pin
i know what the problem is
what's your issue with applying the info about special triangles to your problem
it doesn't follow either of those ratios
note that here the ratio of a leg to hyp is 100/200 = 1/2,
and if you're looking at the correct stuff you should see something related to that
only one of the legs match 1/2 h but its the wrong one
wdym by wrong one?
on my triangle the vertical is 1/2 h
so?
on the special triangle the bottom one is
instead of insisting the must have the same orientation
rotate or reflect the image if you have to
on a side note, how could i solve it with trig
consider what your me trying to find, and the relative positions of the given information
and use the appropriate trig function
its the inverse of the cosine ?
what's it
inverse cos of what
theta ig
what's theta represent
a question mark
$\theta = \cos^{-1}\theta$?
ℝamonov
yes
?
and I gtg someone else would need to take over
hi
its in the pin
but now its about specifically using trig
how would I solve this with trig
and not special triangles
uhhh soo I think you should solve for the two other angles, then subtract them from 180
Wait now
I was looking at wrong spot
yeah you were
It’s just using sin
inverse of sin or just sin
Since angle between horizontal and string has opposite and hypotenuse
Sin is when you have angle, , sin(angle) is just opp/hyp
Arcsin of opp/hyp is angle
yes arcsin(op/hyp)
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when i completed the square
i got (5,-1) for the vertex
but idk how they gpt thus
notice that b is 5/2 and c is -1/2
exactly half of your coordinates
the reason it is half is because of the leading term of x^2 is 2
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I don't understand why |x| = -x here when x < 0
shouldn't the | | make it always positive?
Hello, when x<0, x is negative
but the absolute value signs turn it positive, no?
suppose you have x = -3
then |x| = -(-3) = 3
for example
when x is negative, -x is positive
ok, i forgot -x is not the input
i thought they said the result of |x| = -x
which is incorrect right
yeah x is the input, and -x is the output when x < 0
so |x| = -x is true
when x < 0
this is just saying, if x is positive, then just return it unchanged
if x is negative, then flip it to positive
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thanks
awesome! no problem
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How do I do this
first what is the prime factorization of 240
3 x 5 x 2^4
Chinese remainder theorem
fr
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ideas on this?
tried writing out the first few terms but, since the index variable has to be zero kinda stuck
$c_{n}=(\frac{1}{4})^{[\frac{n}{2}]}(\frac{1+(-1)^{n}}{2}c_{0}+\frac{1-(-1)^{n}}{2}c_{1})$ so $\sum_{n \geq 0} (\frac{1}{4})^{[\frac{n}{2}]}(\frac{1+(-1)^{n}}{2}c_{0}+\frac{1-(-1)^{n}}{2}c_{1})x^{n}$
Cogwheels of the mind
@warm thunder Has your question been resolved?
how did you get this?/
From your recurrence relation
well you can quite literally skip the whole Ansatz of the infinite sum since you're given the relation, all you need to do is plug in values of $n$
More generally, suppose you are given $a_{km+i}=a_{i,k}$, then let $w=\cos(\frac{2π}{n})+\sin(\frac{2π}{n})i$, we have $a_{n}=\sum_{i} \frac{\prod_{j \neq i}(w^{n}-w^{j})}{\prod_{j \neq i}(w^{i}-w^{j})}a_{i,[\frac{n}{m}]}$
Cogwheels of the mind
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Question, in regards of space vectors and eigenspaces.
Given the linear operator T:V->V, can V have multiple eigenspaces each one different form the other?
sure
one with respect to the eigenvalue 2, one with respect to the eigenvalue 17, whatever
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"If a population grows at a constant rate of 2.8% per year, then what percent will it grow over the next 10 years?"
How do I solve for that
@icy acorn Has your question been resolved?
"grows at a constant rate of 2.8%" actually means each year is 2.8% larger than the year before
So for example if in 2022 it was let say p, in 2023 what will be the population ?
If we generalize the process for any year, we get something recursive
So it's just basic multiplication?
Yes
2.8 x 10 is all I need to get the answer?
Mhh no
Or is it like working with exponential bases
when we say that the population increased by 2.8%, it is the population + 2.8% of the population, so if p is the population it's p + 2.8% of p, or p(1+0.028)
And we do the same thing each year, we multiplie the population by 1+0.028
Is there a way I can convert that to exponential form
no need number e, just power
Population after 10 years is then
((p x 1.028) x 1.028) x 1.028 .... 10 times
Mhh
This next problem is similar to it
Have you ever seen the geometric progression ?
"The half-life of a radioactive material is the amount of time it takes for 50% of it's radioactivity to decrease. If a particular material has a half-life of 35 years, then what percent will remain radioactive after 100 years?"
What's that
If you understand this kind of problem you understand geometric progression, it's just the name for something general for all this kind of problem
We can translate this in terms of power
My problem is mostly setting the problem up
A summary
if we want " what percent will it grow over the next 10 years?", we want the ratio in percentage between the 10th and the initial year so p(n)/p(0) * 100
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How do I tell if it’s y coordinate is 160 or if it’s X coordinate is 160?
cos is always x coordinate
sin is always y coordinate
On the unit circle
It's how cos and sin are defined
Okay thank u
@fiery raptor Has your question been resolved?
this is true because if you take the cos of the angle the ratio would be that adjacent side over 1 so it would just be the length of the side
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just to clarify, the problem is that you have $$f(x) = \ln\left(\sqrt[3]{1+2x^4}\right)$$ and you want to figure out what $f'(x)$ is?
Eric Tao (he/him)
g(x)=lnf(x)
g'(x)=f'(x)/f(x)
okay got it
so basically you have to apply the chain rule 3 times here
your notation is not quite correct, but I think you are doing it right
they do it on the next line
Ohh
I think they just wrote the wrong symbol
It confused me too lol
okay
well first can you tell me what the chain rule says
yup!
or rather
the derivative of f(g(x)) with respect to x is f'(g(x)) g'(x)
so in this example let's choose f(x) = ln x and g(x) = cube root of (1 + 2x^4)
then, $$\f\dd{\dd x} \ln\left(\sqrt[3]{1+2x^4}\right) = \f1{\sqrt[3]{1+2x^4}} \f\dd{\dd x}\sqrt[3]{1+2x^4}$$
Eric Tao (he/him)
yep
so applying the chain rule again, you will get
then, $$\begin{aligned}\f\dd{\dd x} \ln\left(\sqrt[3]{1+2x^4}\right) &= \f1{\sqrt[3]{1+2x^4}} \f\dd{\dd x}\sqrt[3]{1+2x^4}\&= \f1{\sqrt[3]{1+2x^4}} \f83x^3(1+2x^4)^{-\f23}\end{aligned}$$
Eric Tao (he/him)
don't forget the factor of 1/3 :)
and then you can simplify that a little
yep!
and then simplify a little
Rewrite the expression to the power of -2/3 as a fraction with a cube root at the denominator
Then you'll be able to multiply it by the other fraction to simplify
No it's an exponent
It's negative, so the expression is going to go in the denominator
Let me write it
$$\frac{1}{³\sqrt{(1+2x^4)^2}}$$
Andrea276
Can you see how you can rewrite it that way?
$(1+2x^4)^{-\frac{2}{3}}$
You have this
Andrea276
It becomes:
$\frac{1}{(1+2x^4)^{\frac{2}{3}}}$
Andrea276
Right?
Then this
Then you can multiply that with the other fraction
Yes
8x³/3
$$\frac{1}{³\sqrt{(1+2x^4)^2}}\times\frac{1}{³\sqrt{(1+2x^4)}}=\frac{1}{1+2x^4}$$
Yep that's right, that's what you should get
You've got this multiplied by 8x³/3, which is the same as your answer
That's basically $\frac{1}{a^{\frac{2}{3}}}\times \frac{1}{ a^{\frac{1}{3}}}=\frac{1}{a^{\frac{2}{3}+\frac{1}{3}}}=\frac{1}{a}$
Andrea276
The thing I did there
this was a pain to write
correct, good job
yw
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yeah i think so
instead of 6
that means there are 20 ways no?
because it leads to the 11 becoming 10
then 10 + 7 + 2 + 1 is 20
the 7 should become a 6
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Hi there, can someone help me with this problem? I got the answer wrong although I don't know where I went wrong. After checking everything I realized that for the Volume of the cone I squared the height instead of the radius, but even after correcting this mistake my answer was still wrong. Any help would be greatly appreciated :)
(Also sorry about the vertical image idk how to fix it)
@timid silo Has your question been resolved?
<@&286206848099549185>
@timid silo Has your question been resolved?
I haven’t gone through the whole problem, so this might not be the only mistake. But the volume of your cone is incorrect since the radius should be squared not the height.
I think the rest of it is right it’s just a calculation error
yes I know, I said I realised this - after substituting 96 pi instead of 128 pi it was still wrong
if it's a calculation error can you double check? becuase I've checked numerous times and I get the sme answer
which is wrong
the actual answer is 159/2 pi
@timid silo Has your question been resolved?
I'm not sure where you got (0,8)
this is what I did and it looks right. I revolved it from (0,4)
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how do computers factor math. Like what is the exact formula they use to factor
or logic i guess
i want to understand factoring and simplifying completely. Because ive always been terrible at it
@sand crystal Has your question been resolved?
what is "factor math"
are you talking about sympy? https://www.sympy.org/en/index.html
i said "how do computers factor math" i dont recall saying "factor math"
sorry my connection is bad
i just want to know the exact, logic/steps taken by a computer to factor a mathmatical expression
so i know exactly how to factor
i said "how do computers factor math" i dont recall saying "factor math"
sorry bad connection
i didnt mean to repeat that message
by mathematical expression, do you mean polynomials?
i just want a deterministic ruleset for factoring or simplifiying
that i can follow
instead of using my intuition
give an example
ok gimme a sec
it feels like factoring techniques are very specific, and sort of rely on the persons judgement to figure out how a math expression is factored or simplified. like this for example: the tutorial I was watching says that if you have an expression with an x^2 and a x^3 you factor out the x^2 along with the number next to it. But if it was 5x -15 i would be factoring out the 5 instead. It just feels like there are specific rules for almost every eqaution i need to memorize or detect using my intuition. I wish there was some unifying rules that different forms of factoring all had in common
ah, I totally misread your situation lmao
I'm sure a cas factoring algorithm is deterministic, but I doubt most people (me included) would understand how its done
i would like to know how its done
look it up then
sage is open source
sympy is also open source
but humans usually factor using what you call "intuition"
yeah im not into that whole intuition thing
theres a set of stuff to do, such as first finding the gcd of all the terms, then finding linear factors
but any more than linear factors is usually guessing
its intuition, guessing or educated guessing most of the time unfortunately :/
if its a quadratic, then we have the quadratic formula
and there are special forms of polys like difference of two cubes that are easy to remember
i dont get why there isnt a branch of mathematics dedicated to deterministically factoring/simplifying equations
there probably is
and factoring is deterministic
but its not feasible for a human to do by hand most of the time
I'll look up the sage source code for you
what is sage
its a cas
computer algebra system
looks like they pass it on to pari
lol
idk how to look up source for pari, so would have to research it yourself @sand crystal
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Have a question around sets/subsets
A={u,v,w,x,y,z}
then what does the following mean?
{X = P(A) | u=X, v doesnt= X}
where the = are the weird C= thing
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Hi, i have a question and im a bit confused.
A person competing in an orienteering course travelled 5.0 km due East, then 4.0 km North East and then finally 6.0 km due South.
a. what distance has the person travelled?
