#help-33
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no x²-2x +1 = (x-1)²
my brain running on hopes and prayers actually
x²-x+1 = (x+1)²-3x
intel pentium type shit
so you wrote it like that?
Yes I want you to write it like this
Where x = tg²x
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also
what do i do after i write it
the way you said
Did you write ?
i wrote exactly what u said
So (1+tan²x) = sec²x
and nothing more
Can you do this ?
In deno
no
We get sec⁴x + tan²x
sec^2 - 3tg^2?
divide by sec⁴x 😭
ah
Like you get
ok
couldnt we also just write tg^2 x as sec^2 u -1?
and then separate the thing again?
From where ?
what do we do from here
So it's sec⁴x - 3tan²x
Have you reached here ?
yea
Woahh
Now sin²xcos²x -1/3 + 1/3
this exercise should not be so complicated
i feel like there should be more normal way of solving this exercise
1/3 × 1/( 1-3sin²xcos²x)
we somehow chose the longest solution known to man for this exercise
😭
Let's reach the answer
See
no no
you see
big bro, i wrote well over 3 pages with your solution and we still aint done yet
How can someone think of multiplying that factor, without extensively solving the problem?
It's better to know how to solve
It's ofcourse the best , I won't disagree
yea but you wont know it unless you're the one who made the problem
Truly !
so while i like your solution
Else someone exceptional can surely
Unfortunately I ain't !
Ok lets just complete it
the point is to find the shortest solution possible
this exam has 20 exercises like this
1% remaining
So this
rest in piece dude
Next we know
aha
Sin²xcos²x = (sin²2x)/4
So it's just
1/ (1+ k sin²2x )
Now you know how to do them by making the deno quadratic and dividing by cos²x and that tanx = z sub
Or just by visualisation
sure
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Hiii
I need some help with this question
I'll walk through my steps
I drew this triangle
I got AB to be a+b
Similarly work on others.
i got something of a question like that but it's basic one idk it can work here I used herons in it
In that one of mine the values were given of CB
It was to find AC and AB and CB was given where O as perpendicular
Nevermind 💀 i haven't saw vector
@eternal fog Has your question been resolved?
If AB was equal to a+b P would need to be somewhere on AB
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hello, im working on this problem, and I was wondering if my work looks correct thus far, if not, how can i fix it?
lol wish i could help but i think im abt to learn sin, cos and tan next year
use sin^2+cos^2=1
slight error in 2nd step
$cos 2x - (1-cos^2 x) = cos 2x - 1 + cos^2 x$
you have changed -1 to +1
i can see the first block modified
but cant understand how its still 2cos^2 x = 3cos x after that
my apologies, i wrote the corrected solution on the bottom
@smoky elm Has your question been resolved?
@smoky elm Has your question been resolved?
let y = cos(x) or something like that then solve it like youd solve any other quadratic equation
once you get solutions for y replace y with cos(x) and then you use inverse cos to find x
correct, now substitute cos x = n and youll get a quadratic
like said above
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how does partial derivitives work on ln(xy^2z^3) for example?
Partial derivatives are with respect to a particular variable
You just pretend everything else is a constant
yeah im just confused to why partial derivitive for x isnt 1/y^2z^3 and is instead 1/x
maybe i forgot some rule
Log properties
Log laws
Log(abc) = loga+logb+logc
Well, what’s the derivative of ln(2x)
You don’t really need log laws if you don’t want to
yeahhhh that was it
My point is that if you fail to derive this
Perhaps you would fail at deriving ln(2x) as well
Which means your issue is not with partial derivatives
Instead your misunderstanding lies just in normal differentiation
1/2x * 2? = 1/x
(2x)
Now replace the 2 with all the other stuff
And you end up with still just 1/x
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P can be anywhere
it can be inside the triangle it can be outside the triangle, it can be on the triangle
wherever they want
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✅
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Hi I need to show check whether this holds $\lim\limits_{n \to \infty} \frac{n-1}{n+1} = 1$
p1za
using the following:
Let $b_n$ be a null sequence and $\vert a_n - a | \leq b_n, then \lim\limits_{n \to \infty} a_n = a$
p1za
Im not sure how i should approach this problem
i cant really see the connection yet between the sequence and the rule I have given
i mean what is the definition of a null sequence
the limit of the sequence is 0
Let $b_n = \frac{2}{n}$, is a null sequence. Now can you work around $a_n - a$?
Arya
I dont think I understand
Firstly, do you get that the b_n I gave is a null sequence?
write out (n-1)/(n+1) - 1, and simplify this expression, what do you get?
now do you see the connection with the value given by Arya?
- 2/(n+1) ?
Yes, |a_n - a| = 2/(n+1) ≤ 2/n = b_n, which is a null sequence
Arya
okay so I got that this is a null sequence
but where do I get that the limit is 1?
you used the limit = 1 when selecting a.
One more thing if you dont mind:
if I need to prove that the product of a bounded sequence a_n and a null sequence b_n is another null sequence: can I do it like this?
| a_n | ≤ C
which is equivalent to
| a_n | * | b_n | ≤ C * | b_n |
and that is equivalent to
| a_n * b_n | ≤ C * | b_n |
which is just
| a_n * b_n - 0 | ≤ C * | b_n |
And now applying the theorem above
the limit of a_n * b_n is 0?
sorry for no latex
looks good to me.
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Hi
Do you have any shortcut for this?
My attempt
Can we ignore the root?
I mean mod
That looks like too much work. Instead, use a number line and mark points -2/3, 2/3 as points A, B.
Before A, the inequality goes: -6x ≤ 8
Between A n B, it's 4 ≤ 8
After B, it's 6x ≤ 8
Club the solutions (take intersection)

@slim escarp Has your question been resolved?
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Can someone please help me with this question:
<@&286206848099549185>
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time at faster speed + 0.5 hr = time at normal speed
okay
great, can you now set up the other equation?
wait
yeah okay you're using x for speed I see
(x+8) = (120/s) - 1/2hr
i don't know how to write the 30 minutes in corresponding to the variables, so i'll just write it like that
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you're super close
it's just (x + 8) = 120/(t - 1/2)
you just substitute in the new speed and the new time
new speed = old speed + 8 (mph) = x + 8
new time = old time - 0.5 (hours) = t - 0.5
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Trying to determine if this converges.
\
\
I was thinking of the ratio test, which gives $\lim_{n \to \infty} \frac{sin(1/n+1)}{\sqrt{n+1}} \cdot \frac{\sqrt{n}}{\sin(1/n)} = 1$. It thus doesn't converge
math rocks(wai)
sinx = x - x³/3! + x⁵/5! ...
or try multiplying and dividing by 1/n and then using the comparison test
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are both these results true?
yes
I know about x limit infinity=0, but not sure about x limit 0=1
@clever sigil Has your question been resolved?
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Can someone explain how this integral is transformed?
when i complete the square of the expression under the root i get
this
but now im stuck
rainy
make a substitution to put it in the form of sort u^2+1
you can think about transforming 2(x - 1/4)^2 to 7/8 u^2 then factoring out the 7/8
you could
and multiply it by someting to cancel it out
if you do that you'd then have (x - 1/4)^2 + 7/16
rainy
and now just get that 2 out of the sqrt
and then you could just ignore the sqrt(2)
then you can do x - 1/4 = sqrt(7/16) u
so that itll be sqrt(7/16 u^2 + 7/16)
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Why won't the sine rule give the correct answer in this example (which uses the cosine rule)
angle FBA is not 24 degrees
only angle FBC is 24 degrees
yea now it makes sense lol, thank you!!!
np!
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Given that the perimeter of a triangle is 2p find the lenght of the sides, that arise when we turn the triangle around one of the sides
So I have some ideas but they don't seem to work
First of all the we have to maximaze the r^2*l
Where we can transfer r*l into a Heron formula
Due to that we have a function of only 2 variable
But it doesn't look like it is working
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I need some help with improper integrals
I have this steps for solving the problem
but what do I do in this case?
if the domain was something like (a, b) I would go
lim x->b- F(x) - lim x->a+ F(x)
but I am not really sure how to approach this one
why do you think the same thing doesn't work?
limits at infinity are well defined
lim x->inf F(x) - F(1)?
if you want to be more precise it would be $\lim_{b\to\infty}F(b)-\lim_{a\to 1^+}F(a)$
kheerii
because 1 is included in the domain is it necessarily to have the second limit?
ohh okay
what do you mean?
+infinity is important ig
so the domain of the funciton is something like [a, inf),
and I thought because of the closed side we don't really need to use the limit when applying L-N
integrals are always defined as limits
the only reason you can write F(1) like you did above is that F(x) is a differentiable function (by definition) and so by extension it is also continuous
you usually don't have to worry about open vs closed intervals for integration
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first what are the conditions needed for a function to be integrable
continuous and differentiable
and its not continuous
so its not integratable
so now, is it strictly monotone? it looks like it to me honestly
technically only continuity is needed for integrability
what?
really?
recall the definition of a Riemann integral
oh yea i dont know those
thats the only thing im left to study
about integrals
its volumes, and Riemann integrals
f is subjective right ?
volumes are easy tho
why do you think that?
Draw the curve of the function
? for volumes?
i dont wanna study those rn
Nah
?
F(x) in 2d
you are replying to the wrong messages
ok sure
you might be right
but, why isnt it strictly monotone?
when you do the derivative for each branch you get something bigger than 0, which means its strictly increasing
At x = 1.1
y = 0.2
At x = 1, y = 1
why are you checking like that?
Doesn't that hamper nature ?
,w graph f(x) = x for x in [0,1] and f(x) = 2x-2 for x in (1,2]
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Monotonicity is checked for continuous functions
f(x)'s continuity is compromised after x = 1, it remains a monotonically increasing function but you see there x's value decreases
i dont see the graph
but damn
i didnt know that a function isnt monotonous if its not continuous
makes sense tho
i see
Yes !
so now, we are only left with surjectivity and injectivity
so how would you check for that analitically
without using the graph?
to be surjective means that its Im f = [0,2]
but since it not continuous at 1, would it not mean that its not surjective?
what's the definition of injectivity ?
that the function is strictly increasing or decreasing
f(x1) = f(x2), implies x1 = x2
you can check like that too
but wouldnt it work my way too?
That's the way of checking 😭
theres 2 ways of checking for injectivity and surjectivity
I just founded y = 0.2 for x = 1.1
you can check it with or without derivatives
And also y = 0.2 for x = 0.2
or looking at the graph i guess, but the point is to do it by myself
It's clearly not bijective !
Graphs are the easiest way to visualise
It's not injective !
Injective means one to one mapping
so you do it this way, right?
For a single y you will get a single x !
i see, so like this?
A counter example works in most of the cases, but you can generalise !
I don't !
The overlapping region of y, for the graph would provide, why it isn't injective !
ok bud, i agree, its not injective, is this the correct way of checking that its not injective?
You can write statements like for x € (1,1.5] we get range € (0,1) which is also achieved for x € (0,1]
You can't say this for a discontinuous function! You will need to define the domain of x in each case because that changes the definition. An analysis is best
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If I need to show that the sequence n-1 has no upper bound is it ok if I assume that it has an upper bound C that is a natural number and then contradict my initial statement by showing that (C+2)-1 >= C. Im asking because usually the upper bound is defined as a real number
no you cant immediately assume the upper bound is a natural number
however, if you have an upper bound which is non-natural, can you find a natural number which is even bigger?
well yes but im not sure how to express that mathematically, i have seen these ceil symbols but we never used them in uni so Im not sure if we are allowed to use them
do you know the archimedean property?
yes, natural numbers are unbounded
i thought about this too, not sure how to apply it tho
hmm i also kinda dont understand why i cant do this if we are not talking about the minimal upper bound
ok
so you do know that for every real number there is a bigger natural number
so if your upper bound is some real number, you can take a bigger natural number
which will again be an upper bound
and then you can do the rest of the proof
yeah so why cant I immediately assume that the upper bound is a natural number?
since there always is a bigger natural number
like if it has an upper bound that is a real number it also has an upper bound that is a natural number no?
if you have to reason why you can assume it then thats a good indicator for why you cant immediately assume it, no?
at this level you do have to make this argument
@lime bison Has your question been resolved?
Yeah i guess thats true
is there any formal way of saying "take the next bigger natural number"?
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showing that the "next" bigger natural number exists needs a slightly longer argument
if x is given, then the set {n in N: n > x} is nonempty by the archimedian property
so then by the well ordering principle it has a least element
you can take that
although for your proof you really only need some natural number bigger than x
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.reopen how do I express that then
✅
and do I also need to prove that?
can we really not use the archimedean property to my advantage here?
well we did none of that in class the thing is all we did is we said that the archimedean property tells us that N is unbounded
like is there no easier way? I dont think this type of proof is expected
or maybe a different idea to prove that n-1 is unbounded?
@lime bison Has your question been resolved?
n-1 is just N but in a trenchcoat
but I assume you arent allowed to just say "obviously"
you started this channel with asking whether you can assume that your upper bound is a natural number
its not like you actually need that
why tho?
my approach was to use C+2 as an index for the sequence
but the index for a sequence needs to be a natural number obv
assume the sequence is bounded, so there is some upper bound C
then there exists a natural number bigger than it because N is unbounded
and then use that
I mean thats not a crazy proof
there is no way around using that N is unbounded
(my point is that you dont explicitly need that C itself is natural)
yeah i guess thats pretty straight forward
thank you for time, i really appreciate it!
going to close this now
.close
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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 was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
contradiction is probably not the best way to do this
if you can simply find 3 vectors a, b, c where the equality is not true, you're done
uh
For example if I said
Prove that span(a,b) != span(a)
you could say
let a=(1,0), b=(0,1) then span(a)=span((1,0)) clearly does not equal span(a,b)=R^2
and hence it is disproven
they have to prove that it never holds
oh
the first point of your argument actually showed the opposite of what you wrote down
it showed that a+b, b-c, c+a are in span(a,b,c), so that span(a+b,...) is a subset of span(a,b,c)
now you need to show its a proper subset
isnt this my second point
@split vigil Has your question been resolved?
Can you enlighten me
well ok I chose bad words
both of your points show the same thing
namely that span(a+b,...) is a subset of span(a,b,c)
whichever you want
you need to show that the other subset relation doesnt hold
for example by finding a vector which is in one of the spans but not the other
austin mentioned doing an example
that might help with finding which vector to choose
uh
can i say for the scalars lambda1 = -1
lambda2 = 1
and lambda3 = 1
the vector [-1, 1, 1]T adds up to 0
therefore there exists a non trivial solution
@split vigil Has your question been resolved?
@split vigil Has your question been resolved?
@split vigil Has your question been resolved?
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Ivan and Adeline are in a classroom with a chalkboard. They are standing on different halves of the board, and on each half, the number $2$ is written. When Ivan's teacher gives a signal, Ivan multiplies the number on his side of the board by $-2$ and writes the answer on the board, erasing the number he started with. Adeline does the same on each signal, except that she multiplies by $2$. The teacher gives $10$ signals in total. How many times (including the initial number) do Ivan and Adeline have the same number written on the board?
938c2cc0dcc05f2b68c4287040cfcf71
Hint: ||the absolute value of both numbers are always equal.||
additional hint: ||since the multipliers (-2 and 2) are opposite, you can think of this as an alternating sequence||
wdym? can you elaborate the idea?
the fact that they both have 2 is actually irrelevant
but think about it like this
how about we go through each time the teacher gives the signal
what would Ivan and Adelines number be on the first signal
8 -8
4x2 = 8
-4 x -2 = 8
yep
and now they have the same number
alright how about on the third signal
16
-16
and the fourth?
32
32
nope
well look
every other signal
they have the same number
so initially they had the same
the first signal they didnt
the second signal they did
third they didnt
fourth they did
so every "even" signal they will have the same value
1 - no
2 yes
3 no
4 yes
10 is even
so how many times (including the beginning) did they have the same value
5
close
2 4 6 8 10
dammit
ye
we need to wait for the negatives to cancel for them to have the same number on the board
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Is it possible to do this question with the box method?
Or do i HAVE to do long division
cs that TLmaths guy on yt said the box method works for everything
Show what the box method is
(x^2-x+2)(4x^2+4x-3)
i think
im in bed rn so i just thoguht abt it
no need to divide u can just figure out the coefficients by thinking abt it
Wdym
ok so you have (x^2-x+2)(?x^2 + ?x + ?) = x^4+ax^2+11x+b
they ? r the coefficient u need to figure out
so u know the first one is 4 since x^2 * 4x^2 =4x^4
however for the next one u notice there is no x^3 term
we are at (x^2-x+2)(4x^2 + ?x + ?) = x^4+ax^2+11x+b and only an x^2 * x can prduce an x^3 term
so u have -4x^3 which we know, and then x^2*?x = 4x^3 since they x^3 term need to cancel out
so now u are at (x^2-x+2)(4x^2 + 4x + ?)
and u need 11x
we have 2*4x = 8x and we need 3x
so -x * ?=3x, ? = -3
so the factorization is (x^2-x+2)(4x^2+4x-3)
then expand to find a and b
can someone verify
Why did the 4x^3 turn negative here
(x^2-x+2)(4x^2 + ?x + ?) cuz u multiply -x*4x^2, 2nd term of first polynomial multiply 1st term of second polynomial
OHHHH SHITTTT THATS SO SMART BRU
The train of thought felt almost identical to doing the box method except there was no box
Thats so cool
do u get it now
Yeahhh
yw
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oh yeah it basaically is box method
just use that
i couldnt do it since i was in bed
but box method makes it simpler and more organized
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How many two-digit prime numbers can be formed by choosing two different digits from the set ${2, 7, 8, 9}$ to be used as the tens digit and units digit?
938c2cc0dcc05f2b68c4287040cfcf71
I don't think there's any nice way to do this
you have to list out the two digit primes and then compare
I think you can avoid some bad cases
if the digits are the same, it won't work - why?
the last digit can't be 2 or 8 - why?
if the digits are the same is div 11?
yup
unit digit can't be 2, 8 because then is div 2
29
89
97
79
okay that was awkward
yeah those are the 4
yeah i keep wondering wtf is this exercise
if you are allowed to flip numbers upside down you can get 67 also
it just said you had to use them
it didn't say that you couldn't do something to the digits
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Function is continuous and differentiable everywhere. F'(x)>=8 . F(3) is -2. What can we say about f(5)
Did you mean to capitalise F
f(x)
Ah alright
Welp I'd say then that f(5) would be positive
I mean it's not a very specific question
I mean yea
Uh so the derivative is always greater than or equal to 8
So the lowest f(5) could be is if the function was a straight line with gradient 8 from x=3 to x=5
From there you can find the bounds of the value f(5) can actually be
Which I think is that they want
@glass locust
@glass locust Has your question been resolved?
apply MVT?
I didn't understand MVT :((
Oh alright cool thanks!
Is this what MVT is?
Mean value theorem
I just use common sense I don't really know what mean value theorem is
Oh alright, this was quite comfortable of a logic. Thanks!
Could you just introduce MVT please
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hey trignometry doubt here:
we r given that
tanΘ + cotΘ = (3)^1/2
to find:
tan^6(Θ)+cot^6(Θ)
I think this is more algebra than trig
that should work
I somehow ended up with tan theta + cot theta = 0
x+1/x = √3
yeah it's basically algebra because you have x + 1/x = sqrt3 and you want to find x^6 + 1/x^6
if you don't mind finding x^4 + 1/x^4 first
you don't need to though
then (x^4 + 1/x^4)(x^2 + 1/x^2) = x^6 + 1/x^6 + x^2 + 1/x^2
if you want to avoid cubing
yeah fair
x²+1/x² = 1
Guys what abt the root 3=0
,w solve x + 1/x = 1
well tan and cot here take imaginary values
the trig is irrelevant they just didn't want to stir your brain by using x and 1/x
if you know complex numbers gg
K thanks
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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 was told that it's wrong.
4. I got an answer and would like my work checked.
5. I have a question about someone else's work/solution.
6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
2
im almost there but can't figure it out
this would be the figure
the rhombus side is the radius which is 8
as in the question
so one diagonal would be 8
wait bruhhhh
i think i found it
!status
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6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
and altitude of them is root 3/2 * side
and that would be root 3/2*8 which is 4root 3
2 of those
so 8 root3
?
@severe owl
Pythagoras?
Surely !
Anything works in geometry problems !
yess it's 8 root 3
i solved my own question silly me
thanks anyways
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i have another question but it's algebra
thought it'd be a waste of tickets
so posting it here
@severe owl can u help in this one
!status
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7. None of the above
1
Try multiplying with the conjugate of deno
49-48 = 1 in deno
Surely
Is this what you get in the numerator?
This is under √
2, 3, 4, 6, 11, 12, 22, 33, 44, 66
Result:
66
We need factors of 66
Are you sure it was 229 ?
,calc 179 + 323
Result:
249
This gives me 249 though !!
323??
32*3
expansion of (19+8 root 3)(7+4 root 3) becomes 133 + 76 root 3 + 56 root 3 + 96
<@&286206848099549185>
It's 153
Oh soryy
19*7 is 133
Wth am I doing
happens
sure
I'm extremely sorry, I really messed up 2 grade calculations !
So done ?
a²+2ab+b²
ohh
so 11 + 6 root 3
answer's 17 in the ak
and 11+6 is 17
nice
ty
I messed up real bad
it's fine
Sorry again !
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Hello
can someone help me with this (integration with variable shift)
I've seen many examples but I still can't understand it fully
\
can u highlight or explain the part you dont understand?
@rugged pendant Has your question been resolved?
so, we write t = \sqrt{u}
but then i don't understand the du part
because we multiply by 2t instead of the derivative of sqrt u
but why do we multiply by 2t and not 1/2t in this case?
you wanna solve for du
you wanna rewrite the same integral in terms of t
thats the whole point
sorry i still don't get vit.
$\frac{dt}{du} = \frac{1}{2\sqrt{u}} \iff dt = \frac{du}{2\sqrt{u}}$
Badr
how to go from this to 2t? what am i doing wrong?
𝔸dωn𝓲²s
remember that t = sqrt(u) in the first place so they substituted it right away thus multiplying by 2t insteaf 2sqrt(u) but they are both the same literally
yes
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Here to derive the equation (1.5) they have taken u as dependent variable on x and y right?
yes
@wary yew Has your question been resolved?
so if I do partial derivative of phi_1 with respect to x, we get 1+ u_x right?
@hazy lion
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I don’t understand how they got the partial derivatives as 2x, -2y
because u depends on x and y
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I don’t really know what is going on,
Can also try #odes-and-pdes
Or even #multivariable-calculus
Sure
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$x^2(a-1)-9a+9$
again, can someone please explain how we factor from here
Simon James B
Other channel closed lol
what sing do we consider
you factor out a-1
if you factor by -9 you gotta remember to swap the sign of every thing inside
in this case -9 because then the inside is (a-1)
and if we do +9 they remain the same
try -9 to see if you get it
$x^2(a-1)-9(a-1)$
Simon James B
$(a-1)(x^2-9)$?
Simon James B
yes but you're not done yet
i see it
yep
yep
$(a-1)(x-3)(x+3)$
Simon James B
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How do I go about solving this?
In this section we’ll determine the surface area of a solid of revolution, i.e. a solid obtained by rotating a region bounded by two curves about a vertical or horizontal axis.
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@calm robin Has your question been resolved?
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Hi, so I'm stuck figuring out something with the variables I've gotten


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