#help-19
1 messages · Page 44 of 1
Joanna Angel
idk if i understand it but i can apply it xd
that formual describes the theorem about substitution in integrating, sayign ti infromally
yeah its like a reverse chain rule
yes but it is harder to notice
but very alike
so in your integral iii)
you must decide what is
g(x)
and
what is g'(x)
if you identifgy it well, that is great
sometimes it needs slight manipulation too
before aplyign such formuala
yeah i felt like i can manipulate it somehow by seeing that 1/x was lnx which would give me e^lnx
1/x is a derivative of lnx
yeah and whats under the integral is the derivative no?
last integral iii) ?
then no any lnx theer
lnx is absoluteley useless
you have to look at yoru integrand
insuch a WAY:
first decude waht is inenr function, emans g(x)
inner = = inside
and then
calcualte its derivative
i shwo you diff interaglnow look :
$\int_{}^{}x^{2}e^{x^{3}}dx$
Joanna Angel
yo can seehere,
multipliocation
of two things
exponential function
and quadratic function
addtioanlly
expoenthial function is not simple but it is compsoed
and you can see, that inside this expoent
you can find cubic function
do you see it ?
in oher words, cubic function is inside, inenr function
yeah i see it
so it can be our g(x)
so probably we can assume
t = x^3
but before
we do it
we must calcualte its derivative
derivative of x^3 is
3x^2
right ?
so it stands in your expresiosn
differnce is the constant only
3
but rememebrt
we never eve rare afraid of cosntants
since
every and each cosntat can be taken out of integral
hence
yeah i know that
i know how to do it
and now coming to your iii) integral
the "inner" function loks liek 1/x
so we can assume
that g(x) = 1/x
but now lets get its derivative
its derivative is equal to:
g'(x) = -1/x^2
and now, we can see some maybe problem
since
before exponent we can see
1/x^3
and it is diffeertn than our derivative
so wwe can be confused but now
becasue
1/x^3 = 1/x * 1/x^2
so we do such sligth manipualtion
$\int_{}^{}\frac{1}{x^{3}}e^{\frac{1}{x}}dx=\int_{}^{}\frac{1}{x}e^{\frac{1}{x}}\frac{1}{x^{2}}dx$
Joanna Angel
$f\left[ g\left( x \right) \right]=\frac{1}{x}e^{\frac{1}{x}}$
Joanna Angel
Joanna Angel
Joanna Angel
I suppose that you should do it now ,
yeah
after this substitution you should reach an integral, that will need integraiotn by parts s well
but first step is substituion
i also need integration by parts?
not at once, but after substituion
yeah
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Hi I need help with getting all the solutions for x in [0,360degrees) for the equation
2 sin(2x)-tan(2x)=0
2x = y
2 sin y = tan y
2 sin y = sin y / cos y
2 sin y cos y - sin y = 0
sin y (2cos y - 1) = 0
sin y = 0
y = 0, 180
x = 0, 90
2 cos y - 1 = 0
cos y = 1/2
y = 60, 300
x = 30, 150
0, 30, 90, and 150 are probably not ALL the solutions within [0,360)
this was a quiz question recently and in the quiz i used double angle indentities and did not get all the solutions
can someone help?
oH WAIT 330 is also a solution
oh 180 as well
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yo
!status
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7. None of the above
bruh
I used the cosine law
lets put it like that
and I didnt get what I wanted
you're trying to find the distance between those two buildings?
well whats your answer
you sure your calculator is in the right mode?
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can anyone help
Look at your denominator
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Gremlin
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
nvm i got it
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I'm working on this problem and I honestly have no clue how to progress this to a point where it does not equal 0 over 0
that wouldn't be very helpful considering this line is the only thing i wrote
jan Nejon
so 2sin(x^2)
In the denominator you haven't applied the chain rule [correctly]
2xsin(x^2)
how so
Differentiating cos^2(x) gives 2cosx(-sinx)
oh
yes
sorry this is a review packet and we've been doing integrals for months
I don't know how I've forgotten everything
Don't apologize lmao
ok
so from there
what do I do to progress it
@long tinsel
<@&286206848099549185>
(solving problems of simultaneous linear equations with two variables) im stuck in 3d=e+7 3e=d-8
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Is the dependable variable x or y?
How I remember it is DRY MIX
D - Dependent
R - Responding
Y - Y axis
M - Manipulated
I - Independent
X - X axis
Tysm!
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@hallow pelican Has your question been resolved?
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tryna do this green's theorem exercise
but could someone give me a hint as to how i can find the bounds for the x domain?
i get in terms of why the region is bounded from x^2 to x
(il fix)
but for the the x domain itself i can't make heads of tails
im trying to understand the process intuitely because we wont be given graphing calcs or be expected to know how to draw some of hte more complex functions
or vectors rather
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Please just when I put a number like 2 is it then -2^2 or (-2)^2
@sharp karma Has your question been resolved?
-2^2
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Is there any numerical set in which √x=-1 has a solution?
no
I think there's no solution even for complex numbers
sqrt is always positive
alright, sorry
yes
there are solutions for $x^{\frac{1}{2}} = -1$ tho
artemetra
I heard that the sqrt only gives positive numbers because that's a function or something like that
oh nvm
kinda
formally speaking it only gives the principal root
So in the complex numbers
The sqrt would be also defined only for values in which the complex and the real part are superior to 0?
not understanding
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All i need to prove is the reciprocal
yo @mystic saffron if you got any idea it would be appreciated
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@bronze cradle Has your question been resolved?
Not sure, distance?
Distance between z and -a
so you are adding the distances of a point z from 2 points a and -a
(u can substitute z=x+iy as well, I think)
yes you can do that too
To prove the reciprocal?
yea do that, that would be easier
Oke, then what's next?
I could give an example of a number that fits the criteria and it should prove since it's an existence connector
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I thought for the limit divergence test
If it wasn't 0 it diverges
so why does it converge since it goes to 4.
You are mixing up series and sequences I guess
ohh i misread i thought it said series haha
for sequences is that the only test for it?
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I proved that the vectors are linearly dependent but vector c doesn't belong to the line and I don't get why 😭
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Bekah has four brass house number digits: $2$, $3$, $5$ and $7$, and only has one of each number. How many distinct numbers can she form using one or more of the digits?
龖
i have no idea what to do
wait i think i have. ideaa
so first single digits the possibilities are just : 2,3,5,7 : 4 numbers
double digits : 4x3 = 12 numbers
triple digits: 4x3x2 = 24 numbers
4 digits : 4x3x2 = 24 numbers
4+12+24+24=64 ?
can someone verify if my solution is correct
That's right
Correct
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In writing the integers from $10$ through $99$ inclusive, how many times is the digit $6$ written?
龖
i got 16,26,36,46,56,76,86,96 and 60,61,62,63,64,65,66,67,68,69
so i got 18 but its incorrect
66 has two sixes
oh when they say written do they mean like the number 66 would count twice
they do
so its 19?
yes
if we start from 0 and write 00, 01, 02.. 99, we would get 200 digits total, and no digit would be special, so each would appear 20 times
so 19 makes sense mathematically, since we skip the 06
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What is the sum of all the positive two-digit integers where one of the digits is three times the other?
i got 10-19 = 13
20-29 = 26
30-39= 39,31
40-49 = 0
50-59 = 0
60-69 = 62
70-79 = 0
89-89 = 0
90-99 = 93
so i got 264
is that correct
it looks right
Let $\Delta ABC$ be an equilateral triangle. How many squares in the same plane as $\Delta ABC$ share two vertices with the triangle?
龖
no idea how to do this
isnt it just 6
like each two vertices of the triangle can connect 2 squares
so its 6?
but thats wrong
consider a diagonal of a square
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How many numbers can you get by multiplying two or more distinct members of the set ${1,2,3,5,11}$ together?
龖
multiplying 2 numbers:10 possible values
multiplying 3 numbers:4 possible values
multiplying 4 numbers:1 possible value
but for example if i get 30 as a value in 4 numbers and also as a value in 3 numbers does it count twice?
did i do it correct
like if you multiply 5 digits together you get 330, but multiplying 4 digits together also gives you a value of 330 so does that mean theres no possible values of 5 numbers?
Basically
Everything is coprime except 1, which doesn’t change the value
So I think you can just take 1 out of the set and every subset of the new set will give a distinct number
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someone help me please
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6. I have completed the problem and don't need help anymore. Thank you.
7. None of the above
@latent plaza Has your question been resolved?
To find the length of the sides in a dilated image, multiply the length of the pre-image sides by the scale factor
wouldn’t i be multiplying them values by 2 though
if the dilation is halfing them
because we dk the pre image only the image
what is bro yapping about
|A'B'| = 20
how😭😭
FORMUALA
adn base on it, you have to find AB
aren’t we reversing the dilation though
🙂
No it's 5
if A’B’ is 20 would that mean AB is 40
right
becasue
40* (1/2) = 20
okay thank you
i wrote a hint above
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help
Find the starting one
Find the last one
find the ratio to get from the first distance to the second distance
thats ur scale factor
how do i do that
it says it
6?
14 is P
p' is after
after is 6
so what do you multiply 14 by to get to 6
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wdym
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z(x,y) is the number of ways to get from (0,0) the origin to (x,y), using only North, east, and north east movements. each movement is an increment of 1 in either direction, north east is +1 in both m and k directions obviously. how would i create a recursion relation that recurrs on m and n to count z(x,y)?
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$\int \frac{1}{\sqrt{2x-x^2}}$
Merineth
I’m trying to integrate this
I want to utilize the arcsin formula for it
So I rewrote it as
$\int \frac{1}{\sqrt{1 -(x-1})^2}$
Merineth
However now I’m stuck
1 can be written as sqrt(1) ^2
To make the formula usable but
Then what? :(
You mean x-1?
Oh
To slow haha
But if I substitute it with t
Do I have to divide with t after?
Is that the rule
Because every integral have dx after integral and you want to have only t when you substitute x-1 you have to do it with dx too
Okay, but what does that mean to replace dx with dt?
dx=d(t+1)=dt
Haha that doesn’t tell me much
What steps do I need to do to solve it?
This is the formula im going to utilize
x is my t and a is sqrt(1)
have you learnt u substitution?
No, I haven’t :(
All I heard about it, is that it is reverse chain rule
So I assumed it was going to be division but I have no idea tbh
Ok!
to turn the integral with respect to u
first find du/dx
then multiply dx to the right side
Because of this?
Well I just used the formula
Merineth
Yeah I do not understand the steps of sub u
ok lemme show you the steps
u = x-1
du/dx=1
du=dx
substitute u=x-1 and du=dx to get $\int \frac{1}{\sqrt{1-(x-1)^2}}dx=\int\frac{1}{\sqrt{1-u^2}}du$
WhereWolf(ping if needed)
important part here is that du might not be dx
maybe du=x^2dx or something
for other integrals
say we have $\int 3x^2\sin{(x^3)}dx$
WhereWolf(ping if needed)
WhereWolf(ping if needed)
btw you also need to turn u back to x
Makes sense
But
Shouldn’t it be like that?
Why do you remove 3x^2?
$\int 3x^2sin(u)du$
Merineth
no
Why
you don't just turn dx to du
using this we turn 3x^2dx to du
Merineth
And now we want to make it du?
Like can we do it stepwise
WhereWolf(ping if needed)
it's easy to integrate and remember to turn u back to x
btw when doing definite integral the bounds would change
Habit sorry
Merineth
we get just -cos(u)
WhereWolf(ping if needed)
WhereWolf(ping if needed)
just -cos(x) right
Yes
so just -cos(u)
Yes
-cos(x^3)
So 3x^2 just disappears to nowhere? Lol
I tried using that method on my integral
But I’m getting the wrong answer
According to wolf
please show your work
$\int \frac{1}{\sqrt{2x-x^2}} dx = \int \frac{1}{\sqrt{1-u^2}}du$
Merineth
wait a sec
Merineth
So what I wrote is right?
they differ by a constant
yes
Merineth
Is that equivalent to this ^?
What constant?
@twilit spoke Has your question been resolved?
Well I got two different answers when I put In my integral
<@&286206848099549185>
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$\int (x-5)e^{\frac{x}{2}}$
Merineth
did u use integration by parts ?
damn
by parts you should differentiate x-5 instead of integrating it
distribute and split the integral then integrate by parts
I’d suggest you, $\int (x-5)e^{\frac{x}{2}}dx $= $\int x e^{\frac{x}{2}}dx$ — $\int 5 e^{\frac{x}{2}}dx$
.doc
he took the first function as e^{x/2}
Yes and he should take u = x-5 du = 1 and dv = e^(x/2) v = 2e^(x/2)
everyone should learn the tabular method 
not sure what you mean by firt function tho
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How would this be written if it were on paper
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hey
How to show that 2nCn = [nCO]^2 + [nC1]^2 +…+ [nCn]^2?
been thinking but have no idea
Show what
this
Yea
First of all
is the C refering to combinations ?$
And if not then what is it
Mhm
vandermonde 
you should know what C is to answer first yk 
@brisk garden Has your question been resolved?
Did you try induction
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Hey guys
I need help with this, please
I think I've made a mistake in my calculations so now I'm stuck.
It tells me to find angle B and I used the laws of sine ** (B = sin^-1 (b*sin A)/a**
But it's given that angle B is greater than angle C, so I don't think it could be 28° that I got it to.
Recall that $$\sin(180^{\circ}-x)=\sin(x)$$
Civil Service Pigeon
There is more than one possible solution for angle B
I also did it like this, which tells that angle B is 102° but I need to answer it in 2 decimal-form
(I don't know if it's correct)
The triangle isn’t necessarily isosceles
law of sines should work? what did you input into the calculator?
The point of discussion is why we reject the acute case from the law of sines
B = sin^-1 (12*sin 39)/16
and got 28
.
how do I calculate it?
Let’s say x was your first solution for B
180-x is also a solution for B
That’s all the equation is saying (in this context)
Actually I should rlly say identity instead of equation
so since I got 28 first
could it then be: sin(180-28) = sin(28) ?
last question.
I tried calculating: is it 43,69° ?
,w 180-(180/pi)arcsin(16sin(39 deg)/12)
nvm
thanks for your help, I appreciate it
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what is the matrxi for T1 relative to the ordered basis B = [1, x, x^2,x^3] for P_3 and the base B* [1] for R
matrix?
What you can do first is apply the transformation T1 to each vector in the basis B
and then you can maybe express the results as linear combinations of the basis B*.
linear transformation T1 applying to each vector in B
So I guess that would be
T1(1) = 1
T1(x) = 1 + x
T1(x^2) = 1 + x + x^2
T1(x^3) = 1 + x + x^2 + x^3
Correct me if I'm wrong
nah
they didn't specify the transformation
"find the matrix of T1 relative to bases .... and ....."
if you don't know what T1 is you can't answer the question
i think i did it now
What you got?
but yes t1(p) = p(1)
i got the matrix to be [1,1,1,1]
idk if that is correc ttho
Mmmm okay. Mine is
[1, 1, 1, 1]
[0, 1, 1, 1]
[0, 0, 1, 1]
[0, 0, 0, 1]
hahaha anyways
yea seems good
Let T-1 -> P_3 -> R be given by T1(p) = p(1)
I just insertet x=1 on in the basis
my main problem is linear algebra is that sometimes im not certain on what i am being asked
well the main thing in intro lin alg is understanding the question
then it's just solving a linear system or pattern matching a lot of the time
Ah okay got it. So T1 takes a polynomial p(x) of degree 3 or less and evaluates it at x = 1. So yes you're right, T1(p) = p(1) 🙂
A question
It goes from P_3 to a real number
what do they mean by that
it takes a four dimensional input
and it outputs a real number
no?
imagine I take the polynomial p=x^3 + 2x^2 + 4x +1
what's p(1)?
it's certainly not a vector
x^3 + 2x^2 + 4x +1 = 1+2+4+1=8
yea
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[z^4 = -1 + i \sqrt 3 = |z^4|(\cos(4 \theta) + \sin(4 \theta)i)]
Could one notice the values of theta here?
Or would you use a different approach
To find z
are you trying to find the fourth roots of z^4?
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so to get the vector of the normal line to the plane, I know it's lambda<2x - 1, 2y, -1 > = <-6, 4, 2 >. After doing some calculations, I know that the normal line vector is <3, -2, -1 >
but I also need a point to get the equation of a plane. I don't know how to obtain that point
i can also expand on these calculations if need be
apply the equation of the tangent plant to a surface :)
that should help you restrict and solve for your x_0 and y_0
but the equation would be 3(x-x0) -2(y-y0) -1(z-z0) = 0, right?
is there an equation that I am missing?
because the one i have has 3 unknowns
z0 can be written in terms of x0 and y0...
and also you have tangent plant equation
here's the solution my professor did:
i understand how <-6, 4, 2 > can be used as teh vector for the normal, but why is the point (2, -1, 3)?
well, they used the fact that the the gradient of the surface is also determined by x,y,z coordinates
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how do i find the discount rate with the value for original
so i just make one up??
what's the actual problem?
- How much does a discount rate have to be so that the total (after 15% tax) comes to half the original price?
<@&286206848099549185>
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Hello, I need some help trying to understand integrals, I am new to this but I know an integral of something is the area behind the curve of the function, so I tried to find the integral for the area of a right triangle, I got this function f(x) = a - ax/b, and now I am stuck integrating it integral from x=0 to x=b (a-ax/b)dx, like, what is dx? how I solve this? I have to much questions and not to many answers, so I wanted to see if someone knew a good video series on integrals or something
have you tried something like https://www.khanacademy.org/math/calculus-1 ?
I am a kid, I have no money to pay a course :(
bruh but isn't khan academy free?
its free
watch essence of calculus by 3b1b on youtube
I ain't native to english so, when I saw something to paid I was like "ow", but it was for donations ( I don't know why it is the first thing that appears when you enter the page but, well, it is what it is ),
haha lmao
I've just goggled now: integrals for dummies , and there are tones of very elementar sources
wait, dx is the derivative of x? or the derivative of f(x)? ( haven't checked anything yet, I will check what you guys recomended but I want to see if I get an answer )
without mathematical formalism, for you, dx means with respect to what you integrate, = which is the integration variable, and other letters are constants like numbers
in your triangle case, x is a variable, but a is a constant
and if you wrote, assume, da, then a wud be a variable, but x wud be a constant
later you find out more
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help, where do I get P(-B|A)? It's probably the last thing I need to complete the solution. or if I'm totally way off with my solution, please let me know
@tepid maple Has your question been resolved?
note the relationship between P(-B|A) and P(B|A)
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help please
suppose a = 0 then a=1
what lol
for the first one recall the tables of AND (*) and OR (+)
if a=0, then a*a = 0
if a=1, then a*a = 1
oh okay
this is so stupid, i was never taught any of this
I havent missed a single day either
smh
if a=0 a*a = 0, what about OR? if a=1 a+a=2? right?
I could just use truth table?
but if a=1, a+a=1
for OR?
yes
but for my question
since there is only a
and no b
for the first one
would i just do
top 2 of each row?
like
let me write this
a = 0 1
a*a = 0 1
a + a = 0 1
?
huh?
i confused
okay :)
you have ONLY multiplication
so a*a
yes
it doesn't talk about + at all
consider a=0
a*a = 0*0 = 0 = a
consider a=1
a*a = 1*1 = 1 = a
that's all
uhm i would just write a= 0 a*a = 0, a = 1, at**a = 1?
yea
maybe you want to reference the laws
yeah
yes?
don't forget to write =a
like here
at the end?
yes
ok :)
that's it for question 1
oki :D
yes
well
1=0

UHHH
1
yep
oh okay
1 + 1 = 1?
yes
it might be easier understand if you just don't think of + as plus, but rather as OR
1 OR 1 is 1
0 OR 1 is 1
in any case
this question is done
oki
wait let me try the next one
3 is interesting
yes
what about a=1, b=0
and a=0, b=1
so we have do 4
yes
yes
but
it would be much more succinct in a truth table
and!
yes?
okay, well, can you reference the book in the homework?
the hw is not from the book, he makes the questions himself
oh the chapters in the book
ye
i'm just asking if i can send you some useful properties
and whether you can use them
without proof
$\vee$ is $+$\
$\wedge$ is $\cdot$
artemetra
got it
not relevant to you, you can ignore
so Absorption 1 is the law you are supposed to use
so i could just write
according to Absorption 1, this is true
see idk
technically yes but these names aren't fixed
if you could reference what the book uses it should be fine
but you can prove it on your own too
Its ok because in one of the exams we had a question, and i guess it was de morgan theorem. I just wrote " This is true because it follows de morgan theorem" and he gave me a 100 for that answer
it's not difficult
oki :D
let's make a truth table
okay
for a and b
,tex
\begin{center}
\begin{tabular}{ c c c c }
a & b & (a+b) & (a+b)\cdot a\
\hline
0 & 0 & ? & ? \
0 & 1 & ? & ? \
1 & 0 & ? & ? \
1 & 1 & ? & ? \
\end{tabular}
\end{center}
precisely
oo okay
it's easy to see why
oh wait so 6?
$2^n$
artemetra
no
You're just giving them the answer
