#help-0
1 messages Ā· Page 247 of 1
hypotenuse
so cos(x) = 5.5/4.5?
$cos(\theta) = \frac{4.5}{5.5}$
Akira
0.8181818181818182
Akira
this ^
i dont know what that is
im confused
do you have a calculator?
yes
wait let me show you
those things are called arsin, arcos and artan
you need to use this to find the theta
yes
wait i got 38.99644581
did you write all this
yes
you should write it just like this
if you're using a real calculator by hand then you gotta type it like this $cos^{-1}(0.8181818181818182)$
Akira
sorry im trying to find my phone so i can send you a photo
nvm my calculator has been wrong before
oh I see
oki
you because you were finding for H
...
on what
uh sure
will you be on in 12 hours?
k cuz its 12am for me and im tired
yeah i was up earlier to do research on a battle for history
now my desk is covered in paper and books
mmm
ok so ill hopefully talk to you in like 12 hours
maybe earlier
goodnight
or goodday
idk
good night
bye
thanks
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Assuming tan(a) - tan(b) = x, and cot(b) - cot(a) = y, find cot(a-b) in terms of x and y.
I know that cot(a-b) = 1+tan(a)tan(b)/tan(a)-tan(b)
so it is $\frac{1 + \tan a * \tan b}{x}$
dork9399
You can find tan(a)tan(b)
rewrite cot(b)-cot(a) in terms of tan
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Back at it again with the basic mathematics, I'm not seeming to remember how to solve this, for some reason.
$\frac{-3}{4}+C=2$
huntifer
yo
Is it not multiply the reciprocal of the fraction by both sides?
add some thing to both sides, so that on the left side only the C remains
Ah, so its not using reciprocals here?
solving for c?
Ahhh.
That makes sense
try adding 3/4 on both sides
i wanted him to figure that out on his own, since he knows he just forgot
I see what you're saying, make it 0/4, which is 0.
And in this instance its 2+3/4
which is actually 8/4+3/4
So its then 11/4
yep
That makes a lot more sense
I was sitting here like
"Reciprocal not comprende?"
So if addition, get rid of fraction with addition, if multiplication by the variable, get rid of fraction with multiplication
and if its division, use the fraction rules
Cool, thanks lots!
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Here, in the circle, RS = SM = 6 units. Radius of the circle equals to 5 units. Find RM. Feel free to ask if anything's unclear, the drawing may be a bit shabby. Try not to use too advanced math(not above trig). Thanks.
what have you tried?
@cosmic coral Has your question been resolved?
i drew a radius from O to R and O to M
but then i couldn't figure out anything
draw a line from O to P
yeah i did that too
introduce a variable like x for OP for convenience
PS can be expressed in terms of x
OM is a radius, so also has length 5
an expression for PM can be obtained from both right triangles
an expression for PM can be obtained from both right triangles
set those two expressions equal to each other to determine x and hence PM
if you do what's been outlined, you'll get the result
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is it possible to do smth to this using quadratic formula
its a quadratic in h, so yes
could i have some help doing that
this is mostly just an exercise in keeping things organized
idek which side i'm meant to do what to
if you have it written down on a paper, it might help to eg mark all the terms that have h^2 in them in red, all those with just h in blue and the rest in green
or by underlining them in three different ways or something
gotcha
what you want to do in the end is to get (some long expression)*h^2 + (other long expression)*h + (third long expression) = 0
i'm sorry it's rlly late and i don't rlly get how to use quad formula here
do you know how to use the quadratic formula on eg 7h^2-13h+27=0 ?
also it's meant to be h^2 at the very start i think
yea
then here its the same just that the numbers look uglier
so do i have to include cot in it?
cot(56) is just some number
you could calculate it with a calculator if it bothers you
(although that will introduce rounding errors)
i see
i frankly can't get it
i got to
100cot^2(56)+sqrt (-100cot^2(56))^2-4(cot^2(56))(2500cot^2(55))
all over 2cot^2(56)
no
you ignored the right side
you have to bring everything to the left side before you apply the quadratic formula
oh and have 0 on the other side?
yes
i see
what do i do with the final part of the equation
the 2(61)(hcot55 thingy
boi what the
what the
what do i do with the cos58 at the end š
wait nm
nvm
i just times it by both
yes
dont troll in help channels
but I don't trolling, I really dont know
How old are you?
23
at the very least open your own help channel
dont interrupt somebody elses
,rotate
oh and -61^2
that looks good
unless I missed something
now you can factor h^2 out of the first two terms and h out of the next few
ohh
yup
got that
and now it should look like this
-h*(expression) = h*(-expression)
should i switch it
now you can apply the quadratic formula
although at this point it would probably be fine to first calculate these long expressions, shouldnt introduce too much rounding errors
Tryna do that now
I have to go now but you can definitely finish it from here
@autumn mountain Has your question been resolved?
Yes
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can anyone let me know if this statement is somehow true, pulled this out on a midterm and got full marks
but it was a complete guess as i was stuck
so just interested in knowing if this step specifically has any merit
the ms paint writing
What are A and B
ah
i knew how to find the inverse but couldnt come up with anything quick
to prove it was invertable
and i just dont see my statement having any correlation to invertability
im thinking it mustve been a marker error
we got these back in a day so its likely they just let it slide lol
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yo can anyone help me with this
don't know how to start
I don't like how the denominator 1-sin²x part
Let's change it to cos²x first, shall we, since x -> Ļ/2 and sinx becomes 1, not 0
alright
I also hate how it's sin²2x instead of being with sinx and cos x
Have you learnt the trig identity sin2x= 2sinxcosx?
i learned that like 20 mins ago
Okay then you know it :D
So finally the limit equation becomes 4cos²x sin²x / cos²x
This limit is now much more solvable
That's it
(2cosxsinx)²
General tip: if you see + or - signs on fractional limits you generally want to consider factorising or changing into more favorable terms
Especially for trigs.
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how can i prove that if x² is a multiple of 3, then x is a multiple of 3
i thought about doing it using a contradiction, but how can i express that a number can't be divided by 3 mathematically?
Considering the cases x = 0, 1, 2 (mod 3) is one way
Just show that x^2 = 0 (mod 3) happens only in the first case, meaning x = 0 (mod 3) must be true
Meaning x is a multiple of 3
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I didn't get why they said r cong to r-9 (mod 9)
You don't get why it's true or you don't know where they've used it?
I couldn't understand the solution, my reasoning is that, set of possible least residues modulo 9 are {0,1,...8}
so x^2, has to be square congruent to square of each of them
resulting in x^2 cong to {1,4,7,9} (mod 9)
Where did you get 3 from?
Right, that's the same as they're doing
Just that they've used for example that 7 = -2 mod 9
To make calculations easier (not that they're overly difficult without)
why is it +- ?
they didn't do the sepearetly right?
as in they didn't compute 5,6, 7, 8, but rather used that fact 5 mod 9 is cong to -4 mod 9
similarly for others
Yes
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how do we get 1/2 here?
divide both sides by A_0
as said on the image
well, the original 1/2 gets here
because you are finding the half life
(A_0)/2 is half of the original amount
np
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for the covariance of 2 rvs to be defined, do they need to be on the same probability space?
@weary wyvern Has your question been resolved?
surely, they ought to be otherwise you can't take the expected value of their product
E((X-E(X))(Y-E(Y))
E(XY) - E(X)E(Y)
either way you need XY to be defined and to be able to take the expected value of that, so you need a common probability space
makes sense
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hint plz š
I can share what I did but I'm getting into problems
I need to find fx
sure
hint comes after
ok
uploading
its tricky
I tried this but it wont help I guess
since dt is dividing
and then to the right you can see my last attempt
and it doesnt look right at all
alright yea you seem kinda lost
indeed
this one actually seperates quite nicely
ya
going
ok done
ah
ok lemme see if I can do it now
finishing
1 moment
doesnt look good either š¤£
is this right? š¤
it sounds like you split your fraction by the denominator to integrate your function
but fractions don't work like that
you're not an algebra 1 student in disguise aren't you?
bruh
right
yeah fucked up mistake just saw it lmao
hahahaha

thanks I'll re-do it š
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Hey all
that is what it is asking yes
Awesome
XD
Math with teachers for whom English is a second language can be tricky
I've lost more than a few marks over the terms
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Khan Academy and YouTube are good online places to independently study mathematics :) that's how I started but there are many ways to approach
I'd suggest the basic algebra section on Khan Academy
what have you studied so far/
Or if you want to get more basic, pre-algebra might be good
Yes
There's also the section 7th grade math, which also may help
Because math is not just algebra
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idk what i did wrong for the domain
can x be less than -2?
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nah
what is the answer?
How though how about the other line and the closed circle on 1
look at the piecewise definition
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Hello could someone check this for me : )
yeah they look fine
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anyone have all formulars for y11 GCSE
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whats the difference between
i mean yeah
but im stil stuck
i get what the difference is but im lost here
i just need some more thinking give me a sec
i have no idea
which one u don't know?
all below f(x-1)
read the first f(x) till the end
and if you know what's f(-x) you'll be able to solve it
here's an example
y axis flip
i see that
so (x-1) is supposed to change the x value
by +1
doesnt that mean that y is unaffected??
for -1 it's f(-2)
so just type f(-2) in
which is
the key says the answer was 1?
Yeah you have to reference the original function values
Hm?
on x's
W
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For question 4
i cannot seem to solve it for a reason
quadratic formula and man does not work
caculate the angle that a line with a slope of 4 makes with the x-axis
another question i do not understand
Do you know about the discriminant
Oh wai
It asks for the actual zeros not number of zeros
Sorry misread
Why doesnt quadratic formula work?
Oh does it mean to say x^2 - 2x + 24 it might be cut off
@kind wind Has your question been resolved?
the
_4ac part
-4ac
it is a negative under a root so my calculator keeps saying math error
Right
gives me like -59 or someting
so how do i get the zeros
What that means is that the quadratic equation produces invalid values
This means that there actually are no zeroes
yes
Assuming you havn't learned about complex numbers, then yes there are no zeroes
š
idk how to do this question still tho
You gotta use trig
i dont know how to apply slope tho
like if it gives me a side length or something maybe i can get the angle
it confuses me
this is what i have
What's an equation of a line with slope 4
4/1
Equation of a line
yes
That means that for every increase of x by 1, y increases by 4
Think about how that fact can give you a triangle
i dnot understand
i thought abput it
and its not giving me triangle
ya
ohhhhhh
A right triangle
With side lengths you know
Or at least you know two of them easily
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And then use trig with the angle
Right
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i get it now, thanks alot dude
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Is possible to evaluate value of trig functions like sin(76.2) etc without calculator
And arctan arcsin arccos?
Is it difficult?
depends on the angle
With that quadrant trick right?
It can't get values like 67 72.4 etc
you can do series expansion
there are ways to get those values approximately without using a calculator, but it is difficult. Why are you asking?
you can solve it numerically like calculators do
Taylor one right?
of course angles that are on the unit circle, or near angles on the unit circle, that is not so hard
Just in case
in case...??
in case all calculators and tech in the world get fried and you must know the exact value of arcsin(72.4)?
nah it's a valid question to ask how to numerically approximate something like that
just wait until robot overlords take over all technology. Then we'll be happy we know how to find sin(76.2) by hand
(I'd say if it was a valid question, the reason would have to be more valid than "just in case", but I digress lol)
Yes
@glass onyx Has your question been resolved?
@glass onyx Has your question been resolved?
@glass onyx Has your question been resolved?
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how did they solve it when inside the root is negative
uh
49-196=-147
so it's root(-147)
which
using index laws
is root(-1) times root(147)
root -1 is i
firstly do you get the i part
yes
if so then 147=7x7x3
so you take make it root(49) times root(3)
root 49 is 7
I can write out the working out if you want
ok so root of 49 and root of 3
root of 49 simplifies to 7
how did it disappear
now i see
7/2 root 3
they simplified the denom
yeah ok 
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Hey
Just need a quick help
How are we able to turn 5 into 1/5 those are not the same in this instance
dividing by 5 is the same as multiplying by 1/5
@queen lion Has your question been resolved?
dividing 1/5 = multiplying 5
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can anyone help or refer me to where I can learn how to graph/plot simple linear equations on my HP prime G2 calculator?
there aren't really any good tutorials out there
you might just have to explore
i found the manual http://h10032.www1.hp.com/ctg/Manual/c05332710.pdf plotting seems to be starting on page 72 or so
@rare bay Has your question been resolved?
thanks
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Solo and James are standing at the seashore 35 miles apart. The coastline is a straight line between them. Both can see the same ship in the water. The angle between the coastline and the line between the ship and Solo is 40°. The angle between the coastline and the line between the ship and James is 62°. How far is the ship from Solo?
Here's my take on the problem. Though, I'm not sure if it is correct. Please point out my mistakes if there are any
uhh how is the angle in the middle 62 and 40? @grand berry
tbh the angles are very wrong
the angle that the line from the ship to the coastline makes would sum up to 180 since the coastline is a straight line
hello?
you here?
you don't need it tho
but the angles you wrote down was wrong
@grand berry Has your question been resolved?
are you familiar with the sine formula?
Yes
try using it
Uhh use it how exactly?
sinA/a = sinB/b = sinC/c
yes
you have the angles and you have one of the sides (the coastline)
try inserting it into the formula
Well wouldn't the triangle split into two triangles? I'm just puzzled as to how I should 'insert' it
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Not completely sure what I'm missing here... What is f(x)? Its not explicitly shown?
f(x) is that plot
OH. I'm dumb.
You're using that to find the area from 5 to 9
I was looking at the x axis
Its asking for what the height is on the y axis
š¤¦āāļø
Sorry lol, silly question, thank you for pointing that out
.close
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guys my professor corrected something for me and I've few mistakes, I understand them all except from the integral
to start with, why does he write that everywhere?
I'm integrating by parts.
it's like if idk how to solve a simple integral :/
am I missing something
no
yes
that straight line means you do F(a) - F(b) where F(x) is the integral of f(x)
for eg. if you have the integral of cos(x) (indefinite)
we have sin(x)
if you consider the definite integral it must have some bounds
say 0 (lower) and pi/2 (upper)
we would write it as $\int_{0}^{\frac{\pi}{2}} cos(x) dx$
itzkraken.
itzkraken.
now you do F(b) - F(a) (a=0, b=pi/2)
that straight line is standard notation for evaluating an integral
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how would you do this ?
Try differentiating under the integral sign
i did u substitution of u=y+1 but really didnt do anything
Geometry or trig sub, which path do you want to go with?
umm trig sub because i could do it geometrically
Then consider either one of y = sin(theta) or y = cos(theta)
Well, let us pick y = sin(theta)
oh the root3/2 is a giveaway i guess to do trig sub
No
The sqrt(1 - y^2) hints at trib sub
hmm yea
Then dy = cos(theta) dtheta and the integral becomes
$\int_0^{\frac{\pi}3}\sqrt{1 - \sin^2\theta}(\cos\theta\dd\theta)$
alonelybean
Or simply $\int_0^{\frac{\pi}3}\cos^2\theta\dd\theta$
alonelybean
Ever integrated cos^2 before?
The double angle identity for cosine states that [ \cos2\theta = 2\cos^2\theta - 1]
Rearranging the terms here, we get [ \cos^2\theta = \frac{\cos2\theta + 1}2]
alonelybean
ah yep i know that one
and now cos becomes
1/a sin
right
so here it would be 1/4 sin theta +1/2theta?
2theta ofc
soz
Yes
Divide both side by 2??
,w a^2-2a+2=0
oh
$(2^{\sin^2{x}})^2 \ne 2^{\sin^4{x}}$ btw
alonelybean
oh yeah oops
And A^ - 2A + 2 =/= (A - 1)^2
Instead it should be (A - 1)^2 = -1, hence no real solutions
oh that makes sense
quick question, when doing solids of revolution and rotating about the y axis
since it becomes pi integral x^2
do i just rewrite f(x) in terms of x
No, it's x^2 dy
Yup
ive identified it to be B or D, but im not too sure on the bounds
do i find the y intercepts of f(x) to find the bounds?
Should be from y = 0 to y = 0.6pi
hmm not sure how you would derive that
No, it's just that cos^-1(x - 1) goes from 0 to pi by the definition of its range
ah i c
So y goes from 0.6 * 0 to 0.6 * pi
thanks
for this integral, for what bounds do i integrate the positive case and what bounds do i integrate the negative case?
You can immedialy rewrite that as 2 times the same integral but going from 0 to 1
Because the integrand is an even function
Generally $\int_{-a}^af(x)\dd{x} = 2\int_0^af(x)\dd{x}$ if $f$ is even
alonelybean
yep
And, |x^2 - 1| = |x - 1| * |x + 1|, but now we are taking 0 < x < 1, so this is equal to (1 - x) * (x + 1)
is this the case when x^2-1 >_0 since we are only looking at the right side
wait no
oh i see just -x^2+1
Yes
oh yeah makes sense cuz from 0<x<1 we take the positive case and theres a minus in front
is that somewhat right
Yes, that is right
Even if we were not to half the interval
We would have -1 < x < 1
Meaning 0 <= x^2 < 1 and -1 <= x^2 - 1 < 0
|x^2 - 1| = 1 - x^2
-|x^2 - 1| = x^2 - 1
huh
There is a negative in front of the absolute value
|x^2 - 1| = 1 - x^2
So
-|x^2 - 1| + 1 = -(1 - x^2) + 1 = x^2 - 1 + 1 = x^2
sorry why does the thing inside the absolute value become switched
|z| = -z when z is negative
We showed that x^2 - 1 is negative
Meaning |x^2 - 1| = -(x^2 - 1)
oh r u saying that x^2-1 has negative y value for the given bounds
that makes sense
sorry im quite sloq
It is fine, take your time
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Find the value of
$cos 20 + 2 sin^2 55 - \sqrt 2 sin 65$
omniscientzenith
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That's an mc in disguise of an npc

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You guys do science physics here?
I think there's another server dedicated to that
but idk maybe
someone here probably knows
in #old-network
yep
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hello, I must find this function's primitive:
also btw is the primitive just the antiderivative?
omg it's 2x!!
I'm not an expert at all but yes, the primitive is the function that's not derivatedš¤ I've the derivated function, I have to find the non-derivated function called primitive
I'll just stick to my derivative and antiderivative lol
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Hi, could anyone please explain why the bounded area integral trick top function - bottom function doesn't work for this question, and when in general it can be used. Thanks in advance
how do you intend to use it
I tried doing integral from 0 to 1(x^r-tangent line)dx but it didn't work
well there's a simple reason why it didn't work. you calculated the area of the wrong region!
I know we could do the integral from 0 to 1 (x^r)dx and subtract a triangle area but I am confused as to when the bounded area thing can be used
Oh wait what
this is the region bounded by y=x^r and the tangent line between x=0 and x=1.
Okay wait so if I draw a line where the area starts and it hits both curves and then I do it again for where the area ends. If these 2 conditions are met and then I do top - bottom integral it gives me the total area between 2 curves
Could this be a way to think about it?
But there has to be a clear top and bottom curve. For example it wouldn't work here because there is no top and bottom curve and the lines at the start and end of the area don't hit both curves?
But there has to be a clear top and bottom curve
yes
Alright thank you so much Ann I think I understand when I can use it now, when the lines hit both curves and there is a top and bottom curve. Have a great day!
Would anyone know how I close this channel?
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can someone explaine this step to me? Idont know where the +4x² at the end come from.
$(2x)^2$
bettimsucks
use $(a-b)^2 = a^2 - 2ab + b^2$ with $a=x^2, b=2x$
itzkraken.
k thx a lot
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can anyone confirm if it's -1/2 or 0
I'm not sure how it could be negative or zero because all of the terms are positive
as this is a series of positive terms both values are wrong
I made it into sum (1/k) - sum (1/(k+1))
and what did you get for sum(1/k)?
Telescoping series
what did you do after that
1/n which I feel is wrong
can you show your work
sure
Then write it as sum from k=1 to n
You only have 2 terms that donāt get cancelled
Then take limit
What is $$\sum_{k=1}^5 \frac{1}{k}-\frac{1}{k+1}$$ for example?
scapeprof
(1/5) -(1/6) ??
no
No
do you understand summation notation
yes i do but it isn't geometric or arithemtic
can you write what
$$\sum_{k=1}^5 \frac{1}{k}$$
represents, leaving that as a sum, don't bother simplifying
āamonov
1 + (1/2 )+ (1/3) +(1/4) + (1/5)
āamonov
hence what do you get for:
$$\sum_{k=1}^5 \br{\frac{1}{k} - \frac{1}{k+1}} = \sum_{k=1}^5 \frac{1}{k}- \sum_{k=1}^5 \frac{1}{k+1}$$
āamonov
1+(1/6) ?
is this correct ?
for what i was asing for, yes
yes
forgot the sign
So can you say what $$\sum_{k=1}^n \frac{1}{k}-\frac{1}{k+1}$$ is now?
scapeprof
1-(1/(n+1))??
Yes
Yes
i got it thank you
helps to write out a few terms and align stuff
$\begin{aligned} 1 &+ \frac12 + \frac13 + \dots + \frac1n \
&- \frac12 - \frac 13 - \dots -\frac1n - \frac{1}{n+1} \end{aligned}$
āamonov
(-1)^n is undefined right?
there are real value outputs for integer n