#help-10
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Evaluate the double integral of (x² + y²) over the region R, where R is the area inside the circle x² + y² = 4 but outside the circle x² + y² = 1.
Can a helper pin this question?
The region R here is a ring shape (annulus).
Can you identify the inner and outer boundaries?
(in the future, please lead with the question so that the bot pins it and helpers can start work immediately.)
@static beacon Has your question been resolved?
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how can i proceed
Have you tried square those equations up?
It would be a good move to determine a function's formula.
like both side square
Yes.
it was written in question that i need to find the intersection
i got the point of intersection
i need to find the equation of locus
but i will try ur way
For example, $x\cos{\theta}+y\sin{\theta}=a$ can be written as: $(x\cos{\theta}+y\sin{\theta})^2=a^2$
Mercury.
You got the point of intersection, but the question is asking, what shape is the function.
No need to, you can just make a blank space below and try second way.
Then you can compare your way and my way to see the differences, because it doesn't look bad for me.
If you got it, feel free to update it here and ping me!
(are you thinking of how to simplify the expression for x that you have?)
sorry for my bad handwriting
No, it is magnificent 
Let me check it again.
to do that way
thisis
Hmm, from what I can see, that is not wrong, but it is for "hard mode".
alr
You picked right the hard part, but logically correct.
yeahh its hard to graph those points and find the locus
thanks i am closing this now i will open again if i needed
And at that last part just substitute in $1 - \sin^2 \theta = \cos^2 \theta$ and you are done!
Mercury.
Over here.
Correct, it should give a beautiful solution.
x = a - bsintheta
Wouldn't it be $x=a\cos{\theta}+b\sin{\theta}$?
Mercury.
I think you missed a plus sign?
It should be this.
there is minus here
can anyone tell me what does mean touching y-axis at the origin
i think that means the circle pass through y-axis at (0,0)
or just basically, passes through origin
so
but "touching" in this context sometimes has another meaning
which means just passes through y-axis "at one point"
Biscuity is correct.
Can you pin this message Biscuity?
so, something like (I'll tryna draw)
Thank you Biscuity!
something like this
but for Multiple choices, there's another way to tackle this question
do tell if you need more help😁 @zenith vale
hmm
yes i did that
@glossy basalt
nice!
i dont know if this correct
check B
again
not yet correct
I'll check now
I don't think none of those is the correct option.
Recall the circle formula: $(x-a)^2+(y-b)^2 = r^2$.
Mercury.
Oh, what was your final solution?
Correct!
did you mixed up b and c in the last part?
Agree, b is not correct.
c is correct
option
on that one
i checked both points
first i checked the -2,0
then only b and c were satisfying
then i checked 0,-2
That's the difference between b and c.
yes
What would it be then?
and yes, c is the answer
I do not think so.
Since the circle passes through the point (1,2), which is in the first quadrant, the center of the circle must also be in the first quadrant, right?
And when a circle touches both the x and y axis, the distance from the center to each axis must be equal to the radius r, if you see.
Then, recalling the circle formula $(x-a)^2+(y-b)^2=r^2$, we have:
Mercury.
$(x-r)^2+(y-r)^2=r^2$
Mercury.
ohh
so we need to put r=1
so that we can get the options
@stoic breach can u tell me if a circle is passing through a point why is it not the solution of that question
why only r=1?
What do you mean by this?
lets a circle is passing throuh a point that point should satisfy the equation
From here, since the circle cuts point (1,2), subs it in x and y.
Ah yes, please do so.
we can get radius
and then we can get equation
Mercury.
Correct.
Now let's solve the quadratic equation.
Factorisation would be nice.
Right.
Now we have two cases.
Either r=1 or r=5.
Now can you subs r=1 and r=5 respectively into the original equation?
what is QED
Quod Et Demonstratum - As desired.
Completing the square.
i know that r^2 = f^2 + g^2
No worries 
Looks right.
Could be a mixed test, i do not certain about this.
u need help with that prob question ??
check if the 2 points lie on the circle
is my diagram correct
i know
yeah
umm
the second equation is h+k = 7(from the circle equation)
everything else is correct
.close
Closed by @zenith vale
Use .reopen if this was a mistake.
Looks fairly right to me, OP.
28/4 is 7 they wrote 6, remaining all is correct ig
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i was doing this and when I went to look at the answer
my answers were flipped around and I don't get it
If cosx =-1/5, what does it says about the quadrant?
,rcw
my cos^-1 was 101.5 but my teachers was 78.5
and I don't get it cuz we did the same thing
That is fairly strange, since it should be in 2nd and 3rd quadrants...
how the 2nd
(I don't get the A but ik it means all)
Cos is negative right
Then either 2nd or 3rd quadrant cos is not positive
oh
how did my teacher get the 1st quadrant then
cuz I thought it was the first aswell
I sorta get that
Hmm, but having the point there on first quadrant doesn't seems logic to me (Your teacher's answer).
But let me do a quick look.
urs i think is right..
yeah cos(x) = -0.2 is defeintly 101.5 what??
how did ur teacher get 78??
the only possible angelts are 101.5 and (258 i belive?)
Correct point.
mines also the first quadrant tho
no cos is impossible to be negative in first quadrant
No, that is 2nd and 3rd.
I believe that is wrong.
look at this gif here^
(cosine is width)
-# Good gif by the way.
notice how its only negative when its on the left?
Indeed, and maybe your teacher too.
No, cos = -1/5 here.
ur first answer was correct..
do u understand this kxro? this is really helpfully to understand btw^^
what is sin? what do u know is sins defention?
is tan not going up and down??
hell nah
sin = opp /hyp right?
..
I'm slow
opposite??
here
which side is oppoiste to the angle?
Just focus on the sine and cosine here specifically, the tangient one is just the derive of sine and cosine.
okay
i want u to open ur fingers like so ✌️
and image a line connecting the tips of them
notice how when u make the angle bettween ur finger bigger or smaller it affects how long that line is?
yes
SO thats is what (a little oversimplfied) bassicly sine means!
it bassicly says that when u have angel the side opposite to it grow porportianitly to that angle makes sense?
YESSSS
YESS
GDJGHJ WELL DONEE!!
TYY
WAIT WHA-
so notice how in the first and second quadrant the hieght is postive right?
everyone else that's told me the stuff about trig equations ( functions part mainly) I don't get them
your example helped more
Congrats!!
I think?
how it the left positive tho
look at the red line!
ohhh
even when u have it so the traingle is on the left its hieght is still Upwards right?
BUT in the 3rd and 4th quadrant its going Down!!
And so that means?
its okay tyt!!
it's negative?
YES!
i want you to imagne it urself
make ur hand into fists
and make one the center of a circle and the other any other points on the circle
and start to rotate ur hands
and think about hieght when is the hieght upwards and when is the hieght downwrds
nope one is the center so doesnt move
yeah I thought that
(think of it as planet earth orbiting the sun)
when my hands at the top it's always positive
when it's below it's negative
bc the height
yes!!
so when ur hand at the top from waht angle do u have
u have from 1 - 180 right?
but after u cross 180 its all negatives
does that make sense?
well done btw!!
tyyy
?
like 180 up/down?
notice how this circle only exsists between angels 0 just looking straight to the right) and angle 180 looking to the left
(hint u can see the exactly Angle in the gif at the top at any moment in time)
and then after 180 degrees (so u are looking left u wuld start looking left and EVER so slightly downwards
then it goes negative below that black line
which would give us negative hieght
yes
so does it make sense why now sin is neg in quadrant 3 and 4?
now i want u to image Cosine (which is the width)
(so bassicly when the width is on the right ((remeber center is 0)) we say that the width is postive
BUttt when its on the left We say its Negative
knwing this information i want u to try to derive When cosine would be postive or negative!!
cosine is negative on the left??
I just took that from what U said here
-# @dusty relic let me know if u need any hints btw!!
I may need that hint
YESS!!
SOOHO
okay so look at this gif again and focus on width
WOOHOO
no I get that left is negative
look at
bc you asked if I need the hint before you said my answer was right
so I thought bc you didn't answer it mightve been wrong
bc left has a negative symbol and right is positivr?
dwwww
YUP!
woohoo!
well actually more precisly this is because we are using a graph!!
and yk how on graphs when u go left
its negative??
YES!
and because we have our center at 0, 0
when the angle croses 90 we start going more left!
wait so are all graphs technically the functions??
anyways now you probably understand when sin or cos are + and -
can you test me again😭
I wanna make sure
I have an exam next week and I'm tryna bump up my grade
okays 3rd quadrant!! what is cos and sin?
Yes!! but imagne it goes all the way to the 3rd quadrant
and ask urself
am i more left or right from the center?
and am i up or down from the cneter?
and these are ur answers!!
(ignore astc rule for now)
just imagne
left and down?
if u had ur hand on the third quarter
and ur other hand was at the center
describe to me where ur second hand is compared to ur main hand (center)
YESSSS!!
OHHHHH
POSTIVE
FOR HEIGHT OR WIDTH OR BOTH?
BOTH??
TELL IT TO ME IN TERMS OF LEFT RIGHT UP DOWN AND THEN TRANSLATE
UP RIGHT
^^
RIGHT IS ALWAYS POSITIVE
UP IS ALWAYS POSITIVE
second quarant!
I THINK
-# that is first quadrant
OHH
NO LISTEN
whenever I do cast diagram
I think of sin being first
I got confused by everything
second quadrant is:
left up
width-negative
height-positive
TYY
up right
SO?
both positive
YES
AND YK HOW SIN = OPP/HYP
AND COS = ADJ /HYP
SO WE CAN SAY THAT TAN = (OPP/HYP) / (ADJ/HYP)
AND SINCE BOTH HAVE HYP
WE CAN JUST DO
-# sorry for butting in pluto is such a hype squad i love this LOL
wait I need to process this again
why bro is typing everything in CAPS
I don't get this
it's helpful
and makes it seem like you acc care
i am exicteedd okayy- well iwas anyways ;c
okay okay so so lets explain this!!
if i have 10 * 2 / 6 *2
i can just says that 2/2 = 1 and therfore its (10/6 )* 1
so its just 10/6 right?
yes ofcourse!!
ohhh
so like
10 and 6 the OPP/ADJ
2 is the HYP
since this can juse become OPP/ADJ / (HYP/HYP)
and because anything divded itself is 1
we just get opp/adj!
yesyes
ad yk how OPP / HYP = SIN and ADJ/HYP = COS
it means u need to look for top to bottom
OPP * ADJ
AND HYP * HYP= 1
(well its divide but same thing)
@dusty relic ^
do u udnerstand this?
so sin is P/H and cos is B/H and tan is P/B
and cosec is H/P and sec is H/B and cot is B/P
is that not the explanation
(well its divide not multiply BUT YES)
yeah I meant to say divide
@dusty relic u can remember this
maybe
this will help
OKAY SO NOW we can conclude!! TAN = Sin/Cos
ive not seen this notation before
soh cah toa up on top
I am the notation
@dusty relic makes sense?
did u saw it now
is it make sense
to u
yesss
soh cah toa
sine = opposite/hypotenuse
cosine = adjacent/hypotenuse
tangent = opposite/adjacent
yeah ive just not seem adjacent expressed as b and opposite as p
(sorry for butting in again)
AND SINCE TAN = SIN/COS
AND we know when SIN and COS are NEg or postive KNOw we can also GET TAN IN EVERY QUADRANT!!
So in the 1st quadrant Since everything is postive can uguess waht tan wil lbe?
(pos)/(pos) = ? pos or neg?
Pandit bhudri parasad har har bolo sona chandi tolo
tf
mm, not quite
This is a trick to find any trigonometric functions
positive / positive = positive
yup!!
and now in the second quadrants! can u get both sin and cos
then do sin/cos!
to get tan!
and u can do this for every quadrant!!
OMDS I SEE WHERE I WENT WRONG I THINK
does this gif make sense now??
I can't explain it now
it only makes sense in my head
Nope eee
-# oh wouldu also like to understand?
oKAY OKAY so YOU KNOW HOW TO GET ALL OF SIN and ALL OF COS RIGHT?
we already did that earlier!!
Bro u wanna do some inverse integral questions
please no 
🥲🥲heheheheheh
-# also please no offtopic-
Bro u wanna just not?
hey this is a help channel which is specifically intended to help specifically the question asker, sorry if this is kind of crude but please stay on topic or just take this to #discussion or #math-discussion or contribute here!
how did we do that again
on hand center!
O YES
yes ges
check hieght for sin
planets n stuff
and cos for width!
Why r u angry
she isnt
it's just simple facts
it's literally just interrupting
yes yes
sorry if it came off that way but yeah, its interrupting and not the place to ask LOL
-# please there is alot of channel on the serverrrr just go to somewhere i promise poeple there would reply to you alot more than we do..
okay go for it!! tell me sin and cos in 2nd quadrant!!
is the second quadrant the top left
so that would be?
and so sin/cos will be?
(if u cant colsve it think of just any postive / negative number over any postive / negative number depening on ur result ofc
so for example here sin is postive so we can do 1(sine)/-1(cos) ((since cos is neg here)
so that means that tan will be waht pos or neg?
it's like how tan= sin/cos
but since we have a negative
it stays
so -tanx
yes
so what is answer for 3rd quadrant!
so pos or neg?
YESSS!!
THIS IS WHY 3rd quadrant is CALLED TAN!
does it make sense now??
now now try 4th quadtant!!
because
we have a -width and -height
it is the quadrant where only TAN is postive!
OHHH
THIS IS BTW WHY
WDYM
^^
I genuinely forgot about that..
"cos is impossible to be negative in first quadrant"
first quadrant is top right..
oh
it's just the way I've been perceiving it
we start Looking to the right and we start turn left that is how we number each quadrant
OHHHH
YESSSSSSS!
OHHHH
LOOK AT TAN LINE HERE
NOTCE HOW IS 2nd AND FOURTH ITS DOWN?
oh wait lemme send u the vid
soeme sent it earlier!
oaky yeah look at it!
notice how TAN line is DOWN when its 2nd ANd 4th quadrant!!
does that make sense now?
but it isn't down in the 2nd?
i was like looking at red
wait so what is tan
tan is Hieght/width
ohh
This is why its areally long line because it appreoaches stuff like 0.9999/0.001
because as sin (hieght) gets taller
cos (width) get smaller
so tan cant be negative either?
no tan IS negative! at the 2nd quadrant and 4th quadrant jsut like we calculated earlier!!
remeber tan = sin/cos
yes
(Down means neg)
although dont include tan in ur hand orbit ismulation thingy
cause it will confuse u
i am just explaning the gif further!
YUP!
ahhhhhhhhh
this is why when i saw cosx = -0.2 IK it had to be in either 2nd or 3rd quadrant!
Because it is IMMPOSSIBLE for the cos (wdith) to be negative in the first quadrant!!
does that answer ur question now?
ur cos was 101.5
and that is correct!
so I would get full marks for that question??
A brief description and guide on how to use me was sent to your DMs!
Please use ,list to see a list of all my commands, and ,help cmd to get detailed help on a command!
ahh
-# if ur proffesour realizes they are wrong then yes..
ALTHOUGH
FUNFACT-
YES
there is actually TWO possible angels here!
if one of the is 101.5
I WANT U TO TRY To think AT WHAT OTHER ANGLE
could we possible get a width of -0.2
also u dont have to tell me the exacl angle just the quadrant!!
nope..
-0.2 describes the distance of a line to the left
wait let me draw -0.2 for you
so cos(x) = -0.2 that means that whatever angle is in cos it gives us a width of 0,2 (the green line)
notice how the red line for example is from point 0,0 and -0.5 FOR example!
yeah
OKAY SO SO
Q
IF U HAD TO VISuALIZE
101.5
HOW WOULD U VISUALIZE IT
JUST A LITTLE OVER 90* right?
what's the * meant to be
yeah
degrees-
ohhh
OAKY SO NOTICE HOW AT 101 DEGREES NOTICE HOW THE WIDTH IS A LITTLE LINE TO THE LEFT (NEG)
THAT IS BASSICLY THE Q
THE Q ASKS AT WHAT ANGLEEE DO WE HAVE A LINE OF WIDTH -0.2
does that make sense? @dusty relic
101.5
SO THATS WHAT THE INVERSE IS?
THAT IS X IF U DO COS(101.5) U GET -0.2
wdym by inverse-
cos^-1
ohhh
OKAY OAKY BUT LET ME SHOW U SOMETHING REALLY COOL
YES
LOOK ATTHIS VIDEO
AND ASSUME POINT 0.2 IS KIND OF LIKE A FRIEND WE SAY HI TO EACH TIME WE PASS
IN A FULL ROTATION (360) DEGREES HOW MANY TIMES WOULD WE SAY HI?
1?
look at the videoooo-
or is it both -0.2 and 0.2
lets say you walk from home to school everyday-
nope-
^^
damn
oui
and on ur way u see an old grandpa sitting on his lawn chair in the street
so u say hi to him everyday u see him
now remeberr u have to GO to school and also COME back from school
2
how many times do u say hello to him?
YESS!!
SO IF UR HOME IS 0,0
AND SCHOL is (-1,0)
HOW MANY TIMES WOULD U PASS POINT -0.2
2??
YESSS
THIS IS WHY cos(x) = -0.2 SECRETLY HAS 2 SOLUTIONS!!
YES 101.5 IS CORRECT (and u probably dont need to know the 2nd solutiion for now BUT)
LEMME SHOW U SOMETHING
YES
SO NOTICE HOW IF WE WAIT UNTIL HIEGHT GOES DOWARDS WE CAN GET A POINTWHERE WE ARE -0.2 TO THE LEFT
SO THIS IS the 2ND TIME WE WILL GET -0.2 WHEN WE ARE RETURNING
CAUSE IF U NOTICE WIDTH GOES FROM 0 -> (-1) THEN (-1) -> 0 AGAIN
OH YEAHHH
SO ALTHOUGH 101.5 IS THE FIRST TIME WE MEET THE POINT (-0.2) ON THE WIDTH
WHILE COMING BACK WE ALSO MEET IT
BC IT GOES TO SCHOOL THEN GOES BACK HOME (WTV THE REFERENCE WAS)
OO
AAND BECAUSE WE KNOW THE ANGLE DICTATES HOW (WIDE) WE ARE THAT MEANS THAT THE ANGLE THAT MADE THE FIRST TRAINGLE (-0.2) WIDE IS ALSO THE SAME ANGLE (SINCE IT THE EXACT SIAM TRAINGLE JUST FLIPPED) SO THE ANGLE IS ALSO FLIPPED
SO FROM THIS IMAGE WE CAN FIGURE OUT THAT SINCE OUR ORIGNAIL ANSWER WAS FROM THIS TRAINGLE
CAN U GUESS HOW MUCH X IS IF WE KNOW THAT THE ENITRE ANGLE IS
IF WE KNOW GREEN IS 101.5 CAN WE GET X?
((thinkabout it u got this))
why 180?
101.5-90
YESSSS!
AND SO THE ANGLE LEFT 11.5
AND HERE IS THE COOL PART YK HOW THIS ANGLE IS OPOPOSITE TO THE WIDTH HERE
DO U KNOW WHAT SIN(11.5) WILL GIVE US NOW?
LOOK
OK IM BACK
WELCOME BACKKK!
YESS
BECAUSE THAT GIVES US THE ACTUAL WITH
BUT ITS POSTIVE BECAUSE REMEBER WE ARE ONLY DOING 11.5
NORMALLY 11.5 IS IN WHAT QUADRANT
WE KNOW 1-90 IS FIRST QAUDRANT SO
1
mods ban him- nickeh30 ref
OKAY SO SO
YES
NOW HERE IS THE HARDDD PART-
SO KNOW THAT WE KNOW x = 11.5 CAN U TRY TO GET THE TOTAL ANGLE HERE AS IN THE ANGLE OF THE GREEN PART
BECAUSE IF WE PUT THAT ANGLE INTO COS
IT SHOULD GIVE US ALSO -0.2
OKAY SO SO LETME ASK U
HOW MUCH ANGLE IS IT IF U GO ALL THE WAY TO 3 QUADRANTS?
huh
1
no the green part
how many 90 degrees are in the green part
0
okay wait maybe this maybe be more helpfull
look at this?
how many 90 degree angels does it have?
3
YESSS!
(for future refrence each quadrant always has 90 degrees)
SO WHAT IS THE TOTAL ANGLE
270
uhh
okay lemme simply theimage!
ty
so we need to get the pink angle!!
and we solved for x earlier and it was 11.5 !!
So knowing that!!
how do u get pink angle?
why plus?
for refrence here is how 270+ 11.5 would look like
258.5??
YESSS!!!
WELL DONEEE
BC WE TAKEAWAY
YESSS
SINCE WERE IN TAN
OKAY NOW NOW
YES
THIS IS WHY I SAID THIS ^^
YES ITS ALSO -0.2
SO 258.5 IS THE SECRET SECOND ANSWER TO THIS QUESTION
ALTHOUGH U PROBABLY DIDNT TAKE THIS YET SO DONT TELL ANYONE
We've been talking about this for 2 hours now...
DO U GET IT NOW??
well yeah we are donee!!
sorry for the time btw 
DID U UDNERSTAND THOUGH??
OH TELL ME
WDYM BY CAST DIAGRAM
AS IN ASTC
TO CHECK FOR POS / NEG ON SIN AND COS?
YEAH
YES U CAN!!
ACTUALLY FUNFACT TRY IT IF UAHVE THE TIME AND COMPARE IT TO ASTC!! AND U WILL NOTICE ITS THE SAME!!
Oo
THE HAND ORBIIT IS WHAT MADE ASTC
OHHH
LITTERLY ASTC IS MADE FROM THE FACT THAT NUMBERS ARE POS AND NEG ON UP AND DOWN AND LEFT AND RIGHTACORDING TO WIDTH AND HIEGHT
THIS IS THE REASON IT IS THE ORIGIN
YES ALSO U CAN SOLVE A QUESTION AND COME BACK!
OHHHHHHH
do you want me to DM???
so I can close this so others can get help?
for math questions ehh prefferbly not because here other helpers can see and help if i cant help (or if i make a mistake or if i dont understand) or i if i am gone!!
BUT if u wanna explinations on certain topics form time to time u can ask anywhere u like!! here or dms!!
oh yeah fair enough
u can close here! and reopen it later ORR u can just open a new one and Ping mee!!
well i really like the comfort of knowing i can always ask out for help from other helpers since iam not perfect at math either!!
yeah I totally get that
BUT REGARDLESS FEEL FREE TO DM IF U NEED ANYTHING ANYWAYS I WILL ALWAYS HELP REGARDLESS!!
yes!!
do I write it as 1/7
yeah u can!
up to you it doesnt matter
ohh okayy
unless ur prof is extremly strict and prefers it written in acertain way..
but this bassicly means that the hieght of the traingle is pos (0.14)
bc sin is the height
YESSSS!!
