#geometry-and-trigonometry
1 messages · Page 252 of 1
Yes, hunans
What rokabe is talking about is when trig gets fun
does this type of geometry ever get used except trig?
I have never used it tbh
in like any of my classes
Wait
is it like way higher level math?
It's hella important in tons of fields
You'll learn it almost right after you learn about sets & functions in more detail.
Higher maths, applied sciences, applications, trig and trig functions show up everywhere
Anyways, it's not the geometry that's super important. It's the concept of a function that is more general.
$\tan\alpha =\frac{\sin\alpha}{\cos\alpha}$
PristineWolf:
well yea trig, but I have yet to use concepts such as triangle similarity
$\sin\alpha=\cos\alpha\cdot\tan\alpha$
PristineWolf:
You'll use similarity in calculus
oh cool
Since calculus, as it is taught normally, is mostly geometric
Yeah that's valid @lofty scaffold
$\cos\alpha=\frac{\sin\alpha}{\tan\alpha}$
You can play with all the trig identities algebraically like this
PristineWolf:
Inb4 alpha = 90
Inb4?
Okay in that case it's wrong lol
But assuming theta is just theta its oke
can all trig identities be derived from tangent?
For this year teacher said only acute angles no 0° no 90°
All trig identities can be derived from other identities
What's an actute angle?
probably
So my formulas are right?
Yes
@weak shoal an angle less than 90°
There's cooler formulas you'll learn later too
By definition, I read it in Euclid's Book
Oh cool, thanks
Ah lmao didn't see it
why no 0 degrees?
Vats, I'll meme a surprise limit
0 and 90 cause interesting things to happen
No u
Depending on the trig function you're working with
So the teach is probably avoiding that
Vats what did it feel like for Rokabe to get rekt by 14yo
lol my geometry teacher was quite interesting to say the least
By interesting I really just mean "it might be undefined"
Radians are very important and they'll never go away
yea but in geometry its confusing
Vats IQ$= \lim_{x→∞}\frac {x^\frac{1}{x}}{x} = 0$
it was a summer class so thats probably why
Prank
Wtf
my teacher got mad at me for not using limits for end behavior statements
PristineWolf:
That's a new one
she said "you're an e v o l v i n g math student, no more baby stuff"
Well if that's the case did she make you define limits in terms of epsilon-delta
no
IDK what her deal was then lmao
Ohh you hate it now but it'll be a huge boon in higher courses
It's very nice to be able to look at a function and have an idea of what it'll look like without any extra work
i just hate looking at piecewise graphs
Pff
Why? You can use them for many interesting things
and like having to write every little thing down about it
Implying I need a piecewise function to make phallic graphs
You underestimate my power
yea we did a whole unit on piecewises
but like I just hate it cause its mostly review
like finding absolute extrema, or intervals of increasing
You'll see those again in calc
Turns out knowing absolute extrema is pretty helpful
I guess
idk just seems like a lot of things we do in class is kinda useless, but maybe Im just totally ignorant on whats to come
I understand that feeling
we had one extension that felt extremely useless
Later on you'll appreciate it, but learning stuff in a vacuum always has this feeling of "why bother??"
it was like find f(g(f'(g(g'(f(f''(g))))))
Are you using 'for inverse or for prime
inverse
Okay

I was about to be like "Christ"
Welfare, it's just your bread and butter stuff. You gotta do all of that before you get to the cutting edge stuff.
If it makes you feel better, everyone here had to do it lol
i guess one pro of it is my algebra skills have like improved a lot
$\sin 30 = \frac 12 \sin 60$
PristineWolf:
That's not valid right?
another thing, if you exclude the degree symbol, i'm reading the left side as sin(30 rad)
This Rokabe guy..... nerd
,calc sin(30)-1/2*sin(60)
Result:
-0.83562631354175
who's Rokabe
rudy is nerd also
I need Proof of pythagorean theorem
there are many
look up "pythagorean theorem" in wikipedia
you'll get like a dozen different proofs
@floral harbor
Hello
Can someone help me
Why does sine work?
Why can we say that the ratio of opposite to hypotenuse is the same for any two congruent angles between 0 and 90 degrees?
@upper karma tl;dr similar triangles
@dark sparrow what do you mean by similar trianglee, how doees similar triangle help us prove that any two congrueent angles between 0 and 90 degrees are same
sorry for the tag if you don't like getting tagged
two triangles are similar whenever their angles match
and two triangles being similar means the ratios of their corresponding sides are the same
right
Ohhh
I see
But
Why can wee say that ratio of oppo and hypo is same with two congruent angle
is it because theeir have the corresponding sides?
...yes
i mean
if your TRIANGLES are CONGRUENT
their corresponding sides match up
so of course the ratios do too
Right
Which quadrant is -pi/4 (clockwise) located?
-pi/2 or -2pi/4 is right between quad 3 & 4
okay cool
Why cos(π)=-1
why not
😄
cos(pi)=cos(2*pi/2)=1-2sin^2(pi/2)=-1
but why 
show your work
mistake in the very first line
24 and 20 aren't the side lengths of your 2nd triangle
wait 1 sec
I got 12. 5 now
what you want is something like:
$\frac{4x-6}{(4x - 6) + 24} = \frac{3x-2}{ (3x-2) + 20}$
ramonov:
Ohhhhh were doing that thing
I thought you didn’t need that like
When you have the parallel things
And are only doing the outsides
you're applying the properties of similar triangles
the side AM = 4x-6 of the smaller triangle corresponds to
the side AB = 4x -6 +24 of the bigger triangle
similar for AN and AC
as for 17, first identify the similar triangles
which allows to conclude something special about triangle WYZ
which then allows you to apply something starting with ||p||
and to reinforce that comment about rounding:
$\frac{104}{3} \neq 34.7$
ramonov:
wait 1 sec, it does work; been a while
fml
sry about that
yeh, mistake was you used 4x - 26 instead of 4x-6
solving:
$$\frac{4x-6}{24} = \frac{3x-2}{20}$$
should be fine
ramonov:
Oh, thanks
Dw it’s all good my teacher himself makes mistakes all the time
For this,
Why would I put 46+n as the numerator?
Like, why does n have to be the bottom
proportion isn't set up right i don't think
should be 36 over 46.8-n equals 42 over n
if i send my hw here can u guys do it for me
im a female
ok bull dinky he is a guy
but whhhyyyy not
because that goes against the server rules
rules smules
you are welcome to send your assignment and specify what you need help on
but we can't do the assignment for you as that is your responsibility
You'll want to set up a Pythagorean Theorem in each of the two triangles
Ya
ok
The line "144-100 = 44" is strange. I get you're trying to show how you rearranged that equation, but you'll be a bit cleaner if you write the next line as
x² = 144 - 100
instead
Do rearrangements mentally imo
Otherwise your work is very clean @crisp phoenix
ok, i have a lot more questions so be prepared lmao
Sounds good!
@limpid vector just send it
find the total area of the circle
what is the formula for finding the area of a circle
A= pie r to the 2nd
What effects tension of a cord between 2 masses on an inclined plane? Coefficient, the angle, or the masses?
guys i need help with one question please
ill be eternally grateful if someone could help me find the answers
@crisp phoenix
ye
This is fairly simple
ok
There are a few ways to go about it
ok
Yep
So since we have two side lengths we can use the inverse trigonometric functions to determine the angles within the triangle
Because we know that the triangle is a right angled triangle.
ok
Also, you know that if one of the angles aren't 30, 45 or 60, it belongs to neither triangle because a 180 in a triangle, 90 degrees from the right angle, therefore 90 for the other two angles, so if one angle is 60 degrees, the other has to be 30, but say one is 15, the has to be 75.
If that makes sense.
not rlly but loo
look
heres what i came up with, is this correct @winged zinc ?
@winged zinc hello?
How does Sin work? I know its the opposite side divided by the hypotenuse, but how does the sin button on calculator get that ratio from an angle
Flexify
yesir
Do you know about inverse trig functions?
yeh
So you know that since sin(X)=o/h
yeah
Then X =sin^-1(o/h)
So you know the hypotenuse is 2
So you take one of the side lengths, say 1, and do sin^-1(1/2)
yeah
What does it evaluate to? Should be 60 degrees.
i think so, im not sure
Do it on your calculator
My point is not getting the value of an angle using sides
its 30 @winged zinc
My point is, when you do sin(90) for instance, how does it give you 1
Or sin(56(
How does sin function work
When you press sin on your calculator and put 56 as the input
What does your calculator do to get the ratio of opposite over hypotenuse
ohhh
Especially since it doesn't know any of the sides
i just press 2nd
@sonic perch
look
https://nj.testnav.com/client/index.html#login?username=LGN415881023&password=GTCWK5S6 this is the calculator i use
I do agree with you learning about what trig functions and ratios are
But I think it is first best to learn about how to simply use them
i know that In mathematics, the trigonometric functions are real functions which relate an angle of a right-angled triangle to ratios of two side lengths.
Mate I'm in Calc AB
I know fully well how to use them
I want to understand them now
No
I mean how they worm
Work
You normally find the sin of an angle by taking the ratio of the opposite side of a right triangle over the hypotenuse of said right triangle
But calculators simply have a degree or radian as input
How do they figure out that ratio with that simple information?
Is there a formula or equation that allows you to get the ratio of an angle from just that angle
There most definitely is, otherwise calculators would be pulling this scheisse out of its behind
@sonic perch in retrospect, trig functions just compress basic theorems to do things quicker
they arent very complex
Yeah, there is
I want to know what that is
@sonic perch read away https://en.wikipedia.org/wiki/Trigonometric_functions
That
Ok, let me try and explain this now
So we have a unit circle
And if we draw a radius with some angle theta between the positive x axis and the radius going in a counter clock wise direction
The position of where the line touches the circle is the coordinate (cos(theta), sin(theta)) - this is if the circle is centred at (0,0).
@sonic perch
Yeah I know that much already
And because of the right triangle formed by angle theta with the hypotenuse being the radius
Then cos^2+sin^2 = 1
As it should as the circle has the equation x^2 + y^2 = 1, and every point on its graph should be 1 away from center
Ok what next
Can someone give me the answer to this please ????A spring is attached to the ceiling and pulled 20 cm down from equilibrium and released. The amplitude decreases by 5% each second. The spring oscillates 9 times each second. Find an equation for the distance, D the end of the spring is below equilibrium in terms of seconds, t.?
@sonic perch There is no simple formula you can use
There is an infinite series that converges to the correct value.
@upper karma
Are you saying the spring's amplitude of oscillation reduces exponentially or linearly?
Thank you
There is one for cosine and tangent - along with other things like e^x
Have a look at taylor series.
Hmm
Doesn't say
Because it could say be an amp of 20 at t=0
Then amp of 19 at t=1, and then at t=2 have an amp of 19*0.95
Or it could be 20, 19, 18, ...
But anyway, the position of the end of the spring is going to be modelled by either a cosine or sine curve
Let us use a cosine because it has a max at 0 when there is no horizontal translation
Now we know that it will be in the form of Acos(bx)+c
Calculating b is simple enough
T=2pi/b
where T is the period
Period is the time divided by the number of oscillations
As for c
We are going to make it such that y=0 is when the spring is in the equilibrium position
And so we don't need to worry about the c value
As for A
It is difficult
It could either be an exponential or as a linear function
@upper karma
i think its linear because the next question asks exponential
Ok
So we some function of time that describes the sequence, (20, 19, 18, ...)
What do you think that is?
is it just -1
Expression please
Haha
im so bad at this 💀
and its due in 12 minutes 😫
Is the amplitude at t=0, t=1, ...
And that is described by the equation 6(1-0.2t)
So our final equation is 6(1-0.2t)cos(n2pit)
Where n is the number of oscillations a second
and we were told 8
So D=6(1-0.2t)cos(2nt*pi)
Should be the equation you are looking for.
oh okay
Well then I'm not sure sorry
Can the spring go 'above' the equilibrium?
it says below
Yeah, but spring typically exhibit harmonic motion. so they go below then above, then below and so fourth
what would it be if it was above
It should be described by that equation
Are you meant to answer only with sine or something? Anything about how answers should be expressed?
That equation should describe the harmonic motion of a spring
Ohh rip
Did it matter much?
not really its just hw
Graded?
yeah
Summative?
yeah
i have good quiz scores and did good in my mid term so i should be fine
i appreciate the time you gave to help me tho
@winged zinc
yeah i know 😅
That way people can explain it and let you get there - we don't love simply giving people answers
i just totally forgot about it
All good
That is what I found online
Phi is simply a phase shift
But if we wanted to write the answer in terms of cos
we just need to change the phase shift
So I'm still unsure as to why it was wrong
yeah idk
Unless it was exponential
yeah
Nice, doing what degree?
Nice
yeah im majoring in computer science
I don't really understand the logic behind calculating the area of a hexagon.. anybody mind explaining
why is this not true man 😂
the blue height isn't 4 and even if it were the area would not be 4 + (2*4)*4
where would -pi/4 clockwise be?
what
Well it's a linear algebra question. I'll just post the quesiton in linear algebra
i dont know if this belongs here because in my country we dont use these terms but can someone explain this to me?
this was what i tried (sorry for bad camera quality) but this is not what sin(3a) equals to
(task is to prove the equality)
You need to do some more work, I think it would've been easier if you started with sin(2a + a) then expand
then expand 2a into a + a
sorry for the inconvenience, i looked into it some more and found out that tripple angle formulas exist
and the thing i have in my last line is one of them for sin(3a)
yeah they do
np you didnt say if you were allowed to use triple angle identities
we havent learned them yet sadly
@devout harbor hm i dont see how i could do it with the method you suggested, i tried it out but didnt work
i cant seem to get the pi/3 into the equation
are you just asked to prove that identity?
yea
like u can expand sin(a+b)?
yup
ok thats all u need tbh
yea
expand the sines on the rhs
yeah thats what i went with
just expanded those and then solved the stuff i got
but now i need to prove that sin(3a) = what i made the RHS equal to
and that isnt working out for some odd reason
you should get 3sinx-4sin^3(x) eventually
got it
ty
wait no @dire rampart im supposed to get 3cos²(a)sin(a)-sin³(a)
i simplified the rhs down to the top one
but i cant get sin(3a) to equal it aswell
so dumb
cos^2=1-sin^2
Can y’all help me on this? Maybe give me a private session?
find the coordinates of the point that divides the segment joining (-2,0) and (3,4) into the ratio of 1:2. Ratio is to be considered from left to right.
anyone have like a song or anything to help memorize the, sum to product and product to sum trig things?
yeah I’m not even in geometry anymore but how do you do this again lmao
sin73 = 6.3/x
cause sin of that angle is equal to opposite (6.3) over hypotenuse (x)
okur just making sure
bruh what is it not 9.3
@nocturne grove
I’m TRIPPING hard
make sure your calculator is in degrees not radians
I hate calculators
rip lol
ok I just got like 5 wrong in a row because of that I actually feel bad for my friends
;rotate
what’s the command to rotate
you’re telling me
That is not 1..7
11.7
,rotate 270
i got 11.6 dunno
Yeah I’m gonna have an aneurism why would you actually use 0.600860619 be 0.6
find the coordinates of the point that divides the segment joining (-2,0) and (3,4) into the ratio of 1:2. Ratio is to be considered from left to right. can someone help me?
uh graph it?
but still how do i find the coordinates
@visual mist think about it this way
What is the vertical and horizontal distance between those points
vertical is 4 and horizontal is 5
If I were to guess Id say A
Cause it should be Regular hexagon area minus the all unnecessary parts
what is a in that formula
the answer A
and also how do i find the "unnecessay parts"
Ye I said "If I were to guess" im tryinf to figute out how to get them
oh ok
can't be A cause 6sqrt(3) is the hexagon, 3pi is the area of the 6 half circles of radius 1
but there's an overlap
check out this parallelogram, with that corner of 60 degrees
there are 6 grey copies, and you have a simple circle sector to take out of that parallelogram to compute the area
Is anyone familiar with how to do these kind of problems
@dense sky radius is perpendicular to tangent
Can you help me
which problem
It’s like a retake form
wats dat
Cuz I messed up on a test
@zenith ember is this allowed?
just had a very quick look at the last one and that looks like sin/cos formulas galore
sk is this graded?
oki
Okay then ig ill help you?
id try helping but not home atm sadly
@gritty flare can u use sin and cos formulas for this? yeh right
After samantha confirms i can help

You dont need sin/cos
thats how id solve it
We can't be certain. Helping is a reasonable action.
Alright
A central angle is __ its intercepted arc (degrees)
Do you know this
Its a rule that we cant give you answer directly
so sorry
i wanna know nr 1 now
i dont understand the question cuz not native tho xdd
Dude
Now what is said that:
Central angle is always equal to the arc measure it is intercepting
Please the number 5..
i wanna know

Is it Pythagorean’s theorem
Radius is perpendicular to Tangent line at the point of touching
so ye it si Pythagorean theorem
What is OV then
One sec
👀
Some pythagorean triples which are really helpful to know:
Side-Side-Hypotenuse
3-4-5
6-8-10 (multiplied by 2 3-4-5)
5-12-13
^remember these
definitely
Is OV 5?
Is it 9?
Mm yes
Ok on to number 7
How do I do this
Okay another property
If the radius is perpendicular to a chord it splits the chord into half
Now you should be able to do this
I can’t remember the parts
can i put my answer in spoil things
No
bruh
Some people are impatient and click
yeah fair
What’s the formula .-.
for pythagorem?
No for number 7
There is no formula
Am I cutting 17 in half then doing the theorem?
no
can i say what he cuts in half or should i sh?
Am I doing 8^2+b=17?
thats a good start but keep in mind its b²
DO I CUT 8
and 17²
Okay now
OK is 8 (Distance from centre O to midpoint of chord K)
OA is 17 (Radius of the circle)
By the problem text itself
Ok so..
p y t h a g o r e a n ?


I don’t know what it finds but
Can you write out the pythagorean theorem for right triangle pls?
It’s 15?
no almost
I want you to write it out to understand what youre finding
What do you mean almost?

ignore him he is just making mt job harder
a^2+b^2=c^2?
That is not what I want
What do YOU WANT
use his letters


Ok I see it
help 
write the formula using his letters
AOK WHAT DOES IT EQUAL

pythagorem
with his letters
side opposite of a point(angle) = lowercase of that points letter
18
what
I don’t know
dont guess :(
write pythagorem with his letters and then itll be noice to solve the problem
OK + OA?
wait lemme draw u smth aswell

@dense sky look at the drawing I sent
THEN look at the TRIANGLE AKO/AOK/OKA WHO GIVES A SHIT
then write out the pythagorean theorem for the SIDES
USING THE LETTERS FOR THE SIDES
...
Like if we have a line with one end having point A and second end having point B then that line is AB

Ill send my picture again
Focus on the triangle AOK
The one which is created by the lines AO:OK:AK

AO+OK= AK? ._.
It needs practice nothing else
^
Okay look
Pythagorean theorem: The sum of the squares of the sides of a right triangle is equal to square of the hypotenuse
AK²+OK²=AO²
Now we know OK =8 ans AO=17
OH
AK
8
yes
OH
wat
AK
AB
It’s 34
Wait nvm
So If AK is 15 what is KB
Oh
If AK is 15 what is KB
15


30
yes
8 is the same youll do it
while you do ill see 9
tell me the anewer you get on 8
ye it is 16
Awesome
okay now 9
Alright
Isn’t it just 3-10
Is the answer 7
And is the next one 3
do we ask questions here about trigonometry or #❓how-to-get-help
Both
@gritty flare Dont leave me ;-;
Are you O levels?
??
just asking
What do you mean
Nothing
omg thata a lot
Are you willing to help ._.
You need to try yourself first
Yes but no
Okay
Another thinf for you
two Tangent lines coming from the same point until the touching to the circle are equal
lets say we have two tangent lines coming from point O and touching the circle at A and B
them OA=OB
this should be enough to solve this problem
So
^ Iscoceles triangle
DZ=ZW?
Yes
WHAT IS EQUAL
Okay lemme draw it to you
Yes @vale nimbus
I'm not takin anything I was just asking sk
np
CZ is tangent
Now what I want you to do on your paper is
mark where the tangent line DW touches the circle
and name it some letter name

and tell me what you named it
X
Is this Pythagorean’s theorem
nope
Is their a formula for this
Lemme think
Nope
its not 16
You have to use the property i fucking told you
I wouldnt tell you if it wasnt used


Bruh..
Ye it is 13
Actually?????
But are tou fully sure you solved it
100%
I dont think you understood the whole thing
so im gonna explain now
So I was correct?
Okay
By the property I gave you
ZC=ZN
DC=DX
WN=WX
Do yoy understand why this is?
Yes
Next by the problem DZ=12 and ZC=5 so DC=7
ZN=ZC=5; by problem ZW=11 so NW=6
DW=DX+WX
DX=DC=7
WX=WN=6
DW=7+6=13
👍
Youll be able to solve next one by the same way
Okay did you get thr answer on the next one?
Is it a low number
6
thats correct
Really?
I had the answer for awhile
It was a simple trick to make you douvt yourself






