#geometry-and-trigonometry
1 messages Β· Page 256 of 1
i guess 1 degree
Bro I dont know
it doesnt say
$\tan(1)$ or $\tan\inv(1)$?
best way without calculator is just messing with identities
RokettoJanpu:
the right one
you got this then
what is the best way
ok
ask yourself what angle between -pi/2 and pi/2 is such that tan of that angle produces 1
sin/cos
so if sin/cos=1, what does that imply
yes
what is a
b*1
so a = b
yes
do i need the unit circle memorized for this
kind of
crap
not really tho if you know your special right triangles
hint: it involves pi
Nah im just going to open a new tab
i have the degrees memorized just not the square roots
Its 45
π
bro dont roast
oh ok
so i have to memorize the square root part of the unit circle to do these
Can anyone help me with this? been trying it out myself but I can't even finish it without getting a super crazy number
try this
$\sin^{-1}(- \frac{3}{5}) = \alpha \
\tan^{-1}(\frac{2}{7}) = \beta$
holy shit
Cytis:
make this substitution
I've done that for the difference of sine
what did you get
i have no clue how to do this
WAT
when you do what I told you to do, you should just get this
$\sin{\alpha - \beta}$
Cytis:
okay so sin (a-b) = sin(a)cos(b)-sin(b)cos(a)
use the sin subtraction identity
yes
and then evaluate each term individually
in order to do this
you have to know the domain of your inverse trigonometry
yeah I am lost with finding the domain of the inverse.
So is this where I find out which quadrant they are in?
so a = Q2 and b = Q1
Okay, so I've been trying to figure out the rest of this and im having trouble with the 2/7 part. when completing the triangle I keep getting sqaure root of 53.
Im just not sure if im doing it wrong
so it would be (-3/5)(7sqrt53/53)-(2sqrt53/53)(-4/5)
I think I know where I messed up.
Thanks for the help @cinder portal and @rich wolf
the (-4/5) is supposed to be (4/5)
Ann:
π¦
@plucky jacinth what is giving you trouble here?
all of it
0
does the mnemonic "SOH CAH TOA" ring any bells
it's a definitional mnemonic. the one exception.
no i have not been to school for 2 weeks
have this, then.
@cinder portal so with a calculator I got -0.79 etc and without using one I got 94.64 for that problem you were helping me with
so 94.64 is better to use
I hate using calculators but I use them to reference what I should aim for in an answer, should I not be doing that?
actually try to compute each term
you can do it without a calculator
and the answer comes out incredibly nice
symbolab 
@rich wolf what are those?
don't bother with symbolab. it's crap.
Say what you want about symbolab but its free
it's free crap.
Photomath also works
WA is of course top tier
what is WA
But sometimes you dont feel like matching your grouping symbols
Also kind of expensive
@compact spire it is an easy way to get answers
But dont use it unless you're really stuck on something
Im really stuck on all my homework im doing because school is cancelled and my professor is leaving us to learn everything on our own. But thank you all for the help so far. I greatly appreciate it.
OMG
I think I got it
(-3/5)(7sqrt53/53)-(2sqrt53/53)(4/5) = -29sqrt53/265
@cinder portal
looks correct
YES!
compare it with ur calculator
nice
Thank you so much
no need, u did all the work
Is there a limit of help I can ask for?
@compact spire no more than once every minute
Okay
so im pretty sure I just sub the tan-1x for a and sin-1y for B and do the difference of cosine
yup
which has me at cos a cos B - sin a sin B
oh really?
I thought since it was minus it would be minus, is it the opposite of what is shown?
well you WILL need to simplify $\cos(\arctan(x))$, $\sin(\arctan(x))$, $\cos(\arcsin(y))$ and $\sin(\arcsin(y))$
Ann:
simplify?
Okay
$x = \frac{x}{1}$
Cytis:
that's the hint for ya
how do you mean?
i mean exactly what i said
if you had marked the angle arctan(x) in your triangle, you'd be able to find its sine and cosine with ease now
Im sorry, my brain isnt processing so well. been working like crazy
Okay, I think I got it
$frac{sqrt{1-y^2} + xy}{sqrt{1 +x^2}}$
Pony Boy:
\ \ \ \ \ \
Was trying to learn but didnt workout
you droped some of these
$\frac{sqrt{1-y^2} + xy}{sqrt{1 +x^2}}$
Pony Boy:
Pony Boy:
Okay, thats what I got.
ok so this actually was alright and it really did only look sus and that's it
Is e the ans
Is e the ans
@dense trail π¦
Is e the ans
@dense trail the ans is c
Are there any relation betwwn the radii of the circle
Are there any relation betwwn the radii of the circle
@dense trail idk
Its not working
Okay im back, does anyone know what I should google to learn how to solve this problem? I have 0 clue on how to solve this
@compact spire use a graphing calculator
I don't have one.
so .14 and 3.0
Thanks for the help @rich wolf
the formula is 2sinxcosx
=2(3/5)(4/5)
=2(12/5)
am I on the right track?
That's exactly right
=24/5 ?
Oh oop. (3/5)(4/5) = 12/25
You can also use a calculator to confirm the answer. It is correct here.
Awesome, thank you
okay so half angle formula would be cosx/2 = +- sqrt 1+cos2x/2
I tried
Pony Boy:
$ cos(\frac{x}{2}) = Β± \frac{\sqrt{1+cos(x)}{2}$
```Compile error! Output:
! File ended while scanning use of \frac .
<inserted text>
\par
<*> 98531807913349120.tex
I suspect you have forgotten a }', causing me to read past where you wanted me to stop. I'll try to recover; but if the error is serious, you'd better type E' or `X' now and fix your file.
If x is 45, then the left side is cos(22.5) which is what we want
You could try it, but you'll find quickly it doesn't work here
Okay
so Β±β[(1+cos(45))/2]
do I just plug this into a calculator?
wait
cos of 45 is just β2/2
so = β[(1+β2/2)/2]
Yep, that's a way you can express it
You can clean it up a little by multiplying numerator and denominator by 2
$=\frac{\sqrt{2+\sqrt{2}}}{2}$
Pony Boy:
Yus that works
double angle identities no bueno?
Well I was supposed to learn double and half angle this week but schools been cancelled so im trying to learn on my own
Nothing you aren't capable of. That Β² should scream "quadratic" at you, so see if you can get rid of the cos(2x)
Does anyone know this one?
yeah
If you're lit with your unit circle, that should ring a bell
pi/6
Also [0, 2Ο) solution range
You're correct with Ο/6
The other would have been 11Ο/6
can someone please explain to me why these are parallel, coplanar lines? https://i.imgur.com/kBH8GFe.png
this hurts me
i have 2 hours to take and turn in a test i have no idea on how do this
were you asked to round to ten decimal places
yes
to ten decimal places?
I am getting 64/40 can someone check?
@plucky jacinth ANGLES should be rounded to the NEAREST DEGREE, and even otherwise there's a BIG DIFFERENCE between "TEN DECIMAL PLACES" and "TO THE NEAREST TENTH"
so 49.5
49
to the NEAREST DEGREE.
there we go
rounding Ο to the nearest tenth gives 3.1
while rounding Ο to ten decimal places gives 3.1415926536
just so you know
35
$$\tan(\theta)=\frac{opposite}{adjacent}
Jaboi:
Compile Error! Click the
reaction for details. (You may edit your message)
soo arctan(27/38)
so the thing here i want you to do is to draw what is given
@plucky jacinth
if you can, take a picture of your drawing with the given dimensions in the right places
sin68 x/15
$$sin(68)=\frac{x}{15}
Jaboi:
Compile Error! Click the
reaction for details. (You may edit your message)
how would i put that into a a calculator
@paper mauve \sin
@plucky jacinth you wouldn't, unless you're allergic to algebra you should be able to solve this rather simple equation for x
$x = 15 \sin(68)$
Ann:
so I googled double angle identities and I have 3 options I guess for cos2(x) so I can use 2cos^2(x)-1
is that correct?
@dark sparrow ty
$2cos^2(x) - 1$
my answer from my problem was -7/25 can anyone confirm that for me?
Pony Boy:
$2(\frac{3}{5})^2 - 1$
Pony Boy:
$2(\frac{9}{25})-1$
Pony Boy:
$\frac{18}{25}-\frac{25}{25}$
Pony Boy:
$= -\frac{7}{25}$
Pony Boy:
Can someone help me with reducing cos^4(x) to the first power?
Can you reduce cosΒ²x into first power ?
wait, you want linear terms with the same angle i.e x and not like 2x or sth?
My professor never taught us anything like this so I'm trying to learn on my own since he can't
Isn't $((1+cos2 x)/2)^2)$ a valid answer then?
Vatsal:
How would I get rid of the fraction in that situation
because it says to factor out all fractions
so $cos^2(x) = \frac{1}{2}[1+cos2(x)]$
Pony Boy:
that's correct?
yes
okay so if it were the fourth power it would just be
$cos^4(x) = (\frac{1}{2}[1+cos2(x)])^2$
Pony Boy:
Yea exactly
Pony Boy:
which I need to get rid of as it says in the problem
how would I go about doing that
or am I just overthinking it
I have a strange question.
When I was looking at how Archimedes approximated Pi, I was wondering about a few assumptions.
When he was inscribing and circumscribing a circle with polygons, how can he assume that the circumference is between the two perimeters?
I can also draw a picture like this.
In my 2nd diagram, you can easily see that the white perimeter is way bigger than the outer square.
If he were comparing the area of the circle with the area of the two polygons, it would be obvious to understand, but Iβm troubled that he used perimeters instead.
Can anyone help me in any information or step Iβm missing?
bisecting and intersecting chords theorem
We are given 2 radius's and the distance between centers, no other information, how do I find the area of the intersection?
can u send the full qn
Hi, can someone help me out with this triangle? I'm given the angle in A and told that the bisectors of B and C intersect at I (incenter). I have to find the angle BIC.
,rotate
nvm
hey, so i have a quiz on circles coming up, would anyone be able to help me find the answers while im doing it? would highly appreciate it since theres some very smart ppl in here
no
we will help you understand the concepts before the quiz
but while you're doing the quiz you're on your own
Is there any comments on how you should do it?
No
Then, just plug it into the calculator if you don't need an exact form
Wth
hello friends
i have a kind of dumb question
how exactly is multiplication and division defined geometrically
i've been thinking about the tangent function
and how it is sin/cos
i get that sin is vertical
and cos is the horizontal part
but what does the tangent of that tirangle look like
how exactly is multiplication and division defined geometrically
wdym
Space Pirate Wesley:
but what does the tangent of that tirangle look like
@ionic bluff
The tangent is the slope of the terminal arm
z2 - z1 is the line AB
ye
z3 - z2 is the line BC
When you divide one complex number by another, you subtract their angles
That is,
Arg(a/b) = Arg(a) - Arg(b)
I'm not crazy certain what the arg of either is
Hi. I have some struggles with proofs in coordinate geometry. From the textbooks I saw, it seems to be common practice to only prove statements in the first quadrant. So, for example, say I wanna find general equation for a line that has intercepts with axes of x and y at a and b at the respective axes. Then its equation will be:
$\frac{x}{a} + \frac{y}{b} = 1$
TimkaSolnze:
And almost always, when authors prove it, they 1. Pick up a line that has positive a and b intercepts, 2. Pick up a point on the line that is in first quadrant.
I want to know, why do they do so? Is there's a reason why we don't have to prove statements in other quadrants? Does proof in the first quadrant immediately applies to any other quadrant? Is there a shortcut(s) for proving for all the quadrants and their combinations(i.e., say a line might occupy 1, 2 and 4 quadrants, or 1, 2 and 3.)?
there's like 6 problems here all with multiple subproblems
So its cos(90-35)=sine 55
which one are you talking about
yes
My workings r all not relevant to question
can you do anything/ apply any identities to:
cos(310Β°)?
Not to my knowledge
express in terms of relative angle?
not -
thats just cos50
^
Z
cos is positive in fourth quadrant
Rite
which gets you: $\cos^2(50\deg)$
ramonov:
and you should be able to get the required answer now
Idgi
idgi?
how ironic
whats the question actually
3ii
3ii
here you can apply something very famous
i cant read it ;-;
those most common trig identity
which is essentially pythagoras
$\sin^2(x) + \cos^2(x) = 1$
ramonov:
because you know sin(50)=b
you had sin(40Β°) = cos(50Β°) right?
Yes
and we established just then that cos(310Β°) is also equal to cos(50Β°) right?
Yes
so there is your cos^2(50)
oof
which gets you
cos(50Β°) * cos(50Β°) = cos^2(50Β°)
cos(310) = cos(-50) = cos(50)
cos is 360Β° periodic and even
Oh ya cuz in
Then 4th quad
Everything becomes pos
Cos(50) =/= b or a
Sine 40 =/= b or a
Sine 40 isnt b or a in the question
so the whole expression becomes cos^2(50)
which gets you
cos(50Β°) * cos(50Β°) = cos^2(50Β°)
^
They want me to express the equation in b or a
that is what we're trying to do..
$\sin^2(x) + \cos^2(x) = 1$
ramonov:
$\sin^2(50\deg) + \cos^2(50\deg) = 1$
do you see a or b anywhere there?
aw cmon
hah
Sine(50)=b
custom tex π
Sine^2(50)= b
no
no
B^2
still questionable
^
math is case senstive
lol
b^2
Haiz
and what's your final answer
lowercase cos but seems ok
Thanks
Not at all.
do you think you could explain it
Sure, the formula you wrote for a cosine of an angle works only for angles between cathetus and hypothenuse
YO! do i need to calculator to find the max of y=2cos^2(x/2) in the closed interval from -Ο/2 to 3Ο/2?
No. Think about the shape of the cos(x/2) graph and where it would be a maximum then work out what the maximum y value for your specific function would be in that interval
I donβt understand the law of sine
Beef101:
What do you not get?
A better way to phrase it in English is that the law of sines states "the ratio of any side and the sine of the opposite angle are the same"
Since you already have the triangles labelled, you can just plug values into the equation
Lets look at the last triangle you posted
Ok
Wait, you did it correctly
Wait for angles is it b/B sin
And for degrees is it B/bsin
Or is it the same for both
Opposite over hypotenuse
Wait for angles is it b/B sin
@rapid pollen
Yes
I meant what is this referring to? Sin has no argument
I mean for the equation a/sin A= b/Bsin
b/sinB?
Oh it is
Yeah, this is correct
Iβm just tired I should go to sleep lol. Iβm studying for pre calculus after trigonometry whatβs next?
Law of cosines if you didn't learn it yet
Then, you will probably learn about graphing trig functions
Is that the same as law of sines
Uhhh, yeah
Sounds great π
Is there more info?
yeah thats what i think it is
Wdym think
also poco this one
That is the answer
Try it yourself first
So the stuff entered is what you think is correct
What is arc WTU
230 degrees
So do you know any theorems relating an inscribed angle to the arc it intercepts
ok wvu would be 115 correct?
yeah the intercepted arc is half the length of the arc length right?
Should be
Please stop pinging me for every question, expecting me to be there
He already got it
Would this be a case of alternate interior angles?
And the line is not tranversal right, it would have to be a straight angle
So the sum should be 80 + 30?
,rotate
sorry about that, cool bot though
And the line is not tranversal right, it would have to be a straight angle
what's that in reference to
that'd be 2 separate lines
yes
y is 80, x is 30
ty
there's a theorem here that says alternate interior angles formed by two lines cut by a tranversal are congruent if and only if the lines are parallel
so I wonder how does the problem I Showed you relate to this
Does anyone have a decent proof for this? (I couldn't find out how to place arrows above letters but a and b are vectors in the second half of the equation)
Are you asking why half of the length of cross product equals half of the area between two vectors?
Uh, well. My teacher just showed us that the area formula for a triangle can be rewritten as half of the vector product of a and b
And I'm trying to find a mathematical proof for that
Basically, cross product is defined to have a length of a parallelogram between those two vectors and if you connect any two opposite points of a parallelogram you'd divide it in half(because two those triangles are equal because their sides are equal).
area* not length
Or that formula could be proven without cross product. Just take a regular formula with triangle height and express that height using sine.
magnitude of cross product = area of parallelogram
oh and 1/2*parallelogram is a triangle
Sure, I never said length of a parallelogram, I've said length of a cross product.
Basically, cross product is defined to have a length of a parallelogram between those two vectors
lol
Lol, how did I write that, hah
Nah, what I meant is that a vector of a cross product has length equal to the area of that parallelogram.
oh and the cross product of two vectors yields a perpendicular vector?
is that a given?
Yep, that's part of a definition
wait but how is that relevant here? Is it? lol I'm confusing myself
Nah, in that case we don't care at all where our vectors point.
can someone give me SOHCAHTOA problems?
gimme a moment.
tnks bro
i'm not your "bro". and would prefer not to be addressed as such.
anyway, here
make sure to read the instructions carefully.
if you want to check your answers then pm them to me indicating which problem you're giving me the answer to. but do take note that i can and will reject answers which are not properly formatted. you may omit the degree sign in problems that ask you to find the angle.
ok ok thank youu
Can anyone help me with my math soon
I took a look at it before, had a lot of trouble with it, took out the dog and Iβll be back soon
wdym by "things like"
the two i stated
i mean, tan(-ΞΈ) = -tan(ΞΈ) for all ΞΈ where both sides make sense
but if you didn't know anything about tan, then you could not say automatically that negating the input and then passing it through the function would just so happen to produce the same result as passing your input through the function and then negating the output
So its similar but diff
...
tan(-ΞΈ) and -tan(ΞΈ) are EQUAL.
functions for which this thing works are called "odd functions"
A1bi) if they question asks for -tan(theta) steps wld be same?
"the" steps?
Working
if they asked for -tan(ΞΈ) then maybe you could cut the step where tan(-ΞΈ) is replaced by -tan(ΞΈ) out of the solution
so maybe no the exact set of steps could differ
What the heck
you ask a stupid question you get a stupid answer
:(
"what's the difference between these two things that are actually the same"
"would The Stepsβ’οΈ differ for these two superficially different problems even though each problem admits multiple different sequences of steps to solve it so the question as stated just doesn't make any sense and there is no constructive answer to it"
consider that you can calculate the lengths of DB and EB
EB is the opposite side of triangle BDE
and 8 is the hyp
so u should use $sin25=\frac{8}{EB}$ and solve for EB
Hmm:
@storm cave
Ohhh I see! Thank you!
:))
yes EB
For EB?
it's $\sin(25) = \frac{EB}{8}$
Ann:
fuck(
8 is the hypotenuse.
REEEEEEEEEEEEEEEEEEEE
hahhahhahhahahhahaha i am rart
sure
thanks st. big brain ann
The answer is -0,016... I doubt thats correct.... Is it my calculator?
Hmm:
hehe
,w calculate sin 25
,w calculate 8(sin25)
there u go @storm cave
It's my calculator.... Sin(25) gives me -0.13
Any idea how to fix that?
TI-84 Plus
Also thank you
Radian
its supposed to be in degree
Ohh yes I see, thank you!
Wait do I need DB to get A?
yes
wait i thought u were finding a length mb
ignore the subtract part
after u find AB use cosA to find A
isnt it tan?
You're good, thanks for the help man :)
sorry for fucking up my ratios so badly omg
It's fine man, ty!
Last one
If C1 has r = 2 and C2 has r = 3, how do you go about calculating PS?
i have literally 0 clue what this is asking me to do
lel
Yo nvm had to inverse
@storm cave what have you tried
nothing much.... I dont understand it at all
do you know what similar triangles are or trigonometry
,w calculate sin(25 rad)
then what is it?
i graphed both on desmos and its a mirror
thats not very helpful by just saying im wrong
must've put in a different equation my bad
Lmao
f(x) =1,5x-18
g(x)=0.5x+6
how can i calulate the angle?
Does anyone know how to do this? I got it wrong and I have no idea how to to get -5,7
I think I can help, imagine a coordinate grid, and the point (3, -1) on it, if we reflect it across the line y = 3 (a horizontal line that crosses (0, 3)) then we just take the distance the current point is from the line and move it that length away in the other direction
That's not a great explanation, but in this case, since the y value of (3, -1) is 4 away from +3, the new y value is 4 away on the opposite side of the line
(3 + 4 = 7, so the new point is at (x, 7)) then do the same thing across the vertical line x = -1
@wind heart feel free to ping me if you need any further assistance :)
Oh thanks sm!
@loud pike ?
btw here's a geo problem it's kinda competition math
Solution:
||So what I did was first make the square into a 3x3 grid. The total area is 9. Then, I drew the diagonal from the top left to the bottom right. That diagonal will divide the square into 1/2, so you know that the non-hashed area divided by that diagonal is 9/2. Then you want to find the area of that trapezoid, so you set up two equations:
y = -x + 2
y = -3x + 3
Solve for the system of equations:
-x + 2 = -3x + 3
2x = 1
x = 1/2
y = 3/2
Now, find the distance from that to (2,0), which is root(2)/2.
The other side is similar, so you subtract the 2(root(2)/2) from 2(root(2)).
You then get root(2). That is the first base of the trapezoid.
You can get the second base, which is just the diagonal, which is 3(root(3)).
If you have the grid drawn out, you can recognize that the height of the trapezoid is root(2)/2.
The average of root(2) and 3(root(2)) is 2(root(2)).
Now, multiply root(2)/2 and 2(root(2) to find the area of the trapezoid.
You get 2.
9/2 + 2 = 13/2
(13/2)/9 = 13/18
But don't forget that we have only calculated for the non-hashed out area!
The final solution is 5/18!||
That's awesome, I'll give it a go, wish me luck
Can anyone help me Iβm stuck.
is the tank meant to be cylindrical
I believe so
yup
and it stands to reason that 15 ft and 20 ft are the dimensions of the interior of the tank
ie the part that actually holds water
15-ft in diameter and 20-ft tall.
so really it's a cylinder with a diameter of 15'1" and a height of 20'1" with a hole inside shaped like a cylinder of diameter 15' and 20'
1 inch bc the half-inch of steel contributes to the diameter and height on both sides
anyway, with that in mind, you should be able to figure out the volume of steel used in the making of the tank
yup
yeah ofc i'm leaving the specific calculations to you
in part bc i'm a bit too lazy to do them
ππΏ
so i don't think i can check them if you send them to me
it fine, thank!
alright yeah i guess i'm gonna have to ask for help again lmao
let Ξ±, Ξ² and Ξ³ be the angles of a triangle. prove that sin(Ξ±)sin(Ξ²)sin(Ξ³) β€ 3sqrt(3)/8 and find all triangles for which this inequality becomes an equality
i have a hunch that equality holds iff Ξ±=Ξ²=Ξ³=Ο/3 and i've tried naΓ―vely applying am-gm but this didn't really get me anywhere productive
i have... this?
where a, b and c are the sides of the triangle and S is the area
but honestly i have little to no clue how to progress
i've got another four of these angle inequality problems and honestly i'm just as stuck on them as on this one
hang on
i think i have an idea.
yeah nvm, i solved it.
turns out jensen's inequality did the trick lmfao
how can I prove that x is 35?
the remote interior angles on the left should be 60 + 70 = 130, but that won't work.
x = 35.
what's known about that angle next to x
yeah man
the middle line is not even straight, so it doesn't seem like a bisector.
the middle line can be swung back and forth as much as you want within that triangle, and x will change but none of the other data will
so you MUST be omitting some info
can you show the problem exactly as stated
ok yea this question is broken
lol
who gave you a question in the format of ms paint?
I copied it from my book.
ms paint is just useful as hell for this lol
would be nice for a more professional software
so you drew this, it's not the original problem
you really should take the advice that's given to you and take a picture of the problem
lol I drew it exactly but ok I'll take a picture
its fine, we cant track where you are when you send a pic
Number 11
lmao

they make a lot of spelling errors in this book, probably rushed
ok now I'm stuck on #17
I don't see same side interior angles, corresponding angles, alternate interior or exterior angles
I tried using the remote interior angles trick
that doesn't help either
^ did you get x?
no
I saw the answer in the book but no
I don't think y is 30 though, it could easily be 20
by same logic
well x is alternate interior to the 30Β°
are you able to spot it after i tell you?
ah yeah I see that
and then to find y, consider the external angle theorem
and/or angle sum of triangle + angle sum on straight line
thanks
Need some help: is sin(wt-phi) = -sin(wt+phi)?
it doesn't quite work with phi=0 for example
Oh yes, the geometry question
@timber coral how would i go about finding the locus
it's just a quartercircle
right
I'm trying to find the equation of the hyperbola: Foci (0,-8), (0,8); difference of focal radii is 10
I've been looking online for hours on how to solve this problem and all I can muster up is that apparently C = 8, which means that A = 4. But 64 = 16 + B^2 makes B = positive negative 6.92820323028 please halp
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