#help-13
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<@&286206848099549185>
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is $\frac{2\cos x-1}{\sqrt{1-\cos^2 x}}=\tan(x/2)$
XxmastersmithxX
Deep
Absolute value tho
Yup
wym
There should be | | around the tan
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Can someone help me
I do not know how to solve number 3 and 4
how familiar are you with basic trigonometry?
Use definition of tan in a right triangle in order to get expressions for tan(25) and tan(a) in 3
like, SOHCAHTOA
yeah i know a bit
sin = opposite/ hypotenos
cos = adjacent / hypotenos
tan = opposite/ adjacent
I still do not understand
Okay, what would tan(25) be by looking at the triangle on the right?
Ohhhh waiit wait so
tan (25) = h /12??
Yes, can you solve for h from here?
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Thanks for the help !
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I need help with number 3
I keep getting a surd number but when i look at the answers its just a fraction
what have you tried?
we have two equations l + b = 7.9 and lb = 13.5
ahh you have to divide the equation by -1 first and then use the formular to solve for x
you got -x^2+7.9x-13.5 = 0
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no problem😁
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$r^5+r^6=r^{11}?$
hyperlix26
no
what's your question?
maybe find values of r?
alright, so it stays like that
Yel
bruh
Yep
I just wanted to know if that worked
Know the exponent rules!!!
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$a+ar+ar^2$ that's 3a right?
hyperlix26
$3ar+r^2?$
hyperlix26
Ann
hyperlix26
is that it
$$5\times2+5\times2^2+5\times2^3$$
$$= 5\times2+5\times4+5\times8$$
$$= 3\times5\times2+4$$
Is what you're trying to do?
Shuri2060
You seem to have to wrong idea about how to factorise
@wanton glacier Has your question been resolved?
oh wait that's it
you can't separate r and a
so it stays like that
all of the terms have a
so you can factor that out
$a(r^2+r+1)$
hyperlix26
$ar^5(r^2+r+1) \implies ar^7+ar^6+ar^5$ right
hyperlix26
<@&286206848099549185>
not implies.
equals.
And you can check equality of algebraic expressions in wolfram.
,w simplify [a r^5(r^2+r+1) - (a r^7+a r^6+a r^5)]
the heck?
when its not being dumb that is

hyperlix26
Yes, you can check in wolfram (with spaces or on the actual website)
hyperlix26
,w simplify r^5(a+ar+ar^2)
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Hello
For the derivative of e and log, if we apply the chain rule then why do we need ln e or ln a?
cause... that's the derivative
If we have function x^2 and we take the derivative
2(x) (1)
$\dv{x}a^{u(x)}=a^uu'(x)\ln(a)$
Mosh
Yes, why ln(a) is there?
$\dv{x}a^x=a^x\ln(a)$
Mosh
$\dv{x}a^x=\dv{x}e^{\ln(a)x}=\ln(a)e^{\ln(a)x}=\ln(a)a^x$
Mosh
No.
So, here we are applying chain rule thrice. Am I right?
It isn't.
no
once
a^x is a function
u(x) is a function
OH WAIT THAT IS FOR X TO THE POWER OF SMTH
you have a single layer of composition
the derivation of the a^x rule requires chain rule on e^u(x)
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If I were to calculate the log of a scientifically notated number ig 5*10^5 could I simply remove the *10^5, calculate the log of 5 and then add it back in after?
$\log(a \cdot b) = \log(a)+\log(b)$
PapaBread
beat me to it haha
Np
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I need help with vectors, the question just confuses me
idk how you think you were going to do a vectors question with no diagram
@glacial solstice Has your question been resolved?
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im lost
@mighty quarry Has your question been resolved?
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@summer arch Has your question been resolved?
Can we get any context at all?
sure
sorry about that
It's the proof that functions can have only one inversive function
We assumed that f^-1 and g are the inversive functions of function f
what are A and B?
if you want to flip them, it would need to be $g \circ 1_B$, then
phlp
It should work either way. Why don't you try both?
...but the original is correct. g maps B to A, $1_A$ maps A to A, so $1_A \circ g$ maps B to A to A
phlp
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I am having trouble finding the second derivative here. Its a summation of two product rules correct?
Yea
I think I figured out my mistake as soon as I posted it. Just messy handwriting...
thanks for confirming though
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<@&286206848099549185>
This doesn't really look like math
@wet gorge Has your question been resolved?
is formal language theory not a branch of math?
it's in my computer science program as a math class
it seems very similar to set theory to me but idk
Regular expression is definitely not a math thing
You're more likely to get help in a CS server
The notation might be math related but the theory and specifically what property it is relates more to CS
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i cant find any CS servers
There's one in #old-network
.
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help?
,rccw
what is giving you trouble here?
how do i start?
have you worked with piecewise functions before?
nope
so this is your first time seeing a definition like this?
yes
a little
ok great
def f(x):
if x <= -2:
return -4
else if -2 < x < 1:
return x
else if x >= 1:
return x^2 - 1
this is that function definition translated into python (with some small syntax non-conformities)
does this help you understand the definition better
yup ok
are you able to continue from here
do i substitute in -1?
i mean...
yes, if you so insist,
but you have to identify where to substitute it into
based on those case conditions in the function defn
okay, so: which of the following three inequalities is satisfied by x = -1?
x <= -2
-2 < x < 1
x >= 1
the second
okay, and what's the formula next to it in the definition?
x
so what's f(-1)?
-1?
yeah all cool me too
i think they are separate equations
i just checked my answer sheet and it says -4 lol what
yes
hold on what?
oh then the answers are probably wrong right?
are you sure you're looking in the right place for the answer key
yeah idk it says -4
i’m pretty sure it’s -1 tho
thanks for helping me out!
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The supposed answer to this question is 0.65
But to my understanding it should be 0.8
Can anyone explain why?
you're confusing 'independent' with 'mutually exclusive'
So how do you work it out?
P(A)+P(B)-P(A and B)
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Show that angles MNR and RAN are equal.
@fluid swift Has your question been resolved?
MAR or MNR
MNR
Is RA a bisector?
yes of course
DR too?
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@fluid swift Has your question been resolved?
the motive is to prove that the angle bisector of A is concurrent with the incenter of triangle DMN yes !? (interesting 1.1)
Actually it's to prove AMRN is cyclic. (I just don't know how else to do that.)
<@&286206848099549185>
@fluid swift Has your question been resolved?
@fluid swift show that points M A R N lie on a circle
im curious
i dont think they are necessarily cyclic
ping me if u have proof
or at least not enough info from the question to show they are cyclic
@fluid swift post the full info of the question if u have it
(Just fyi they are indeed cyclic.)
I am clueless.
I still can't prove it
I am bad at geometry :(
Is this an Olympiad question?
if I'm not wrong about this, it's probably an entrance level oly question (@_@;)
that's, like, the most useless advice ever
i know srry
Eden anything you tried?
For all I know, I can see anti-parallel lines and recall my oly. camp which I flawlessly bunked [and now rethink my life choices]
I messed around with the circle D for a bit. Found nothing.
Where did you get this problem
IMO 2004 p1 - Maybe this is an xyproblem moment :\
hence proved lmao
not really!! It tends to get like that at times when one's unable (@_@;)
u have a proof?
im imagining ok suppose it is cyclic, then what if I take the centre of the circle to be A'
A' is an angle bisector too, just like A
What's the difference between A and A' then in the construction?
Apart from it being an IMO problem and the GeoGebra calculator confirming the facts, I'd need some more time if you want more proof lol
the construction is as follows:
Consider triangle ABC, draw a circle with BC as diameter, let the circle intersect sides AC and AB at points M and N respectively. Let the midpoint of side BC be D. Let the angle bisector of MDN and angle bisector of angle BAC intersect at R. Prove that AMRN is cyclic.
extend NM to meet BC at G. Maybe you can use menelaus to somehow manage to get the similarity in triangles AFM and NFR or something
@fluid swift If you're not exclusively looking for a geometric proof, maybe this could satisfy you atm:
i dont even know menelaus....
Do you know sine law?
i actually dont want to use trig
so
well
Ah'
yes i can prove using sine law
smh, so bad :c I figured the trig solution
but i dont ws=ant to do that
but just can't find a geometric one
however there being a trig solution implies similarity is due
Oh then replace sine with ratio and prove
Uh I mean don't use sine cos
But instead use ratio side
Lik sin =ab/BC like that
there you go.. just focus on proving this is cyclic lol
i literally have no idea what this is
Nvm
did you just go straight to international math olympiad and dunk it in help
no
lol
this is practice
without ever doing IMO
it's not that tough bm, you could do it with trig easy, but uhh
mate's looking for a geometry soln.
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wait Eden lol
Oh
wow (@_@;)
i claim this
Wait how do I solve it help
.open
.claim 😎
*this
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claim
UwU
lol
to prove ANRM is cyclic
Here
no mine wth,, my channell
..
its looks cyclic already so it is cyclic
except given MRA not ARN UwU
that was what tripped me up earlier
i did exactly what u did
i reduced it to ur diagram
and then was like hey taht doesnt need to be concylic
lol
with trig it's easy to see: sin(AMR) = AR (sin(MAR) / MR) = AR(sin(NAR) / NR) = sin(ANR)
what is S
nvm I step out of trigo
AMR must be 90° no?
👀
wha-
See
why-
what are the implications of this
Look at original pic
AMR+ANR=180deg
implication: AMR + ANR = 180 or AMR = ANR ; but AMR = ANR is ruled out atq
i see
nice>
how to do geometrically T_T
(ansh come help me later ;-;)
prove the sine rule geometrically
and then just use it
or cosine rule
cosine rule works the same here
Oh wut this was so easy there was just a trick to it
original picture ? what? 
clusterfuck
How tf is AMR = ANR = 90°?
I was trying to prove it congruent lol
This
Yeah lmao
TriMCB is on radius of circle
reducing it is the best lol
ok
tbh i think its fine
u use sin rule to prove it
since sin rule is proved geometrically also 
we can join points M and N?
lol
and
it is a isosceles triangle
angle NMR = angle RNM
what is its use lol
nvm
nvm i'll just use trig
i like combinatorics olympiad the most
those are the most fun to me
even tho i suck at those
a question for you as well then
no like geometry
Help me out with this one:
post
I will just store questions to solve later lol
Number of n lettered words made out of n A's and n B's such that the number of A's from the left is at all times not less than the number of B's from the left.
it's literally from international math olympiad
IMO ?
i dont understand the q
..
if you make it out of n As and nBs isnt it a 2n lettered word
"A's from the left is at all times greater than the number of B's from the left."
what does this mean?
AAABB
A's from the left?
type series
B's from the left?
yeah
Like.. AABABAA is valid
because 2A before first B and 3 A before 2nd B
but AABBB isn't valid
ok so n lettered words
because there's 2 A before 3 Bs
yeah
ok
nu 0_0
lol
my first instinct is to write a recursion
hmm so
so we split it into the difference of total As and Bs
the first letter must be A
or for some string that is valid let f(string) by the difference in the number of As and Bs
big hmm
I got nothing but I will watch
so suppose we have n A’s and n B’s in two bags
how many ways can we form a sequence
such that there are always less A’s than B’s?
@fallen heath you have algebra question? I want to see if I can solve lol
or maybe later
Is the solution algebraic or numeric?
we’ve got two counters that can count from 0 to n, how can we always have the left counter displaying a bigger/equal number
maybe this is easier
lmao
lol
So if there are p A's ther can only be p-1 B's or less than that such that it starts with 2 A's
Wait lemme figure one.
ok
cause if you have a valid string
you can either append an A or B to the end of it
to get a string of length n+1
if the string ends with the same number of As and Bs you cant append a B
Shouldn't the string be of n
that's where this chart be comes from
if oyu have a string of length n*
you can append an A or B at the end
to get a string of length n+1
and if the string ends with the same numbers of As and Bs you cant append a B
there you go (@_@;) but I already know the ans. so it's just for gift sake-
that's a recursive way to find the number of ways
quickly
but idk how it relates to a simple formula
(@_@;) if it's a recursion.. maybe I can follow from there
Do you know one that helps here?
nope
im looking at the first row
1 / 0 / 1 / 0 / 2 / 0 /5 / 0 / 14 / 0 / 42
what are these numbers
it's like a pascals triangle
but cut
welp, think about it and lemme knowww (ヘ・_・)ヘ┳━┳
I think I need to revise how sine law was derived in the first place smh
big thonk
i arrived at y² - 22y - 3 = 8√y
XD question's free for anyone..
is there an elegant way to solve this
actually hold on
These are catalan numbers
1,1,2,5,14,42
🤷♂️
how do ;-;
n = 3 is already out of your sequence lol
me dumb
n =3 has AAA, AAB, ABA
.
use bwane (@_@;)
rational root theorem tells me there are no integer roots lol
the recursive formula is:
For n odd:
f(n+1) = 2f(n)
For n even
f(n+1) = 2f(n) - C(n/2) where C(x) is the xth catalan number
so by common sense i do (x² + ax + b) (x² + px + q) expansion
i was looking at what we are subtracting
then do annoying as fuck system
and noticed it is the catalan numbers
XD
*when you realize the solution yourself (@_@;)
i dont care tell me :((
I read on dyck words too.. not the same thing tho
one hint and it'd be out there in the open smh
(the solution)
purchase a shotgun?
im just reading on catalan numbers
wow this is a rly big field of maths i had no clue about ;')
or idk how big it is
but a lot of interesting things to learn it seems
no idea 😦
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lemme know if you figure plz ;-;
I did something similar previously in hs but uh (ヘ・_・)ヘ┳━┳ I forgot how
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What does the number outside of a square root mean? Example:
yea
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can someone help me find a
y = a(x - h)^2 + k
yea so i got everything but a, i tried puting in the given point but got it wrong
yes
ohhh
i got it now! thanks!!!!!
-1/9
no
tf
why you need a girl?
i see you i see you bro
LMAO
we all need some, we kinda down bad huh
send me the problem bro
im two time back to back gold champ
But why? That's weird
@brisk forge stop being weird
@azure canyon Has your question been resolved?
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yo anyone know y we do L = 50 - W?
,rotate
You can, if you want
wait but would it give the same results?
It should
so are they both the right answer?
Yes
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does anyone know how to enter a matrix in mymathlab by code, instead of manually selecting from the menu
when i paste this @MATX{{-3};{1};{1}}, it works perfectly
when i type it out it doesnt work
@copper peak Has your question been resolved?
u can do it in wolfram alpha like {{1, 2, 3}, {3, 2, 1}, {1, 2, 3}} + {{4, 5, 6}, {6, 5, 4}, {4, 6, 5}} for example
or symbolab with
\begin{pmatrix}2&3&4&5\\ 6&7&8&9\end{pmatrix}```
MattDog_222
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
BritS
$\begin{pmatrix}6&9&6&9\\ 6&9&6&9\end{pmatrix}$
There you go
yeah but these dont work in mymathlab which is my homework website
and entering it manually from the menu is very tedious
mylab math
that doesn't show the code
yeah it doesn't
||Why did I see these numbers?|| <-- ignore this
nope
this works when i copy paste it
MattDog_222
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its more subtle now
so maybe i have to add something before it?
could try \[\begin{bmatrix}3&3\\ 23&46\end{bmatrix}\]
MattDog_222
or dollar signs $\begin{bmatrix}3&3\\ 23&46\end{bmatrix}$
MattDog_222
Try writing [[6 9][6 9]]
doesnt work
i tried it
there must be a way
idk im just fishin, [1,2;3,4]
no lmao
okay i give up
thanks for helping tho lol :)
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Hi,
I have no idea how to solve this sum. I tried making a triangle with an angle 30 at the corner but it hasn't worked. Could someone please help? Thank you
Right, so um the triangle ABC is equilateral correct?
yes
all are 60
Correct.
Since the triangle def is formed by lines parallel to the original triangle, they both should be similar
True?
ya
So each angle of def is?
all are 60 even the inner ones
yes.
Since the original triangle had sides equal to 10cm, and new one has 1cm less in all directions.
Shouldn't each side be 2cm less than 10?
It's not I think, still.
it's not that simple unfortunately
Where the perpendicular is 1cm.
Label the points it'd be easier.
So we get the base √3 in this smaller triangle, no?
Same for all other sides?
Yes
Since equilateral triangle is a regular figure.
So yeah new sides of this triangle,
Shouldn't they be like 10-(2√3)
In cm.
Oh so
30 - 6root3 then?
I believe.
You're welcome!
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I figured some stuff on my own too.
First of all we have the general form
ax²+bx+c=0
Where a,b,c are odd and integers.
a≠0
Also if the equation has unreal roots that proves the thing easily, so we will talk about real roots only.
So ∆≥0
Also, for rational roots, ∆ must be a perfect square of a rational number.
So we have to contradict this.
also ∆=b²-4ac
b² is odd, 4ac is even, ∆ is definitely odd.
Also, b a and c are integers, therefore ∆ is an integer.
Let ∆ be square of some integer $\sigma$
Sakata Yaksha
Sakata Yaksha
$\sigma^2=b²-4ac$
Sakata Yaksha
$4ac= b² - \sigma^2$
Sakata Yaksha
b and sigma both are odd therefore their difference is even. This is what bugs Me, we had to contradict this from happening.
@dusty hazel Has your question been resolved?
<@&286206848099549185>
@dusty hazel Has your question been resolved?
I suspect if you take this mod 4, the result might come out
Oh thanks, finally someone saw my question.
or some other mod if not thay
Mod 4 is simply four though, and that's what I wrote.
what?
Elaborate what you meant please, I didn't follow.
consider cases in modular arithmetic
It doesnt work for now, actually.
But thats the first thing that came to mind
Ah ok, I can see a factorisation
Right.
Youre not stuck here.
Am I not?
I can factorise that surely.
Also b and $\sigma$ are odd.
let $b =2k+1 and \sigma =2h+1$
what?
I mean
I got till here.
You literally wrote it in this form
There is an obvious factorisation to do here, surely.
Sakata Yaksha
right.
I also concluded
Then there should be cases to consider in modular arithmetic or similar
b and $\sigma$ are both odd.
Sakata Yaksha
Both b - sigma and b + sigma should be even
I have to prove this using basic stuff nothing that fancy.
Correct, we are contradicting though. Please read all my previous messages if you can, I'd appreciate it. I concluded lots of stuff, and it'd make us all understand what I am approaching and what I should have done if that's now what I should have done.
So, the statement you have started with - does that have any counter examples?
If you're arriving at a contradiction then the statement might jot actually be true
I mean I have to prove it does not have rational roots, so I assumed it has rational roots. Now we're contradicting this.
Let me try something and then come back if I find something
Sure, thanks!

do we not get a contradiction mod 8?
What's that?
have you seen modular arithmetic?
Like I told, that's not what I can use in this question.
I'm asking, I haven't tried btw
Also, I have not.
are you sure you can't use it?
why
My bad.
modular arithmetic is no different from essentially considering remainders
you can literally do this with just the numbers and it makes no difference in logic
you should lookit up
modular arithmetic
quicker
than me saying
Look on brilliant or similar
Numbers mod 4 are 0, 1, 2 or 3 for example...
mod 4
I thought that was |4|
Absolute value function.
I'll google it real quick then.
@dusty hazel Can we prove the discriminant of the new equation with k as variable is less than zero?
And even if it is not less than zero, it is not a perfect square?
They are talking about congruence
Like
8 = 0 mod 4
13 = 1 mod 4
Yes, I got it.
We use mod only and only for modulus generally.
So I didn't know earlier.
Yes it's not necessarily a perfect square, true.
But if it is a perfect square, the roots are automatically rational.
If it's less than zero we have a very solid proof
Yes indeed.
And I meant the discriminant of the newer equation
The last discriminant in this paper
I'm extremely sorry, I did not see this at all. I'll check.
Yes, I was about to say.
Let me do it from scratch
Hey
The first one was correct
k²+k+4ac...
I'm sorry for confusing you
Exactly
Yeah lol, also this is exactly what my proof looks like.
Here.
Just we use 2k+1 and stuff for odd integers now.
Yes, I just assumed your a as 2a + 1 so I can make it necessarily odd from the start 👍
I'm not saying modular arithmetic necessarily helps btw. But it is something worth trying
I just saw what it was, although I'm not aware of it's applications.
You told to use mod 8 though, correct?
squares cannot be 3 mod 4 for example
didnt work though
yes mod 8
To make some parity argument
Sakata Yaksha
$4ac=(b+\sigma)(b-\sigma)$
Sakata Yaksha
Ohh lol I figured it out maybe.
If only this is correct, I'll be done for the day and sleep nicely.
Yes, I'm very positive I did it.
!!!!!!
@jaunty mural thanks, 8 really is a good number.
@limpid plume thanks, for your help.
So we prove this like this
The difference of squares of two odd integers is a multiple of 8!
While on LHS we have 4ac, where a and c are odd.
Which contradicts.
I just proved this too.
That's exactly what I found just now, it's in a Number Theory course I did a few months back
Also
Alternative proof I justade
Made*
Yes, sure I'd like to have a look.
$4ac= 8n$ as $b²-\sigma^2$ is always a multiple of 8.
Sakata Yaksha
We get, $ac=2n$ which is never possible as a and c are odd.
Sakata Yaksha
👌
I apologise for bad handwriting
Thanks, I'll also look everything about modular arithmetic today.
Bad handwriting, that's the reason I use the bot XD. I'm no good.
Competitive exams have done so much harm to me it's not even funny anymore
Not only it gave me depression at one point, it also made my handwriting bad an my ability to write subjective answers bad
MCQs are just not the way to live 😭
Hmmmm, you're Indian I assume? (A very random guess, no offense)
I see, I'm checking your proof, we'll have our talk then.
Yes, your proof was all worth it.
Thanks mate.
Now, let's take this to dms and close the channel as we're done here.
I wrote some letters wrong in the last I think, but you got the idea right?
Yes.
Yes, pqrs all odd. So yeah I got that.
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I did something wrong here, but I don't know what:
sin(2x) = 4sin(x)
sin(2x) - 4sin(x) = 0
sin(2x) = sinxcosx + cosxsinx = 2sinxcosx
2sinxcosx - 4sinx = 0
sinxcosx - 2sinx = 0
cosx - 2 = 0
You divided by sin(x)
Is that not permissible?
you only can divide by something nonzero. So if you divide by sinx, you also need to deal with the case that sinx=0
you also need to deal with the case that sinx=0
Why's that?
cause sin(x) is a factor of the LHS...
apply zero product property.
ab=0 iff a=0 or b=0
you get sinx(cosx-2)=0 so either sinx=0 or cosx-2=0
ah that's true
well cosx-2 = 0 can't be correct because cosine can't be greater than 1
yep.
Yes, sin(x)=0 when x=pi*n, n in Z
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guys can somebody explain to me how this was simplified?
Change tan(x) to sin(x) / cos(x)

