#Trig (simple stuff for you)
485 messages · Page 1 of 1 (latest)
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@shut marten
Also I did ex 4 I need to solve the determinant and got x^3+x^2-10x+8
Is there a easy way to solve this
This cubic equation =0
Well, what would a be if x=2pi/3 is one of the solutions?
You can try the rational root theorem.
Just try to plug in x=2pi/3 into the equation.
And what I get
Is there a reason why I do that
And also does it affect if I have || on coax
To find a.
Well, remember the formula for cos(2x)?
Oh yea double how stupid I’m
:)))))
No I don’t know that thing
Let me check on google
But there are many formulas
How do I know which to apply?
2cos^2-1
Also, you should probably learn it, it's one of the basic ones.
Yes. Don't forget the argument, though.
It’s not like I use it every day
That's not the point.
So, we have:
4|cos(x)| + 3 = -10(2cos(x)^2 - 1)
Let me write it
Now, for real t we always t^2 = |t|^2, right?
Yeah, that works.
Ok and t applys from when ?
Yeah! Since cos(x)^2 = |cos(x)|^2, we can just take t = |cos(x)|.
And we're left with a quadratic equation.
Like the domain
Worry about that later.
Range, rather.
Anyway, you can just find t first.
I’m gonna be working it out here, don’t look at the spoiled stuff. ||4t+3=-10(2t^2-1)||
Right.
Now we return to this. Your thoughts?
T=-7/10 and t=1/2
||20t^2+4t-7=0||, ||20t^2+14t-10t-7=0||, ||2t(10t+7)-(10t+7)=0||, ||t=1/2, -7/10||
Good.
Well, t = |cos(x)|, so what values can t take?
Positive
No.
Why no
There are certain bounds.
Yeah.
Has to do with the range of |cos(x)|.
Ok and
Well, what is it?
We got the solution
We haven't solved the problem yet.
And we need to see the values that cost can take right?
Yeah, but maybe one is extraneous. So we have to rule out if they’re extraneous using the range of |cos(x)|, since that’s how it would work.
From -1 to 1
That's cos(x).
Not necessarily.
What about |cos(x)|?
Yeah.
0 to 1 lock in
More specifically, [0, 1].
Yes
So, which value of t works?
No, I get that, but which of the ones that we got?
From the solutions of t earlier.
Only 1/2 but my question is why -7/10 wouldn’t work if is modul
Because the absolute value can't be negative.
So, now you just need to solve |cos(x)| = 1/2.
How
You can start by squaring both sides.
(Or you can take plus or minus on both sides.)
Or that.
We set cosx=t
Now we want x.
The solution will look a bit nicer if you square, though (two series instead of four series).
No.
No, we took t = |cos(x)|.
And this didn’t affect the cos^2x?
No, since |x|^2=x^2.
As I said, start by squaring both sides.
Cos^2x=1/4
Right.
Now you can use the half-angle (or power reduction, whatever you like to call it) formula for cos(x)^2.
You need to review trigonometric identities.
Yes...
Ok and now subtract 1?
Yes.
And now
And now it's an elementary trigonometric equation.
Cos2x=-1/2
Yes.
How to solve
Uh...
You don't know how to solve elementary trigonometric equations?
You need to review how to do that, then.
You should've already learned it if you are solving problems like this.
If you don't know at all, then learn the topic first.
I know but I don’t remember
Very well
I see that cos2x=-1/2
From my equation
And is 4pi/3
You need all solutions.
And 2pi/3?
You need all solutions.
And I don’t see anymore
An elementary trigonometric equation has infinitely many solutions.
Like, sorry, but if you can't see more, then you just haven't learned this topic.
Or don't remember it at all.
I don’t remember
In any case, you need to review it.
I forgot my main text book in class
On how to solve
But I just started to solve again
Just look up any school-level algebra textbook.
I wrote that thing from October and I frogot till now
Can I Finnish this first
I have still one more question
I don’t want to be unfinished
If you are encountering questions like this, you need to be able to solve trigonometric equations.
Right. What is arccos(-1/2)?
2pi/3
I just checked on google don’t worry I didn’t knew that
Thus, what is x?
Yeah. Though, you can obviously simplify 2/6 a bit.
Other than that, yeah, that's the answer.
Intervals come up in inequalities, not equations.
Well, I mean, they can sometimes come up in equations, too, but that is usually when you have some tricky stuff with absolute values and all that.
This solution can be also positive and negative?
That isn't related to this problem.
Can you show?
Well, I just don't really understand what intervals you want here.
The set of solutions is discrete, it doesn't contain any intervals.
So there was an interval for what x can take solutions
Oh, that!
Well, yes, some problems include an interval that you need to pick the solutions from.
Not here, though.
OP means "original poster".
As in, you're the one who created the post.
Oh yea
Ok now this one is the last
So we need to find the determinant and put = 0
I assume you need to find the values of x for which the matrix is invertible?
Or not invertible?
In any case, yes.
Is inversable
And I got x^3+x^2-10x+8=0
How I can solve this
Like is there a trick or something
Try using integer root theorem.
Show me
If you don't know it, just seach what it is and try it yourself first.
You also use this method?
Actually, hold on. Are you sure about that determinant?
Ah, wait.
You canceled by 2 already, nevermind.
And yeah, I would.
It’s already late here and need to wake up at 6
I will make it tomorrow
,to
,ti
The current time for gicu4130 is 11:19 PM (EET) on Thu, 30/01/2025.
@shut marten ,ti
Nah, I slept for a couple of hours during the day. Not sleepy yet.
You should sleep, though.
You're welcome!
What do you mean?
Hmm.
Well, their answer is right, but not specific enough?
No, like, what's the problem?
They (the answer key) got -pi/3+2pik, npi, and 2pi/3+2pik as solutions.
Yeah, same as what we got.
Just written in a longer way.
Hence.
No, I mean, it's correct. They just obviously did cos(x) = ±1/2 and didn't bother checking whether the two series can be combined into one.
It's like writing x ∈ {-1, 1} instead of x = ±1.
Hello.
Sure.
Can you translate it?
,rcw
My first attempt would be to consider cyclic quadrilaterals.
I translated it to the best of my ability without a software so I might be wrong if I made a few assumptions.
you think i know what is cyclic quadrialitias?
I can't help you, as I don't know the language.
wait let me translate
It’s simply a quadrilateral that is contained inside of a circle.
no
If not that, you can note that the diagonals of a rhombus intersect perpendicularly.
And that they bisect their respective angles.
We consider to have a diamond ABCD with m(<ABC)=120*, AC∩BD = [O]. Let it be a point M in the middle of the side [BC], AM∩BD= [E] and OE=2cm. Find the area of the diamond ABCD.
@shut marten
@dark vigil
this is how i would translate
No need to ping all the time.
Oh, so M is a midpoint, as I expected. This makes it much easier.
ok
By diamond, I assume a rhombus is meant.
yes
Try drawing it out first. I had my drawing but I am leaving for someplace so I don’t have it anymore.
We can ||drop a perpendicular from M onto AC||, which allows us to ||find BO by using some similar triangles||. And it's easy after that.
lord if you make this problem u for real genius
how
my teacher used other stuffs here but i frogot how he solved
he even sat and think like 5 min how to solve
You’ve used similar triangles before, right?
the only thing i remember he used ao=xsqrt3over2
not really
Ah.
And how do you think that came up?
Well, I mean, there's probably more than one way to solve it.
u can see its a equirateral triangle
Remember? You've seen this problem before?
I don't want to use that.
why
We are given an angle α and a distance x, that's enough for me.
ok lets do your method after the teacher method
No, I was working on it an hour ago.
explain please your aproach
Ohh, ok.
approach or aproach?
Yeah, you can just cheese it and ||make x any value that makes sense||.
no
@shut marten you here?
Yes.
Well, I've written the basic idea of my approach here.
how do you know is similar
The first thing to do is to recognize which triangles are similar.
how
Do you know the rules for similarity?
i found something else
what if we go from M to DC
and we make another side from A to N
so we have an isoscel triangle
Same concept, just with the isosceles instead of the right triangles.
Yeah, same thing.
ok how to solve
Similar triangles.
how
Do you know the rules for similarity?
no
Okay.
Teach me and I will know
Three rules:
• AAA similarity (3 angles in 2 triangles are congruent)
• SAS similarity (Two sides and an angle between the two sides are the same)
• AAS similarity (two angles and a side between are the same)
So what you can do here is identify which is similar using these rules, then apply a ratio.
Aaa
But I don’t see it
@shut marten
And what we can find with your method
If we create a side till AC
We can see let’s say similarity with abo and let’s call Ann
Amj
You don’t get anything
@cobalt gulch Let’s say we have 2 similar triangles ABC and DEF; then we can create a ratio AB/DE=BC/EF.
Sorry, I was in an area with no service.
Note that triangles inside each other are similar. By what property is this true?
Ok they are similar
But I can’t get anything from them
I don’t like this
I want to solve the problem
And after that to ask question
I waste so much
Much
Much
Time by doing this
Ratios.
Show me
Find the line segment from M to AC first, then use that to find BO.
Since M is the midpoint, what does that line segment from M to AC do to triangle BOC?
Right triangle
Ok I give up on this
Good. Sorry, I was somewhere else and didn't have good service.
Oh, this is so trippy...

And now
Brother just show me you way to solve
We waste s-o much time
After that I can ask questions
@shut marten show the way sir
Пж
Have you at least tried the approach I proposed above?
But I don’t see what you see
I stare at that rhombus like a mannequin
To see the idea but I can’t
Have you drawn the perpendicular?
I mean, if you don’t follow, why don’t you try and learn it?
How i cam learn?
Visual patterns. And the rules I gave earlier.
Im dumb to use it
Use ratios.
Tell me
I can’t.
We make proportion
I’m asking you, what ratios can we form from this triangle.
Give an example with ratio
Let me see if I can draw something.
The area of ABO is 2 times bigger than AMK?
What are O and K?
O the center of rhombus and K the line down for mm
From M
Do the problem
After We talk
You need 40 min to make a draw
Nu e
Nu e
Nice
I have classes. Calm down.
I’ll try to figure this out when I get home.
Ping me when you solve it
I already did.
,time @dark vigil
The current time for exiled_hype is 02:50 PM (EST) on Mon, 03/02/2025.
gicu4130 is 7 hours ahead, at 09:50 PM (EET) on Mon, 03/02/2025.
Look, I’ve already solved it, but I don’t have paper on me and it might take 2 more hours for me to get home at worst.
What response you got?
I can’t give you the answer.
I aleardy tot the answer i want to see if you got it
I aleardy made the problem
But other way
Best server ever
@cobalt gulch
Hello gicu4130, this is a friendly reminder that your help request has been inactive for more than 24 hours. If you no longer need assistance, please consider closing the thread using the +close command. This thread will be automatically closed in 3 days if it remains inactive.
