#Trig (simple stuff for you)

485 messages · Page 1 of 1 (latest)

cobalt gulch
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Ex 5 solve în R the equation if you know one of the solution is x=2pi/3

verbal bladeBOT
#
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cobalt gulch
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@shut marten

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Also I did ex 4 I need to solve the determinant and got x^3+x^2-10x+8

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Is there a easy way to solve this

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This cubic equation =0

dark vigil
dark vigil
dark vigil
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Just try to plug in x=2pi/3 into the equation.

cobalt gulch
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And what I get

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Is there a reason why I do that

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And also does it affect if I have || on coax

shut marten
cobalt gulch
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Done

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Is -10

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And after

shut marten
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Well, remember the formula for cos(2x)?

cobalt gulch
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Hmmmmmm

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Let me think let me think

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(Sin2x-1)/2

shut marten
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Uh, no.

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I mean the double-angle formula.

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And that isn't correct, anyway.

cobalt gulch
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Oh yea double how stupid I’m

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:)))))

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No I don’t know that thing

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Let me check on google

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But there are many formulas

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How do I know which to apply?

shut marten
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Well, we want just cosines.

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So, the one that only has a cosine in it.

cobalt gulch
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2cos^2-1

shut marten
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Also, you should probably learn it, it's one of the basic ones.

shut marten
cobalt gulch
shut marten
#

So, we have:
4|cos(x)| + 3 = -10(2cos(x)^2 - 1)

cobalt gulch
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Let me write it

shut marten
#

Now, for real t we always t^2 = |t|^2, right?

cobalt gulch
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Done

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We sub t?

dark vigil
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Yeah, that works.

cobalt gulch
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Ok and t applys from when ?

shut marten
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Yeah! Since cos(x)^2 = |cos(x)|^2, we can just take t = |cos(x)|.

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And we're left with a quadratic equation.

cobalt gulch
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Like the domain

shut marten
dark vigil
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What is the domain of cosine?

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Oh, alright.

shut marten
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Anyway, you can just find t first.

dark vigil
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I’m gonna be working it out here, don’t look at the spoiled stuff. ||4t+3=-10(2t^2-1)||

cobalt gulch
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576 sort

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Sqrt of 576

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Fast

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Quick math

dark vigil
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||4t+3=-20t^2+10||, ||-20t^2-4t+7=0||

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It’s 24.

cobalt gulch
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Ok

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Ok

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I got the t

shut marten
cobalt gulch
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T=-7/10 and t=1/2

dark vigil
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||20t^2+4t-7=0||, ||20t^2+14t-10t-7=0||, ||2t(10t+7)-(10t+7)=0||, ||t=1/2, -7/10||

dark vigil
cobalt gulch
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And now

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We do what

shut marten
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Well, t = |cos(x)|, so what values can t take?

cobalt gulch
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Positive

shut marten
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No.

cobalt gulch
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Why no

dark vigil
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There are certain bounds.

shut marten
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Yeah.

dark vigil
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Has to do with the range of |cos(x)|.

cobalt gulch
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Ok and

shut marten
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Well, what is it?

cobalt gulch
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We got the solution

shut marten
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We haven't solved the problem yet.

cobalt gulch
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And we need to see the values that cost can take right?

shut marten
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Yes.

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If t = |cos(x)|, what values can t take?

dark vigil
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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.

cobalt gulch
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From -1 to 1

shut marten
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That's cos(x).

dark vigil
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Not necessarily.

shut marten
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What about |cos(x)|?

cobalt gulch
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From 0 to 1

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Wait

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It’s right

shut marten
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Yeah.

cobalt gulch
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0 to 1 lock in

shut marten
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More specifically, [0, 1].

cobalt gulch
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Yes

shut marten
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So, which value of t works?

cobalt gulch
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From 0 to 1

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😉

shut marten
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No, I get that, but which of the ones that we got?

dark vigil
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From the solutions of t earlier.

cobalt gulch
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Only 1/2 but my question is why -7/10 wouldn’t work if is modul

shut marten
dark vigil
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Becuase |x| has only positive ouputs.

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Outputs is key here.

cobalt gulch
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Ok

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And now

shut marten
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So, now you just need to solve |cos(x)| = 1/2.

cobalt gulch
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How

shut marten
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You can start by squaring both sides.

cobalt gulch
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Wait

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But why |cosx|

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And now cosx

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And not

dark vigil
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(Or you can take plus or minus on both sides.)

shut marten
dark vigil
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We set t=|cos(x)| earlier.

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We solved for t.

cobalt gulch
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We set cosx=t

dark vigil
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Now we want x.

shut marten
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The solution will look a bit nicer if you square, though (two series instead of four series).

dark vigil
shut marten
cobalt gulch
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And this didn’t affect the cos^2x?

dark vigil
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No, since |x|^2=x^2.

cobalt gulch
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Ok how to solve

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?

shut marten
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As I said, start by squaring both sides.

cobalt gulch
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Cos^2x=1/4

shut marten
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Right.

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Now you can use the half-angle (or power reduction, whatever you like to call it) formula for cos(x)^2.

cobalt gulch
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What formula

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Is this

shut marten
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You need to review trigonometric identities.

cobalt gulch
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1+cos2x/2

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This one

shut marten
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(1 + cos(2x))/2, rather. Right.

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So, (1 + cos(2x))/2 = 1/4.

cobalt gulch
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Yes

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Not

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Now

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We multiply by 2?

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@shut marten

shut marten
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Yes...

cobalt gulch
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Ok and now subtract 1?

shut marten
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Yes.

cobalt gulch
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And now

shut marten
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And now it's an elementary trigonometric equation.

cobalt gulch
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Cos2x=-1/2

shut marten
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Yes.

cobalt gulch
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How to solve

shut marten
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Uh...

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You don't know how to solve elementary trigonometric equations?

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You need to review how to do that, then.

cobalt gulch
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😦

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Teach me and I will know

shut marten
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You should've already learned it if you are solving problems like this.

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If you don't know at all, then learn the topic first.

cobalt gulch
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I know but I don’t remember

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Very well

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I see that cos2x=-1/2

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From my equation

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And is 4pi/3

shut marten
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You need all solutions.

cobalt gulch
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And 2pi/3?

shut marten
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You need all solutions.

cobalt gulch
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And I don’t see anymore

shut marten
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An elementary trigonometric equation has infinitely many solutions.

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Like, sorry, but if you can't see more, then you just haven't learned this topic.

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Or don't remember it at all.

cobalt gulch
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I don’t remember

shut marten
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In any case, you need to review it.

cobalt gulch
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I forgot my main text book in class

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On how to solve

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But I just started to solve again

shut marten
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Just look up any school-level algebra textbook.

cobalt gulch
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I wrote that thing from October and I frogot till now

cobalt gulch
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I have still one more question

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I don’t want to be unfinished

shut marten
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If you are encountering questions like this, you need to be able to solve trigonometric equations.

cobalt gulch
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Ok

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How to solve it

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Now

shut marten
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Ugh, fine...

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The solutions of cos(x) = a are x = ±arccos(a) + 2πn, n ∈ ℤ.

cobalt gulch
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Yes

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I remember something like this

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But in my case I have cos2x

shut marten
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Well, that doesn't really matter.

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Express 2x first.

cobalt gulch
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Like this?

shut marten
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Right. What is arccos(-1/2)?

cobalt gulch
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2pi/3

shut marten
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Yeah.

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So, 2x = ±2π/3 + 2πn, n ∈ ℤ.

cobalt gulch
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I just checked on google don’t worry I didn’t knew that

shut marten
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Thus, what is x?

cobalt gulch
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Like this?

shut marten
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Yeah. Though, you can obviously simplify 2/6 a bit.

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Other than that, yeah, that's the answer.

cobalt gulch
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But I remember from book it was something like that

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()U()

shut marten
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Intervals come up in inequalities, not equations.

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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.

cobalt gulch
#

So like the way we solved is also correct

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?

shut marten
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Well, not really "also".

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We just solved it, that's it.

cobalt gulch
#

This solution can be also positive and negative?

shut marten
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Well, obviously.

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Why not?

cobalt gulch
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Just check

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Ok so if we would need to make and intervals how we can make it

shut marten
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That isn't related to this problem.

cobalt gulch
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Yea but this is the solution

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And interval

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An

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I remember very well

shut marten
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What are you talking about?

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We found the solution, that's it.

cobalt gulch
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The solution

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From the book the solution is an interval

shut marten
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Can you show?

cobalt gulch
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I can’t right now

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It’s also at school

shut marten
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Well, I just don't really understand what intervals you want here.

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The set of solutions is discrete, it doesn't contain any intervals.

cobalt gulch
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So there was an interval for what x can take solutions

shut marten
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Oh, that!

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Well, yes, some problems include an interval that you need to pick the solutions from.

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Not here, though.

cobalt gulch
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Ok

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Why I have op on my name?

shut marten
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As in, you're the one who created the post.

cobalt gulch
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Oh yea

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Ok now this one is the last

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So we need to find the determinant and put = 0

shut marten
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I assume you need to find the values of x for which the matrix is invertible?

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Or not invertible?

shut marten
cobalt gulch
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Is inversable

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And I got x^3+x^2-10x+8=0

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How I can solve this

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Like is there a trick or something

shut marten
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Try using integer root theorem.

cobalt gulch
#

Show me

shut marten
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If you don't know it, just seach what it is and try it yourself first.

cobalt gulch
#

You also use this method?

shut marten
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Actually, hold on. Are you sure about that determinant?

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Ah, wait.

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You canceled by 2 already, nevermind.

shut marten
cobalt gulch
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It’s already late here and need to wake up at 6

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I will make it tomorrow

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,to

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,ti

glass locustBOT
#

The current time for gicu4130 is 11:19 PM (EET) on Thu, 30/01/2025.

cobalt gulch
#

@shut marten ,ti

shut marten
#

Just one hour of difference.

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It's 12:19 AM for me now.

cobalt gulch
#

Why you don’t sleep

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Get some rest :))

shut marten
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Nah, I slept for a couple of hours during the day. Not sleepy yet.

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You should sleep, though.

cobalt gulch
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Ok man

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Спасибо за помощь

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😌

shut marten
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You're welcome!

cobalt gulch
#

We did something wrong

shut marten
#

What do you mean?

cobalt gulch
#

I got pol

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Pik

dark vigil
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Hmm.

shut marten
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What?

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I don't understand what you're saying, sorry.

dark vigil
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Well, their answer is right, but not specific enough?

shut marten
#

No, like, what's the problem?

dark vigil
shut marten
#

Just written in a longer way.

shut marten
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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.

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It's like writing x ∈ {-1, 1} instead of x = ±1.

cobalt gulch
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@shut marten

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Hello

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Have some time to talk?

shut marten
cobalt gulch
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Problem 8

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For me i wasted 1-2 hours to make it but cant

shut marten
#

Can you translate it?

dark vigil
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,rcw

glass locustBOT
dark vigil
#

Oh, geometry.

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Glad I just finished that chapter.

dark vigil
# cobalt gulch

My first attempt would be to consider cyclic quadrilaterals.

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I translated it to the best of my ability without a software so I might be wrong if I made a few assumptions.

cobalt gulch
#

I dont know how to Translate romb

cobalt gulch
#

help

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@shut marten

cobalt gulch
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you think i know what is cyclic quadrialitias?

shut marten
cobalt gulch
#

wait let me translate

dark vigil
cobalt gulch
#

no

dark vigil
#

If not that, you can note that the diagonals of a rhombus intersect perpendicularly.

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And that they bisect their respective angles.

cobalt gulch
#

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.

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@shut marten

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@dark vigil

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this is how i would translate

shut marten
#

No need to ping all the time.

dark vigil
cobalt gulch
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ok

shut marten
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By diamond, I assume a rhombus is meant.

cobalt gulch
#

yes

dark vigil
#

Try drawing it out first. I had my drawing but I am leaving for someplace so I don’t have it anymore.

cobalt gulch
#

ok wait

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This îs al that i ca-n make

dark vigil
#

Yeah, that’s what I had.

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Let me re-analyze it.

shut marten
#

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.

cobalt gulch
#

lord if you make this problem u for real genius

cobalt gulch
#

my teacher used other stuffs here but i frogot how he solved

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he even sat and think like 5 min how to solve

dark vigil
#

You’ve used similar triangles before, right?

cobalt gulch
#

the only thing i remember he used ao=xsqrt3over2

cobalt gulch
dark vigil
#

Ah.

dark vigil
shut marten
dark vigil
#

I remember writing down some trig bash.

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I’ll see if I recall it.

cobalt gulch
shut marten
shut marten
cobalt gulch
#

why

shut marten
#

We are given an angle α and a distance x, that's enough for me.

cobalt gulch
#

ok lets do your method after the teacher method

dark vigil
cobalt gulch
#

explain please your aproach

shut marten
cobalt gulch
#

approach or aproach?

dark vigil
#

Yeah, you can just cheese it and ||make x any value that makes sense||.

dark vigil
cobalt gulch
#

@shut marten you here?

shut marten
#

Yes.

cobalt gulch
#

lets see you vs my teacher

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he is also ex soviet

shut marten
#

Try it yourself first.

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It's a geometry probem, I'm not that interested in it.

cobalt gulch
#

i tried like 1-2 hours

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and cant get the responde

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response

shut marten
cobalt gulch
#

how do you know is similar

dark vigil
#

The first thing to do is to recognize which triangles are similar.

cobalt gulch
#

how

dark vigil
#

Do you know the rules for similarity?

cobalt gulch
#

i found something else

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what if we go from M to DC

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and we make another side from A to N

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so we have an isoscel triangle

dark vigil
#

Same concept, just with the isosceles instead of the right triangles.

cobalt gulch
#

Like this

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is this a way?

dark vigil
#

Yeah, same thing.

cobalt gulch
#

ok how to solve

dark vigil
#

Similar triangles.

cobalt gulch
#

how

dark vigil
#

Do you know the rules for similarity?

cobalt gulch
#

no

dark vigil
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Okay.

cobalt gulch
#

Teach me and I will know

dark vigil
#

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)

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So what you can do here is identify which is similar using these rules, then apply a ratio.

cobalt gulch
#

Aaa

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But I don’t see it

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@shut marten

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And what we can find with your method

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If we create a side till AC

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We can see let’s say similarity with abo and let’s call Ann

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Amj

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You don’t get anything

dark vigil
#

@cobalt gulch Let’s say we have 2 similar triangles ABC and DEF; then we can create a ratio AB/DE=BC/EF.

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Sorry, I was in an area with no service.

cobalt gulch
#

Ok

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And in my case

dark vigil
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Note that triangles inside each other are similar. By what property is this true?

cobalt gulch
#

Ok they are similar

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But I can’t get anything from them

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I don’t like this

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I want to solve the problem

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And after that to ask question

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I waste so much

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Much

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Much

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Time by doing this

dark vigil
cobalt gulch
#

Show me

dark vigil
#

Find the line segment from M to AC first, then use that to find BO.

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Since M is the midpoint, what does that line segment from M to AC do to triangle BOC?

cobalt gulch
#

Right triangle

cobalt gulch
#

Ok I give up on this

cobalt gulch
#

If anyone want to solve I will be happy

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@glacial dune

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Yo bro

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How is going

glacial dune
#

holy shit

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idk what the question is

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nor am i in any mood to help

dark vigil
shut marten
dark vigil
cobalt gulch
#

Brother just show me you way to solve

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We waste s-o much time

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After that I can ask questions

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@shut marten show the way sir

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Пж

shut marten
#

Have you at least tried the approach I proposed above?

cobalt gulch
#

But I don’t see what you see

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I stare at that rhombus like a mannequin

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To see the idea but I can’t

shut marten
#

Have you drawn the perpendicular?

cobalt gulch
#

Urs

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Yes

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ABO~AMK

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What i get

cobalt gulch
#

Thanks guy 4 days for a problem

#

The best server

dark vigil
cobalt gulch
#

How i cam learn?

dark vigil
#

Visual patterns. And the rules I gave earlier.

cobalt gulch
#

Im dumb to use it

dark vigil
cobalt gulch
#

What’s next

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I want to understand the logic

dark vigil
#

I know.

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What ratios can we form in similar triangles?

cobalt gulch
#

Tell me

dark vigil
#

I can’t.

cobalt gulch
#

We make proportion

dark vigil
#

I’m asking you, what ratios can we form from this triangle.

cobalt gulch
#

Give an example with ratio

dark vigil
#

Let me see if I can draw something.

cobalt gulch
#

The area of ABO is 2 times bigger than AMK?

dark vigil
#

What are O and K?

cobalt gulch
#

O the center of rhombus and K the line down for mm

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From M

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Do the problem

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After We talk

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You need 40 min to make a draw

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Nu e

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Nu e

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Nice

dark vigil
#

I’ll try to figure this out when I get home.

cobalt gulch
#

Ping me when you solve it

dark vigil
#

I already did.

cobalt gulch
#

,time @dark vigil

glass locustBOT
#

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.

dark vigil
cobalt gulch
#

What response you got?

dark vigil
#

I can’t give you the answer.

cobalt gulch
#

I aleardy tot the answer i want to see if you got it

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I aleardy made the problem

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But other way

glacial dune
#

Best server ever

obtuse robinBOT
#

@cobalt gulch

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