Need Math Help?

[Lixivium]

I was just wondering if there was a way to isolate for x in the following equation:

x sin x = a

Where a is a constant

My friend just asked me this and I had no idea what the answer was...

I don't think there is a way to do this algebraically.

 

[GoldShadow]

I was just wondering if there was a way to isolate for x in the following equation:

x sin x = a

Where a is a constant

My friend just asked me this and I had no idea what the answer was...

x=(42/5)a


You'll just have to take my word for it. The answer came to me in a dream.

 

[Masque]

x=(42/5)a


You'll just have to take my word for it. The answer came to me in a dream.

Some proof would be nice.

 

[Retroking2000]

thumbs up to the author of this thread best LOL I have done today

 

[TheKruskinator]

Wait, what?

 

[Gerbil]

Let x = 1 – 1 + 1 – 1 + 1 …
X = (1 – 1) + (1 – 1) + (1 – 1) +…
X = 0 + 0 + 0 + …
X = 0
Let x = 1 – 1 + 1 – 1 + 1 …
X = 1 + (-1 + 1) + (-1 + 1) + (-1 + 1) …
X = 1 + 0 + 0 + 0 + 0…
X = 1
Thus,
1 = 0

Satisfied? I have an entire thread for this stuff. It's on the next page of threads.

Did anyone prove you wrong in the tons of pages? I read the first page, saw this, and laughed lol. You can't use ellipses when applying the addition property. In fact, you can't use ellipses when applying ANY of the basic properties. So this hypothesis is null. (I tried to trick my teacher with this once lol, so I'm not being mean, I'm actually understanding here) I'm a Math major btw.

Anyways, I'm only a freshman so I'm not as knowledgeable, but I too, can help with anything up to Calc and potentially discrete math (I'm starting the course this semester). I've gotta go through Calc IV here, along with about a dozen additional math courses on the side. Since I'm combining the Math degree with Secondary Ed, my school requires I complete the BA for Math a year early, so my 4th year can be focused a bit more on the Secondary Ed part.

 

[Doraki]

Well, x cos x + sin x = 0, and that won't really get you anywhere. But good thought, though!

that gets you to the extrema of the x.sin x function, and has absolutely nothing to do with the problem.
x.sin x = a has an infinite number of solutions, you can get a good asymptotical approximation of them, but there's no way to get them exactly.

Did anyone prove you wrong in the tons of pages? I read the first page, saw this, and laughed lol. You can't use ellipses when applying the addition property. In fact, you can't use ellipses when applying ANY of the basic properties. So this hypothesis is null. (I tried to trick my teacher with this once lol, so I'm not being mean, I'm actually understanding here) I'm a Math major btw.

The problem there is that the serie (-1)^n doesn't converge when you take its absolute values, so 1-1+1-1+1... doesn't even exist, and it's wrong to do anything with it : you get inconsistent results if you do.

 

[AltF4]

Wow! This thread got active all of a sudden!

DigitalMaster: Hmm... An algebraic solution to that isn't striking me right away. It's early... let me think about it. (Though it will have infinite solutions like GS said)

Thekrustinator: Noooooo!!! Btw, isn't your sig from Futurama?

Gerbil: Yea... GS kinda beat me to it again, but the problem isn't so much with the ellipses, but with the fact that the series given is divergent. You CAN add series, and you CAN show them with ellipses:

.1 + .01 . +.001 + .0001 + .00001 = .11111...
or
.111111... + .22222222... = .33333...

It's just an informal notation for "this pattern repeating infinitely" just the same as putting a line above the letters. (I can't type it here)

The series 1 - 1 + 1 - 1 + 1... is divergent, which means it has no sum. So you can't say it "equals 0" because it doesn't equal anything, it has no sum.

GoldShadow: You beat me to it again! I have to watch this thread more diligently! ()

 

[Metal_Dave]

EDIT: Nevermind I didn't check the last recent posts to see if this was still going on, but I'll have my questions ready this week as I start my math class this Tuesday.

 

[TheFifthMan]

Integrate me: Integral(e^(1/x) dx)

This came up in my diff equations class.

 

[vericz]

Integrate me: Integral(e^(1/x) dx)

This came up in my diff equations class.

I have a quiz on this tomorrow

 

[thesage]

so ummm... I was wondering if you guys could help me prepare for calculus and ****. Math is really easy for me. I spend pre-calc making kirby's with my graphing calculator. Any topic really. Mabye you could put it up on your first post?

(^+(o.O))+ Kudos to anyone who sees that.

 

[vericz]

alright quick question:

find y' if y=ln(x²+y²)

im getting y'=2x+2y/x²+y² and the answer in the back is y'=2x/(x²+y²-2y)

what did i do wrong?? I cant get it

 

[Doraki]

vericz, the derivative of y² is 2y'y, not 2y.

 

[Lightsaberboy]

I have a quiz on this tomorrow

I believe it's -(x^2)e^(1/x)

if u = (1/x), then du = -1/x^2

then- x^2 integral(e^u)

which would be -(x^2)e^(1/x)

if you take the derivate back from that, you should end up with what you started.

 

[AltF4]

Cool Website Alert:

http://integrals.wolfram.com/index.jsp

For all of your integrating needs. Enjoy.

 

[TheFifthMan]

I believe it's -(x^2)e^(1/x)

if u = (1/x), then du = -1/x^2

then- x^2 integral(e^u)

which would be -(x^2)e^(1/x)

if you take the derivate back from that, you should end up with what you started.

That's not it. I ran it through an integrator and it gave me

xe^(1/x)-Ei(1/x)

Thanks for the integrator link, AltF4. Although someone taught me how to do MATLAB integration...

 

[TheFifthMan]

I fail at life, please ignore me

 

[TheFifthMan]

because I don't know how

 

[TheFifthMan]

to click a button one time.

 

[vericz]

vericz, the derivative of y² is 2y'y, not 2y.

Yea i feel like a noob for forgetting that, btw i owned that quiz

 

[Lightsaberboy]

That's not it. I ran it through an integrator and it gave me

xe^(1/x)-Ei(1/x)

Thanks for the integrator link, AltF4. Although someone taught me how to do MATLAB integration...

alright, alright. you don't have to rub it in my face by constantly repeating yourself!

 

[AltF4]

Ohsnap, epic quadruple post, FifthMan. But yea, MatLab and Maple are both really good tools if you can get your hands on them.

 

[TheFifthMan]

whoa... sorry about that... I'll blame that on the server load problems we had last week.

in b4 johns... and oh! I'd also like to offer my services. I think that all of us should list our qualifications and people can PM us based on our abilities or something.

 

[South_Paw]

Bumping for brain-exploding justice

Alice has seven times the amount of pens that Maurice has. Paul has two-thirds of the amount of pens as Alice and Suzy have combined. Dawn has a dozen more pens than Paul. Suzy has half the pens that Maurice has. If Suzy has 2 pens, how many does Dawn have?

for funsies... i looked up some word problems like these. i usually just plug and play random numbers till i get it right, i never was one for 'showing my work'... but ones this long lead you really far before you discover the dead end. so... how?

 

[Greenstreet]

good job. finally an educational thread

 

[AltF4]

Hey! I forgot about this thread. We should revive it now that school's starting again.

Here you go, Coty.


Alice = A
Maurice = M
Paul = P
Suzy = S
Dawn = D


1) A = 7M
2) P = (A+S) (2/3)
3) D = P + 12
4) S = M / 2
5) S = 2


Substitute 5) into 4) ->
2 = M / 2
M = 4

Substitute the result into 1)
A = 7 * 4
A = 28

Substitute the result into 2)
P = (28 + 2) (2/3)
P = (30) (2/3)
P = 20

Substitute the result into 3)
D = 20 + 12
D = 32

Dawn has 32 pens.

 

[vericz]

Good idea, class doesnt start for me till the 26th tho

 

[SkylerOcon]

I have a question. I'm starting High School this year and I will be taking Pre-AP Geometry. Any ideas of what to expect or any reminders of what we went over in Algebra?

 

[Puffin]

----------

 

[Proud_Smash_N00b]

^
I just do homework for other classes

---

I just took Trig and I'm going straight to AP Calculus AB. (skipped precal)
I'm also taking AP Physics this year (in case the whole "you need to be in calculus to do good in physics" thing is true)

Is it a bad move on my part or can I adapt to the situation and stay even with everyone else in class?

 

[Puffin]

----------

 

[AltF4]

When you take Calculus and Physics (AP of both) simultaneously, you should realize after not long that they are nearly the same class, with differing emphases. It really is worth it, Smash Noob.

 

[Proud_Smash_N00b]

At my school, trig and pre-calculus are bundled together, so I don't have that luxury. But I'm sure that if you're intelligent enough, you can skip pre-calculus. Given, I haven't had any calculus experience... But schools walk the less smart kids through everything. You'll probably get almost a full review of pre-cal before you even start any new material.

Same in my school. I took trig cuz it counts as credits for pre-calculus in my school and I can immediately take AP calculus.

and thanks AltF4 for the advice.

 

[Mr.GAW]

I have a question. I'm starting High School this year and I will be taking Pre-AP Geometry. Any ideas of what to expect or any reminders of what we went over in Algebra?

Geometry really is just a matter of remembering laws and formulas. It's pretty much hit or miss, but it's hit for most. The algebra is really pretty basic in honors geometry (which I'm assuming is the same thing as Pre-AP) if I remember correctly- you really shouldn't have any trouble. If you're lucky, you'll even be able to use your notes on tests like I did. (God that was the simplest class I've ever taken because of that.)

 

[Red Hawk One]

Given f(x)= ((x^2+2x+1)/(x))-3
1. Find the inverse
2. Prove f^-1(x) is a function
3. find the vertical, horizontal, and slant asymtopes.

I'm having a little trouble with proving/disproving the inverse as a function, as well as finding how the -3 (or any other numbers outside the fraction) affect the asymptotes in rational expressions with a slant asymptote.

Thanks in advance for any tips. My pre-cal/trig class has a test on this in two days.

 

[AltF4]

You may have trouble proving #2, Red Hawk, because that function's inverse is not a function. And since it's not a function, you can't express it as such. Unless your teacher wants you to write the parameterize the inverse for #1, it doesn't really have an answer. Or at the very least is an unfair question.

In order to find the inverse of a function, you just swap X and Y. If you've got a graphing calculator, plot it.

You can use an example as a proof of something not being a function. Clearly, for example, when f(x) = 2, x can be either ~2.61 or ~.381. Thus it is not a function.

 

[Kinzer]

How does multiplying two negative numbers give you a positive product, I just can't see the logical reasoning behind it...

 

[Tee ay eye]

I'll attempt it.. but I'm not sure lol

Negative = opposite

So, negative x negative is the opposite of a negative.. which is a positive.

I'm sure Dan can give you a more legitimate answer.

 

[psicicle]

ehh that explanation doesn't explain addition, where the negative is kept

O yeah for the other topic, I think in general the AP courses in high school are junky- AP calculus is not at all rigorous (they don't even do the epsilon-delta definition of a limit!), AP chemistry was pretty much memorization and solving cookie cutter problems (so was calc). I haven't done physics yet, but I will be doing physics C. But I looked over the curriculum and I don't knmow how they will stretch out the topics to a year-long course. When I saw mechanics I was hoping to see like lagrangians and hamiltonians and symmetries, which would indeed make the course pretty hard. Oh well.