Maybe....

(ninja-ed!!)

Last Q on a piece of homework is a decidedly evil differentiation question.

Normal differentiation I can do fine, where y = something in x, find dy/dx etc.

This one, I have x = something in y but still need to find dy/dx, and the normal to the curve at y = 0

Anyone know how it works when x and y are swapped in the question but not in the dy/dx bit, or whether I can just ignore that and do it the same as normal, or what the heck is going on...

and I guess I deserved the ninja-ing, what with leaving the topic open in General... and my frequent ninja-ing of others  

hehehe Couldn't help it.

Fair 'nough

Any idea about differentiation?

Whoa... this question will take serious recollection on my part. Haven't differentiated anything for about 7 years.

Any way you could put the equation up?

Difficult with the lack of superscript for the stuff to the power of other stuff, but I'll use ^ for that

x = e^y (2y^2 - 3y + 4)

Thinking about it, if you have x = something in y, and you need to find dy/dx, isn't the process to make the equation into y = something in x and then differentiate that?

Maybe

But the equation looks too evil to put it into x = stuff

Oh wait...

yeah

I could do the question if y and x were reversed, it's the fact that I'm still finding dy/dx that's confusing me...

No, there's a way to do it....

the x bit will take on log. No?

with e it would be ln, (log to base e) but yeah... maybe

Hang on, I'm gonna find a maths book and paper, and see if I can work this out. Enough guessing

If x = e^y (2y^2 - 3y + 4)

Then ln x = ln [e^y (2y^2 - 3y + 4)]

ln e^y = y, but I don't know what happens with the part in brackets when you start throwing ln's around

According to the internets, I can find dx/dy then take the inverse of that

Which makes sense, since inverting dx/dy would logically give dy/dx

That's true...

it won't be pretty but it could well work

which also would be the same as making the equation y=something in x and differenting that

ok, I be done

I probably should have googled around first, the answer was surprisingly easy to find... even though normally looking for things like "dy/dx" confuses google with it's punctuation-ignoring ways.

So that worked?

Seemed to 

Woo hoo!

You've reminded me how much I used to know, and how much I miss it now. Might actually revisit it... I can't believe I couldn't remember the simple stuff!

If I've re-ignited a love affair with differentiation (or other maths), then maybe the topic was all worth it after all....

hehe, everyone else is going to come in here and see this topic... all full of posts (28 and counting)

but it's all over already

hahahah

Yeah, I used to LOVE differentiation.

I liked manipulating the equations for some reason.... and it made more sense than integration which I mainly hated

I know what you mean... making the little numbers dance 

Always satisfying when something looks like the most horribly snarled-up equation in the history of forever, but then it ends up mostly cancelling itself out and boils down to something nice and simple.

hhehehe Yeah!!

Dance is the word I was just thinking of while reminiscing

And the precision of it all too... that i miss. everything has it's place, it's purpose.

Ok, I shaddup now

you definitely resparked my interest in math.

this was beyond where i ever was, but i used to love math.

i loved it until i had a teacher in college (the first time around) ruined it for me. the man could not have cared less about math, it was horrible. i had come from a small high school, where i had 1 math teacher for 3 years and he had instilled a serious love of math in me.

oh well, i'll be taking some math again in the fall (most likely) and hopefully, i will be reminded even more of my past love.

thanks, guys.

Sometimes I think there's someone out there reading my thoughts -

Link

lol!

Y = Mx + B

we were taught y = mx + c, none of this crazy B stuff 

Y-axis formula

where m is the slope of the line and b is the y-intercept, which is the y-coordinate of the point where the line crosses the y axis. This can be seen by letting x = 0, which immediately gives y = b

Formula Y = Mx + b

Yes.

y = mx + c works too, we just got taught with a different letter 

Cool

I did mathematics at university.  I was pretty good at it then and I must admit that I have held on pretty well to the algorythmic concepts. However, I can't add a column of numbers up and get the same answer twice without a spreadsheet...

LOL!

Those formulas in the box above I still remember

toa cah soh.

Now, what did we use it for.... *thinks*

we had to use it for finding the missing piece of a triangle.

that reminds me, is algebra as useless in real life as i think it is?

Lemme think....

Not completely useless, I don't think

Algebra, as in pure algebra, is quite useful as a concept.  The importance of remembering the the techniques is important for low-level software development but most of the time the development toolkits will do the number crunching for you.

I did have a project last year which I had to engage a maths PhD to help out with.  It was quite strange, the PhD was 30 and the software developer was 58, I'd have expected it to be the other way around.  However, all the mainstream developers these days are all into C#, .NET, C++, Java and so on, so finding someone who can write in non-compiled code means looking to the older generation.

hello super king

add me

thanks

Question on Statistics:

Ok, a bag has 5 marbles in it. One marble is red, Four marbles are blue.
Each time you take out a marble, you do not look at what colour it is. You do not return it to the bag.
At the moment, the chances of pulling out the red marble are 1 in 5.

What are the chances of pulling out the red marble, if, each time you take a marble, the colour of the marble stays unknown, and the number of the marbles in the bag is reduced by 1 each time.

Eg:
5 Marbles in bag: 1 in 5 chance. (marble is not seen or replaced)
4 Marbles in bag: ...??...chance (marble is not seen or replaced)
3 Marbles in bag: ...??...chance (marble is not seen or replaced)
etc...
etc...

Damn I hate these questions

It's no wonder I had to repeat Stats in uni, and yet barely passed it the second time

I consider myself extremely good at maths, but statistics, I never got it

no idea why..

It just didn't seem very logical to me - mathematics based on chance

If I remember correctly, you have to take into account the fact that there are less marbles in the bag + the chance that the red is already out.... or something along those lines

yeah and then multiply it by the divisor of the rocks on the moon.. blaaahhhh

http://en.wikipedia.org/wiki/Analysis_of_variance

So yeah, if anyone can answer that for me, I'd be really grateful

Won't help much, but that's the sub-part - variant stats

LOL - if it won't help, then why post it

and that was damn quick!! you have that in your bookmarks or somethin?!?!

No, I searched for it. I knew what to look for, just couldn't remember the term.

Well, I posted it as a starting point if you wanted to look into it more!

oohh.. picky picky

*walks away, shoulders slumped*

oh, come back!! I didn't mean it like that!

Fine! I'm gonna make it my life's mission to find you a formula

I posted this on Yahoo! Answers as well and have this response (which is sort of the answer I was expecting):

There is a hard way and an easy way to do this. You can use logic to see that regardless of what happens on previous draws, your chance is always going to be 1/5 to pick the red marble (up to the 5th draw) because you don't have any information about the previous draws.

This can also be done using conditional probability (Bayes' rule).

For example, with 4 marbles in the bag, you calculate the probability that you pick a red marble given that a red marble was picked on the first draw and the probability that you pick a red marble given that a blue marble was picked on the first draw and then weight these probabilities by the probabilities of picking a red on the first draw and blue on the first draw, respectively.

i.e. Pr (red with 4 marbles in bag) =
Pr (red with 4 marbles in bag | red on first draw)*Pr (red on first draw) +
Pr (red with 4 marbles in bag | blue on first draw)*Pr (blue on first draw)
= (0/4)*(1/5) + (1/4)*(4/5) = 1/5.

The same method can be applied to future draws from the bag.

I suppose it makes sense, right?

Ah yes... that looks familiar

Ok, I also found this which should help:

http://www.abwcorporation.com/AIMS-Ch-2.pdf

Thanks!

I'm not great at stats... I'm having problems even understanding what the question is.

So you take a marble from the bag and what... don't see it? Then put it aside so it's out of the equation, and you need to know the chance of picking the red one on each turn?

yep

On turn 1, chance of a red is 20%

To pick red on turn 2 you would need to pick blue on turn 1 (80%), then red (from a choice of 4, so 25%), 0.8 * 0.25 = 20%

To pick red on turn 3 you would need to pick blue on turn 1 (80%), then again on turn 2 (75%) then red on turn 3 (33%) = 20%

To pick red on turn 4 you would need to pick blue on turns 1 through 3 (80%, 75% and 66%) then red on turn 4 (50%) =  20%

To pick red on turn 5 would need to pick blue on all previous turns (80%, 75%, 66% and 50%) which we just saw produces 20%, then pick out the one remaining which will be red (choice of 1 from 1).

So yeah.. always 20%, when you don't know anything about the results of previous picks.

Probability I can do, other stats stuff... not so much 

what's that......up in the sky?

it's a bird.    it's a plane.      it's super king!

faster than a speeding bullet.....

able to solve probability stats in a single bound.....

heheheh I like it!

Although it's strange that you take the first step into account all the time?

Yeah? I didn't understand it either, but the working seems to make sense.

Ok, I read thru the pdf thing again... and I understand why you take the first step into account.

I guess the bit about the colour of the marble picked being unknown kinda threw me for a bit

42

hahahaha

Lies, damn lies and statistics.

I like that one...

ah yes - i forgot about your namesake Arthur.

Who's that?

the guy that woke up with a hangover only to discover that his house was scheduled to be demolished. Of course that is by the by as his world (earth) was also scheduled to be demolished. Luckily his best friend was in fact an alien. All you need is the guide and a towel.

Right.... when you said name sake, I thought you meant someone else

i never did finish that story Simon

you should. Douglas Adams is (was) a very clever man.

although on saying that, his books aren't everybodies cup of tea

Not for everybody, but then there's always the radio show, or the movie

i never finished the movie either

Gah!

what're we gonna do woth you!!

did you not finish the movie through choice or mitigating circumstances?

there is only one movie i have never finished - i remember it all too well - it was called The Pest and it had John Leguiziamo in it (not sure of the spelling and too lazy to look it up). I really really disliked that movie - i cannot bring to mind a worse waste of money and time to make crap like that.

all the books are awesome.

so clever and funny.......definitely worth it.

The original radio series (from the late 70's early 80's) is a pure gem.  They were broadcast before the book was written.  The TV series was OK but the recent film was awful.

My grandparents have what's either an earlier film, or the TV series on video 

The books are probably my media-form of choice, but I never heard the radio show so I guess that was kind of inevitable.

Recent film... had some decent moments, if it wasn't in the shadow of all the previous HHGttG stuff it might even seem good, but as an addition to what's gone before, sub-par.

They'll have the TV series on video.  You can also get all the radio stuff on CD.

ah...'a trilogy in five parts'.......an appropriate topic for this, yes?

when i recently decided to read the entire series....i found a "complete version", which had been put together before douglas adams died.......it included a really nice preface where he discusses the whole history and makes a sort of time-line......and also a related short story.......

i thoroughly enjoyed it.

i agree with sk that the movie would have been better if it weren't for all that was already out there.

Read The Salmon of Doubt its the last book Douglas Adams "wrote" before he died and proves that he invented the method of texting. Im a big Adams fan Im in the middle of Dirk Gently atm.

happy.....are you back? i thought you had 2 more days of holiday.....

thanks for the tip.

yup I gots back yesterday I recieved 12 bruises!!!!

How'd you manage that?

Water slides...cos of my tallness I no longer fit properly .

Oh, damn...

I had a friend once, claimed to have slid up onto the "ceiling" of a water slide on a particularly vicious corner (presumably followed by a painful landing) and also to have "skipped" on exiting a slide at high speed.

I would take both of these with a more than generous pinch of salt though, he wasn't known for his reliability when it came to adherence to the truth 

Yeh my injuries were sustained by the fact that the floor of the slide was sharp and pointy in places lol.

hey happy...are you sure that wasn't the laundry chute?.....there was actually water in this water slide?

now that you mention it...

well.......welcome back, bruises and all.

hope you had fun.........because i would be very upset if i missed a week of happy for a miserable reason.

Oh the bruises were more than worth it lol.

good.

YAAAY! Happy's back!!

Hang on....it's been 12 days already?!

i thought he was supposed to be gone monday to monday....

Oh, my bad.... Dunno why I thought that

Damn did i say that? I meant Monday to Friday. What is up with my brain this summer? :S

it's okay, happy.........

1. you've been preoccupied

2. you wanted us to think you were going away for longer, so that we would be blissfully surprised when you showed up earlier.

Summer? *sniff*

I wanna be where it's warm!! - although the weather is taking a turn for the better, here in Sydney. There are less and less cruddy days now, but we're still not out of winter weather - even though it is now spring.

Happy Spring Everybody!!

(and Happy Autumn/Fall for everyone in the opposite hemisphere!)

It's SPRING!!!!! Spring i sez!!!

Woooo HOOOO!!!

*hops around wildly*

*hops around too*

hehehehe

I was soooo sick of the cold. Couldn't wait for winter to end.

And isn't it just the perfect day today? So Springy

The breeze is still a bit chilly, but once you get out of the city, it's perfect! And the Sky!!! it's soooo blue!!

Yes!

It's a Springy sky!

Breeze is nice too.

It's just so.... happee!

If I weren't so mad at my comp situation, I'd have a grin plastered on my face all the time

It's so good to see people in clothes, and not layers LOL

hahahah I wouldn't know...

?????

I don't look at what people wear.... and I don't layer up, so I can't relate

Ohhh.... I get it

spring?! its the end of summer over here :[

You know why I lurrrve this time of the year?

On Fri, the trees along the street were still bare.... today, they're sprouting green! I love how insync they are

They're not really doing that, it's just the City of Sydney and their council and their tourism board have elected to paint all the trees to make it aesthetically pleasing.

And I'm not making it up!! I actually saw people replacing a tree last week!!

They pulled the old, wintery/dead-looking one out of the ground, and put a green one in its place!

wow thats messed up morgan

I know...

it's just frickin' hot where i am........

Do they replace trees in arizona too?

Can't wait for it to get hot again, It's threatening to rain here in Brissie..

i don't know, morgan.......all i know is that it is frickin' hot!

*scratching head*

They might do that in the city, where it matters but I highly doubt they care what this area looks like....

PLUS - these trees are taller than the buildings on the street.... I would notice if they got replaced!

LOL - nobody cares about ultimo...

Eggactly.....

It's a great place tho! 10 000 times better than the crappy city

Yeah, it's not everyday that you get to see exploding chicken shops!

See, it's a regular circus on this end!

hehehe

Yeah, it's not everyday that you get to see exploding chicken shops!

Hanson  ??

mmmbop

(i know.....i know......)

Ok, spit it out....

Exploding chicken shop: http://www.smh.com.au/news/national/blast-shop-victim-critical/2008/02/04/1201973771925.html

Heheh... knew that would cause some stumped heads!

Cos, I mean, it's not like it clear if we were talking about a chicken shop which exploded.... or a shop which sells exploding chickens

Shite, how come I didn't hear about that before, or maybe I did and don't remember.

So how much does an exploding chicken cost then?

Depends on the exploding chicken exchange rate...

lmao......

happy is back...

1 exploding chicken = 0.606 of a bicycle riding gerbil

(exchange rate is due to the short lived nature of an exploding chicken, where you can watch a bicycle riding gerbil for at least three hours before you get tired of it, plus the bicycle is made from steel which is going up in price)

Good explanation simon, I was just about to disagree with the rate before you mentioned that.

yes......i'm impressed.

Bluegirl!! Aren't you usually in bed atm?

Hmm...  maybe I have my time zone conversions wrong..

um....yeah....it's 6:30 pm......

Oops

if you use firefox....you could check out foxclocks

I rely on my memory... Which has proven on many occasions to be an unreliable source.

When all else fails, Google is my friend.

Just plus 7 to us Morgan. And then swap the a/pm

Oh... Isee I always try to subtract 13 or 15 or something, then get confused with daylight savings, then for some reason i end up adding 13something hours and subtract a day....

See... very unreliable source...

Anyone know where I can get a trade-in?

LOL!!

Yeah, I'm not good with counting more than 12 hrs, so I do it this way...

Mind you, soon it'll be +5 and swap

and i will make it more confusing.......arizona does not observe daylight savings....

Bluegirl, just because you don't look at them, doesn't mean they aren't there.. LOL

D'oh @ no daylight savings in Arizona!!

this is not my decision......i'm new here and i don't like being confused....

hehehe I know, I know....

Wait till it summer hits here... andro and I will be in different time zones!

Yeah, Aus has 3 timezones - in daylight savings there's 5!!

irritating....

Wait till it summer hits here... andro and I will be in different time zones!

Yeah, just because some country folk think that (during daylight savings) the extra hour of sunlight will fade their curtains......  

Then why didn't they call it "curtain-savings-time"??

Ummmm............because we don't have it here in Qld??

We had a few trials of daylight savings here a few years ago, but the (then) premier Joh Bjelke-Peterson, reckoned that the sun shone out of his arse and he wasn't getting out of bed an hour earlier for anyone..

See, the thing is, it all sorta made sense when we didn't have ELECTRICITY...

We don't live strictly by the sun's hours anymore, so daylight savings makes less and less sense.

Yeah, but most of us don't work from dawn to dusk anymore either..

in arizona ......it's just too frickin' hot......we don't need longer...and therefore more frickin' hot....days..

Yeah, but if you start work earlier (when it's cooler) and then finish earlier, you have the extra daylight to enjoy at the end of the day..

i have nothing to do with these decisions!

I bet you do....

Meddler.....

Run for governor, moneypenny..

Yeah, you could so do it!

Yeah, but if you start work earlier (when it's cooler) and then finish earlier, you have the extra daylight to enjoy at the end of the day..

Which is actually what they should do for winter!

Who likes getting up earlier on winter mornings??

I really think they should reverse the daylight savongs times.

Like instead of adding an hour in summer, they should add it in winter instead.

5pm and its dark in sydney - wouldn't it be good if there was still light then, and it got dark at 6 instead>?

why would any sane person run for a government office.....

....oh yeah.....i forgot....i am fucking insane.....

Andro - what Morgan said

bluegirl - I'd vote for you!

But, but, you'd be going to work in the dark then..and as I said "who likes getting up early on cold dark mornings"?

You get more daylight in Syd than we do in Bris, there's no twilight here, one minute it's daylight and the next it is dark. (I'm talking about the winter time here)

why would any sane person run for a government office.....

To make a lot of corrupt money and change the laws to suit yourself.

well that's not me......

Andro, it's dark in the mornings anyway...

Yes it is, I spent most of my life getting out of bed in the dark (in winter) but I like to stay in bed as long as possible on a cold morning....

And what are you going to do with the last hour of daylight on a cold winters afternoon?

I dunno, maybe it'll be at least 1 degree warmer when I walk out of the office I don't have to freeze to death quite as much?

It'd make me feel happier for one

Not me, I'm not a morning person, I'm a creature of the night....

Yeah, but the feeling of seeing the sun go down while still in the office, and heading home when dark is very depressing.

Winter is very depressing to me.....

It's not as bad here, where it's usually still sunny.

I'd lose my head if I had to live in places that have a harsh gloomy winter. I don't know how the people there do it!

i love harsh gloomy winters. except for when i have to march out an stand on the bus stop.

Brrrrrrr

Yeah the walk to the train station is the worst for me

I used to travel to work on a ferry, and the 1½ km walk from the ferry to work was a killer, when the winter westerlies were blowing..

"westerlies" looks like a funny word

Westerly's, (Just leave out the lies)

its ok, i understood it

Them lyin' winds!

Ya cant trust em!

hahahaha

Next time, ask these people for maths help:

Hahaha, epic

And it makes sense too! (sorta...)

I like that! It's so clever!!

And whatever happened to them? I used to love watching reruns on the telly!

Thats brilliantly written

Hahahaha, that brought back memories, I used to love 'Ma and Pa Kettle' movies when I was a kid.

Marjorie Main and  Percy Kilbride, were the actors..