Posted by kimcheeboi
eidt:lets confine this craze to one thread, then!
Ok, since everyone is posting their math homework, i decided to post soemthing from 6 chapters ahead, just so i get a head start.
find the area of the part of the parabloid z=x^2+y^2 that lies under the plane z=9
oh and prove that something can have an infinite surface area but a limited volume.
the prize?
You get a electronic pat on the back (fine, a gmail account if you want) and you get to go, "nanny nanny nanny, im smarter than you, esato!"
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[ This Message was edited by: kimcheeboi on 2004-10-21 23:31 ]
Posted by Ayush
Posted by plasmadog
what the heck's a parabloid?
like a parabola?? haven't even heard ot it!!
hmm...5 papers of math in engineering and i still can't solve it!!!
Posted by Ayush
I'm not the only one.!
Posted by maddav
I would try and answer, but we haven't covered co-ordinate geometry in the x,y,z planes in maths yet, only x,y.
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[ This Message was edited by: maddav on 2004-10-21 19:57 ]
Posted by kimcheeboi
i'll give you all hints
the first problem is solved with applying a simple double integral. A parabloid is a 3-d parabola.
problem 2:
use y=e^(-x), or something like that (gabriel's horn)
Posted by masseur
Its not parabloid, its paraboloid and if memory serves this is a calculus question, specifically double integrals but again its been a very long time since I had to do this, in fact not since my scientific programming work at Plessey Research in the late 70's early 80's.
given that info I'll leave it for someone else to work out but its got my interested enough to read some of my old text books at the weekend because I always found calculus fun!
edit: oh! looks like you were giving the clues as I was writing this! oh well....
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[ This Message was edited by: masseur on 2004-10-21 20:20 ]
Posted by plasmadog
Weekends at the Masseur house must be great fun! Seriously calculus? You must've been quite a nerd during school. Okay kim for the second one, you can use limits, so when area tends to infinity... You solve along those lines. Its 1am, will do the rest tomm:-).
Posted by maddav
Hey, I'm doing calculus next year. No fair
Posted by masseur
@plasmadog,
no, just once in a while when something like this comes up it sparks my interest. its that or helpmy wife with her craft activities 
I was definitly no nerd at school, just top of the maths class but that was about the only subject I was top at, except IT which was brand new at my school in those days... punch cards and paper tape!
but we digress... I'm hoping someone will solve this soon
Posted by kimcheeboi
For 2 you use limits, but you gotta use them with improper integrals (volume and surface area). Geez i'm giving it away!
Posted by Krubach
@kimcheeboi
You really need to get a life...
Posted by kimcheeboi
Lol it's called school :xx , and if you didn't know calculus is my fav ;-)
Posted by maddav
I can't wait for next year, A-Level maths
Do you mind if i post my own question here Kim?
(Maybe we could start a thread...)
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[ This Message was edited by: maddav on 2004-10-21 21:35 ]
Posted by Payalnik
The first is very easy, but i'm almost asleep, so maybe tomorrow when i get a sheet of paper. The proof of the 2nd is a simple plane.
Posted by maddav
That's it, i remembered something!
it's about rotating across the x axis on 2 hyperbola, but I can't remember, i know you eventually you get the infinite surface area, and finite volume.
I remembered our physics teacher that was going on about theories of the 'shape' of the universe, and he expained the gabriel's horn shape, and we were asking if that was A-level, he said no, and that it was just kind of interesting..
well he was right
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[ This Message was edited by: maddav on 2004-10-21 22:08 ]
Posted by kimcheeboi
Sure, post your own problems! I'll post some linear algebra and differential eqs too if anyone wants. Btw to win the #1 you need to use 2 integrals. Very simple problem. ;-)
Posted by mixin
I passed my A-level Maths 2 and a half years ago. Now managed to wipe all of it from the brain
Posted by RichLok
This is as far as I got in math... and that's by watching an episode of "The Simpsons". The one with Barney (The purple dinosaur) on it...
"Two plus two is four.... Two plus two is four... Two plus two is four...:"
Posted by kimcheeboi
here's a good one!
A series circuit contains a resistor with R= 40 ohms, an inductor with L=2H, a capacitor with C=0.0025 F, and a 12-V batter. The initial charge is Q=.01C and the initial current is 0. Find the charge at time t.
Posted by maddav
This is an easy one I did a couple of weeks ago, so it should be REALLY EASY for you lot!
Solve the equation to find the co-ordinates of each intersection
x(x-3) = x^2(1-x)
@Kimcheeboi: Damn, I can't do it, you seem to be posting all questions just out of my grasp, haven't covered inductors etc. in physics yet!
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[ This Message was edited by: maddav on 2004-10-21 23:43 ]
Posted by kimcheeboi
x=plus or minus sqrrt or 3 or 0
@maddav
fine!
here ya go:
integrate:
x^3/(4x^2+9)^(3/2)
Posted by maddav
almost there Kim, but i said co-ordinates
Posted by kimcheeboi
i wasn't paying attention
btw how are you supposed to find the coordinates of a linear equation? it's not even on a plane!
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Is this where the tortured and the troubled find their own
so co.
"conspiraqcy theories"-meths
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[ This Message was edited by: kimcheeboi on 2004-10-22 00:08 ]
Posted by maddav
OK, I'm really tired and I missed out the VERY top part of my notes (the y's), but i think this is what i did (that's re-assuring
)
y=x(x-3)
y=x^2(1-x)
you should end up with what you got
(x)(x^2-3)
therefore y= (x)(x^2-3)
when x =0, y = 0
when x = +rt3
y= (rt3)(3-3)
y= 3-3rt3 or 3(1-rt3)
and the same for -rt3, i would do it, but I've got to go to bed now.
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[ This Message was edited by: maddav on 2004-10-22 00:34 ]
Posted by maddav
@anyone:
I've got some homework, and i solved this question, but the book says I'm wrong
our teacher said there was a number of mistakes in it as well, so it's really annoying. Anyway, here it is, just the y values please, haven't bothered solving the x values yet.
Simultaneous equations:
x=2y-2
x^2 = y^2 +7
Thanks!
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[ This Message was edited by: maddav on 2004-10-28 18:22 ]
Posted by 50Cent
x=2
y^2= -3
if u want explanation ask (check my answers with the books and urs)
Explanation:
take
x=2y-2 and square it
x^2=4y^2-2
x^2=y^2+7
rearrange
x^2 - 4y^2=-2
x^2 - y^2=7
subtract
-3y^2=9
divide by -3
y^2=-3
substitue into x^2=y^2+7
x^2= -3 +7
x^2=4
x=2
i'm probably wrong as always but its my offering
50
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[ This Message was edited by: 50Cent on 2004-10-28 18:08 ]
[ This Message was edited by: 50Cent on 2004-10-28 18:15 ]
Posted by BobaFett
When i was in general school, it was a usually question of math teachers to students: a ship is 55 m long and there are 273 passangers on board. How old is the captain?
Posted by 50Cent
thats a tough one
just gimme a month to find a 55m boat that has a 279 passenger capacity den i'll just ask the captain
Posted by maddav
@boba:
@50: Ummm, it's a simultaneous equation, with an x^2 and y^2 values, so there should be 2 values for x. This is what i got:
x = 2y-2
x^2 = y^2 + 7
Substitute the value for x, into the second equation:
(2y-2)(2y-2) = y^2 + 7
= 4y^2 -4y -4y +4 = y^2 +7
= 3y^2 - 8y -11 = 0
= (y+1)(3y-11) = 0
y+1=0 y=-1
OR
3y-11=0 y=11/3
3y=11
y=11/3
That's the y values but the book has y=3 or -1/3
Posted by 50Cent
oh noooooo. i just learnt that,
obviously hasnt sunk in yet!
Posted by maddav
That's alright, I'm confused as to how the book got the answer (as the answers are just in listed in the back, no explanation).
I'll just wait patiently for Kim!
Posted by k4m!k4ze
i got the answer as y=3, -1/3
Here's how -
eqns - x = 2y - 2
and x^2 = y^2 + 7
substitue value of x in eqn 1 in eqn 2,
(2y - 2)^2 = y^2 + 7
=> 4y^2 + 4 - 8y = y^2 + 7
=> 3y^2 - 8y - 3 = 0
So by splitting middle term technique,
prod = -9
Sum = -8
so -8y can be split as 9y - y
3y^2 + 9y - y -3 = 0
3y(y+3) - 1(y+3) = 0
(3y - 1) (y+3) = 0
so y=1/3 and y=-3
Simple
This is the technique i was taught. Quite simple eh ?
@kimcheeboi - Man, if you had given those calculus and parabola sums a few years (3) back i woulda solved them but i forgot all those now.
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[ This Message was edited by: kllr_dude on 2004-10-28 18:43 ]
Posted by k4m!k4ze
@maddav - here's where you went wrong -
4y^2 -4y -4y +4 = y^2 +7
is 3y^2 - 8y - 3 = 0
and not 3y^2 - 8y -11 = 0 as you said.
@50 cents - You really need tutoring buddy -
squaring x = 2y - 2
gives x^2 = 4y^2 + 4 - 8y
and not x^2=4y^2-2.
Posted by maddav
That's it!
I realised my earlier mistake of putting in -11, instead of -3. I don't know how i did that one!
Thanks kllr_dude
Posted by k4m!k4ze
Man ! I MUST BE CRAZY !
I didnt even solve such sums in high school even though the teacher begged us to do so !
Of course we solved it once she threatened to call up our parents.
And now i'm sitting here solving them instead of studying for my upcoming exams and that too voluntarily.
Just wish there was somethin like this when i was in high school. Woulda studied better !
Posted by maddav
It's always better with people you can ask
Posted by 50Cent
| Quote: |
|
tell me about it
got a A* in maths tho
Posted by maddav
Well you beat me then, i got an A.
Posted by k4m!k4ze
I got an A+ too but that was in 10th standard (95 %)
I dont know much bout grades cuz over here we talk mainly in terms of percentage.
But i got a pitiful 75 % in my 12th ( i dont know the equivalent of 12th or 10th in US and other countries) .
Posted by 50Cent
we cant probably determine that via ur age. I'm 17 and took the exams earlier this year.
Posted by k4m!k4ze
I'm 20 and i'm gonna finish four years of college by June 2005. So that means i wrote the 12th exams when i was 16.
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[ This Message was edited by: kllr_dude on 2004-10-28 19:52 ]
Posted by maddav
Sounds similar to the GCSE's I took, in which i got an A, but in all fairness, grades on an exam, don't always translate, to good/bad overall competence in a subject.
Just my thoughts!
Posted by 50Cent
as i have just proved
cant even square terms
Posted by 50Cent
y=2x + 1
y^2=2x^2 +x
how do i do this
Posted by k4m!k4ze
x = -1 and x = -1/2
Same technique as above
y=2x+1
y^2=2x^2+x
subst y value in eqn 1 in eqn 2
(2x+1)^2=2x^2+x
=> 2x^2+3x+1=0
=> 2x^2 + 2x + x + 1 = 0
=> (2x + 1) ( x +1 ) = 0
so u get x, subst both values in eqn 1 to get y values
Posted by 50Cent
| Quote: |
|
ah right so
y=(2 x -1) +1
y=-1
and
y=(2 x -1/2)+1
y=0
i think.
Posted by fatreg
This so isnt the maths i did at school!
and i went to a grammar school? what went wrong!?
we were all about algebra, but saying that i never did get all the z,y's so maybe i aint got a hope in hell of getting calculus?
fatreg
Posted by kimcheeboi
help me with series, peeps!
power, taylor, and maclaurin series!
Posted by maddav
I need help, i just can't work out what to do, I know about half of this problem, and the answer, but I need to know how to finish it, I'm sure it's really simple but I just can't get my head round it, here it is:
I need the gradient for the curve f(x) at point A (2,13)
f(x) = 3x² + 2x¯¹
f¹(x) = 6x - 2x¯²
I'm sure for the gradient, i need to do something like substituting the x co-ordinate value, but then I don't know what to do next:
f¹(2) =
Help me please