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Author Topic: Kal-KOO-Luss
Dr Psyclops
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Icon 1 posted January 14, 2004 18:33      Profile for Dr Psyclops         Edit/Delete Post   Reply With Quote 
So...

If i have equation [ f(x) ]
to find the area under the curve (Integration w/ limits), I integrate f(x) and subtract f(b) (upper limit) from f(a) (lower limit).

A= f(b) - f(a), right?

my paperwork and my calculator are not agreeing.

--------------------
Wherever I am, anyone in need has a friend.
Whenever I return home, everyone is glad I am there.
-Robert L. Humphrey

Posts: 132 | From: Escaped into the waves... | Registered: Nov 2003  |  IP: Logged
Xanthine

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Icon 1 posted January 14, 2004 18:44      Profile for Xanthine     Send New Private Message       Edit/Delete Post   Reply With Quote 
Looks okay.

Check your work. You might be entering something into your calculator wrong. Or doing it wrong on paper.

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And it's one, two, three / On the wrong side of the lee / What were you meant for? / What were you meant for?
- The Decemberists

Posts: 7670 | From: the lab | Registered: Mar 2001  |  IP: Logged
The-Tech
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Icon 1 posted January 14, 2004 18:57      Profile for The-Tech     Send New Private Message       Edit/Delete Post   Reply With Quote 
f(x2) - f(x1) is correct.

What is f(x) ?

If we know what function your integrating we can check the integration and figure out where it went awry.
Dave

--------------------
God not only plays dice with the universe,
he sometimes throws them where they cannot be seen
--- Stephen Hawking

A fanatic is one who can't change his mind and won't change the subject -- Winston Churchill

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Dr Psyclops
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Icon 1 posted January 14, 2004 19:58      Profile for Dr Psyclops         Edit/Delete Post   Reply With Quote 
f(x) = function of x
I got the problem from my notes. I take bad notes.

remember to multiply by g'(x). Thats screwed me up more than once.

--------------------
Wherever I am, anyone in need has a friend.
Whenever I return home, everyone is glad I am there.
-Robert L. Humphrey

Posts: 132 | From: Escaped into the waves... | Registered: Nov 2003  |  IP: Logged
Xanthine

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Icon 1 posted January 14, 2004 20:22      Profile for Xanthine     Send New Private Message       Edit/Delete Post   Reply With Quote 
Yea but waht's the function? I don't pretend to be any good at this sort of thing, but there are a lot of people on these boards who are.

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And it's one, two, three / On the wrong side of the lee / What were you meant for? / What were you meant for?
- The Decemberists

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spungo
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Icon 1 posted January 15, 2004 03:03      Profile for spungo     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Dr Psyclops:
f(x) = function of x
I got the problem from my notes. I take bad notes.

remember to multiply by g'(x). Thats screwed me up more than once.

Uhh... dude - you're not being very clear. What the hell is g'(x)?

--------------------
Shameless plug. (Please forgive me.)

Posts: 6529 | From: Noba Scoba | Registered: Jan 2002  |  IP: Logged
The-Tech
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Icon 1 posted January 15, 2004 08:36      Profile for The-Tech     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by spungo:
quote:
Originally posted by Dr Psyclops:
f(x) = function of x
I got the problem from my notes. I take bad notes.

remember to multiply by g'(x). Thats screwed me up more than once.

Uhh... dude - you're not being very clear. What the hell is g'(x)?
g'(x) would be the first derivitive of g(x). I don't know why you would multiply by that though. The area is calculated by breaking up the area under the curve into rectangles whose length is f(x) and whose width is dx. dx is a small area. The summ of these area's is the intergral of f(x)dx . Sooo as we have all been asking what is the function you are trying to use?

If you are just trying to see if the method works start simple with f(x) = a constant and limits from 0 to 10. Basically you'll be calculating a rectangle with length K and width 10. If you go good there then try f(x) = x which would be the area of a right triangle.

Dave

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spungo
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Icon 1 posted January 15, 2004 08:57      Profile for spungo     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by The-Tech:
g'(x) would be the first derivitive of g(x).

Well, spank my ass and call me Susan!! No feckin' guff. What I meant was - where the hell did 'g' come from? (It hadn't appeared in the thread prior to that post.)

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Shameless plug. (Please forgive me.)

Posts: 6529 | From: Noba Scoba | Registered: Jan 2002  |  IP: Logged
Dr Psyclops
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Icon 1 posted January 15, 2004 11:22      Profile for Dr Psyclops         Edit/Delete Post   Reply With Quote 
Whoops.

d/dx f(g(x)) = f'(g(x)) * g'(x)

I think

Fairly often I would forget to multiply by g'(x). I probibly should have mentioned it. my bad.

g(x) had nothing to do with my area problem.

--------------------
Wherever I am, anyone in need has a friend.
Whenever I return home, everyone is glad I am there.
-Robert L. Humphrey

Posts: 132 | From: Escaped into the waves... | Registered: Nov 2003  |  IP: Logged
Xanthine

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Icon 1 posted January 15, 2004 11:35      Profile for Xanthine     Send New Private Message       Edit/Delete Post   Reply With Quote 
Oooo, the chain rule. That takes me back to places I really don't want to go. [Razz]

So what is this function you're sweating bullets over anyways? I want to see if I still remember how to solve an integral (in biochem we just take logs and reciprocals so we can linearize everything).

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And it's one, two, three / On the wrong side of the lee / What were you meant for? / What were you meant for?
- The Decemberists

Posts: 7670 | From: the lab | Registered: Mar 2001  |  IP: Logged
The-Tech
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Icon 1 posted January 15, 2004 12:58      Profile for The-Tech     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Dr Psyclops:

g(x) had nothing to do with my area problem.

That should make Susan [Big Grin] ... I mean Spungo Happy.
Well not as Happy as the spanking [Big Grin]

--------------------
God not only plays dice with the universe,
he sometimes throws them where they cannot be seen
--- Stephen Hawking

A fanatic is one who can't change his mind and won't change the subject -- Winston Churchill

Posts: 128 | From: Third Stone from the Sun | Registered: Dec 2003  |  IP: Logged
The Famous Druid

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Icon 1 posted January 15, 2004 13:28      Profile for The Famous Druid     Send New Private Message       Edit/Delete Post   Reply With Quote 
quote:
Originally posted by Xanthine:
Oooo, the chain rule. That takes me back to places I really don't want to go. [Razz]

<kinky-homer>
Hmmm.... Chains Rule !
aaaghghghghghghgh.......
</kinky-homer>

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If you watch 'The History Of NASA' backwards, it's about a space agency that has no manned spaceflight capability, then does low-orbit flights, then lands on the Moon.

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Dr Psyclops
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Icon 1 posted January 15, 2004 17:38      Profile for Dr Psyclops         Edit/Delete Post   Reply With Quote 
Okay...

*takes a swig of Dr. Pepper*

...heres the whole tragic story. I bombed my math placement exam upon entering NMIMT, and so I'm all behind in math classes. So, just to keep myself busy over the winter break, ive been reviewing my old calc notes. One problem i left unfinished was really getting to me for no particular reason, the integration was correct, the limits were correct, but it was'nt matching up with what my calculator said it should be.

Thanks, all! [Big Grin]

--------------------
Wherever I am, anyone in need has a friend.
Whenever I return home, everyone is glad I am there.
-Robert L. Humphrey

Posts: 132 | From: Escaped into the waves... | Registered: Nov 2003  |  IP: Logged


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