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Mathematics Maths Logic?, hope you guys can make sense out of it

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loongchai
post Jul 14 2009, 06:12 PM

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d/dx(x^2)=2x
d/dx(x+x+x+...+x+x)=1+1+1+1+...+1+1+1 (2x number of times)
which equals to 2x

therefore,
2x=2x,
2=2
loongchai
post Jul 15 2009, 11:37 PM

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QUOTE(lin00b @ Jul 15 2009, 06:03 PM)


how does d[x+x+x+..+x (x times)]/dx = 1+1+1+...+1 (2x times)?
*
d/dx(x^2)=2x
d/dx(x+x+x+...+x+x)=1+1+1+1+...+1+1+1 (2x number of times)

2x because of d/dx(x^2)=2x

d/dx(x^2) = d/dx(x+x+x+...+x+x)

and

2x = 1+1+1+1+...+1+1+1 (2x number of times)

rclxub.gif


loongchai
post Jul 16 2009, 01:40 AM

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QUOTE(lin00b @ Jul 15 2009, 11:44 PM)
d/dx(x) = 1
d/dx(x+x) = 1+1
d/dx(x+x+x)=1+1+1
...
d/dx(x+x+x+...+x [x number of times])=1+1+1+...+1 [x number of times]

no?
*
u should look at it this way:

d/dx(x) = 1
d/dx(x+x) = 1+1
d/dx(x+x+x)=1+1+1
...
d/dx(x+x+x+...+x [y number of times])=1+1+1+...+1 [y number of times]

d/dx(yx)=1+1+1+...+1 [y number of times]
d/dx(yx)=y

use y as a factor instead of x, so it won't affect the differentiation in terms of x.

I guess, to really understand this, u gotta search deep into the Differentiation from First Principle

This post has been edited by loongchai: Jul 16 2009, 01:49 AM
loongchai
post Jul 16 2009, 06:09 PM

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QUOTE(bgeh @ Jul 16 2009, 01:54 AM)
But what happens if y = x? That's the interesting part
*
y is a factor.

y cannot be x because it causes the line of the graph to be different.

Differentiation is derived from graphs.


For example,

From the straight line equation, y=mx+c,

dy/dx is the slope of the graph or m.

If you were to replace m with x, the graph would not be linear anymore. (y = x^2 + c) You would be changing the linear line to a curve.

In this case, m is a factor. Same goes to y from the TS's question.

unsure.gif I am not very good at explaining.

loongchai
post Jul 16 2009, 06:14 PM

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QUOTE(bgeh @ Jul 16 2009, 06:10 PM)
Then you're claiming that it's useless to even try to differentiate anything more than a linear function, which is quite a dangerous proposition, no?

[and no, it's not only from graphs - graphs are useful because they give us an intuitive idea of what differentiation does]
*
No, of course we can differentiate more than a linear graph. If you were to add a x factor to a linear function, it turns to a curve. And if you were to add another x to the curve function, it becomes another type of graph. And it goes on. However, adding a factor instead of x would only change the scale of the graph.

This post has been edited by loongchai: Jul 16 2009, 06:15 PM
loongchai
post Jul 16 2009, 07:01 PM

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QUOTE(bgeh @ Jul 16 2009, 06:17 PM)
Okay, let's examine your claims:

You've gone on to consider another problem, which is the case where the variable we differentiate wrt (x) is different (in this case, you denoted it by y)

But what relevance does it have compared to the original problem at hand firstly?
*
The original problem will only happen if we were to equate y to x or y=x. I am trying to prove that y cannot be equal to x. This is because if y=x, then the graph will be different, which affects the differentiation. y, being a factor will only affect the scale of the graph, not the shape of it.
loongchai
post Jul 16 2009, 11:23 PM

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QUOTE(bgeh @ Jul 16 2009, 11:17 PM)
But then the question would be: How would you differentiate x^2 then, if y can never be equal to x? The thing should give consistent results no matter what representation you use. If one representation gives you a result but the other doesn't you're in trouble!
*
You are making things complicated...

y can never be equal to x? That only applies to the original question.



This post has been edited by loongchai: Jul 16 2009, 11:25 PM

 

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