QUOTE(MattL @ Jul 16 2009, 08:42 PM)
Wah this discussion still going on arr... See the wiki site on the previous page la... While it's true that
x^2=x+x+x+x+...+x+x (x number of times)
and
d/dx(x^2)=2x,
the mistake is
d/dx(x+x+x+...+x+x)=1+1+1+1+...+1+1+1 (
x number of times)
because x here is not held constant.
true, the explanation is there, but how many actually understand the explanation?
and whats the problem with x not being held constant? is any mathematical laws being broken by letting x remain a variable?
Added on July 30, 2009, 1:39 pmQUOTE(Aurora @ Jul 28 2009, 11:44 PM)
d/dx (x+x+...x+x) is in fact flawed. Remember that x increase at the magnitude of power of 2;
Let say x = 10
d/dx(x^2) = x+x+...x+x (10 times, with the value of x = 10)
Let say x = 11
d/dx(x^2) = x+x+...x+x (11 times, with the value of x = 11)
Why I say it is flawed, because the "x number of times" is not reflected in the equation, but only the value of x.
The true definition of d/dx is rate of change. For the equation y=x^2, the derivative (d/dx=2x) simply means the rate of change for the function when x is at certain value.
Let x = 10;
d/dx (x^2) = 2x = 20;
By rate of change, it means that any changes to the value, it is effectively scaled with that magnitude.
Say x = 10.001; the change (dx) = 0.001;
Effectively, the result should be = 10 + 0.001*20 = 10.02
Double check 10.001^2 = 10.020001
let x = 10,
2x = 1+1+1+... (10 times)
20 = 10
iirc, small changes is only used when there is 2 or more variable in a function? (could be wrong though)
This post has been edited by lin00b: Jul 30 2009, 01:39 PM