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derivative of: sqrt(x) - x using the first principal. Please show work. The answer should be 1/[2*sqrt(x)]-1 I cant get the minus 1!

Mathematics
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i guess you know how to find the derivate of x ... so just find for sqrt(x)
f(x) = \[\sqrt{x} -x \]
oh...so just do them one at a time?:| That actually makes a lot of sense. the problem is I have the equation in the "definition of the derivative formula" and its not simplifying down right.

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Other answers:

where you take the limit as h-->0
lim dx->0 (sqrt(x+dx) - sqrt(x))/dx now sqrt(x+dx) = sqrt(x)*sqrt(1+dx/x) using binomial expansion, and removing higher terms --- close to linear expression we have: sqrt(x)(1+1/2*dx/x) or, lim dx->0 (sqrt(x)(1+1/2*dx/x) - sqrt(x))/dx or, lim dx->0 (1/2*dx/sqrt(x))/dx = 1/(2sqrt(x)) hence proved
seems he wants the increment thingy...the limits
@Ravus , are you asking to take the derivative using the definition? (limit definition of derivative)
@experimentX how do you get this sqrt(x+dx) = sqrt(x)*sqrt(1+dx/x)
@perl, nice avatar!
hehe
yes I want the "increment thingy"<<
@perl .. take x common!
huh?
|dw:1333351654824:dw| plug it in to that...
(x+dx)^1/2 = x^1/2 + ...
ohhhh
yeah I did plug it in, and I get the right answer almost. I get 1/2*sqrt(x) but that whole thing should have a "-1"! i dont get that bit
@experimentX (x+dx)^1/2 = x^1/2 ( 1 + dx/x ) ^1/2
dx is supposed to be del x ... or better h
|dw:1333351804706:dw| do some algebra here....
ok... too many cooks... i'll quit.
yeah I know what the formula is, but the algebra is giving me trouble
@experimentX Very clever argument, so you looked at the binomial series and took the first two terms (linear )
yes .. since dx^higer would be very less ... it would seem better to take linear term.
then you factored out sqrt x
yes .. and that would cancel out .. sqrt(x) leaving dx/(2sqrt(x)
omg wow finally got it. simple algebra really. lmfao............
congrats
|dw:1333354174909:dw|

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