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Simple derivative problem

  • #1
Here is the equation and my attempt on a dry-erase board:

bijd3b.jpg


My steps are similar to the textbook's up until I hit that 3x^1/2. Why is it disappearing with their method? It's late at night and my brain is fried; I have a feeling this will be painfully obvious to me in the morning, but in case it isn't, perhaps someone can fill me in on what I missed?
 

Answers and Replies

  • #2
Ray Vickson
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Here is the equation and my attempt on a dry-erase board:

bijd3b.jpg


My steps are similar to the textbook's up until I hit that 3x^1/2. Why is it disappearing with their method? It's late at night and my brain is fried; I have a feeling this will be painfully obvious to me in the morning, but in case it isn't, perhaps someone can fill me in on what I missed?
Recall that ##1/\sqrt{x} = x^{-1/2},## so
[tex] \frac{d}{dx} \frac{2x-1}{\sqrt{x}} = x^{-1/2}\frac{d}{dx} (2x-1)
+ (2x-1) \frac{d}{dx} x^{-1/2}.[/tex]
You had written ##(d/dx) x^{1/2}.##

RGV
 

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