Derivative of (x^2+5x-1)/(x^2)

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SUMMARY

The discussion focuses on finding the first derivative of the function (x^2 + 5x - 1)/(x^2). The initial attempt at a solution yields the derivative y' = (-5x + 2)/x^3, which is confirmed to be correct. An alternative method is suggested, simplifying the function to 1 + 5x^(-1) - x^(-2) before differentiating, resulting in the same derivative. The use of the product rule is also recommended for more complex denominators.

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Homework Statement

Find the first derivative of [...] (below)



Homework Equations



((x^2)+5x-1)/(x^2)

The Attempt at a Solution



(x^2+5x-1)/(x^2)

y&#039; = \frac{(x^2)(2x+5-0)-((x^2)+5x+-1)(2x)}{x^4}<br /> <br /> \\ <br /> y&#039; = \frac{2x^3+5x^2-2x^3-10x^2+2x}{x^4}<br /> <br /> \\ y&#039; = \frac{(-5x^2)+2x}{x^4}<br /> <br /> \\ y&#039; = \frac{-5x+2}{x^3}<br /> <br />

Is this correct? It feels "off."
 
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thats what i got... =]
 
Cool. Thank you. :)
 
However, the simplest way to do that is write
\frac{x^2+ 5x- 1}{x^2}= \frac{x^2}{x^2}+ \frac{5x}{x^2}- \frac{1}{x^2}= 1+ 5x^{-1}- x^{-2}

The derivative of that is, of course, -5x^{-2}+ 2x^{-3}.

Can you see that that is equal to your result?
 
You can also apply the product rule if HallsofIvy's method doesn't work out (for example, if the denominator is more complicated).
 

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