Answer
$s^{\prime}(x)=\displaystyle \frac{4}{x^{3}}$
Work Step by Step
SUMMARY:
The Power Rule$:\ \ \ [x^{n}]^{\prime}=nx^{n-1 } $
Sum Rule: $\ \ \ \ \ \ [f\pm g]^{\prime}(x)=f^{\prime}(x)\pm g^{\prime}(x) $
Constant Multiple Rule:$\ \ \ [cf]^{\prime}(x)=cf^{\prime}(x) $
Constant times x:$\ \ \ \displaystyle \frac{d}{dx}(cx)=c $
Constant:$\displaystyle \ \ \ \ \ \frac{d}{dx}(c)=0 $
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After expanding:
$s(x)=x^{-1}x^{1}-2x^{-1}x^{-1}=x^{0}-2x^{-2}=1-2x^{-2}$
First term is a constant,
second term: Constant Multiple, and then Power Rule:
$s^{\prime}(x)=0-2(-2x^{-3})$
$s^{\prime}(x)=\displaystyle \frac{4}{x^{3}}$
