Answer
$-0.5x^{-0.5}$
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:$\ \ \ [cf]^{\prime}(x)=cf^{\prime}(x)\\$
$\displaystyle \frac{d}{dx}(cx)=c,\ \ \ \ \ \frac{d}{dx}(c)=0\\$
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$[-x^{0.5}]^{\prime}=[(-1)x^{0.25}]^{\prime}$=... Constant Multiple Rule...
= $-[x^{0.5}]^{\prime}$=... Power rule...
$=-0.5x^{0.5-1}$
= $-0.5x^{-0.5}$