b) To evaluate $-\sqrt{-x}$ for $x=-81$, we first find $\sqrt{-x}$, which we already did in part (a):
$-\sqrt{-x} = -9$ when $x=-81$.
c) To evaluate $-\sqrt{x}$ for $x=-81$, we first replace $x$ with $-81$:
$-\sqrt{-81}$
However, we cannot take the square
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