Answer
$D(G)=\{x \in \mathbb{R} : x \leq 1\}$
Work Step by Step
The radicand (expression inside the radical sign) of a square root is not allowed to be negative. Thus, to find the domain of the given functino, we have to solve the ienquality:
$$1-x\ge0$$
Solve the inequality to obtain:
$$\begin{align*}
1-x&\ge0\\
1&\ge x\\
x&\le1
\end{align*}$$
Therefore, the domain of the given function is $\left\{x|x\le1\right\}$.
