Answer
$\{x|x\le1 \}$.
Work Step by Step
Step 1. Domain of $g(x)$: $\{x|x\le1 \}$.
Step 2. For $(f\circ g)(x)$ we need: $g(x)$ can be any real number.
Step 3. Thus Domain of $(f\circ g)(x)$: $\{x|x\le1 \}$.
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