#### Answer

$y=1-\sqrt{-x}$
With domain: $x\leq0$

#### Work Step by Step

We need to solve the equation for $y$:
$x+(y-1)^2=0$
$(y-1)^2=-x$
$y-1=\pm\sqrt{-x}$
$y=1\pm\sqrt{-x}$
Since we need the bottom half of the parabola, we use:
$y=1-\sqrt{-x}$
With domain: $x\leq0$