Question: What would you do to isolate the variable in the equation below, using only one step?
$x + 9 = -12$
1. The problem is to isolate the variable $x$ in the equation $$x + 9 = -12$$ using only one step.
2. To isolate $x$, we need to undo the addition of $9$. The inverse operation of adding $9$ is subtracting $9$.
3. Subtract $9$ from both sides of the equation:
$$x + 9 - \cancel{9} = -12 - 9$$
4. Simplify both sides:
$$x = -21$$
5. Therefore, the solution is $x = -21$.
6. The correct one-step operation is to subtract $9$ from both sides of the equation.