We need to evaluate the expression $\sqrt{[-1 - (-5)]^2}$.

1. Problem Description

We need to evaluate the expression $\sqrt{[-1 - (-5)]^2}$.

2. Solution Steps

First, we simplify the expression inside the square brackets:

$-1 - (-5) = -1 + 5 = 4$

So, the expression becomes $\sqrt{[4]^2}$.

Now, we calculate the square:

$4^2 = 16$

The expression is now $\sqrt{16}$.

Finally, we take the square root:

$\sqrt{16} = 4$

3. Final Answer

4