which of the following is equivalent to 18 - \\sqrt{-25}?\n5i\n18 - 5i\n18 + 5i\n23

Explanation:

Step1: Simplify square - root of negative number

Recall that $\sqrt{-a}=\sqrt{a}\times\sqrt{- 1}$, and $\sqrt{-1}=i$. So, $\sqrt{-25}=\sqrt{25}\times\sqrt{-1}=5i$.

Step2: Substitute into the expression

Substitute $\sqrt{-25} = 5i$ into $18-\sqrt{-25}$. We get $18 - 5i$.

Answer:

$18 - 5i$ (corresponding to the second option)