To simplify the expression $-\sqrt{-60}$ using the imaginary unit $i$, follow these steps:

1. Simplify the negative square root: $-\sqrt{-60} = -\sqrt{60} \cdot \sqrt{-1}$ Since $\sqrt{-1} = i$, the expression becomes: $-\sqrt{60} \cdot i$

2. Simplify the square root of 60: $\sqrt{60} = \sqrt{4 \times 15} = \sqrt{4} \times \sqrt{15} = 2\sqrt{15}$ So the expression becomes: $-2\sqrt{15} \cdot i$

Thus, the simplified form of $-\sqrt{-60}$ as a complex number is:

$-2\sqrt{15}i$

Would you like a detailed explanation of any of these steps?

Here are 5 related questions for further practice:

1. Simplify $\sqrt{-50}$ as a complex number.
2. Simplify $3\sqrt{-20}$ using the imaginary unit $i$.
3. Write $-\sqrt{-75}$ as a complex number.
4. Simplify $\sqrt{-32}$ as a complex number.
5. Simplify $-4\sqrt{-45}$ using the imaginary unit $i$.

Tip: When dealing with square roots of negative numbers, always remember to express $\sqrt{-1}$ as $i$.