The expression $\sqrt{-16}$ involves finding the square root of a negative number, which leads us to the concept of imaginary numbers.

We cannot find the square root of a negative number using real numbers. However, we define the imaginary unit $i$, where:

$i = \sqrt{-1}$

Using this definition, we can rewrite $\sqrt{-16}$ as:

$\sqrt{-16} = \sqrt{16} \times \sqrt{-1} = 4i$

So, $\sqrt{-16} = 4i$.

Would you like more details or have any questions?

Here are 5 related questions:

1. What is $\sqrt{-25}$?
2. How do we handle higher powers of $i$?
3. What is $(4i)^2$?
4. How do imaginary numbers apply in solving quadratic equations?
5. What is the general form of a complex number?

Tip: Imaginary numbers are essential when dealing with equations that don't have real-number solutions, especially in fields like engineering and physics.