To fully simplify $\sqrt{90}$, we need to find the prime factorization of 90.

First, express 90 as a product of prime factors: $90 = 2 \times 3^2 \times 5$

Now, break the square root into parts: $\sqrt{90} = \sqrt{2 \times 3^2 \times 5}$

Since $3^2$ is a perfect square, we can take 3 out of the square root: $\sqrt{90} = 3\sqrt{2 \times 5} = 3\sqrt{10}$

Thus, the fully simplified form of $\sqrt{90}$ is: $\boxed{3\sqrt{10}}$

Would you like further details, or do you have any questions?

Here are 5 related questions:

1. How would you simplify $\sqrt{72}$?
2. Can you express $\sqrt{45}$ in its simplest form?
3. How can prime factorization help simplify square roots?
4. What happens if you try to simplify $\sqrt{200}$?
5. What is the simplest form of $\sqrt{50}$?

Tip: Always look for perfect square factors when simplifying square roots.