It looks like you're working with an expression involving square roots. I believe the expression you meant to write is:

$(\sqrt{5} + \sqrt{4})(\sqrt{5} - \sqrt{4})$

This is a product of two binomials. Notice that this expression is in the form of a difference of squares, which can be simplified using the identity:

$(a + b)(a - b) = a^2 - b^2$

Here, $a = \sqrt{5}$ and $b = \sqrt{4}$. Applying the identity:

$(\sqrt{5} + \sqrt{4})(\sqrt{5} - \sqrt{4}) = (\sqrt{5})^2 - (\sqrt{4})^2$

Now calculate each square:

$(\sqrt{5})^2 = 5 \quad \text{and} \quad (\sqrt{4})^2 = 4$

Thus, the expression simplifies to:

$5 - 4 = 1$

So, the value of the expression is 1.

Would you like further clarification or have any additional questions? Here are some related questions:

1. What is the difference of squares formula, and how can it simplify expressions?
2. How does the distributive property relate to simplifying binomials like this one?
3. What other identities can simplify square root expressions?
4. How can you simplify expressions involving cube roots?
5. Can the difference of squares formula apply to other kinds of algebraic expressions?

Tip: Always check if the expression you're working with can be factored or simplified using common algebraic identities (like the difference of squares), as it can save a lot of time in solving problems.