The image shows the mathematical expression:

$\sqrt{20} - \sqrt{15}$

To simplify or approximate this expression, let's first break down the square roots:

$\sqrt{20} = \sqrt{4 \times 5} = 2\sqrt{5}$ $\sqrt{15} = \sqrt{3 \times 5}$

So the expression becomes:

$2\sqrt{5} - \sqrt{15}$

Since these terms involve different square roots, the expression cannot be simplified further in an exact form. However, if you need an approximate decimal value, we can calculate it:

$\sqrt{20} \approx 4.472 \quad \text{and} \quad \sqrt{15} \approx 3.873$ $\sqrt{20} - \sqrt{15} \approx 4.472 - 3.873 = 0.599$

Thus, the approximate value of the expression is 0.599.

Would you like more details or further clarification?

Here are five related questions for deeper understanding:

1. How would you handle expressions involving the addition of square roots?
2. Can you simplify an expression like $\sqrt{50} - \sqrt{2}$?
3. How do you handle square roots of non-perfect squares?
4. What is the relationship between square roots and powers?
5. What are the common approximations for square roots of small non-perfect square numbers?

Tip: When working with square roots that don't have an exact simplification, consider approximating them using a calculator if a decimal form is acceptable.