## Factoring and Simplifying: (xy-1)(xy+1)(x+3)

This expression involves three factors: (xy-1), (xy+1), and (x+3). To simplify this, we can use the following:

### Recognizing the Difference of Squares

The first two factors, (xy-1) and (xy+1), are in the form of a **difference of squares**. Recall that:

**a² - b² = (a + b)(a - b)**

Applying this to our factors:

- (xy-1) = (xy)² - 1²
- (xy+1) = (xy)² + 1²

Therefore, we can rewrite the entire expression as:

**(xy)² - 1²)(xy)² + 1²)(x+3)**

### Expanding and Simplifying

Now, we can expand the first two factors using the difference of squares pattern:

- [(xy)² - 1²][(xy)² + 1²] = (xy)⁴ - 1⁴

This simplifies to:

**(x⁴y⁴ - 1)(x+3)**

### Final Result

The fully factored and simplified form of the expression (xy-1)(xy+1)(x+3) is **(x⁴y⁴ - 1)(x+3)**.

This can be further expanded if desired, but it is generally considered simplified in its current form.