The given equation is:

$xy + xy$

This can be simplified by factoring out the common term $xy$:

$xy + xy = 2xy$

So, the simplified form of the expression is:

$2xy$

Let me know if you would like more details or have any further questions!

Here are five related questions:

1. What happens when you factor more complex expressions like $3xy + 5xy$?
2. How do you simplify an equation like $2xy + 3x$?
3. How can you solve for $x$ or $y$ if additional terms are introduced?
4. What is the difference between adding and multiplying terms like $xy + x^2y^2$?
5. How would you approach solving for $x$ and $y$ if given $xy = 10$?

Tip: When simplifying expressions, always check for common factors across all terms before performing other operations!