This equation, $9 + (1 + 2) = 9 + (2 + 1)$, can be classified by examining the properties of addition it demonstrates.

Analysis:

• Associative Property: This property states that the way numbers are grouped in addition does not affect the sum. An example of the associative property would involve rearranging parentheses, such as $(9 + 1) + 2 = 9 + (1 + 2)$. In this problem, the grouping has not changed, so it does not demonstrate the associative property.

• Commutative Property: This property states that the order in which numbers are added does not affect the sum. Here, within the parentheses, the terms are rearranged from $1 + 2$ to $2 + 1$, without changing the sum. Therefore, this equation is an example of the commutative property.

Answer:

The correct answer is commutative property.

Would you like further details on commutative and associative properties?

Here are some related questions to expand your understanding:

1. How does the associative property differ from the commutative property in multiplication?
2. Can the commutative property be applied to subtraction or division?
3. Why is the associative property important in simplifying complex expressions?
4. What would an example of both the commutative and associative properties together look like?
5. How can understanding these properties help in solving equations faster?

Tip: For quick identification, remember that the commutative property involves changing the order, while the associative property involves changing the grouping of numbers.