Question

X + 9 = 9 + x. this is an illustration of which property?

Answer 1

It's an illustration of the commutative property of addition.

Definition of the commutative property of addition:

The word "commutative" comes from "commute" or "move around", so the Commutative Property is the one that refers to moving stuff around. For addition, the rule is "a + b = b + a"; in numbers, this means 2 + 3 = 3 + 2. For multiplication, the rule is "ab = ba"; in numbers, this means 2×3 = 3×2.

Answer 2

It's an example of the commutative property of addition.