Illustrative Mathematics
Illustrative Mathematics: Counting Dots in Arrays
This task aims to show students that there is often more than one way to represent a quantity. This lesson also lays a foundation for students to understand the commutative property of multiplication.
McGraw Hill
Mc Graw Hill: The Additive Inverse Property
The sum of any number and its additive inverse is always a zero. This site gives you the rule for this property.
University of St. Andrews (UK)
University of St. Andrews: Brahmagupta
Brahmagupta was a mathematician and an astronomer. He is responsible for the addition and multiplication properties of zero.