Purple Math
Purplemath: Simplifying Expressions With Exponents
A detailed look at how to simplify expressions with exponents and how to apply the rules for exponents. Lots of examples included. The third page provides an interactive widget to use for simplifying expressions with exponents.
Wikimedia
Wikipedia: Additive Inverse
What is additive inverse? It means "opposite." Find out more about this concept in this detailed definition with examples and links to related terms.