Definition:  Distance from zero. 

Example:  l 2 l = 2       l -5 l = 5

Definition:  Number that does not change.

Example:  20, 17, 99

Definition:  Expression that contains <, >, <, >

Example:  5 < 8        5x + 2 > 12

Inverse Operation

Definition:  Opposite

Example:  multiply - divide;  add - subtract

Definition:  Replace

Example:  5m - 2 when m = 3