Equations
4. (Multiplicative Identity) The multiplicative identity is 1.
a ? 1 5 1 ? a 5 a
5. (Additive Inverse) Each element a has an additive inverse, denoted by 2a.
a 1 12a2 5 2a 1 a 5 0
Note that there is a difference between a negative number and the negative of a number.
6. (Multiplicative Inverse) Each nonzero element a has a multiplicative inverse, denoted
by a21.
a # a21 5 a21 # a 5 1
Note that a21 5 1∙a.
7. (Distributive Law) Multiplication is distributive over addition.
a(b 1 c) 5 ab 1 ac
Note that Property 5 provides the means to subtract by defining a 2 b 5 a 1 (2b) and
Property 6 provides a means to divide by defining a 4 b 5 a ? (1∙b). The number 0 has no
multiplicative inverse, so division by 0 is undefined.