Proposition: Multiplication of Integers 

According the definition of integers, we can identify integers \(x,y \in \mathbb Z\) with equivalence classes \(x:=[a,b]\), \(y:=[c,d]\) for some natural numbers \(a,b,c,d\in\mathbb N\).

Based on the addition of natural numbers and the multiplication of natural numbers, we define a new multiplication operation “\( \cdot \)” for all integers by setting

\[\begin{array}{ccl}
x\cdot y:=[a,b] \cdot [c,d] &:=& [a\cdot c + b\cdot d,~ a\cdot d + c\cdot b]=[ac + bd,~ ad + bc],
\end{array}
\]

where \([ac + bd,~ ad + bc]\) is also an integer, called the product of the integers \(x\) and \(y\). The product exists and is well-defined, i.e. it does not depend on the specific representatives \([a,b]\) and \([c,d]\) of \(x\) and \(y\).

| | | | | created: 2014-09-21 14:52:36 | modified: 2019-04-17 06:09:15 | by: bookofproofs | references: [696]

1.Proof: (related to "Multiplication of Integers") 

2.Proposition: Multiplication of Integers Is Associative 

3.Proposition: Multiplication of Integers Is Commutative 

4.Proposition: Multiplication of Integers Is Cancellative 

5.Proposition: Existence of Integer One (Neutral Element of Multiplication of Integers) 

6.Proposition: Uniqueness of Integer One 

7.Proposition: Multiplying Negative and Positive Integers