Key Concepts

• Multiplication of Signed Numbers
  • To determine the sign of the product of two signed numbers:
    

    Same Signs	Product
    Two positives Two negatives	Positive Positive

    Different Signs	Product
    Positive • negative Negative • positive	Negative Negative

• Division of Signed Numbers
  • To determine the sign of the quotient of two signed numbers:
    

    Same Signs	Quotient
    Two positives Two negatives	Positive Positive

    Different Signs	Quotient
    Positive • negative Negative • Positive	Negative Negative

• Multiplication by $-1$
  • Multiplying a number by $-1$ gives its opposite: $-1(a)=-a$
• Division by $-1$
  • Dividing a number by $-1$ gives its opposite: $a\div(-1)=-a$