Algebra Tutorials!  
Friday 19th of July
Rotating a Parabola
Multiplying Fractions
Finding Factors
Miscellaneous Equations
Mixed Numbers and Improper Fractions
Systems of Equations in Two Variables
Literal Numbers
Adding and Subtracting Polynomials
Subtracting Integers
Simplifying Complex Fractions
Decimals and Fractions
Multiplying Integers
Logarithmic Functions
Multiplying Monomials
The Square of a Binomial
Factoring Trinomials
The Pythagorean Theorem
Solving Radical Equations in One Variable
Multiplying Binomials Using the FOIL Method
Imaginary Numbers
Solving Quadratic Equations Using the Quadratic Formula
Solving Quadratic Equations
Order of Operations
Dividing Complex Numbers
The Appearance of a Polynomial Equation
Standard Form of a Line
Positive Integral Divisors
Dividing Fractions
Solving Linear Systems of Equations by Elimination
Multiplying and Dividing Square Roots
Functions and Graphs
Dividing Polynomials
Solving Rational Equations
Use of Parentheses or Brackets (The Distributive Law)
Multiplying and Dividing by Monomials
Solving Quadratic Equations by Graphing
Multiplying Decimals
Use of Parentheses or Brackets (The Distributive Law)
Simplifying Complex Fractions 1
Adding Fractions
Simplifying Complex Fractions
Solutions to Linear Equations in Two Variables
Quadratic Expressions Completing Squares
Dividing Radical Expressions
Rise and Run
Graphing Exponential Functions
Multiplying by a Monomial
The Cartesian Coordinate System
Writing the Terms of a Polynomial in Descending Order
Quadratic Expressions
Solving Inequalities
Solving Rational Inequalities with a Sign Graph
Solving Linear Equations
Solving an Equation with Two Radical Terms
Simplifying Rational Expressions
Intercepts of a Line
Completing the Square
Order of Operations
Factoring Trinomials
Solving Linear Equations
Solving Multi-Step Inequalities
Solving Quadratic Equations Graphically and Algebraically
Collecting Like Terms
Solving Equations with Radicals and Exponents
Percent of Change
Powers of ten (Scientific Notation)
Comparing Integers on a Number Line
Solving Systems of Equations Using Substitution
Factoring Out the Greatest Common Factor
Families of Functions
Monomial Factors
Multiplying and Dividing Complex Numbers
Properties of Exponents
Multiplying Square Roots
Adding or Subtracting Rational Expressions with Different Denominators
Expressions with Variables as Exponents
The Quadratic Formula
Writing a Quadratic with Given Solutions
Simplifying Square Roots
Adding and Subtracting Square Roots
Adding and Subtracting Rational Expressions
Combining Like Radical Terms
Solving Systems of Equations Using Substitution
Dividing Polynomials
Graphing Functions
Product of a Sum and a Difference
Solving First Degree Inequalities
Solving Equations with Radicals and Exponents
Roots and Powers
Multiplying Numbers
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Product of a Sum and a Difference

If we multiply the sum a + b and the difference a - b by using FOIL, we get

(a + b)(a - b) = a2 - ab + ab - b2
  = a2 - b2

The inner and outer products add up to zero, canceling each other out. So the product of a sum and a difference is the difference of two squares, as shown in the following rule.


Rule for the Product of a Sum and a Difference

(a + b)(a - b) = a2 - b2


Example 1

Finding the product of a sum and a difference

Find the products.

a) (x + 3)(x - 3)

b) (a3 + 8)(a3 - 8)

c) (3x2 - y3)(3x2 + y3)


a) (x + 3)(x - 3) = x2 - 9

b) (a3 + 8)(a3 - 8) = a6 - 64

c) (3x2 - y3)(3x2 + y3) = 9x4 - y6

Helpful hint

You can use (a + b)(a - b) = a2 - b2 to perform mental arithmetic tricks such as 59 · 61 = 3600 - 1 = 3599. What is 49 · 51? 28 · 32?

The square of a sum, the square of a difference, and the product of a sum and a difference are referred to as special products. Although the special products can be found by using the distributive property or FOIL, they occur so frequently in algebra that it is essential to learn the new rules. In the next example we use the special product rules to multiply two trinomials and to square a trinomial.


Example 2

Using special product rules to multiply trinomials

Find the products.

a) [(x + y) + 3][(x + y) - 3]

b) [(m - n) + 5]2


a) Use the rule (a + b)(a - b) = a2 - b2 with a = x + y and b = 3:

[(x + y) + 3][(x + y) - 3] = (x + y)2 - 32
  = x2 +2xy + y2 - 9

b) Use the rule (a + b)2 = a2 + 2ab + b2 with a = m - n and b = 5:

[(m - n) + 5]2 = (m - n)2 + 2(m - n)5 + 52
  = m2 - 2mn + n2 + 10m - 10n + 25


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