# FACTORING POLYNOMIALS

Out line
1 Factoring Polynomials
• Terminology
• Factoring

2 Rational Expressions
• Definition
• Manipulating Rational Expressions

Terms

Definition
The terms of an algebraic expression are those elements that are
separated by addition (that is, by plus or minus signs).

The sign of the term is important!

Monomials

Definition
Terms that contain variables with only nonnegative integer
exponents are called monomials.

Polynomials

Definition
A polynomial is a monomial or a finite sum of monomials.

Examples of polynomials

Factoring Out Monomials

The simplest form of factoring polynomials is factoring out the
highest common monomial factor.

• In x2 + 3x, each term contains a factor of x.
x2 + 3x = x(x + 3)

• In 3x4 + 12x2, each term contains a factor of 3x2.
3x4 + 12x2 = 3x2(x2 + 4)

• In 12a2b − 30ab + 18ab2, each term contains a factor of 6ab.
12a2b − 30ab + 18ab2 = 6ab(2a − 5 + 3b)

Factoring By Grouping
Some times we can factor out a binomial by grouping terms in
pairs, and factoring a monomial out of each pair.

• x3 + 2x2 + 3x + 6
= (x3 + 2x2) + (3x + 6)
= x2(x + 2) + 3(x + 2)
= (x2 + 3)(x + 2)

• 3ac + 16b − 4a − 12bc
= 3ac − 12bc − 4a + 16b
= (3ac − 12bc) + (−4a + 16b)
= 3c(a − 4b) − 4(a − 4b)
= (3c − 4)(a − 4b)

Factoring ax2 + bx + c

To factor a quadratic of the form ax2 + bx + c:

Find a pair of numbers, say r and s, whose sum is b
(r + s = b), and whose product is ac (rs = ac).

Write the quadratic as ax2 + rx + sx + c.

Factor by grouping.

Example: 4x2 + 11x + 6 a = 4, b = 11, c = 6

Find two numbers whose product is 24 and whose sum is 11.
r = 3, s = 8

Write the quadratic as 4x2 + 3x + 8x + 6.

Factor by grouping.
4x2 + 3x + 8x + 6
= (4x2 + 8x) + (3x + 6)
= 4x(x + 2) + 3(x + 2)
= (4x + 3)(x + 2)

Special Factoring Patterns

• x2 − y2 = (x + y)(x − y)
• x3 + y3 = (x + y)(x2 − xy + y2)
• x3 − y3 = (x − y)(x2 + xy + y2)

Examples

Factor 9x2 − 25 completely. (3x + 5)(3x − 5)

Factor 9x2y2 − 64 completely. (3xy + 8)(3xy − 8)

Factor a2 + 5a − 24 completely. (a + 8)(a − 3)

Factor 2x2 − 7x − 30 completely. (2x + 5)(x − 6)

Factor x3 + 64 completely. (x + 4)(x2 − 4x + 16)

Factor 2n2 − n − 5 completely. Not factorable

Definition

Definition
The quotient of two polynomials is called a rational expression.
Examples

We will assume that all denominators represent nonzero real
numbers (so we needn’t always write things like “x ≠−2” or
“x ≠1/3”).

Simplifying

• Factor anything you can.
• Cancel factors if possible.
• Remember that rational expressions are just fractions.

We really need to work examples.

Examples

Examples
Simplify

Simplify

Simplify

Simplify
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Simplify

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