Chapter 5 5-3 Adding and subtracting rational functions

Objectives

Add and subtract rational expressions.

Simplify complex fractions.

Adding and subtracting rational expressions• Adding and subtracting rational expressions is similar to

adding and subtracting fractions. To add or subtract rational expressions with like denominators, add or subtract the numerators and use the same denominator.

Example #1• Add or subtract. Identify any x-values for which the

expression is undefined.

x – 3

x + 4 +

x – 2x + 4

Example#2• Add or subtract. Identify any x-values for which the

expression is undefined.

3x – 4

x2 + 1 –

6x + 1

x2 + 1

Example#3• Add or subtract. Identify any x-values for which the

expression is undefined. 3x2 – 5

3x – 1 –

2x2 – 3x – 2

3x – 1

Student guided practice• Do problems 2-4 in your book page 332

Adding and subtracting rational expressions• To add or subtract rational expressions with unlike

denominators, first find the least common denominator (LCD). The LCD is the least common multiple of the polynomials in the denominators.

Finding LCM• Find the least common multiple for each pair.• a. 4x3y7 and 3x5y4

• b. x2 – 4 and x2 + 5x + 6

Adding and subtracting rational expressions• To add rational expressions with unlike denominators, rewrite

both expressions with the LCD. This process is similar to adding fractions.

Example#4• Add. Identify any x-values for which the expression is

undefined.

x – 3

x2 + 3x – 4+

2x

x + 4

Example#5• Add. Identify any x-values for which the expression is

undefined.

x

x + 2+

–8

x2 – 4

Example#6• Add. Identify any x-values for which the expression is

undefined.

3x

2x – 2+

3x – 2

3x – 3

Example#7

• Subtract . Identify any x-values for which the

expression is undefined.

Student guided practice• Do problems 7-10 in your book page 332

Complex fraction• Some rational expressions are complex fractions. A complex

fraction contains one or more fractions in its numerator, its denominator, or both. Examples of complex fractions are shown below.

Recall that the bar in a fraction represents division. Therefore, you can rewrite a complex fraction as a division problem and then simplify. You can also simplify complex fractions by using the LCD of the fractions in the numerator and denominator.

Example • Simplify. Assume that all expressions are defined.

x + 2x – 1x – 3x + 5

Example • Simplify. Assume that all expressions are defined.

x – 1x

x2

3x

+

Example • Simplify. Assume that all expressions are defined.

20x – 1

63x – 3

Student guided practice• Do problems 13-15 in your book page 332

Homework • Do problems even numbers from 17-28 in your book page

332.

Closure

• Today we learned how to add and subtract rational expressions

• Next class we are going to continue with rational functions.