Adding and Subtracting Rational Expressions - Cobb .Adding and Subtracting Rational Expressions

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• Holt McDougal Algebra 2

Rational Expressions

Rational Expressions

Holt Algebra 2

Warm Up

Lesson Presentation

Lesson Quiz

Holt McDougal Algebra 2

• Holt McDougal Algebra 2

Rational Expressions

1.

2.

3.

4.

x 0

1324

x 1, x 1

Simplify. Identify any x-values for which the expression is undefined.

1315

1112

38

715

25

+

x 1x2 1

1x + 1

13

x64x9

12x3

• Holt McDougal Algebra 2

Rational Expressions

Simplify complex fractions.

Objectives

• Holt McDougal Algebra 2

Rational Expressions

complex fraction

Vocabulary

• Holt McDougal Algebra 2

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.

• Holt McDougal Algebra 2

Rational Expressions

Add or subtract. Identify any x-values for which the expression is undefined.

Example 1A: Adding and Subtracting Rational

Expressions with Like Denominators

The expression is undefined at x = 4 because this value makes x + 4 equal 0.

x 3x + 4

+x 2x + 4

x 3 +x + 4

x 2

2x 5x + 4

Combine like terms.

• Holt McDougal Algebra 2

Rational Expressions

Add or subtract. Identify any x-values for which the expression is undefined.

Example 1B: Adding and Subtracting Rational

Expressions with Like Denominators

Subtract the numerators.

There is no real value of x for which x2 + 1 = 0; the expression is always defined.

3x 4x2 + 1

6x + 1x2 + 1

3x 4 x2 + 1

(6x + 1)

3x 5x2 + 1 Combine like terms.

Distribute the negative sign.3x 4

x2 + 16x 1

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 1a

Add or subtract. Identify any x-values for which the expression is undefined.

6x + 5x2 3

+3x 1x2 3

6x + 5 +x2 3

3x 1

9x + 4x2 3

Combine like terms.

The expression is undefined at x = because this value makes x2 3 equal 0.

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 1b

Add or subtract. Identify any x-values for which the expression is undefined.

Subtract the numerators.

3x2 53x 1

2x2 3x 2

3x 1

3x 13x2 5 (2x2 3x 2)

x2 + 3x 33x 1 Combine like terms.

Distribute the negative sign.3x2 5

3x 12x2 + 3x + 2

The expression is undefined at x = because this value makes 3x 1 equal 0.

13

• Holt McDougal Algebra 2

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.

• Holt McDougal Algebra 2

Rational Expressions

Find the least common multiple for each pair.

Example 2: Finding the Least Common Multiple of

Polynomials

A. 4x2y3 and 6x4y5

4x2y3 = 2 2 x2 y3

6x4y5 = 3 2 x4 y5

The LCM is 2 2 3 x4 y5, or 12x4y5.

B. x2 2x 3 and x2 x 6

x2 2x 3 = (x 3)(x + 1)

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

The LCM is (x 3)(x + 1)(x + 2).

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 2

Find the least common multiple for each pair.

a. 4x3y7 and 3x5y4

4x3y7 = 2 2 x3 y7

3x5y4 = 3 x5 y4

The LCM is 2 2 3 x5 y7, or 12x5y7.

b. x2 4 and x2 + 5x + 6

x2 4 = (x 2)(x + 2)

x2 + 5x + 6 = (x + 2)(x + 3)

The LCM is (x 2)(x + 2)(x + 3).

• Holt McDougal Algebra 2

Rational Expressions

To add rational expressions with unlike denominators, rewrite both expressions with the LCD. This process is similar to adding fractions.

• Holt McDougal Algebra 2

Rational Expressions

Add. Identify any x-values for which the expression is undefined.

x 3x2 + 3x 4

+2x

x + 4

x 3(x + 4)(x 1)

+2x

x + 4Factor the denominators.

The LCD is (x + 4)(x 1), so multiply by . 2x

x + 4

x 1x 1

x 3(x + 4)(x 1)

+2x

x + 4x 1x 1

• Holt McDougal Algebra 2

Rational Expressions

x 3 + 2x(x 1)(x + 4)(x 1)

2x2 x 3(x + 4)(x 1)

Simplify the numerator.

Example 3A Continued

Add. Identify any x-values for which the expression is undefined.

Write the sum in

factored or expanded

form.

2x2 x 3(x + 4)(x 1)

2x2 x 3x2 + 3x 4

or

The expression is undefined at x = 4 and x = 1 because these values of x make the factors (x + 4) and (x 1) equal 0.

• Holt McDougal Algebra 2

Rational Expressions

Add. Identify any x-values for which the expression is undefined.

x x + 2

+8

x2 4

x x + 2

+8

(x + 2)(x 2)Factor the denominator.

The LCD is (x + 2)(x 2), so multiply by . x

x + 2

x 2x 2

x 2x 2

x x + 2

+8

(x + 2)(x 2)

x(x 2) + (8) (x + 2)(x 2)

• Holt McDougal Algebra 2

Rational Expressions

x2 2x 8 (x + 2)(x 2)

Write the numerator in

standard form.

Add. Identify any x-values for which the expression is undefined.

Example 3B Continued

(x + 2)(x 4)(x + 2)(x 2)

Factor the numerator.

x 4x 2

Divide out common

factors.

The expression is undefined at x = 2 and x = 2 because these values of x make the factors (x + 2) and (x 2) equal 0.

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 3a

Add. Identify any x-values for which the expression is undefined.

3x 2x 2

+3x 23x 3

Factor the denominators.

The LCD is 6(x 1), so

multiply by 3 and

by 2.

3x 2(x 1)

3x 23(x 1)

3x 2(x 1)

+3x 2

3(x 1)

33

3x 2(x 1)

+3x 2

3(x 1)22

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 3a Continued

Add. Identify any x-values for which the expression is undefined.

15x 46(x 1)

Simplify the numerator.

The expression is undefined at x = 1 because this value of x make the factor (x 1) equal 0.

Add the numerators.9x + 6x 4

6(x 1)

• Holt McDougal Algebra 2

Rational Expressions

Add. Identify any x-values for which the expression is undefined.

2x + 6x2 + 6x + 9

+x

x + 3

Factor the denominators.

Check It Out! Example 3b

2x + 6(x + 3)(x + 3)

+x

x + 3

The LCD is (x + 3)(x + 3),

so multiply by .x

(x + 3)(x + 3) (x + 3)

2x + 6(x + 3)(x + 3)

+x

x + 3x + 3x + 3

Add the numerators.x2 + 3x + 2x + 6

(x + 3)(x + 3)

• Holt McDougal Algebra 2

Rational Expressions

Check It Out! Example 3b Continued

Add. Identify any x-values for which the expression is undefined.

Write the numerator in

standard form.

(x + 3)(x + 2)(x + 3)(x + 3)

Factor the numerator.

x + 2x + 3

Divide out common

factors.

The expression is undefined at x = 3 because this value of x make the factors (x + 3) and (x + 3) equal 0.

x2 + 5x + 6 (x + 3)(x + 3)

• Holt McDougal Algebra 2

Rational Expressions

Example 4: Subtracting Rational Expressions

Factor the denominators.

Subtract . Identify any x-

values for which the expression is undefined.

2x2 30

x2 9

x + 3

x + 5

2x2 30

(x 3)(x + 3)

x + 3

x + 5

The LCD is (x 3)(x + 3),

so multiply by .x + 5 x + 3

(x 3) (x 3)

2x2 30

(x 3)(x + 3)

x + 3

x + 5 x 3x 3

2x2 30 (x + 5)(x 3)(x 3)(x + 3)

Subtract the numerators.

2x2 30 (x2 + 2x 15)(x 3)(x + 3)

Multiply the binomials in

the numerator.

• Holt McDougal Algebra 2

Rational Expressions

Example 4 Continued

Subtract . Identify any x-

values for which the expression is undefined.

2x2 30

x2 9

x + 3

x + 5

2x2 30 x2 2x + 15(x 3)(x + 3)

Distribute the negative sign.

x2 2x 15(x 3)(x + 3)

Write the numerator in

st

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