Multiplying and Dividing Rational Expressions
Learning Outcomes
- Simplify rational expressions.
- Multiply and divide rational expressions.
Simplifying Rational Expressions
The quotient of two polynomial expressions is called a rational expression. We can apply the properties of fractions to rational expressions such as simplifying the expressions by canceling common factors from the numerator and the denominator. To do this, we first need to factor both the numerator and denominator. Let’s start with the rational expression shown.[latex]\frac{{x}^{2}+8x+16}{{x}^{2}+11x+28}[/latex]
[latex-display]\\[/latex]We can factor the numerator and denominator to rewrite the expression as [latex]\frac{{\left(x+4\right)}^{2}}{\left(x+4\right)\left(x+7\right)}[/latex-display]How To: Given a rational expression, simplify it
- Factor the numerator and denominator.
- Cancel any common factors.
Example: Simplifying Rational Expressions
Simplify [latex]\frac{{x}^{2}-9}{{x}^{2}+4x+3}[/latex].Answer: [latex-display]\begin{array}{lllllllll}\frac{\left(x+3\right)\left(x - 3\right)}{\left(x+3\right)\left(x+1\right)}\hfill & \hfill & \hfill & \hfill & \text{Factor the numerator and the denominator}.\hfill \\ \frac{x - 3}{x+1}\hfill & \hfill & \hfill & \hfill & \text{Cancel common factor }\left(x+3\right).\hfill \end{array}[/latex-display]
Analysis of the Solution
We can cancel the common factor because any expression divided by itself is equal to 1.Q & A
Can the [latex]{x}^{2}[/latex] term be cancelled in the above example? No. A factor is an expression that is multiplied by another expression. The [latex]{x}^{2}[/latex] term is not a factor of the numerator or the denominator.Try It
Simplify [latex]\frac{x - 6}{{x}^{2}-36}[/latex].Answer: [latex]\frac{1}{x+6}[/latex]
[ohm_question]110917-110916[/ohm_question]Multiplying Rational Expressions
Recall Multiplying fractions
To multiply fractions, multiply the numerators and place them over the product of the denominators.
[latex]\dfrac{a}{b}\cdot\dfrac{c}{d} = \dfrac {ac}{bd}[/latex]
It is helpful to factor the numerator and denominator and cancel common factors before multiplying terms together.How To: Given two rational expressions, multiply them
- Factor the numerator and denominator.
- Multiply the numerators.
- Multiply the denominators.
- Simplify.
Example: Multiplying Rational Expressions
Multiply the rational expressions and show the product in simplest form:Answer:
[latex]\begin{array}{cc}\frac{\left(x+5\right)\left(x - 1\right)}{3\left(x+6\right)}\cdot \frac{\left(2x - 1\right)}{\left(x+5\right)}\hfill & \text{Factor the numerator and denominator}.\hfill \\ \frac{\left(x+5\right)\left(x - 1\right)\left(2x - 1\right)}{3\left(x+6\right)\left(x+5\right)}\hfill & \text{Multiply numerators and denominators}.\hfill \\ \frac{\cancel{\left(x+5\right)}\left(x - 1\right)\left(2x - 1\right)}{3\left(x+6\right)\cancel{\left(x+5\right)}}\hfill & \text{Cancel common factors to simplify}.\hfill \\ \frac{\left(x - 1\right)\left(2x - 1\right)}{3\left(x+6\right)}\hfill & \hfill \end{array}[/latex]
Try It
Multiply the rational expressions and show the product in simplest form:Answer: [latex]\frac{\left(x+5\right)\left(x+6\right)}{\left(x+2\right)\left(x+4\right)}[/latex]
[ohm_question]93841-93844[/ohm_question]Dividing Rational Expressions
recall dividing fractions
To divide fractions, multiply the first by the reciprocal of the second.
[latex]\dfrac{a}{b}\div\dfrac{c}{d}=\dfrac{a}{b}\cdot\dfrac{d}{c}=\dfrac{ad}{bc}[/latex]
Remember to factor first and cancel common factors in the numerator and denominator before multiplying individual terms together.How To: Given two rational expressions, divide them
- Rewrite as the first rational expression multiplied by the reciprocal of the second.
- Factor the numerators and denominators.
- Multiply the numerators.
- Multiply the denominators.
- Simplify.
Example: Dividing Rational Expressions
Divide the rational expressions and express the quotient in simplest form:Answer: [latex-display]\begin{array}\text{ }\frac{2x^{2}+x-6}{x^{2}-1}\cdot\frac{x^{2}+2x+1}{x^{2}-4} \hfill& \text{Rewrite as the first fraction multiplied by the reciprocal of the second fraction.} \\ \frac{\left(2x-3\right)\cancel{\left(x+2\right)}}{\cancel{\left(x+1\right)}\left(x-1\right)}\cdot\frac{\cancel{\left(x+1\right)}\left(x+1\right)}{\cancel{\left(x+2\right)}\left(x-2\right)} \hfill& \text{Factor and cancel common factors.} \\ \frac{\left(2x+3\right)\left(x+1\right)}{\left(x-1\right)\left(x-2\right)} \hfill& \text{Multiply numerators and denominators.} \\ \frac{2x^{2}+5x+3}{x^{2}-3x+2} \hfill& \text{Simplify.}\end{array}[/latex-display]
Try It
Divide the rational expressions and express the quotient in simplest form:Answer: [latex]1[/latex]
[ohm_question]93845-93847[/ohm_question]Licenses & Attributions
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