Chapter 6 Rational Expressions, Functions, and Equations

§ 6.1 Rational Expressions and Functions: Multiplying and Dividing

Blitzer, Intermediate Algebra, 4e – Slide #3 Rational ExpressionsEXAMPLE The rational function models the cost, f (x) in millions of dollars, to inoculate x% of the population against a particular strain of flu. The graph of the rational function is shown. Use the function’s equation to solve the following problem. Find and interpret f (60). Identify your solution as a point on the graph.

Blitzer, Intermediate Algebra, 4e – Slide #4 Rational ExpressionsCONTINUED

Blitzer, Intermediate Algebra, 4e – Slide #5 Rational ExpressionsSOLUTION We use substitution to evaluate a rational function, just as we did to evaluate other functions in Chapter 2. CONTINUED This is the given rational function. Replace each occurrence of x with 60. Perform the indicated operations.

Blitzer, Intermediate Algebra, 4e – Slide #6 Rational Expressions Thus, f (60) = 195. This means that the cost to inoculate 60% of the population against a particular strain of the flu is $195 million. The figure below illustrates the solution by the point (60,195) on the graph of the rational function. CONTINUED (60,195)

Blitzer, Intermediate Algebra, 4e – Slide #7 Rational Expressions - DomainEXAMPLE Find the domain of f if The domain of f is the set of all real numbers except those for which the denominator is zero. We can identify such numbers by setting the denominator equal to zero and solving for x. SOLUTION Set the denominator equal to 0. Factor.

Blitzer, Intermediate Algebra, 4e – Slide #8 Rational Expressions - Domain Because 4 and 9 make the denominator zero, these are the values to exclude. Thus, Set each factor equal to 0. Solve the resulting equations. CONTINUED or

Blitzer, Intermediate Algebra, 4e – Slide #9 Rational Expressions Asymptotes Vertical Asymptotes A vertical line that the graph of a function approaches, but does not touch. Horizontal Asymptotes A horizontal line that the graph of a function approaches as x gets very large or very small. The graph of a function may touch/cross its horizontal asymptote. Simplifying Rational Expressions 1) Factor the numerator and the denominator completely. 2) Divide both the numerator and the denominator by any common factors.

Blitzer, Intermediate Algebra, 4e – Slide #10 Simplifying Rational ExpressionsEXAMPLE Simplify: SOLUTION Factor the numerator and denominator. Divide out the common factor, x + 1. Simplify.

Blitzer, Intermediate Algebra, 4e – Slide #11 Simplifying Rational ExpressionsEXAMPLE Simplify: SOLUTION Factor the numerator and denominator. Rewrite 3 – x as (-1)(-3 + x). Rewrite -3 + x as x – 3.

Blitzer, Intermediate Algebra, 4e – Slide #12 Simplifying Rational Expressions Divide out the common factor, x – 3. Simplify. CONTINUED

Blitzer, Intermediate Algebra, 4e – Slide #13 Multiplying Rational Expressions 1) Factor all numerators and denominators completely. 2) Divide numerators and denominators by common factors. 3) Multiply the remaining factors in the numerators and multiply the remaining factors in the denominators.

Blitzer, Intermediate Algebra, 4e – Slide #14 Multiplying Rational ExpressionsEXAMPLE Multiply: SOLUTION Factor the numerators and denominators completely. Divide numerators and denominators by common factors. This is the original expression.

Blitzer, Intermediate Algebra, 4e – Slide #15 Multiplying Rational Expressions Multiply the remaining factors in the numerators and in the denominators. CONTINUED

Blitzer, Intermediate Algebra, 4e – Slide #16 Dividing Rational Expressions Simplifying Rational Expressions with Opposite Factors in the Numerator and Denominator The quotient of two polynomials that have opposite signs and are additive inverses is -1. Dividing Rational Expressions If P, Q, R, and S are polynomials, where then Change division to multiplication. Replace with its reciprocal by interchanging its numerator and denominator.

Blitzer, Intermediate Algebra, 4e – Slide #17 Multiplying Rational ExpressionsEXAMPLE Multiply: SOLUTION Factor the numerators and denominators completely. Divide numerators and denominators by common factors. Because 3 – y and y -3 are opposites, their quotient is -1. This is the original expression. (-1)

Blitzer, Intermediate Algebra, 4e – Slide #18 Multiplying Rational Expressions Multiply the remaining factors in the numerators and in the denominators. CONTINUED or

Blitzer, Intermediate Algebra, 4e – Slide #19 Dividing Rational ExpressionsEXAMPLE Divide: SOLUTION Invert the divisor and multiply. Factor. This is the original expression.

Blitzer, Intermediate Algebra, 4e – Slide #20 Dividing Rational Expressions Divide numerators and denominators by common factors. CONTINUED Multiply the remaining factors in the numerators and in the denominators.