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Graphing a Simple Rational Function

A rational function is a function of the form where p (x) and q (x) are polynomials and q (x) ≠ 0. p (x) q (x) f (x) = For instance consider the following rational function: 1 x y = The graph of this function is called a hyperbola and is shown below.

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Graphing a Simple Rational Function

Notice the following properties: The x-axis is a horizontal asymptote. The y-axis is a vertical asymptote. The domain and range are all nonzero real numbers. The graph has two symmetrical parts called branches. For each point (x, y) on one branch, there is a corresponding point (–x, –y) on the other branch. 1 4 3 2 – 4 –2 –1 – 1 – 2 – 3 x y – 4 2 1 3 x y

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Graphing a Simple Rational Function

All rational functions of the form have graphs that are hyperbolas with asymptotes at x = h and y = k. a x – h y = + k To draw the graph, plot a couple of points on each side of the vertical asymptote. Then draw the two branches of the hyperbola that approach the asymptotes and pass through the plotted points.

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The range is all real numbers except –1.

Graphing a Rational Function –2 x + 3 Graph State the domain and range. y = – 1 SOLUTION Draw the asymptotes at x = –3 and y = –1. two points to the left of the vertical asymptote, such as (–4, 1) and (–5, 0), and two points to the right, such as (–1, –2), and (0, ). 5 3 – Plot Use the asymptotes and plotted points to draw the branches of the hyperbola. The domain is all real numbers except –3. The range is all real numbers except –1.

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Graphing a Simple Rational Function

All rational functions of the form have graphs that are hyperbolas. a x + b c x + d y = The vertical asymptote occurs at the x-value that makes the denominator zero. The horizontal asymptote is the line a c y =

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Graphing a Rational Function

Graph . State the domain and range. x + 1 2x – 4 y = SOLUTION the asymptotes. Solve 2x – 4 = 0 for x to find the vertical asymptote x = 2.The horizontal asymptote is the line 1 2 = a c y = Draw Plot two points to the left of the vertical asymptote, such as (0, ) and (1, –1), and two points to the right, such as (3, 2), and (4, ). 5 4 1 – Use the asymptotes and plotted points to draw the branches of the hyperbola. The domain is all real numbers except 2. The range is all real numbers except . 1 2

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= Using Rational Functions in Real Life

For a fundraising project, your math club is publishing a fractal art calendar. The cost of the digital images and the permission to use them is $850. In addition to these “one-time” charges, the unit cost of printing each calendar is $3.25. Write a model that gives the average cost per calendar as a function of the number of calendars printed. The average cost is the total cost of making the calendars divided by the number of calendars printed. SOLUTION Verbal Model One-time charges + Unit cost • Number printed Average cost = Number printed …

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Using Rational Functions in Real Life

For a fundraising project, your math club is publishing a fractal art calendar. The cost of the digital images and the permission to use them is $850. In addition to these “one-time” charges, the unit cost of printing each calendar is $3.25. Write a model that gives the average cost per calendar as a function of the number of calendars printed. … Labels Average cost = A (dollars per calendar) One-time charges = 850 (dollars) Unit cost = 3.25 (dollars per calendar) Number printed = x (calendars) x x = Algebraic Model A

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Using Rational Functions in Real Life

For a fundraising project, your math club is publishing a fractal art calendar. The cost of the digital images and the permission to use them is $850. In addition to these “one-time” charges, the unit cost of printing each calendar is $3.25. Use the graph to estimate the number of calendars you need to print before the average cost drops to $5 a calendar. The graph of the model is shown. The A-axis is the vertical asymptote and the line A = 3.25 is the horizontal asymptote. The domain is x > 0 and the range is A > 3.25. When A = 5 the value of x is about 500. So you need to print about 500 calendars before the average cost drops to $5 per calendar.

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Using Rational Functions in Real Life

For a fundraising project, your math club is publishing a fractal art calendar. The cost of the digital images and the permission to use them is $850. In addition to these “one-time” charges, the unit cost of printing each calendar is $3.25. Describe what happens to the average cost as the number of calendars printed increases. As the number of calendars printed increases, the average cost per calendar gets closer and closer to $3.25. For instance,when x = 5000 the average cost is $3.42, and when x = 10,000 the average cost is $3.34.

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