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Find the intercepts and asymptotes, and then sketch a graph of the rational function. Use a graphing device to confirm your answer. $$r(x)=\frac{4 x-4}{x+2}$$

Short Answer

Expert verified
Y-intercept: (0, -2); X-intercept: (1, 0); Vertical asymptote: x = -2; Horizontal asymptote: y = 4. Graph verified.

Step by step solution

01

Identify the Y-intercept

To find the y-intercept of the function, set \( x = 0 \) in the function \( r(x) = \frac{4x - 4}{x + 2} \). This gives \( r(0) = \frac{4(0) - 4}{0 + 2} = \frac{-4}{2} = -2 \). Thus, the y-intercept is the point \((0, -2)\).
02

Identify the X-intercept

The x-intercepts occur when the numerator of the rational function equals zero. Set \( 4x - 4 = 0 \) and solve for \( x \):\[ 4x - 4 = 0 \rightarrow 4x = 4 \rightarrow x = 1 \].Hence, the x-intercept is the point \((1, 0)\).
03

Determine the Vertical Asymptote

The vertical asymptote occurs where the denominator of the function equals zero since division by zero is undefined. Set \( x + 2 = 0 \) and solve for \( x \):\[ x + 2 = 0 \rightarrow x = -2 \].Therefore, the vertical asymptote is at \( x = -2 \).
04

Determine the Horizontal Asymptote

For rational functions where the degrees of the numerator and denominator are equal, the horizontal asymptote is the quotient of the leading coefficients. Here, both the numerator and denominator have degree 1, so the horizontal asymptote is \( y = \frac{4}{1} = 4 \).
05

Sketch the Graph

Using the intercepts and asymptotes found, sketch the graph on the coordinate plane. Plot the y-intercept at \((0, -2)\), the x-intercept at \((1, 0)\), draw a vertical asymptote as a dashed line at \( x = -2 \), and a horizontal asymptote as a dashed line at \( y = 4 \). The curve should approach these asymptotes as \( x \) moves towards infinity but never touch them.
06

Confirm with Graphing Device

Use a graphing calculator or software to plot \( r(x) = \frac{4x - 4}{x + 2} \) and check that the sketch matches: y-intercept at \((0, -2)\), x-intercept at \((1, 0)\), vertical asymptote at \( x = -2 \), and horizontal asymptote at \( y = 4 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Intercepts of Rational Functions
Intercepts are key points where a graph intersects the axes of a coordinate plane. For a rational function like \( r(x) = \frac{4x - 4}{x + 2} \), we have two types of intercepts to consider:
  • Y-Intercept: This is where the graph of the function crosses the y-axis. To find it, we set \( x = 0 \) and solve: \( r(0) = \frac{4(0) - 4}{0 + 2} = -2 \). Thus, the y-intercept is at the point \( (0, -2) \), where the graph meets the y-axis.
  • X-Intercept: This occurs where the graph crosses the x-axis. Setting the numerator equal to zero, \( 4x - 4 = 0 \), and solving for \( x \), we find \( x = 1 \). Therefore, the x-intercept is at \( (1, 0) \).
Identifying these intercepts is crucial for accurately sketching the graph of a rational function.
Asymptotes of Rational Functions
Asymptotes are invisible lines that a graph approaches but never quite touches. They provide important information about the behavior of a rational function as \( x \) approaches certain values.
  • Vertical Asymptote: This occurs where the denominator of the function is zero. For \( r(x) = \frac{4x - 4}{x + 2} \), set \( x + 2 = 0 \). Solving, we get \( x = -2 \). This means there’s a vertical asymptote at \( x = -2 \), indicating the graph will approach this line as \( x \) gets close to -2 but will never cross it.
  • Horizontal Asymptote: To find this, compare the degrees of the numerator and denominator. When they are equal, the horizontal asymptote is the ratio of their leading coefficients. Here, both degrees are 1, leading to a horizontal asymptote at \( y = \frac{4}{1} = 4 \). This line represents the value that the function approaches as \( x \) moves towards infinity.
Understanding asymptotes helps in predicting long-term behavior of the rational function's graph.
Graphing Rational Functions
Graphing rational functions involves combining knowledge of intercepts and asymptotes to sketch the curve accurately.
  • Start by plotting the intercepts: the y-intercept \( (0, -2) \) and the x-intercept \( (1, 0) \). These points provide a starting foundation on the graph.
  • Next, draw the vertical asymptote as a dashed line at \( x = -2 \), since the graph will not cross this line.
  • Similarly, represent the horizontal asymptote as a dashed line at \( y = 4 \), showing that the graph approaches but never reaches this line at infinity.
With these elements in place, sketch the curve: notice how the graph moves away from the intercepts, curves gently towards the asymptotes, and follows their direction without ever touching them. As a final step, use a graphing tool to confirm your plot matches these features.

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