Math Problem Statement

Explain how the graph of the function ​f(x)equalsStartFraction 1 Over x plus 5 EndFraction can be obtained from the graph of yequalsStartFraction 1 Over x EndFraction . Then graph f and give the​ (a) domain and​ (b) range. Determine the largest open intervals of the domain over which the function is​ (c) increasing or​ (d) decreasing.

Solution

Let's begin by understanding the transformation of the graph of the function f(x)=1x+5f(x) = \frac{1}{x+5} from the graph of y=1xy = \frac{1}{x}.

Step 1: Transformation of the Graph

The function f(x)=1x+5f(x) = \frac{1}{x+5} is a horizontal shift of the basic rational function y=1xy = \frac{1}{x}. Here's how the transformation works:

  • The basic graph of y=1xy = \frac{1}{x} has a vertical asymptote at x=0x = 0 and a horizontal asymptote at y=0y = 0.
  • In the equation f(x)=1x+5f(x) = \frac{1}{x+5}, the term +5+5 inside the denominator indicates a horizontal shift of the graph. Specifically, the graph of y=1xy = \frac{1}{x} will be shifted 5 units to the left.

So, the transformation that occurs is a horizontal translation to the left by 5 units.

Step 2: Graph of f(x)=1x+5f(x) = \frac{1}{x+5}

To graph f(x)f(x), follow these steps:

  • Start by graphing the basic function y=1xy = \frac{1}{x}.
  • Move the entire graph 5 units to the left.
  • The vertical asymptote of y=1xy = \frac{1}{x} at x=0x = 0 becomes x=5x = -5 for f(x)f(x).
  • The horizontal asymptote remains y=0y = 0.

The graph of f(x)f(x) will have two branches:

  • One in the first quadrant (as x5+x \to -5^+), and the other in the third quadrant (as x5x \to -5^-).

Step 3: Domain and Range of f(x)f(x)

Domain: The domain of a rational function is all real numbers except where the denominator equals zero. For f(x)=1x+5f(x) = \frac{1}{x+5}, the denominator equals zero when x=5x = -5, so:

Domain: (,5)(5,)(-\infty, -5) \cup (-5, \infty)

Range: The range of y=1xy = \frac{1}{x} is (,0)(0,)(-\infty, 0) \cup (0, \infty). Since the transformation does not affect the range, the range of f(x)=1x+5f(x) = \frac{1}{x+5} is the same.

Range: (,0)(0,)(-\infty, 0) \cup (0, \infty)

Step 4: Intervals of Increase and Decrease

For the function f(x)=1x+5f(x) = \frac{1}{x+5}, it behaves similarly to y=1xy = \frac{1}{x}, but shifted. The general behavior of the rational function y=1xy = \frac{1}{x} is:

  • Decreasing for x>0x > 0.
  • Increasing for x<0x < 0.

Since the graph of f(x)=1x+5f(x) = \frac{1}{x+5} is a horizontal shift of y=1xy = \frac{1}{x}, we will have:

  • Increasing for x<5x < -5 (to the left of the vertical asymptote).
  • Decreasing for x>5x > -5 (to the right of the vertical asymptote).

Summary:

  • Domain: (,5)(5,)(-\infty, -5) \cup (-5, \infty)
  • Range: (,0)(0,)(-\infty, 0) \cup (0, \infty)
  • Intervals of Increase: (,5)(-\infty, -5)
  • Intervals of Decrease: (5,)(-5, \infty)

Graphing the Function

The graph of f(x)=1x+5f(x) = \frac{1}{x+5} can be sketched by shifting the graph of y=1xy = \frac{1}{x} 5 units to the left.

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Math Problem Analysis

Mathematical Concepts

Rational Functions
Graph Transformations
Domain and Range
Intervals of Increase and Decrease

Formulas

f(x) = 1/(x + 5)
y = 1/x

Theorems

Horizontal Shift of Graphs
Asymptotes of Rational Functions

Suitable Grade Level

Grades 9-11