Math Problem Statement

Find the domain, range, x-intercept, and horizontal asymptote of the given logarithmic functions: f(x) = log2(x) + 5, f(x) = log4(2x) + 5, and f(x) = log5(7x - 3).

Solution

You have a table with three logarithmic functions and columns to fill in the Domain, Range, x-intercept, and Horizontal Asymptote (H.A.). Let's go over each function and determine these properties:

1. f(x)=log2(x)+5f(x) = \log_2(x) + 5

  • Domain: The argument inside the logarithm must be greater than zero. Therefore, x>0x > 0.
    Domain: (0,)(0, \infty)

  • Range: The range of any logarithmic function is all real numbers. Adding 5 shifts the function vertically but does not change the range.
    Range: (,)(-\infty, \infty)

  • x-intercept: Set f(x)=0f(x) = 0 to find the x-intercept:
    0=log2(x)+5    log2(x)=5    x=25=1320 = \log_2(x) + 5 \implies \log_2(x) = -5 \implies x = 2^{-5} = \frac{1}{32} x-intercept: x=132x = \frac{1}{32}

  • Horizontal Asymptote (H.A.): A logarithmic function approaches -\infty as xx approaches 0 from the right. The vertical shift by 5 does not affect the horizontal asymptote.
    H.A.: y=5y = 5


2. f(x)=log4(2x)+5f(x) = \log_4(2x) + 5

  • Domain: The argument inside the logarithm must be positive:
    2x>0    x>02x > 0 \implies x > 0.
    Domain: (0,)(0, \infty)

  • Range: The range of the logarithmic function is still all real numbers, unaffected by the 5.
    Range: (,)(-\infty, \infty)

  • x-intercept: Set f(x)=0f(x) = 0 to find the x-intercept:
    0=log4(2x)+5    log4(2x)=5    2x=45=11024    x=120480 = \log_4(2x) + 5 \implies \log_4(2x) = -5 \implies 2x = 4^{-5} = \frac{1}{1024} \implies x = \frac{1}{2048} x-intercept: x=12048x = \frac{1}{2048}

  • Horizontal Asymptote (H.A.): The same reasoning applies as in the first function. The vertical shift of 5 moves the horizontal asymptote to y=5y = 5.
    H.A.: y=5y = 5


3. f(x)=log5(7x3)f(x) = \log_5(7x - 3)

  • Domain: Set the argument inside the logarithm greater than zero:
    7x3>0    x>377x - 3 > 0 \implies x > \frac{3}{7}.
    Domain: (37,)\left( \frac{3}{7}, \infty \right)

  • Range: The range is still all real numbers.
    Range: (,)(-\infty, \infty)

  • x-intercept: Set f(x)=0f(x) = 0 to find the x-intercept:
    0=log5(7x3)    7x3=1    7x=4    x=470 = \log_5(7x - 3) \implies 7x - 3 = 1 \implies 7x = 4 \implies x = \frac{4}{7} x-intercept: x=47x = \frac{4}{7}

  • Horizontal Asymptote (H.A.): For this function, the horizontal asymptote corresponds to the logarithmic behavior as 7x30+7x - 3 \to 0^+, which happens as x37x \to \frac{3}{7} from the right.
    H.A.: No horizontal asymptote for this one, since logarithmic functions typically only have vertical asymptotes based on their domain.


Would you like further clarification or details on these properties?

Here are 5 related questions to explore:

  1. How do vertical and horizontal shifts affect the graph of a logarithmic function?
  2. What happens to the domain if you have a negative coefficient inside the logarithm?
  3. How do you graph a transformed logarithmic function like log2(x)+5\log_2(x) + 5?
  4. What is the general process for solving logb(x)=y\log_b(x) = y?
  5. Can a logarithmic function have more than one x-intercept?

Tip: When working with logarithmic functions, always start by analyzing the domain carefully to ensure you avoid non-real arguments!

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Math Problem Analysis

Mathematical Concepts

Logarithmic Functions
Domain
Range
Intercepts
Asymptotes

Formulas

log_b(x)
Domain: x > 0 for logarithmic functions
Range: (-∞, ∞) for logarithmic functions
x-intercept: Set f(x) = 0 and solve for x

Theorems

Properties of logarithms
Horizontal and vertical shifts of functions

Suitable Grade Level

Grades 9-12