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Characteristics of Logarithmic Functions

Logarithmic functions can be expressed by:
y=logbxy=\log_{b}x
where b>0b>0,b1b\neq1, and x>0x>0.

Characteristics of Logarithmic Functions y=logbx\colorOne{y=\log_{b}x}

  • The graph passes through the point (1,0)(1,0)
  • There is a vertical asymptote at x=0x=0
  • The domain is x>0x>0
  • The range is yRy\in\mathbb{R}
  • The function is increasing and continuous over the interval (0,)(0,\infin)

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Example

The graph ofy=log2xy=\log_{2}x is shown below.
xy1/421/21102142\begin{array}{|c|c|}\hline x&y\\\hline 1/4&-2\\\hline 1/2&-1\\\hline 1&0\\\hline 2&1\\\hline 4&2\\\hline \end{array}
  • The graph passes through the point (1,0)(1,0)
  • There is a vertical asymptote at x=0x=0
  • The domain is x>0x>0
  • The range is yRy\in\mathbb{R}
  • The function is increasing and continuous over the interval (0,)(0,\infin)
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Example: Characteristics of Logarithms

Sketch a graph of y=log3xy=\log_{3}x.

xy1/2731/921/31103192273\begin{array}{r|l} x&y\\\hline\\ 1/27&-3\\\\ 1/9&-2\\\\ 1/3&-1\\\\ 1&0\\\\ 3&1\\\\ 9&2\\\\ 27&3\\\\ \end{array}


Practice: Characteristics of Logarithmic Functions

Sketch a graph of y=log5xy=\log_5x.

Practice: Characteristics of Logarithmic Functions

How are the graphs of y=log2xy=\log_2x and y=log12xy=\log_{\frac{1}{2}}x related?
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Practice: Characteristics of Logarithmic Functions

Sketch a graph of the function y=log23xy=\log_{\frac{2}{3}}{x}.
Extra Practice