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  1. Home
  2. 12th grade
  3. Algebra I
  4. Exercise : Convert between a sum of logarithms and a product

Convert between a sum of logarithms and a product Algebra I

Simplify the following logarithmic expressions.

\log_3\left(2\right) + \log_3\left(6\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(a\right)+ \log_c\left(b\right)=\log_c\left(ab\right)

Therefore:

\log_3\left(2\right) + \log_3\left(6\right) = \log_3\left(2\times 6\right)

\log_3\left(2\right) + \log_3\left(6\right)=\log_3\left(12\right)

\log_2\left(14\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(ab\right) = \log_c\left(a\right)+ \log_c\left(b\right)

Therefore:

\log_2\left(14\right)= \log_2\left(2 \times 7\right)

\log_2\left(14\right)=\log_2\left(2\right) + \log_2\left(7\right)

Notice that:

\log_2\left(2\right)=1

Therefore:

\log_2\left(14\right)=1+\log_2\left(7\right)

\log_{18}\left(3\right) + \log_{18}\left(6\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(a\right)+ \log_c\left(b\right) =\log_c\left(ab\right)

Therefore:

\log_{18}\left(3\right)+ \log_{18}\left(6\right)=\log_{18}\left(3\times 6\right)

\log_{18}\left(3\right)+ \log_{18}\left(6\right)= \log_{18}\left(18\right)

\log_{18}\left(3\right) + \log_{18}\left(6\right) =1

\log_3\left(27\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(ab\right) = \log_c\left(a\right)+ \log_c\left(b\right)

Therefore:

\log_3\left(27\right)= \log_3\left(9 \times 3\right)

\log_3\left(27\right)=\log_3\left(9\right) + \log_3\left(3\right)

Also:

\log_3\left(9\right)=\log_3\left(3 \times 3\right)

\log_3\left(9\right) = \log_3\left(3\right) + \log_3\left(3\right)

Therefore:

\log_3\left(27\right) = \log_3\left(3\right) + \log_3\left(3\right)+ \log_3\left(3\right)

Notice that:

\log_3\left(3\right)=1

Therefore:

\log_3\left(27\right)=3

\log_3\left(48\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(ab\right) = \log_c\left(a\right)+ \log_c\left(b\right)

Therefore:

\log_3\left(48\right)= \log_3\left(3 \times 16\right)

\log_3\left(48\right)= \log_3\left(3\right) + \log_3\left(16\right)

Notice that:

\log_3\left(3\right)=1

Therefore:

\log_3\left(48\right)= 1+ \log_3\left(16\right)

\log_9\left(5\right) + \log_9\left(8\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(a\right)+ \log_c\left(b\right) =\log_c\left(ab\right)

Therefore:

\log_{9}\left(5\right)+ \log_{9}\left(8\right)=\log_{9}\left(5\times 8\right)

\log_{9}\left(5\right)+ \log_{9}\left(8\right)= \log_{9}\left(40\right)

\log_5\left(36\right)

For positive real numbers a,b and c, where c \ne1 :

\log_c\left(ab\right) = \log_c\left(a\right)+ \log_c\left(b\right)

Therefore:

\log_5\left(36\right)= \log_5\left(6\times 6\right)

\log_5\left(36\right)= \log_5\left(6\right) + \log_5\left(6\right)

\log_5\left(36\right)= 2\log_5\left(6\right)

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See also
  • Course : Logarithmic functions
  • Exercise : Determine the domain and range of logarithms from equations of functions
  • Exercise : Match logarithmic functions and graphs
  • Exercise : Convert between a difference of logarithms and a quotient
  • Exercise : Convert between a multi-term sum of logarithms and a power
  • Exercise : Change the base of a logarithm
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