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  1. Home
  2. 12th grade
  3. Algebra I
  4. Exercise : Change the base of a logarithm

Change the base of a logarithm Algebra I

Change the base of the following logarithms.

\log_4\left(62\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_4\left(62\right)=\dfrac{\log_2\left(62\right)}{\log_2\left(4\right)}

We know that:

\log_2\left(4\right)=2 because 2^{2}=4

We conclude that:

\log_4\left(62\right)=\dfrac{\log_2\left(62\right)}2

\log_9\left(73\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_9\left(73\right)=\dfrac{\log_3\left(73\right)}{\log_3\left(9\right)}

We know that:

\log_3\left(9\right)=2 because 3^{2}=9

We conclude that:

\log_9\left(73\right)=\dfrac{\log_3\left(73\right)}2

\log_2\left(\sqrt{e}\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_2\left(\sqrt{e}\right)=\dfrac{\ln\left(\sqrt{e}\right)}{\ln\left(2\right)}

We know that:

\ln\left(\sqrt{e}\right)=\dfrac{1}{2} because e^{\frac{1}{2}}=\sqrt{e}

We conclude that:

\log_2\left(\sqrt{e}\right)=\dfrac{1}{2\ln\left(2\right)}

\log_\dfrac{1}{100}\left(253\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_\dfrac{1}{100}\left(253\right)=\dfrac{\log\left(253\right)}{\log\left(\dfrac{1}{100}\right)}

We know that:

\log\left(\dfrac{1}{100}\right)=-2 because 10^{-2}=\dfrac{1}{100}

We conclude that:

\log_\dfrac{1}{100}\left(253\right)=-\dfrac{1}{2}\log\left(253\right)

\log_\sqrt[3]{5}\left(127\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_\sqrt[3]{5}\left(127\right)=\dfrac{\log_5\left(127\right)}{\log_5\left(\sqrt[3]{5}\right)}

We know that:

\log_5\left(\sqrt[3]{5}\right)=\dfrac{1}{3} because \sqrt[3]{5}=5^{\frac{1}{3}}

We conclude that:

\log_\sqrt[3]{5}\left(127\right)=3\log_5\left(127\right)

\log_8 \left(50\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_8\left(50\right)=\dfrac{\log_2\left(50\right)}{\log_2\left(8\right)}

We know that:

\log_2\left(8\right)=3 because 2^{3}=8

We conclude that:

\log_8\left(50\right)=\dfrac{\log_2\left(50\right)}{3}

\log_\dfrac{1}{\sqrt{e}} \left(12\right)

The formula to change the base of a logarithm is:

\log_a\left(b\right)=\dfrac{\log_m\left(b\right)}{\log_m\left(a\right)}

In our problem:

\log_\dfrac{1}{\sqrt{e}}\left(12\right)=\dfrac{\ln\left(12\right)}{\ln\left(\dfrac{1}{\sqrt{e}}\right)}

We know that:

\ln\left(\dfrac{1}{\sqrt{e}}\right)=-\dfrac{1}{2} because e^{-\frac{1}{2}}=\dfrac{1}{\sqrt{e}}

We conclude that:

\log_\dfrac{1}{\sqrt{e}}\left(12\right)=-2\ln\left(12\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 sum of logarithms and a product
  • Exercise : Convert between a difference of logarithms and a quotient
  • Exercise : Convert between a multi-term sum of logarithms and a power
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