Simple Logarithm

Algebra Level 2

4 log 16 25 = ? \Large 4^{\log_{16}{25}}=\, ?


The answer is 5.

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6 solutions

Take note: b log b x = x \Large b^{\log_{b}x}=x

4 log 16 25 \LARGE 4^{ \log_{16}25} = 4 log 16 5 2 \LARGE =4^{ \log_{16}5^2} = 4 2 log 16 5 \LARGE= 4^{2 \log_{16}5} = 1 6 log 16 5 = 5 \LARGE= 16^{ \log_{16}5}= \boxed{5}

In proper L a T e x LaTex presentation:

4 log 16 25 = 4 log 4 25 log 4 16 = 4 log 4 25 2 = 4 log 4 25 = 4 log 4 5 = 5 \LARGE 4^{\log_{16} 25} = 4^{\frac{\log_{4} 25}{\log_{4} 16}} = 4^{\frac{\log_{4} 25}{2}} = 4^{\log_{4} \sqrt{25}} = 4^{\log_{4} 5} = \boxed{5}

Roger Erisman
Sep 22, 2018

Alec Camhi
Jan 12, 2016

{ 4 }^{ \log _{ 16 }{ 25 } }={ 4 }^{ \frac { 1 }{ 2 } \log _{ 4 }{ 25 } }={ 4 }^{ \log _{ 4 }{ { 25 }^{ \frac { 1 }{ 2 } } } }={ 4 }^{ \log _{ 4 }{ 5 } }=\boxed { 5 }

Michael Fuller
Jan 12, 2016

4 log 16 25 \Large {4}^{\log_{16}{25}}

= 16 1 2 log 16 25 \Large = {16}^{\frac{1}{2}\log_{16}{25}}

= 16 log 16 5 \Large = {16}^{\log_{16}{5}}

= 5 \Large = \color{#20A900}{\boxed{5}}


Note :

a log x b = log x b a \Large \color{#20A900}{a} \log_{x}{\color{#3D99F6}{b}}=\log_{x}{\color{#3D99F6}{b}}^{\color{#20A900}{a}}

a log a b = b \Large \color{#20A900}{a}^{\log_{\color{#20A900}{a}}{\color{#3D99F6}{b}}}=\color{#3D99F6}{b}

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