These Roots And Logs Could Make A Forest

Algebra Level 2

12 5 log 5 4 + log 5 3 3 = ? \large \sqrt[3]{ \displaystyle 125^{\log_5 4 + \log_5 3} } = \, ?


The answer is 12.

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3 solutions

Mateus Gomes
Feb 5, 2016

12 5 log 5 4 + log 5 3 3 = A \sqrt[3]{125^{\log_{5} 4+\log_{5} 3}}=\color{#D61F06}A 12 5 log 5 12 3 \rightarrow\sqrt[3]{125^{\log_{5} 12}} 5 3 log 5 12 3 \rightarrow\sqrt[3]{5^{3\log_{5} 12}} 5 log 5 1 2 3 3 \rightarrow\sqrt[3]{5^{\log_{5} 12^3}} 1 2 3 3 \rightarrow\sqrt[3]{12^{3}} 12 = A \rightarrow{\boxed{12=\color{#D61F06}A}}

I tried to solve this problem but I can't able to understand your 5th step ...will u please explain clearly... Macnath kotapatti ravichandran, EIE branch, LPU universtity, India.

macnath mac - 5 years, 4 months ago

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Hi @macnath mac ! What is done in the fifth step is described as a l o g a b = b a^{log_a b} = b , which is one of the properties of logarithms.

Mehul Arora - 5 years, 3 months ago

I couldn't understand the step in which you removed log( i only know basics of log) Can you please explain it.

bhanu pratap - 5 years, 4 months ago

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If you have log base "b", and you have b^(logb(a)). Then you can logic it out. Log functions take the bottom number and make the exponent required to make b turn into a. Using this logic, if log is the exponent to make b turn to a, then b to the log b of a is just "a". For future reference, if you have something like e^(in(a)), you can simplify to "a".

Zoy Jablabber - 5 years, 4 months ago
Yasir Soltani
Feb 10, 2016

= 12 5 log 5 4 + log 5 3 3 \displaystyle{=\sqrt[3]{125^{\log_54+\log_53} }}

= 12 5 log 5 12 3 ( log Property: log a b + log a c = log a b c ) \displaystyle{ =\sqrt[3]{125^{\log_512}}} \quad \quad \left( \textbf{log Property:} \quad \log_ab+\log_ac=\log_abc\right)

= 5 3 log 5 12 3 \displaystyle{=\sqrt[3]{5^{3\log_512}}}

= 5 log 5 1 2 3 3 ( log Property: p log a b = log a b p ) \displaystyle{=\sqrt[3]{5^{\log_512^3}}} \quad \quad \quad \left( \textbf{log Property:} \quad p\log_ab=\log_ab^p\right)

= 1 2 3 3 ( log Property: a log a b = b ) \displaystyle{=\sqrt[3]{12^3}} \quad \quad \quad \quad \quad \left( \textbf{log Property:}\quad a^{\log_ab}=b\right)

= 12 \displaystyle{=\boxed{12}}

See: b LOG b x + LOG b y = x y \displaystyle{ \sqrt{b^{ \text{LOG}_{b}{x}+ \text{LOG}_{b}{y}}} = \sqrt{ xy} }

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