Logarithm problems

Algebra Level 2

log 5 ( x ) + log 7 ( x ) = log 25 ( x ) \large \log_5 (x) + \log_7(x)=\log_{25}(x)

Find x x .


The answer is 1.

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2 solutions

Chew-Seong Cheong
Oct 21, 2019

log 5 x + log 7 x = log 25 x log x log 5 + log x log 7 = log x log 25 Since 1 log 5 + 1 log 7 1 log 25 log x = 0 x = 1 \begin{aligned} \log_5 x + \log_7 x & = \log_{25} x \\ \frac {\log x}{\log 5} + \frac {\log x}{\log 7} & = \frac {\log x}{\log 25} & \small \blue{\text{Since }\frac 1{\log 5} + \frac 1{\log 7} \ne \frac 1{\log 25}} \\ \implies \log x & = 0 \\ \implies x & = \boxed 1 \end{aligned}

Probably the question asks for the value of x x satisfying the equation l o g 5 x + l o g 7 x = l o g 25 x log_5x+log_7x=log_{25}x . If this is the case then log x log 5 + log x log 7 = log x log 25 \dfrac{ \log x}{\log 5}+\dfrac{\log x}{\log 7}=\dfrac{\log x}{\log {25}} or log x = 0 \log x=0 or x = 1 x=\boxed 1

@Alak Bhattacharya , like other functions in LaTex, we should add a back slash "\" in front the function title. \log x log x \log x Note that log is not in italic and there is a space between log and x. Without \, all log and x are in italic and there is no space between log and x. \sin x sin x \sin x , \cos x cos x \cos x , \int \int , \dfrac \pi 2 π 2 \dfrac \pi 2 ...

Chew-Seong Cheong - 1 year, 7 months ago

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What is the Latex code for approximately equal to?

A Former Brilliant Member - 1 year, 7 months ago

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\approx \approx . You can google to find out.

Chew-Seong Cheong - 1 year, 7 months ago

X = 0 is no possibility: domain is x > 0

Peter van der Linden - 1 year, 7 months ago

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Who demanded that x = 0 x=0 ?

A Former Brilliant Member - 1 year, 7 months ago

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