# If f(x) = log x then AM of f(xy) and f(x/y) is ?

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If f(x) = log x then AM of f(xy) and f(x/y) is ?
1. log xy
2. log  xy
3. log y
4. log x
5. None of these

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Correct Answer - Option 4 : log x

Concept:

The arithmetic mean is the sum of all the numbers in a data set divided by the quantity of numbers in that set.

Arithmetic mean of two positive numbers a and b is $\rm \frac{{a\; + \;b}}{2}$

Logarithmic formula

log mn = log m + log n

$\rm \log (\frac{m}{n}) = \log m - \ log n$

Calculation:

Given: f(x) = log x

To Find: AM of f(xy) and f(x/y)

f(xy) = log (xy) = log x + log y             (∵ log mn = log m + log n)

$\rm f(\frac{x}{y}) = \log (\frac{x}{y}) = \log x - \ log y$

Now, AM of f(xy) and f(x/y) = $\rm \frac{f(xy)+f(\frac{x}{y})}{2}$

$= \rm \frac{\log x+ \log y + \log x - \log y}{2}\\ = \frac{2\log x}{2} \\= \log x$