Skip to main contentSkip to solution

For some positive real number xx, if log⁡3(x)+log⁡x(25)log⁡x(0.008)=163\log_{\sqrt{3}}(x) + \frac{\log_x (25)}{\log_x (0.008)} = \frac{16}{3}, then the value of log⁡3(3x2)\log_3(3x^2) is

Entered answer:

Solution

✅ Correct Answer: 7

First, let us identify what we're working with:

25=5225 = 5^2

0.008=81000=23103=23(2×5)3=153=5−30.008 = \frac{8}{1000} = \frac{2^3}{10^3} = \frac{2^3}{(2 \times 5)^3} = \frac{1}{5^3} = 5^{-3}


Now we can rewrite the second term:

log⁡x(25)log⁡x(0.008)=log⁡x(52)log⁡x(5−3)\frac{\log_x (25)}{\log_x (0.008)} = \frac{\log_x (5^2)}{\log_x (5^{-3})}

Using the logarithm property log⁡a(bn)=nlog⁡a(b)\log_a(b^n) = n\log_a(b):

=2log⁡x5−3log⁡x5=2−3=−23= \frac{2\log_x 5}{-3\log_x 5} = \frac{2}{-3} = -\frac{2}{3}


For log⁡3(x)\log_{\sqrt{3}}(x), we'll use the change of base formula:

log⁡3(x)=log⁡xlog⁡3=log⁡x12log⁡3=2log⁡xlog⁡3=2log⁡3x\log_{\sqrt{3}}(x) = \frac{\log x}{\log \sqrt{3}} = \frac{\log x}{\frac{1}{2}\log 3} = \frac{2\log x}{\log 3} = 2\log_3 x

Substituting into our equation:

2log⁡3x+(−23)=1632\log_3 x + \left(-\frac{2}{3}\right) = \frac{16}{3}

2log⁡3x−23=1632\log_3 x - \frac{2}{3} = \frac{16}{3}

2log⁡3x=163+23=183=62\log_3 x = \frac{16}{3} + \frac{2}{3} = \frac{18}{3} = 6

log⁡3x=3\log_3 x = 3

Therefore: x=33=27x = 3^3 = 27


Now we need to find log⁡3(3x2)\log_3(3x^2):

log⁡3(3x2)\log_3(3x^2)

=log⁡3(3×(27)2) = \log_3(3 \times (27)^2)

=log⁡3(3×(33)2) = \log_3(3 \times (3^3)^2)

=log⁡3(3×36) = \log_3(3 \times 3^6)

=log⁡3(37)=7 = \log_3(3^7) = 7

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question