Logarithmic Functions

  1. Write down an explanation of how you can estimate the value of \(\log_{10}(31415926)\) without appealing to technology.
  2. Without appealing to technology, figure out the exact value of the following logarithms. (Hint: they’re all whole numbers.)
    \(\log_5(625)\)
    \(\log_2(1024)\)
    \(\log_{11}(14641)\)
    \(\ln\bigl(\mathrm{e}^7\bigr)\)
  3. Using a calculator, write down a decimal approximation of each of the following numbers rounded to two decimal places.
    \(\log_{10}(31415926)\)
    \(\ln(100)\)
    \(\log_5(43)\)
  4. Find the value(s) of \(x\) that satisfies each of these equations.
    \(2^x = 4096\)
    \(3^x = 6000\)
    \(3^x2^x = 1234\)
    \(\mathrm{e}^x = 42\)
  5. If \(\log_7(x) = 5,\) what must the value of each of the following expressions be? (Hint: this is an exercise of your effective use of the “rules of logarithms”.)
    \(\displaystyle \log_7\biggl(\frac{x^3}{7}\biggr)\)
    \(\displaystyle \log_7\bigl(49x^2\bigr)\)
    \(\displaystyle \log_7\biggl(\frac{\sqrt{x}}{343}\biggr)\)
  6. If \(\log_5(x) = 3\) and \(\log_5(y) = 10,\) what must the value of each of the following expressions be?
    \(\displaystyle \log_5\biggl(\frac{625x}{y^2}\biggr)\)
    \(\displaystyle \log_5\Bigl(x\sqrt{5y}\Bigr)\)
    \(\displaystyle \frac{\ln\bigl(x^3y\bigr)}{\ln(25)}\)
  7. Rewrite each of the following expressions as a single logarithm. I.e. “simplify” these into a form that looks like \(\log_b(\text{stuff})\) for some \(\text{stuff}.\)
    \(\displaystyle \log_7(x) + 4\log_7(y) \)
    \(\displaystyle \ln(5x) - 3\ln(z) \)
    \(\displaystyle \frac{1}{2}\log_5(4x) + 2\log_5(x+1) \)
  8. Rewrite each of the following expressions as a single logarithm.
    \(\displaystyle -3\log_2(3x) + \sqrt{5}\log_2(y) \)
    \(\displaystyle \frac{3\ln(w) - \frac{1}{3}\ln(y)}{\ln(3)}\)
    \(\displaystyle \frac{2}{3}\log_9(x) - 2\log_9(y-1) + 2\log_9(9) \)
  9. In May 2008 an earthquake of magnitude 6.8 struck Honshu, Japan, causing some injuries and building damage. In March 2011 a magnitude 9.0 earthquake stuck Honshu, killing thousands of people. How much more powerful was this second earthquake?