Solve Logarithmic Inequality: log₁/₄(9) vs log₅(7)/log₅(1/4)

Question

Is inequality true?

\log_{\frac{1}{4}}9<\frac{\log_57}{\log_5\frac{1}{4}}

Video Solution

Solution Steps

00:00 Solve
00:04 We'll use the logarithmic subtraction formula, we'll get log divided by
00:14 We'll use this formula in our exercise
00:19 And this is the solution to the question

Step-by-Step Solution

To solve this problem, we will rewrite both sides of the inequality with the change of base formula and evaluate them:

  • Step 1: Rewrite both logarithms using common base.
    Using the change of base formula, log149=log29log214 \log_{\frac{1}{4}}9 = \frac{\log_29}{\log_2\frac{1}{4}} and log57log514\frac{\log_57}{\log_5\frac{1}{4}} can also be rewritten similarly.
  • Step 2: Recognize that changing everything to base 2 will be beneficial.
    log2(1/4)=log241=2\log_2 (1/4) = \log_2 4^{-1} = -2.
  • Step 3: Evaluate left side.
    log149=log292=log292 \log_{\frac{1}{4}}9 = \frac{\log_2 9}{-2} = -\frac{\log_2 9}{2} .
  • Step 4: Evaluate right side using the same base.
    log57log514=log272 \frac{\log_57}{\log_5\frac{1}{4}} = -\frac{\log_2 7}{2} , where log24=2-\log_2 4 = 2.
  • Step 5: Compare both expressions
    log292<log272=>log29<log27=>9<7-\frac{\log_2 9}{2} < -\frac{\log_2 7}{2} => \log_2 9 < \log_2 7 => 9 < 7.
  • Step 6: Since 9>79 > 7, convert the logarithmic expressions back into log14\log_{\frac{1}{4}}.
    log147\log_{\frac{1}{4}}7 is smaller than log149\log_{\frac{1}{4}}9, so inequation holds.

After comparing these expressions, we see that log149<log147 \log_{\frac{1}{4}}9 < \log_{\frac{1}{4}}7 indeed holds true.

Therefore, the solution is: Yes, since: log149<log147 \log_{\frac{1}{4}}9 < \log_{\frac{1}{4}}7 .

Answer

Yes, since:

\log_{\frac{1}{4}}9<\log_{\frac{1}{4}}7