Solve the Logarithmic Equation: log₃(x²)log₅(27) - log₅(8) = ln(e)

Question

log3x2log527log58=lne \log_3x^2\log_527-\log_58=\ln e

Video Solution

Solution Steps

00:00 Solve
00:09 We'll use the logarithm product formula, switching between bases
00:24 We'll use this formula in our exercise
00:44 Let's calculate the logarithm
00:59 We'll substitute this solution in our exercise and continue solving
01:29 We'll use the power logarithm formula
01:34 We'll use this formula in our exercise
01:54 We'll substitute in our exercise
02:09 We'll use the logarithm quotient formula, we'll get the logarithm of the quotient
02:24 We'll use this formula in our exercise
02:39 We'll convert to logarithm and calculate
02:49 We'll solve according to the logarithm definition
03:09 Let's isolate X
03:34 This is the possible solution, now let's check the domain of definition
03:45 And this is the solution to the question

Step-by-Step Solution

To solve this problem, we'll follow these steps:

  • Step 1: Convert the logarithms into another base using the change of base rule.
  • Step 2: Simplify lne\ln e since lne=1\ln e = 1.
  • Step 3: Simplify the expression using known values.
  • Step 4: Solve the equation for x x .

Now, let's work through each step:

Step 1: Given the equation log3x2log527log58=lne \log_3 x^2 \log_5 27 - \log_5 8 = \ln e , we know that lne=1\ln e = 1. We will first simplify the right side to get:
log3x2log527log58=1 \log_3 x^2 \log_5 27 - \log_5 8 = 1

Step 2: Use the change of base formula.

Using logba=lnalnb\log_b a = \frac{\ln a}{\ln b}, rewrite log527 \log_5 27 and log58 \log_5 8 :

log527=ln27ln5andlog58=ln8ln5 \log_5 27 = \frac{\ln 27}{\ln 5} \quad \text{and} \quad \log_5 8 = \frac{\ln 8}{\ln 5}

Plug in the values:

log3x2ln27ln5ln8ln5=1 \log_3 x^2 \frac{\ln 27}{\ln 5} - \frac{\ln 8}{\ln 5} = 1

Step 3: Multiply through by ln5 \ln 5 to eliminate the denominators:
log3x2ln27ln8=ln5 \log_3 x^2 \ln 27 - \ln 8 = \ln 5

Now knowing ln27=3ln3\ln 27 = 3\ln 3, solve the equation:

log3x2=ln5+ln83ln3 \log_3 x^2 = \frac{\ln 5 + \ln 8}{3 \ln 3}

Apply the logarithm base rule:

x2=3(ln5+ln83ln3) x^2 = 3^{\left(\frac{\ln 5 + \ln 8}{3\ln 3}\right)}

Step 4: Simplify and solve for x x . Recognize this exponent could become ln403ln3\frac{\ln 40}{3\ln 3}:

x2=3ln403ln3=401/3 x^2 = 3^{\frac{\ln 40}{3\ln 3}} = 40^{1/3}

Finally, solve for x x :

x=±406 x = \pm \sqrt[6]{40}

Therefore, the solution to the problem is x=±406 x = \pm\sqrt[6]{40} .

Answer

±406 \pm\sqrt[6]{40}


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