Math Problem Statement

If ln(x) + ln(x - 4) = ln(6x), then x = ?

Solution

The given equation is:

ln(x)+ln(x4)=ln(6x)\ln(x) + \ln(x - 4) = \ln(6x)

Step-by-step solution:

  1. Use the logarithmic property that ln(a)+ln(b)=ln(ab)\ln(a) + \ln(b) = \ln(ab):

    ln(x)+ln(x4)=ln(x(x4))=ln(x24x)\ln(x) + \ln(x - 4) = \ln(x(x - 4)) = \ln(x^2 - 4x)

    So the equation becomes:

    ln(x24x)=ln(6x)\ln(x^2 - 4x) = \ln(6x)

  2. Since the logarithms are equal, the arguments must also be equal:

    x24x=6xx^2 - 4x = 6x

  3. Simplify the quadratic equation:

    x24x6x=0x^2 - 4x - 6x = 0

    x210x=0x^2 - 10x = 0

  4. Factor the equation:

    x(x10)=0x(x - 10) = 0

  5. Solve for xx:

    x=0orx=10x = 0 \quad \text{or} \quad x = 10

  6. Check for extraneous solutions:

    • x=0x = 0 is not a valid solution because ln(0)\ln(0) is undefined.
    • Therefore, the only valid solution is x=10x = 10.

Thus, x=10x = 10.

Would you like more details or have any questions? Here are five related questions to expand your understanding:

  1. How does the property ln(a)+ln(b)=ln(ab)\ln(a) + \ln(b) = \ln(ab) apply to logarithmic equations?
  2. What are the general steps for solving equations involving logarithms?
  3. Can logarithmic functions have negative or zero inputs?
  4. What is an extraneous solution, and why did we discard x=0x = 0?
  5. How do we convert logarithmic equations to exponential form?

Tip: Always check for extraneous solutions when solving logarithmic equations because logarithms are undefined for non-positive numbers.

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Math Problem Analysis

Mathematical Concepts

Logarithms
Quadratic Equations

Formulas

ln(a) + ln(b) = ln(ab)
Quadratic equation: ax^2 + bx + c = 0

Theorems

Logarithmic properties
Quadratic equation factorization

Suitable Grade Level

Grades 10-12