Math Problem Statement

Solve the equation ln(x + 1) - ln(x - 3) = ln 4.

Solution

The equation given in the image is:

ln(x+1)ln(x3)=ln4\ln(x + 1) - \ln(x - 3) = \ln 4

Step-by-step solution:

  1. Apply the logarithmic property: ln(a)ln(b)=ln(ab)\ln(a) - \ln(b) = \ln\left(\frac{a}{b}\right) Using this property, the equation becomes: ln(x+1x3)=ln4\ln\left(\frac{x + 1}{x - 3}\right) = \ln 4

  2. Equate the arguments of the logarithms: If lnA=lnB\ln A = \ln B, then A=BA = B. Therefore: x+1x3=4\frac{x + 1}{x - 3} = 4

  3. Simplify the equation: Multiply both sides by x3x - 3 (assuming x30x - 3 \neq 0): x+1=4(x3)x + 1 = 4(x - 3)

    Expand the right-hand side: x+1=4x12x + 1 = 4x - 12

  4. Solve for xx: Rearrange to isolate xx: 1+12=4xx1 + 12 = 4x - x 13=3x13 = 3x x=133x = \frac{13}{3}

  5. Check the solution: Ensure x=133x = \frac{13}{3} satisfies the domain of the logarithmic functions:

    • The arguments of the logarithms must be positive: x+1>0andx3>0x + 1 > 0 \quad \text{and} \quad x - 3 > 0 For x+1>0x + 1 > 0, x>1x > -1.
      For x3>0x - 3 > 0, x>3x > 3.
      The stricter condition is x>3x > 3.

    Since 1334.33>3\frac{13}{3} \approx 4.33 > 3, the solution is valid.

Final Answer:

x=133x = \frac{13}{3}

Would you like further clarification or details on this solution?


Related Questions:

  1. What is the domain of the given logarithmic equation?
  2. How can the logarithmic property ln(a)ln(b)=ln(ab)\ln(a) - \ln(b) = \ln\left(\frac{a}{b}\right) be derived?
  3. How would the solution change if the right-hand side was a different value (e.g., ln2\ln 2)?
  4. Why is it important to check the domain of logarithmic equations?
  5. Can this equation be solved graphically? How?

Tip: Always check the domain restrictions when working with logarithmic functions to avoid invalid solutions.

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Math Problem Analysis

Mathematical Concepts

Logarithmic Functions
Properties of Logarithms
Equations

Formulas

ln(a) - ln(b) = ln(a/b)
If ln(A) = ln(B), then A = B

Theorems

Properties of Logarithms

Suitable Grade Level

Grades 11-12