Math Problem Statement

Solve for x: log_2(x - 7) = 2 + log_2(x - 4)

Solution

We are given the equation:

log2(x7)=2+log2(x4)\log_2(x - 7) = 2 + \log_2(x - 4)

We need to solve for xx. Let's break it down step by step.

Step 1: Use logarithmic properties

Since we have logarithms on both sides, we can isolate them. First, subtract log2(x4)\log_2(x - 4) from both sides:

log2(x7)log2(x4)=2\log_2(x - 7) - \log_2(x - 4) = 2

Step 2: Apply the logarithmic subtraction rule

The subtraction rule for logarithms states:

logb(A)logb(B)=logb(AB)\log_b(A) - \log_b(B) = \log_b\left(\frac{A}{B}\right)

So, applying this rule:

log2(x7x4)=2\log_2\left(\frac{x - 7}{x - 4}\right) = 2

Step 3: Convert the logarithmic equation to exponential form

Now, rewrite the equation in its exponential form. The logarithmic equation logb(A)=C\log_b(A) = C is equivalent to A=bCA = b^C. So:

x7x4=22\frac{x - 7}{x - 4} = 2^2

This simplifies to:

x7x4=4\frac{x - 7}{x - 4} = 4

Step 4: Solve for xx

Now, multiply both sides by (x4)(x - 4) to eliminate the fraction:

x7=4(x4)x - 7 = 4(x - 4)

Expand the right-hand side:

x7=4x16x - 7 = 4x - 16

Now, solve for xx by bringing all xx-terms to one side:

x4x=16+7x - 4x = -16 + 7

This simplifies to:

3x=9-3x = -9

Divide both sides by 3-3:

x=3x = 3

Step 5: Check the solution

We must check if x=3x = 3 satisfies the original logarithmic conditions. Since the arguments inside the logarithms must be positive:

  • x7=37=4x - 7 = 3 - 7 = -4 (which is negative)

Since log2(x7)\log_2(x - 7) is undefined for negative numbers, x=3x = 3 is not a valid solution.

Final Answer:

There is no solution to this equation.


Would you like further clarification or details? Here are 5 related questions to explore:

  1. How do you convert logarithmic equations to exponential form?
  2. What are the key logarithmic properties used in solving such equations?
  3. How can you determine the domain of a logarithmic function?
  4. Why are negative numbers excluded from the arguments of logarithms?
  5. Can you apply logarithmic transformations to both sides of any equation?

Tip: Always check for restrictions in the domain when solving logarithmic equations.

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Math Problem Analysis

Mathematical Concepts

Logarithms
Exponential Equations
Properties of Logarithms

Formulas

log_b(A) - log_b(B) = log_b(A/B)
log_b(A) = C is equivalent to A = b^C

Theorems

Properties of Logarithms
Logarithmic and Exponential Relationship

Suitable Grade Level

Grades 10-12