対数を組み合わせます:\( \log_2(x(x-3)) = 3 \)。 - United Radiology

April 21, 2026 · United Radiology

["Understanding the Equation: ( \log_2(x(x - 3)) = 3 ) – Solving Logarithmic Expressions", "Solving logarithmic equations is a fundamental skill in algebra, and one commonly encountered form is when logarithms are combined using logarithmic identities. An example that illustrates this concept clearly is the equation:", "[
\n\log_2(x(x - 3)) = 3
\n]", "In this article, we’ll explore how to solve this equation while focusing on the key logarithmic principle—combining logarithms using additive properties, and how it helps unlock the solution.", "---", "### What Does ( \log_b(A) = C ) Mean?", "The equation ( \log_b(A) = C ) means “logarithm base ( b ) of ( A ) equals ( C )”, which translates directly into exponential form:", "[
\nA = b^C
\n]", "In our case,
\n- Base ( b = 2 ),
\n- ( A = x(x - 3) ),
\n- ( C = 3 ).", "So, applying the conversion:", "[
\nx(x - 3) = 2^3
\n]", "[
\nx(x - 3) = 8
\n]", "This transformation combines log and exponentials to remove the logarithm and reveal a quadratic equation—making it solvable using standard algebra.", "---", "### Step-by-Step Solution", "Starting from:", "[
\n\log_2(x(x - 3)) = 3
\n]", "Rewrite in exponential form:", "[
\nx(x - 3) = 2^3 = 8
\n]", "Expand the left-hand side:", "[
\nx^2 - 3x = 8
\n]", "Bring all terms to one side:", "[
\nx^2 - 3x - 8 = 0
\n]", "Now solve the quadratic using the quadratic formula:", "[
\nx = \frac{3 \pm \sqrt{(-3)^2 + 4 \cdot 1 \cdot 8}}{2} = \frac{3 \pm \sqrt{9 + 32}}{2} = \frac{3 \pm \sqrt{41}}{2}
\n]", "Thus, the two solutions are:", "[
\nx = \frac{3 + \sqrt{41}}{2} \quad \ ext{and} \quad x = \frac{3 - \sqrt{41}}{2}
\n]", "---", "### Checking for Valid Solutions", "Since logarithm is only defined for positive arguments, we must ensure ( x(x - 3) > 0 ). Let's verify both solutions:", "1. ( x = \frac{3 + \sqrt{41}}{2} \approx \frac{3 + 6.4}{2} \approx 4.7 )
\n Then ( x - 3 \approx 1.7 > 0 ), so ( x(x - 3) > 0 ) ✅", "2. ( x = \frac{3 - \sqrt{41}}{2} \approx \frac{3 - 6.4}{2} \approx -1.7 )
\n Then ( x - 3 \approx -4.7 ), so ( x(x - 3) \approx (-1.7)(-4.7) > 0 ), still valid ✅", "Both solutions satisfy the domain of the logarithm—no extraneous roots are introduced because we followed proper transformation steps.", "---", "### Why Logarithmic Identity Matters", "The key step in solving ( \log_2(x(x - 3)) = 3 ) is recognizing that logs can be “combined” into exponentials—though here it’s more about transforming logarithms to exponential form. More broadly, logarithmic identities allow combining multiple logs via:", "- ( \log_b x + \log_b y = \log_b(xy) )
\n- ( \log_b x - \log_b y = \log_b\left(\frac{x}{y}\right) )
\n- ( k \log_b x = \log_b(x^k) )", "In real-world problem-solving, such transformations simplify complex expressions and unlock solutions, especially in fields like computer science, engineering, and finance.", "---", "### Summary", "The equation ( \log_2(x(x - 3)) = 3 ) demonstrates a classic use of logarithmic identities: converting a logarithmic equation to exponential form by recognizing logarithm-to-exponent conversion. This approach eliminates the logarithm, yielding a solvable algebraic expression. Proper domain checks ensure only valid solutions are accepted, and understanding how logs combine at the outset streamlines problem-solving and enhances conceptual mastery.", "---", "Key takeaways:
\n- Use ( \log_b A = C \Rightarrow A = b^C ) to eliminate logs.
\n- Always verify solutions satisfy the logarithm’s domain.
\n- Logarithmic identities are powerful tools to simplify and solve equations.", "If you're mastering logarithmic equations, practice boiling down problems using these combining principles—your math skills will grow stronger with each step!", "---", "Keywords for SEO:

\n

LogarithmicEquation #SolveLogarithms #CombiningLogs #MathSolving #ExponentialForm #LogarithmicIdentity #x(x-3) = 8 #SolveQuadratic #MathTips #Algebra101", "Meta Title: Solve ( \log_2(x(x - 3)) = 3 ) – Step-by-step Logarithm Solving Guide

\n

Meta Description: Learn how to solve ( \log_2(x(x - 3)) = 3 ) by combining logs and exponents. Clear steps and validation included.
\nHeader Tags:
\n- #Understanding ( \log_2(x(x - 3)) = 3 )
\n- Step-by-Step: Solve logs using logarithmic identities
\n- Why Combining Logarithms Matters
\n- Valid Solutions: Check domain after solving
\n- Master Algebra with logarithmic equation Solver", "---", "By grasping the transformation of logarithmic equations—such as combining them into exponentials—you unlock powerful problem-solving techniques essential for advanced math and real applications. Start practicing with similar log equations to build fluency today!"]

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