Math Problem Statement

Prove that \(\log_a(xy) = \log_a x + \log_a y\)

Solution

To prove the logarithmic identity:

loga(xy)=logax+logay\log_a(xy) = \log_a x + \log_a y

Proof:

  1. Start with the definition of logarithms: A logarithm is the inverse of exponentiation. By definition, if:

    logax=mthenam=x\log_a x = m \quad \text{then} \quad a^m = x and logay=nthenan=y\log_a y = n \quad \text{then} \quad a^n = y

  2. Multiplying the arguments of the logarithms: From the expressions above, multiplying xx and yy gives: xy=amanx \cdot y = a^m \cdot a^n

  3. Apply exponentiation property: Using the property of exponents aman=am+na^m \cdot a^n = a^{m+n}, we get: xy=am+nx \cdot y = a^{m+n}

  4. Take the logarithm of both sides: Taking the logarithm base aa of both sides, we get: loga(xy)=loga(am+n)\log_a(x \cdot y) = \log_a(a^{m+n})

  5. Use the inverse property of logarithms: Since loga(ak)=k\log_a(a^k) = k, the right-hand side simplifies to: loga(xy)=m+n\log_a(x \cdot y) = m + n

  6. Substitute back the values of mm and nn: Recall that m=logaxm = \log_a x and n=logayn = \log_a y, so we get: loga(xy)=logax+logay\log_a(x \cdot y) = \log_a x + \log_a y

This completes the proof.


Would you like further details or have any other questions?

Here are 5 related questions for deeper understanding:

  1. How does this property of logarithms help in simplifying complex logarithmic expressions?
  2. Can you prove similar properties for logarithmic division?
  3. How can you use this property when solving exponential equations?
  4. What is the geometric interpretation of logarithms?
  5. How does changing the base aa affect this property of logarithms?

Tip: The logarithmic multiplication property is very useful in many areas of mathematics, especially when simplifying multiplication of large numbers or solving equations involving exponents.

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Math Problem Analysis

Mathematical Concepts

Logarithms
Algebra
Exponentiation

Formulas

\(\log_a(xy) = \log_a x + \log_a y\)
\(a^m \cdot a^n = a^{m+n}\)
\(\log_a(a^k) = k\)

Theorems

Logarithmic addition rule
Exponentiation properties

Suitable Grade Level

Grades 10-12