Power Law and Its Proof

Power Law and Its Proof

For \(a>0,\ a\ne1,\ M>0\) and real \(r\):

\(\log_a(M^r)=r\log_a M\)

Examples

ExpressionSimplified form
\(\log_2(5^x)\)
\(\log_3\sqrt{2}\)
\(\lg\sqrt[3]{x},\ x>0\)

Watch the brackets

For \(x>0\): \(\lg(2x^3)=\lg2+3\lg x\), whereas \(\lg((2x)^3)=3\lg(2x)\).

\((\log_a x)^3\) is the cube of the logarithm; the power law does not apply.

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Answer:\(\log_a(b^r)=r\log_a b\)

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