Big Ideas Math Algebra 2, 2014
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Big Ideas Math Algebra 2, 2014 View details
5. Properties of Logarithms
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Exercise 4 Page 327

Start by using two auxiliary logarithmic expressions. Then rewrite them in exponential form and apply the Properties of Exponents. Finally, go back to logarithmic expressions after simplifying.

See solution.

Practice makes perfect
To derive the Properties of Logarithms, we can start by defining two auxiliary general logarithmic expressions. a = log_b m c = log_b n Now, from the definition of logarithm we know that there is an equivalent exponential representation for a logarithmic expression. y= b^x ⇔ x = log_b y We can use this to rewrite our auxiliary logarithmic expressions in exponential form.

a = log_b m c = log_b n ⇕ b^a= m b^c= n This way, we can alter them using the Properties of Exponents. Once we have simplified by using the Properties of Exponents, we can rewrite our result using the corresponding logarithmic expressions. We will now work out some examples.

Deriving the Product Property of Logarithms

Using the expressions introduced before, lets find the product of m and n.
mn = (b^a)(b^c)
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Simplify and rewrite using logarithms
mn = b^(a+c)
log_b(mn) = a+c
log_b(mn) = log_b m + log_b n
This last result is known as the Product Property of Logarithms.

log_b(mn) = log_b m + log_b n

Deriving the Quotient Property of Logarithms

Using the expressions introduced above, we will now find the quotient of m and n.
m/n = b^a/b^c
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Simplify and rewrite using logarithms
m/n = b^(a-c)
log_b(m/n) = a-c
log_b(m/n) = log_b m - log_b n
This last result is known as the Quotient Property of Logarithms.

log_b(m/n) = log_b m - log_b n

Deriving the Power Property of Logarithms

Let's consider the logarithm base b of m^n. Since we know that m = b^a, we can use it in our expression.
log_b( m^n) = log_b(( b^a)^n)
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Simplify and rewrite using logarithms
log_b(m^n) = log_b(b^(an))

log_b(b^m)=m

log_b(m^n) = an
log_b(m^n) = ( log_b m )n
log_b(m^n) = nlog_b m
This last result is known as the Power Property of Logarithms.

log_b(m^n) = nlog_b m