logarithmic functions and their graphs. review: changing between logarithmic and exponential form if...
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Logarithmic Functions and Their Graphs
Review: Changing Between Logarithmic and Exponential Form
• If x > 0 and 0 < b ≠ 1, then
if and only if .
• This statement says that a logarithm is an exponent. Because logarithms are exponents, we can evaluate simple logarithmic expressions using our understanding of exponents.
log ( )by x yb x
Evaluating Logarithmsa.) because .
b.) because .
c.) because
d.) because
e.) because
2log 8 3 32 8
3log 3 1 2 1 23 3
5
1log 2
25 2
2
1 15 .
5 25
4log 1 0 04 1.
7log 7 1 17 7.
Basic Properties of Logarithms• For 0 < b ≠ 1 , x > 0, and any real number y,
logb1 = 0 because b0 = 1.
logbb = 1 because b1 = b.
logbby = y because by = by.
becauselogb xb x
Evaluating Logarithmic and Exponential Expressions
(a)
(b)
(c)
2log 8 32log 2 3.
3log 3 1 23log 3 1 2.
6log 116 11.
Common Logarithms – Base 10• Logarithms with base 10 are called common
logarithms.• Often drop the subscript of 10 for the base when
using common logarithms.• The common logarithmic function:
y = log x if and only if 10y = x.
Basic Properties of Common Logarithms• Let x and y be real numbers with x > 0.
log 1 = 0 because 100 = 1.
log 10 = 1 because 101 = 10.
log 10y = y because 10y = 10y .
because log x = log x.
• Using the definition of common logarithm or these basic properties, we can evaluate expressions involving a base of 10.
log10 x x
Evaluating Logarithmic and Exponential Expressions – Base 10
(a)
(b)
(c)
(d)
log100 10log 100 2
5log 10 1 5log10 1
5
1log1000 3
1log10
3log10 3log610 6
Solving Simple Logarithmic Equations• Solve each equation by changing it to exponential
form:a.) log x = 3 b.)
a.) Changing to exponential form, x = 10³ = 1000.
b.) Changing to exponential form, x = 25 = 32.
2log 5x
Natural Logarithms – Base e
• Logarithms with base e are natural logarithms.– We use the abbreviation “ln” (without a subscript)
to denote a natural logarithm.
Basic Properties of Natural Logarithms• Let x and y be real numbers with x > 0.
ln 1 = 0 because e0 = 1.
ln e = 1 because e1 = e.
ln ey = y because ey = ey.
eln x = x because ln x = ln x.
Transforming Logarithmic Graphs• Describe how to transform the graph of y = ln x or y
= log x into the graph of the given function.a.) g(x) = ln (x + 2)
The graph is obtained by translating the graph of y = ln (x) two units to the LEFT.
Transforming Logarithmic Graphs• Describe how to transform the graph of y = ln x or y
= log x into the graph of the given function.c.) g(x) = 3 log x
The graph is obtained by vertically stretching the graph of f(x) = log x by a factor of 3.
Transforming Logarithmic Graphs• Describe how to transform the graph of y = ln x or y
= log x into the graph of the given function.d.) h(x) = 1+ log x
The graph is obtained by a translation 1 unit up.