introduction to logarithms 5 5. what you should learn: i can convert logarithmic expressions to...
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INTRODUCTION TO LOGARITHMS
5
WHAT YOU SHOULD LEARN:
I can convert logarithmic expressions to exponential expressions and vice
versa.
I can evaluate logarithmic functions.
2.4 I can convert logarithmic expressions to exponential expressions and vice versa.
WHAT IS A LOGARITHM? Definition of a Logarithm
If b > 0, b ≠ 1, and x > 0, then Logarithmic Form Exponential Form
log b x = y iff by = x
base exponent baseexponent
Remember: A logarithm is an exponent!
CONVERT EACH LOGARITHMIC EXPRESSION TO AN EQUIVALENT EXPONENTIAL EXPRESSION.
① Log381 = 4
② Log2 = -3
③ Log10100 = 2
④ Log5 = -3
⑤ Log273 =
34 = 815-3 = 1/125
2-3 = 1/8271/3 = 3
102 = 100
CONVERT EACH EXPONENTIAL EXPRESSION TO AN EQUIVALENT LOGARITHMIC EXPRESSION.
① 92 = 81
② 54 = 625
③ 12-2 =
④ 102 =100
⑤
Log981 = 2log10100 = 2
Log5625 = 4log5√5 = 1/2
log121/144 = -2
THE COMMON LOGARITHM
A logarithm with base 10 or log10 is called a common logarithm.
The common logarithm is often written without the base.
y = logx iff 10y = x
THE NATURAL LOGARITHMRECALL: E ≈ 2.71828…
A logarithm with base e or loge is called a natural logarithm.
The natural logarithm is often written without the base.
y = lnxiff ey = x
CONVERT EACH EXPONENTIAL EXPRESSION TO AN EQUIVALENT LOGARITHMIC EXPRESSION OR VICE VERSA.
① Log x = 2
② Ln 20.0855… ≈ 3
③ e4 ≈ x
④ 106 = 1,000,000
102 = x
e3 ≈ 20.0855…
Ln x = 4
Log 1,000,000 = 6
EVALUATE THE FOLLOWING:① log = x
② log / / = x
③ Log x = 3
④ log x = 0
⑤ log x = -2
⑥ Log x / /
19x = 361x = 2
30 = xx = 1
(1/7)x = 1/49x = 2
9-2 = xx = 1/81
x3 = 216x = 6
X-1/4 = 1/2x = 16
2.5 I can evaluate logarithmic functions in a real world
scenario.
A solution’s pH is given by the function p(t) log(t), where t is the hydronium ion concentration, in moles per liter. A sample of coffee has a pH of 5.0. What is the approximate hydronium ion concentration of the sample?
The wind speed s (in miles per hour) near the center of a tornado is related to the distance d (in miles) the tornado travels by the equation s = 93logd + 65.
a. On March 18, 1925, a tornado whose wind speed was about 280 miles per hour struckthe Midwest. How far did the tornado travel?
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