The laws of logarithms









Properties of Exponents and Logarithms

Properties of Exponents and Logarithms Then the following properties of ... Most calculators can directly compute logs base 10 and the natural log.
Exponents and Logarithms


6.2 Properties of Logarithms

3. ln. ( 3 ex. )2. 4. log 3. √. 100x2 yz5. 5. log117(x2 − 4). Solution. 1. To expand log2. (8 x) we use the Quotient Rule identifying u = 8 and w = x and 
S&Z . & .


Limits involving ln(x)

We can use the rules of logarithms given above to derive the following information about limits. lim x→∞ ln x = ∞ lim x→0.
. Limits Derivatives and Integrals


Significant Figure Rules for logs

Significant Figure Rules for Logarithms. • Things to remember: significant The rule for natural logs (ln) is similar but not quite as clear-cut.
Significant Figure Rules for logs





Elementary Functions Rules for logarithms Exponential Functions

+ 4). By the first inverse property since ln() stands for the logarithm base e
. Working With Logarithms (slides to )


The laws of logarithms

a) 3 log10 5 b) 2 log x
mc bus loglaws


Logarithms

state and use the laws of logarithms. • solve simple equations requiring the use of logarithms. Contents. 1. Introduction log and ln.
mc ty logarithms


Worksheet: Logarithmic Function

(8) −ln. (1 x. ) = lnx. (9) ln√ x xk = 2k. 7. Solve the following logarithmic equations. (1) lnx = −3. (2) log(3x − 2) = 2. (3) 2 log x = log 2 + log(3x 
Exercises LogarithmicFunction





math1414-laws-of-logarithms.pdf

Again we will use the Change of Base Formula. This time we will let the new base be a = e. 5 ln 2.33 log 2.33.
math laws of logarithms


What is a logarithm? Log base 10

And so ln(ex) = x eln(x) = x. • Now we have a new set of rules to add to the others: Table 4. Functions of log base 10 and base e. Exponents. Log base 10.
logarithms


212754 The laws of logarithms

The laws of logarithms

mc-bus-loglaws-2009-1

Introduction

There are a number of rules known as thelaws of logarithms. These allow expressions involving logarithms to be rewritten in a variety of different ways. Thelaws apply to logarithms of any base but the same base must be used throughout a calculation.

The laws of logarithms

The three main laws are stated here:

First Law

logA+ logB= logAB This law tells us how to add two logarithms together. AddinglogAandlogBresults in the logarithm of the product ofAandB, that islogAB.

For example, we can write

log

105 + log104 = log10(5×4) = log1020

The same base, in this case 10, is used throughout the calculation. You should verify this by evaluating both sides separately on your calculator.

Second Law

logA-logB= logA B

So, subtractinglogBfromlogAresults inlogAB.

For example, we can write

log e12-loge2 = loge12

2= loge6

The same base, in this case e, is used throughout the calculation. You should verify this by evaluating

both sides separately on your calculator.

Third Law

logAn=nlogA

So, for example

log

1053= 3log105

You should verify this by evaluating both sides separately on your calculator.

Two other important results are

www.mathcentre.ac.uk 1 c?mathcentre 2009 log1 = 0,logmm= 1 The logarithm of 1 to any base is always 0, and the logarithm ofa number to the same base is always 1. In particular, log

1010 = 1,andlogee = 1

Exercises

1. Use the first law to simplify the following.

a)log106 + log103, b)logx+ logy, c)log4x+ logx, d)loga+ logb2+ logc3.

2. Use the second law to simplify the following.

a)log106-log103, b)logx-logy, c)log4x-logx.

3. Use the third law to write each of the following in an alternative form.

a)3log105, b)2logx, c)log(4x)2, d)5lnx4, e)ln1000.

4. Simplify3logx-logx2.

Answers

1. a)log1018, b)logxy, c)log4x2, d)logab2c3.

2. a)log102, b)logx

y, c)log4.

3. a)log1053orlog10125, b)logx2, c)2log(4x), d)20lnxorlnx20,

e)1000 = 103soln1000 = 3ln10.

4.logx.

www.mathcentre.ac.uk 2 c?mathcentre 2009

The laws of logarithms

mc-bus-loglaws-2009-1

Introduction

There are a number of rules known as thelaws of logarithms. These allow expressions involving logarithms to be rewritten in a variety of different ways. Thelaws apply to logarithms of any base but the same base must be used throughout a calculation.

The laws of logarithms

The three main laws are stated here:

First Law

logA+ logB= logAB This law tells us how to add two logarithms together. AddinglogAandlogBresults in the logarithm of the product ofAandB, that islogAB.

For example, we can write

log

105 + log104 = log10(5×4) = log1020

The same base, in this case 10, is used throughout the calculation. You should verify this by evaluating both sides separately on your calculator.

Second Law

logA-logB= logA B

So, subtractinglogBfromlogAresults inlogAB.

For example, we can write

log e12-loge2 = loge12

2= loge6

The same base, in this case e, is used throughout the calculation. You should verify this by evaluating

both sides separately on your calculator.

Third Law

logAn=nlogA

So, for example

log

1053= 3log105

You should verify this by evaluating both sides separately on your calculator.

Two other important results are

www.mathcentre.ac.uk 1 c?mathcentre 2009 log1 = 0,logmm= 1 The logarithm of 1 to any base is always 0, and the logarithm ofa number to the same base is always 1. In particular, log

1010 = 1,andlogee = 1

Exercises

1. Use the first law to simplify the following.

a)log106 + log103, b)logx+ logy, c)log4x+ logx, d)loga+ logb2+ logc3.

2. Use the second law to simplify the following.

a)log106-log103, b)logx-logy, c)log4x-logx.

3. Use the third law to write each of the following in an alternative form.

a)3log105, b)2logx, c)log(4x)2, d)5lnx4, e)ln1000.

4. Simplify3logx-logx2.

Answers

1. a)log1018, b)logxy, c)log4x2, d)logab2c3.

2. a)log102, b)logx

y, c)log4.

3. a)log1053orlog10125, b)logx2, c)2log(4x), d)20lnxorlnx20,

e)1000 = 103soln1000 = 3ln10.

4.logx.

www.mathcentre.ac.uk 2 c?mathcentre 2009
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