Distributing negative signs in logarithms

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RChristenk
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Homework Statement
Simplify ##\log(A \times B \div C \times D)##
Relevant Equations
Logarithm Rules
Simplify ##\log(A \times B \div C \times D)##

Is it ##\log(A)+\log(B)-(\log(C)+\log(D))## or ##\log(A)+\log(B)-\log(C)+\log(D)##?

I'm leaning toward the former but not sure. Thanks.
 
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  • #2
It depends on whether the statement means
##log[\frac {ab} {cd}]## or ##log[\frac {abd} {c}]##
Normal convention says the latter so log(a)+log(b)-log(c)+log(d)
 
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RChristenk said:
Simplify ##\log(A \times B \div C \times D)##
I have not seen any algebra textbooks that would show problems like this. As already noted, the expression in parentheses should be written as either ##\frac{AB}C \cdot D## or as ##\frac{AB}{CD}##. Failing that, there should at least be parentheses around CD to emphasize that this is the divisor.
Is this a problem from some textbook? If so, my guess is that it is substandard or very old.
Also, algebra textbooks generally don't use the ##\div## sign.
 

FAQ: Distributing negative signs in logarithms

1. What is the basic rule for distributing a negative sign in logarithmic expressions?

The basic rule for distributing a negative sign in logarithmic expressions is to use the property of logarithms that states \(-\log_b(x) = \log_b(1/x)\). This means that a negative sign in front of a logarithm can be interpreted as the logarithm of the reciprocal of the argument.

2. Can you provide an example of distributing a negative sign in a logarithmic expression?

Sure! For example, if you have \(-\log_b(5)\), you can distribute the negative sign by rewriting it as \(\log_b(1/5)\). This uses the property \(-\log_b(x) = \log_b(1/x)\).

3. How does distributing a negative sign affect the logarithm of a product?

When distributing a negative sign in the logarithm of a product, you apply the property to each term individually. For instance, \(-\log_b(xy)\) can be rewritten as \(\log_b(1/(xy))\), which can be further simplified using the logarithm property for division: \(\log_b(1) - \log_b(xy)\), resulting in \(-\log_b(x) - \log_b(y)\).

4. What happens when you distribute a negative sign in a logarithm with a quotient?

When you have a logarithm with a quotient, such as \(-\log_b(x/y)\), you can distribute the negative sign by using the property: \(-\log_b(x/y) = \log_b(1/(x/y)) = \log_b(y/x)\). This changes the order of the terms in the quotient.

5. Are there any common mistakes to avoid when distributing negative signs in logarithms?

A common mistake is to incorrectly handle the negative sign by not applying the logarithmic properties properly. For example, \(-\log_b(x + y)\) should not be simplified to \(\log_b(1/(x + y))\) unless the argument inside the logarithm is a single term. Always ensure that the negative sign is applied correctly using the property \(-\log_b(x) = \log_b(1/x)\).

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