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Ch. 4 - Exponential and Logarithmic Functions
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Non è quello che usi tu?Cambia libro di testo
Capitolo 5, Problema 127

In Exercises 125–128, determine whether each statement is true or false. If the statement is false, make the necessary change(s) to produce a true statement.
logb(x3+y3)=3logbx+3logbylog_{b}(x^3+y^3)=3log_{b}x+3log_{b}y

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Recall the logarithm property for products: logb(x\(\cdot\)y) = logb(x) + logb(y). This means logarithms turn multiplication inside the log into addition outside the log.
Notice that the expression inside the logarithm on the left side is x3 + y3, which is a sum, not a product. The logarithm property for sums is not the same as for products.
The right side of the equation is 3 \(\log\)_b x + 3 \(\log\)_b y, which can be rewritten using the power rule of logarithms as \(\log\)_b (x^3) + \(\log\)_b (y^3). Using the product rule, this equals \(\log\)_b (x^3 y^3).
Since \(\log\)_b (x^3 + y^3) is not equal to \(\log\)_b (x^3 y^3), the original statement is false.
To make the statement true, replace the sum inside the logarithm with a product: \(\log\)_b (x^3 y^3) = 3 \(\log\)_b x + 3 \(\log\)_b y.

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Properties of Logarithms

Logarithms have specific properties that simplify expressions, such as the product rule: log_b(MN) = log_b M + log_b N, and the power rule: log_b(M^k) = k log_b M. Understanding these rules is essential to manipulate and evaluate logarithmic expressions correctly.
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The expression x^3 + y^3 is a sum of cubes, which cannot be factored into a simple product of x and y terms. Since logarithm properties apply to products, not sums, recognizing the difference between sums and products is crucial to avoid incorrect application of log rules.
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