To see the proofs of the product, quotient, and power laws of logarithms, read “Link the Ideas” on pages 394 to 395 of the textbook. Notice how each logarithmic law is proved using the exponent laws.
In Try This 2 you will look at using the laws of logarithms to evaluate an expression.
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Evaluate the expression using the laws of logarithms.
To enter logarithms into your calculator, use the LOG button. Some calculators let you enter the base of the logarithm using this button. For other calculators, the LOG button is the common logarithm with base 10. On these calculators, to enter log2 8, you need to use the change-of-base identity for logarithms. The identity states
To write log2 8 as a logarithm of base 10, the expressions would become
On your calculator you would enter LOG (8) ÷ LOG (2). Remember, when no base is indicated, it is assumed to be base 10.
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