Example 10.39: Solving
To solve the logarithmic equation , first use the Product Property of Logarithms to condense the left side into a single logarithm: . Next, convert this to its equivalent exponential form: . Simplifying both sides gives . Subtract 9 from each side to set the quadratic equation to zero: . Factoring the right side yields . Using the Zero-Product Property, the potential solutions are and . However, substituting into the original equation results in evaluating the logarithm of a negative number, which is undefined. Therefore, is an extraneous solution and is eliminated. The only valid solution is . Checking by substitution gives , confirming the result.
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Ch.10 Exponential and Logarithmic Functions - Intermediate Algebra @ OpenStax
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Example 10.20: Evaluating Logarithmic Equations
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Extraneous Solution to a Logarithmic Equation
Example 10.39: Solving
Try It 10.77 and 10.78: Solving and
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Converting Logarithmic Models to Exponential Form