5 minutes Warm-Up Solve each equation for x. Round your answer to the nearest hundredth, if necessary. 1) log x = 3 2) log x = 0.447 3) ln x = 0 4) ln x = 1.61
6.7 Solving Equations and Modeling Objectives: Solve logarithmic and exponential equations by using algebra and graphs Model and solve real-world problems involving logarithmic and exponential relationships
Summary of Exponential-Logarithmic Definitions and Properties Definition of logarithm y = logb x only if by = x Product Property logb mn = logb m + logb n logb = logb m – logb n m n ( ) Quotient Property Power Property logb mp = p logb m
Summary of Exponential-Logarithmic Definitions and Properties Exp-Log Inverse b logb x = x for x > 0 logb bx = x for all x 1-to-1 for Exponents bx = by; x = y 1-to-1 for Logarithms logb x = logb y; x = y logc a = logb a logb c Change-of-Base
Example 1 Solve for x. 3x – 2 = 4x + 1 log 3x – 2 = log 4x + 1 x log 3 – 2 log 3 = x log 4 + log 4 x log 3 – x log 4 = log 4 + 2 log 3 x (log 3 – log 4) = log 4 + 2 log 3 log 4 + 2 log 3 log 3 – log 4 = x x –12.46
Example 2 Solve for x. log x + log (x + 3) = 1 log [x(x + 3)] = 1
Example 2 Solve for x. log x + log (x + 3) = 1 Check: x = 2,-5 Let x = 2 Let x = -5 log x + log (x + 3) = 1 log x + log (x + 3) = 1 log 2 + log (2 + 3) = 1 log -5 + log (-5 + 3) = 1 log 2 + log 5 = 1 log -5 + log -2 = 1 1 = 1 undefined x = 2
Example 3 Solve for x. 8e2x-5 = 56 e2x-5 = 7 ln e2x-5 = ln 7
Example 4 Suppose that the magnitude, M, of an earthquake measures 7.5 on the Richter scale. Use the formula below to find the amount of energy, E, released by this earthquake.
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