## Precalculus (6th Edition) Blitzer

Published by Pearson

# Chapter 3 - Section 3.4 - Exponential and Logarithmic Equations - Exercise Set - Page 491: 135

#### Answer

$t\approx 7.9$ minutes

#### Work Step by Step

Graphing, the solution is at $t\approx 7.9$ minutes. (see below) Algebraically, $70=145e^{-0.092t}\qquad$ ... $/\div 145$ $\displaystyle \frac{70}{145}=e^{-0.092t}\qquad$... $/\ln(...)$ $\displaystyle \ln(\frac{70}{145})=-0.092t\qquad$... $/\div(-0.092)$ $t=\displaystyle \frac{\ln(70/145)}{-0.092}\approx 7.915635873$ $t\approx 7.9$ minutes

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