Precalculus (6th Edition) Blitzer

Published by Pearson
ISBN 10: 0-13446-914-3
ISBN 13: 978-0-13446-914-0

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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