Algebra 2 Common Core

Published by Prentice Hall
ISBN 10: 0133186024
ISBN 13: 978-0-13318-602-4

Chapter 7 - Exponential and Logarithmic Functions - 7-6 Natural Logarithms - Practice and Problem-Solving Exercises - Page 481: 26

Answer

$x=\dfrac{\pm \sqrt{2e^{\frac{1}{2}}}}{2}$

Work Step by Step

Divide $2$ to both sides: $$\ln{\left(2x^2\right)}=\frac{1}{2}$$ Recall: $$\ln{a}=y \longleftrightarrow e^y=a$$ Use the definition above to obtain: \begin{align*} \ln{\left(2x^2\right)}&=\frac{1}{2}\\\\ e^{\frac{1}{2}}&=2x^2\\\\ \frac{e^{\frac{1}{2}}}{2}&=\frac{2x^2}{2}\\\\ \frac{e^{\frac{1}{2}}}{2}&=x^2\\\\ \pm\sqrt{\frac{e^{\frac{1}{2}}}{2}}&=x\\\\ \pm\sqrt{\frac{e^{\frac{1}{2}}}{2}\cdot \frac{2}{2}}&=x\\\\ \pm\sqrt{\frac{2e^{\frac{1}{2}}}{4}}&=x\\\\ \dfrac{\pm\sqrt{2e^{\frac{1}{2}}}}{2}&=x\\\\ \end{align*} Check: \begin{align*} 2\ln{\left(2\left(\frac{\sqrt{2e^{\frac{1}{2}}}}{2}\right)^2\right)}&\stackrel{?}=1\\\\ 2\ln{\left(2\left(\frac{2e^{\frac{1}{2}}}{4}\right)\right)}&\stackrel{?}=1\\\\ 2\ln{\left(e^{\frac{1}{2}}\right)}&\stackrel{?}=1\\\\ 2\left(\frac{1}{2}\right)&\stackrel{?}=1\\\\ 1&\stackrel{\checkmark}=1 \end{align*} \begin{align*} 2\ln{\left(2\left(\frac{-\sqrt{2e^{\frac{1}{2}}}}{2}\right)^2\right)}&\stackrel{?}=1\\\\ 2\ln{\left(2\left(\frac{2e^{\frac{1}{2}}}{4}\right)\right)}&\stackrel{?}=1\\\\ 2\ln{\left(e^{\frac{1}{2}}\right)}&\stackrel{?}=1\\\\ 2\left(\frac{1}{2}\right)&\stackrel{?}=1\\\\ 1&\stackrel{\checkmark}=1 \end{align*}
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