Finite Math and Applied Calculus (6th Edition)

Published by Brooks Cole
ISBN 10: 1133607705
ISBN 13: 978-1-13360-770-0

Chapter 11 - Section 11.6 - Implicit Differentiation - Exercises - Page 853: 46

Answer

$$\frac{{dy}}{{dx}} = \frac{{{x^2}{{\left( {3x + 1} \right)}^2}}}{{{{\left( {2x - 1} \right)}^3}}}\left( {\frac{2}{x} + \frac{6}{{3x + 1}} - \frac{6}{{2x - 1}}} \right)$$

Work Step by Step

$$\eqalign{ & y = \frac{{{x^2}{{\left( {3x + 1} \right)}^2}}}{{{{\left( {2x - 1} \right)}^3}}} \cr & {\text{Differentiate by logarithmic differentiation}} \cr & {\text{Take the natural logarithm of both sides}} \cr & \ln y = \ln \left( {\frac{{{x^2}{{\left( {3x + 1} \right)}^2}}}{{{{\left( {2x - 1} \right)}^3}}}} \right) \cr & {\text{Use the property }}\ln \left( {\frac{a}{b}} \right) = \ln a - \ln b \cr & \ln y = \ln {x^2}{\left( {3x + 1} \right)^2} - \ln {\left( {2x - 1} \right)^3} \cr & {\text{Use the property }}\ln \left( {ab} \right) = \ln a + \ln b \cr & \ln y = \ln {x^2} + \ln {\left( {3x + 1} \right)^2} - \ln {\left( {2x - 1} \right)^3} \cr & {\text{Use the powe property }}\ln \left( {{a^n}} \right) = n\ln a \cr & \ln y = 2\ln x + 2\ln \left( {3x + 1} \right) - 3\ln \left( {2x - 1} \right) \cr & {\text{Differentiate both sides w}}{\text{.r}}{\text{.t}} \hspace{2mm} x \cr & \frac{d}{{dx}}\left[ {\ln y} \right] = \frac{d}{{dx}}\left[ {2\ln x} \right] + \frac{d}{{dx}}\left[ {2\ln \left( {3x + 1} \right)} \right] - \frac{d}{{dx}}\left[ {3\ln \left( {2x - 1} \right)} \right] \cr & \frac{1}{y}\frac{{dy}}{{dx}} = \frac{2}{x} + \frac{6}{{3x + 1}} - \frac{6}{{2x - 1}} \cr & {\text{Solve for }}\frac{{dy}}{{dx}} \cr & \frac{{dy}}{{dx}} = y\left( {\frac{2}{x} + \frac{6}{{3x + 1}} - \frac{6}{{2x - 1}}} \right) \cr & {\text{Substitute back }}y = \frac{{{x^2}{{\left( {3x + 1} \right)}^2}}}{{{{\left( {2x - 1} \right)}^3}}} \cr & \frac{{dy}}{{dx}} = \frac{{{x^2}{{\left( {3x + 1} \right)}^2}}}{{{{\left( {2x - 1} \right)}^3}}}\left( {\frac{2}{x} + \frac{6}{{3x + 1}} - \frac{6}{{2x - 1}}} \right) \cr} $$
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