Calculus with Applications (10th Edition)

Published by Pearson
ISBN 10: 0321749006
ISBN 13: 978-0-32174-900-0

Chapter 4 - Calculating the Derivative - 4.5 Derivatives of Logarithmic Functions - 4.5 Exercises - Page 240: 17

Answer

$$\frac{{dy}}{{dx}} = \frac{{4x + 7 - 4\ln x}}{{x{{\left( {4x + 7} \right)}^2}}}$$

Work Step by Step

$$\eqalign{ & y = \frac{{\ln x}}{{4x + 7}} \cr & {\text{differentiate with respect to }}x \cr & \frac{{dy}}{{dx}} = \frac{d}{{dx}}\left[ {\frac{{\ln x}}{{4x + 7}}} \right] \cr & {\text{by using quotient rule}} \cr & \frac{{dy}}{{dx}} = \frac{{\left( {4x + 7} \right)\left( {\ln x} \right)' - \left( {\ln x} \right)\left( {4x + 7} \right)'}}{{{{\left( {4x + 7} \right)}^2}}} \cr & {\text{compute derivatives}} \cr & \frac{{dy}}{{dx}} = \frac{{\left( {4x + 7} \right)\left( {1/x} \right) - \left( {\ln x} \right)\left( 4 \right)}}{{{{\left( {4x + 7} \right)}^2}}} \cr & {\text{simplifying}} \cr & \frac{{dy}}{{dx}} = \frac{{4 + 7/x - 4\ln x}}{{{{\left( {4x + 7} \right)}^2}}} \cr & \frac{{dy}}{{dx}} = \frac{{4x + 7 - 4\ln x}}{{x{{\left( {4x + 7} \right)}^2}}} \cr} $$
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