Thomas' Calculus 13th Edition

Published by Pearson
ISBN 10: 0-32187-896-5
ISBN 13: 978-0-32187-896-0

Chapter 3: Derivatives - Section 3.3 Differentiation Rules - Exercises 3.3 - Page 125: 40

Answer

$$\frac{{dp}}{{dq}} = - \frac{1}{{2{q^2}}}{\text{ and }}\frac{{{d^2}p}}{{d{q^2}}} = \frac{1}{{{q^3}}}$$

Work Step by Step

$$\eqalign{ & p = \frac{{{q^2} + 3}}{{{{\left( {q - 1} \right)}^3} + {{\left( {q + 1} \right)}^3}}} \cr & {\text{Simplify the denominator}} \cr & p = \frac{{{q^2} + 3}}{{{q^3} - 3{q^2} + 3q - 1 + {q^3} + 3{q^2} + 3q + 1}} \cr & p = \frac{{{q^2} + 3}}{{2{q^3} + 6q}} \cr & p = \frac{{{q^2} + 3}}{{2q\left( {{q^2} + 3} \right)}} \cr & p = \frac{{{q^2} + 3}}{{2q\left( {{q^2} + 3} \right)}} \cr & p = \frac{1}{{2q}} \cr & p = \frac{1}{2}{q^{ - 1}} \cr & \cr & {\text{Find the first derivative}} \cr & \frac{{dp}}{{dq}} = \frac{d}{{dq}}\left[ {\frac{1}{2}{q^{ - 1}}} \right] \cr & {\text{use }}\frac{d}{{dq}}\left[ {{q^n}} \right] = n{q^{n - 1}} \cr & \frac{{dp}}{{dq}} = \frac{1}{2}\left( { - {q^{ - 2}}} \right) \cr & \frac{{dp}}{{dq}} = - \frac{1}{2}{q^{ - 2}} \cr & \frac{{dp}}{{dq}} = - \frac{1}{{2{q^2}}} \cr & \cr & {\text{Find the second derivative}} \cr & \frac{{{d^2}p}}{{d{q^2}}} = \frac{d}{{dq}}\left[ { - \frac{1}{2}{q^{ - 2}}} \right] \cr & {\text{use }}\frac{d}{{dq}}\left[ {{q^n}} \right] = n{q^{n - 1}}{\text{ }} \cr & \frac{{{d^2}p}}{{d{q^2}}} = - \frac{1}{2}\left( { - 2{q^{ - 3}}} \right) \cr & \frac{{{d^2}p}}{{d{q^2}}} = {q^{ - 3}} \cr & \frac{{{d^2}p}}{{d{q^2}}} = \frac{1}{{{q^3}}} \cr} $$
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